{"id":6285,"date":"2025-06-14T21:36:12","date_gmt":"2025-06-14T21:36:12","guid":{"rendered":"https:\/\/vibromera.eu\/?p=6285"},"modified":"2026-07-03T13:16:10","modified_gmt":"2026-07-03T13:16:10","slug":"technical-diagnostics-vibration-monitoring-marine-equipment","status":"publish","type":"post","link":"https:\/\/vibromera.eu\/pa\/content\/technical-diagnostics-vibration-monitoring-marine-equipment\/","title":{"rendered":"\u0a38\u0a2e\u0a41\u0a70\u0a26\u0a30\u0a40 \u0a09\u0a2a\u0a15\u0a30\u0a23\u0a3e\u0a02 \u0a26\u0a3e \u0a35\u0a3e\u0a08\u0a2c\u0a4d\u0a30\u0a47\u0a38\u0a3c\u0a28 \u0a21\u0a3e\u0a07\u0a17\u0a28\u0a4c\u0a38\u0a1f\u0a3f\u0a15\u0a38"},"content":{"rendered":"<div id=\"pl-6285\"  class=\"panel-layout\" ><div id=\"pg-6285-0\"  class=\"panel-grid panel-no-style\" ><div id=\"pgc-6285-0-0\"  class=\"panel-grid-cell\" ><div id=\"panel-6285-0-0-0\" class=\"widget_text so-panel widget widget_custom_html panel-first-child panel-last-child\" data-index=\"0\" ><div class=\"textwidget custom-html-widget\"><div class=\"mrn-wrap\">\n\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"TechArticle\",\n  \"headline\": \"Vibration Diagnostics of Marine Equipment: Technical Guide\",\n  \"description\": \"In-depth guide to vibration diagnostics and condition monitoring of marine rotating equipment \u2014 measurement methods, signal analysis, fault detection, shaft alignment, field balancing, and shipboard monitoring programmes.\",\n  \"author\": {\n    \"@type\": \"Organization\",\n    \"name\": \"Vibromera\",\n    \"url\": \"https:\/\/vibromera.eu\"\n  },\n  \"publisher\": {\n    \"@type\": \"Organization\",\n    \"name\": \"Vibromera\",\n    \"url\": \"https:\/\/vibromera.eu\"\n  },\n  \"mainEntityOfPage\": \"https:\/\/vibromera.eu\/content\/technical-diagnostics-vibration-monitoring-marine-equipment\/\",\n  \"dateModified\": \"2026-07-03\",\n  \"proficiencyLevel\": \"Expert\",\n  \"dependencies\": \"ISO 20816 series (formerly ISO 10816), ISO 20283 series, ISO 10816-6, ISO 21940-11 (formerly ISO 1940-1), ISO 8528-9\"\n}\n<\/script>\n\n<style>\n.mrn-wrap {\n    --mrn-bg: #f7f8fa;\n    --mrn-surface: #ffffff;\n    --mrn-raised: #f0f2f5;\n    --mrn-navy: #1a2744;\n    --mrn-navy-light: #2b3d5e;\n    --mrn-steel: #4a6180;\n    --mrn-teal: #1a8a7d;\n    --mrn-teal-light: #e6f5f3;\n    --mrn-teal-dark: #14706a;\n    --mrn-amber: #d4930d;\n    --mrn-amber-light: #fef7e8;\n    --mrn-red: #c0392b;\n    --mrn-red-light: #fef2f0;\n    --mrn-green: #1a7a3a;\n    --mrn-green-light: #eef8f0;\n    --mrn-text: #2c3345;\n    --mrn-text-2: #5a6478;\n    --mrn-muted: #8892a4;\n    --mrn-border: #dde1e8;\n    --mrn-border-light: #eceef2;\n    --mrn-radius: 8px;\n    --mrn-radius-lg: 14px;\n    --mrn-shadow: 0 1px 3px rgba(26,39,68,0.06);\n    --mrn-maxw: 860px;\n    --mrn-tocw: 280px;\n    font-family: -apple-system, BlinkMacSystemFont, \"Segoe UI\", Roboto, \"Helvetica Neue\", Arial, sans-serif;\n    color: var(--mrn-text);\n    background: var(--mrn-bg);\n    line-height: 1.7;\n    font-size: 17px;\n    -webkit-font-smoothing: antialiased;\n    margin: 0;\n}\n.mrn-wrap *, .mrn-wrap *::before, .mrn-wrap *::after { box-sizing: border-box; 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max-width: 640px; margin: 0 auto 16px; }\n.mrn-footer-inner a { color: var(--mrn-teal-dark); font-weight: 600; text-decoration: none; }\n\n\/* \u2500\u2500 Responsive \u2500\u2500 *\/\n@media (max-width: 960px) {\n    .mrn-layout { grid-template-columns: 1fr; gap: 0; }\n    .mrn-sidebar { position: static; max-height: none; margin-bottom: 22px; }\n    .mrn-toc { max-height: 55vh; overflow-y: auto; }\n    .mrn-content section { padding: 26px 22px; }\n}\n@media (max-width: 600px) {\n    .mrn-wrap { font-size: 16px; }\n    .mrn-hero { padding: 44px 18px 40px; }\n    .mrn-content section { padding: 22px 16px; }\n    .mrn-glance-card { padding: 20px 18px; }\n    .mrn-footer-inner { padding: 26px 18px; }\n}\n<\/style>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 HERO \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<header class=\"mrn-hero\">\n    <div class=\"mrn-hero-inner\">\n        <span class=\"mrn-hero-label\">Technical Reference<\/span>\n        <h1>Vibration Diagnostics of Marine Equipment<\/h1>\n        <p class=\"mrn-hero-subtitle\">A practical guide to measurement methods, signal analysis, fault detection, shaft alignment, field balancing, and condition monitoring for rotating machinery on ships and offshore installations.<\/p>\n        <div class=\"mrn-hero-meta\">\n            <span>Vibromera Engineering Team<\/span>\n            <span>\u00b7<\/span>\n            <span>Standards: ISO 20816 \u00b7 ISO 20283 \u00b7 ISO 21940-11<\/span>\n        <\/div>\n    <\/div>\n<\/header>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 AT A GLANCE \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<div class=\"mrn-glance\">\n    <div class=\"mrn-glance-card\">\n        <h2>At a glance<\/h2>\n        <div class=\"mrn-glance-grid\">\n            <div><strong>What:<\/strong> vibration-based condition monitoring and fault diagnosis of shipboard rotating machinery \u2014 engines, shaft lines, pumps, fans, generators, turbochargers.<\/div>\n            <div><strong>Key standards:<\/strong> ISO 20816 series (formerly ISO 10816) for machine vibration, ISO 20283 series for vibration measured on ships, ISO 21940-11 (formerly ISO 1940-1) for rotor balance quality.<\/div>\n            <div><strong>Core methods:<\/strong> broadband RMS trending, FFT spectrum analysis, envelope analysis for bearings, order tracking for variable-speed machinery, single- and two-plane field balancing.<\/div>\n            <div><strong>Why it matters:<\/strong> early fault warning measured in weeks, fewer unplanned failures at sea, and maintenance planned around port calls instead of emergencies.<\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 LAYOUT \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<div class=\"mrn-layout\">\n\n<!-- \u2500\u2500 Sidebar \u2500\u2500 -->\n<aside class=\"mrn-sidebar\">\n    <nav class=\"mrn-toc\" aria-label=\"Table of contents\">\n        <div class=\"mrn-toc-title\">Contents<\/div>\n        <ol>\n            <li><a href=\"#s1\">1. Technical Diagnostics Fundamentals<\/a><\/li>\n            <li><a href=\"#s2\">2. Vibration Physics, Units and Standards<\/a><\/li>\n            <li><a href=\"#s3\">3. The Marine Operating Environment<\/a><\/li>\n            <li><a href=\"#s4\">4. Measurement Methods and Sensors<\/a><\/li>\n            <li><a href=\"#s5\">5. Signal Analysis<\/a><\/li>\n            <li><a href=\"#s6\">6. Condition Monitoring Programmes<\/a><\/li>\n            <li><a href=\"#s7\">7. Fault Detection and Identification<\/a><\/li>\n            <li><a href=\"#s8\">8. Alignment and Balancing<\/a><\/li>\n            <li><a href=\"#s9\">9. Emerging Technologies<\/a><\/li>\n            <li><a href=\"#s10\">10. Frequently Asked Questions<\/a><\/li>\n        <\/ol>\n    <\/nav>\n<\/aside>\n\n<!-- \u2500\u2500 Content \u2500\u2500 -->\n<main class=\"mrn-content\">\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 1 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s1\">\n    <h2>1. Technical Diagnostics Fundamentals<\/h2>\n    <p class=\"mrn-lead\">Why vibration analysis became the dominant approach to monitoring rotating marine machinery \u2014 and what alternatives exist.<\/p>\n\n    <h3 id=\"s1-1\">1.1 Diagnostic Principles<\/h3>\n\n    <p>Technical diagnostics is the discipline of assessing the current condition of a machine and predicting how that condition will change over time. For marine equipment this task is especially critical: an unplanned failure at sea can endanger crew, cargo, and the vessel itself.<\/p>\n\n    <p>The central idea is straightforward. Every piece of rotating machinery produces measurable physical signals \u2014 vibration, heat, acoustic emission, oil contamination, and others. As internal components wear, crack, corrode, or loosen, those signals change in ways that are usually predictable. A systematic monitoring programme detects these changes early, classifies them by type and severity, and feeds recommendations into the maintenance schedule.<\/p>\n\n    <h4>Key Terms<\/h4>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Term<\/th>\n                    <th>Definition<\/th>\n                    <th>Marine Example<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>Diagnostic parameter<\/strong><\/td>\n                    <td>A measurable quantity that correlates with equipment condition<\/td>\n                    <td>Vibration velocity RMS on a pump bearing housing<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Diagnostic symptom<\/strong><\/td>\n                    <td>A specific pattern in the measured data<\/td>\n                    <td>Elevated vibration at blade-passing frequency in a centrifugal pump<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Diagnostic sign<\/strong><\/td>\n                    <td>A recognisable indication of a particular condition<\/td>\n                    <td>Sidebands around gear mesh frequency indicating tooth wear<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Recognition algorithm<\/strong><\/td>\n                    <td>A procedure (manual or automatic) that maps measured data to a fault category<\/td>\n                    <td>An expert-system rule set that flags bearing defect frequencies in an envelope spectrum<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>The General Diagnostic Workflow<\/h4>\n\n    <div class=\"mrn-flow\">\n        <span class=\"mrn-flow-step\">Data collection<\/span>\n        <span class=\"mrn-flow-arrow\">\u2192<\/span>\n        <span class=\"mrn-flow-step\">Signal processing<\/span>\n        <span class=\"mrn-flow-arrow\">\u2192<\/span>\n        <span class=\"mrn-flow-step\">Pattern recognition<\/span>\n        <span class=\"mrn-flow-arrow\">\u2192<\/span>\n        <span class=\"mrn-flow-step\">Fault classification<\/span>\n        <span class=\"mrn-flow-arrow\">\u2192<\/span>\n        <span class=\"mrn-flow-step\">Severity assessment<\/span>\n        <span class=\"mrn-flow-arrow\">\u2192<\/span>\n        <span class=\"mrn-flow-step\">Maintenance action<\/span>\n    <\/div>\n\n    <p>In practice the pipeline is iterative: if a pattern does not match any known fault, the analyst goes back, refines the processing, adds new measurement points, or correlates with other diagnostic methods (thermography, oil analysis, ultrasonic testing).<\/p>\n\n    <h4>Functional vs. Test-Bench Diagnostics<\/h4>\n\n    <p><strong>Functional diagnostics<\/strong> collects data while the machine runs under normal load. It reflects realistic operating conditions but limits what tests you can perform \u2014 you cannot, for instance, inject an artificial excitation into a pump that is supplying cooling water to the main engine.<\/p>\n\n    <p><strong>Test-bench (tester) diagnostics<\/strong> applies controlled excitation \u2014 impact hammer, swept-sine shaker, or similar \u2014 usually during a shutdown. It reveals natural frequencies, transfer functions, and structural characteristics that functional diagnostics cannot provide. On board a ship the practical difficulty is obvious: shutdowns are expensive and sometimes impossible for essential systems.<\/p>\n\n    <div class=\"mrn-callout mrn-info\">\n        <div class=\"mrn-callout-title\">Practical note<\/div>\n        <p>A good shipboard programme combines both approaches. Routine functional monitoring covers the large majority of the machinery inventory, while test-bench methods are reserved for commissioning, troubleshooting, and critical systems.<\/p>\n    <\/div>\n\n    <h4>Choosing What to Monitor<\/h4>\n\n    <p>Not every machine on a vessel justifies the same level of attention. Selecting which parameters to track on which equipment requires a trade-off between diagnostic coverage and practical cost. Typical selection criteria include sensitivity to fault development, measurement repeatability, cost of the sensor and installation, and the criticality of the equipment itself.<\/p>\n\n    <h3 id=\"s1-2\">1.2 Maintenance Strategies<\/h3>\n\n    <p>The maritime industry has moved through four broad maintenance philosophies, each with a different cost\u2013risk profile.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Strategy<\/th>\n                    <th>Approach<\/th>\n                    <th>Strengths<\/th>\n                    <th>Weaknesses<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>Reactive<\/strong><\/td>\n                    <td>Run to failure, repair after breakdown<\/td>\n                    <td>Minimal upfront investment<\/td>\n                    <td>Unpredictable downtime, safety risk, secondary damage<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Preventive (time-based)<\/strong><\/td>\n                    <td>Fixed-interval overhauls regardless of condition<\/td>\n                    <td>Predictable schedule<\/td>\n                    <td>Over-maintenance, unnecessary parts replacement<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Condition-based (CBM)<\/strong><\/td>\n                    <td>Maintain when measured parameters exceed thresholds<\/td>\n                    <td>Interventions timed to actual need<\/td>\n                    <td>Requires diagnostic competence and equipment<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Proactive \/ Reliability-centred<\/strong><\/td>\n                    <td>Identify and eliminate root causes of failure<\/td>\n                    <td>Highest long-term reliability<\/td>\n                    <td>High initial investment, cultural change<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <p>Most modern fleets use a combination. Critical propulsion and power-generation machinery gets condition-based or proactive maintenance. Auxiliary equipment may still follow time-based schedules or even run-to-failure where spares are cheap and consequences are minor. Vibration analysis is the backbone of the CBM layer.<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Example<\/div>\n        <p>A container ship's cooling-water pumps were previously overhauled every 3&nbsp;000 operating hours. After implementing vibration-based condition monitoring the operator extended intervals to 4&nbsp;500 hours while substantially reducing unplanned failures. Programmes of this kind typically pay for themselves within the first year or two of operation.<\/p>\n    <\/div>\n\n    <h3 id=\"s1-3\">1.3 Vibration as the Primary Diagnostic Signal<\/h3>\n\n    <p>Vibration analysis dominates marine condition monitoring for several interconnected reasons:<\/p>\n\n    <ul>\n        <li>All rotating machinery produces vibration \u2014 no additional excitation is required.<\/li>\n        <li>Faults change vibration patterns in well-documented, fault-specific ways.<\/li>\n        <li>Measurements are non-intrusive and can be taken while machinery operates normally.<\/li>\n        <li>Early warning times are typically measured in weeks or months, not hours.<\/li>\n        <li>The technique is quantitative \u2014 results map directly to severity zones defined by international standards.<\/li>\n    <\/ul>\n\n    <p>The methodology moves through six stages: baseline establishment, trend monitoring, anomaly detection, fault classification, severity assessment, and prognosis (remaining useful life). Each stage draws on a different toolbox \u2014 from simple RMS trending at the first stage to <a href=\"https:\/\/vibromera.eu\/glossary\/envelope-analysis\/\">envelope analysis<\/a>, cepstrum, and machine-learning classifiers at the later ones.<\/p>\n\n    <h4>Condition States<\/h4>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>State<\/th>\n                    <th>Indicators<\/th>\n                    <th>Recommended Action<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>Good<\/strong><\/td>\n                    <td>Low, stable vibration; no fault frequencies<\/td>\n                    <td>Continue normal monitoring schedule<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Acceptable<\/strong><\/td>\n                    <td>Elevated but stable levels<\/td>\n                    <td>Increase monitoring frequency, investigate root cause<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Unsatisfactory<\/strong><\/td>\n                    <td>High levels or rising trend<\/td>\n                    <td>Plan maintenance at next opportunity<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Unacceptable<\/strong><\/td>\n                    <td>Very high levels or rapid deterioration<\/td>\n                    <td>Shut down or reduce load immediately; emergency maintenance<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Economic Perspective<\/h4>\n\n    <p>Return on investment for shipboard vibration programmes varies, but ratios of 5:1 to 10:1 are frequently cited in the literature. Most of the savings come from three sources: avoiding catastrophic secondary damage (a failed bearing that wrecks a shaft), extending component life by eliminating unnecessary overhauls, and reducing the cost of port-side emergency repairs versus scheduled dockyard work.<\/p>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 2 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s2\">\n    <h2>2. Vibration Physics, Units and Standards<\/h2>\n    <p class=\"mrn-lead\">Displacement, velocity, acceleration \u2014 the three faces of vibration, and the ISO framework used to judge how much is too much.<\/p>\n\n    <h3 id=\"s2-1\">2.1 Core Parameters<\/h3>\n\n    <p>Vibration is the oscillatory motion of a mechanical system around an equilibrium position. It is described by three interrelated kinematic quantities, each useful in a different frequency range.<\/p>\n\n    <div class=\"mrn-formula\">\n        Displacement: &nbsp; x(t) = A \u00b7 sin(\u03c9t + \u03c6)<br>\n        Velocity: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; v(t) = A\u00b7\u03c9 \u00b7 cos(\u03c9t + \u03c6)<br>\n        Acceleration: &nbsp; a(t) = \u2212A\u00b7\u03c9\u00b2 \u00b7 sin(\u03c9t + \u03c6)<br>\n        <br>\n        A \u2014 amplitude &nbsp;|&nbsp; \u03c9 = 2\u03c0f \u2014 angular frequency &nbsp;|&nbsp; \u03c6 \u2014 phase angle\n    <\/div>\n\n    <p>Because velocity scales linearly with frequency (the \u03c9 factor) and acceleration scales with \u03c9\u00b2, the three parameters have very different sensitivities across the spectrum. This is the practical reason engineers choose one over another.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Parameter<\/th>\n                    <th>Unit<\/th>\n                    <th>Best Frequency Range<\/th>\n                    <th>Typical Marine Uses<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>Displacement<\/strong><\/td>\n                    <td>\u03bcm (peak-to-peak), mils<\/td>\n                    <td>Below \u2248 10 Hz<\/td>\n                    <td>Large slow-speed diesel cranks, shaft-relative motion<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Velocity<\/strong><\/td>\n                    <td>mm\/s (RMS)<\/td>\n                    <td>10 Hz \u2013 1 kHz<\/td>\n                    <td>General machinery monitoring; ISO 20816 \/ legacy ISO 10816 evaluations<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Acceleration<\/strong><\/td>\n                    <td>m\/s\u00b2 or g (peak)<\/td>\n                    <td>Above \u2248 1 kHz<\/td>\n                    <td>Rolling-element bearing diagnostics, gear mesh, high-speed pumps<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Statistical Measures<\/h4>\n\n    <p><strong>RMS<\/strong> (root mean square) represents the effective amplitude and correlates with the energy content of vibration. It is the default metric for ISO-based severity evaluation.<\/p>\n\n    <p><strong>Peak value<\/strong> captures maximum instantaneous amplitude \u2014 useful for detecting impacts and transient events.<\/p>\n\n    <p><strong>Peak-to-peak value<\/strong> gives the total swing from positive to negative peak. It is commonly used for displacement measurements and clearance analysis.<\/p>\n\n    <p><strong>Crest factor<\/strong> is the ratio of peak to RMS. The absolute value depends on the machine type, measurement bandwidth, and operating regime \u2014 a pure sinusoid gives \u22481.4, and a healthy rotating machine commonly falls around 3\u20134 \u2014 so there is no single universal \"normal\" number. What matters diagnostically is the <em>trend<\/em>: a rising crest factor indicates growing impulsiveness, a common early sign of bearing surface defects or impacts.<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Diagnostic illustration<\/div>\n        <p>A cargo pump bearing's crest factor rose from 3.2 to 7.8 over six weeks while overall RMS remained almost unchanged. That divergence \u2014 stable energy, increasing spikiness \u2014 is a classic early bearing-defect signature. Subsequent inspection confirmed an outer-race pit.<\/p>\n    <\/div>\n\n    <h3 id=\"s2-2\">2.2 Vibration Types in Marine Systems<\/h3>\n\n    <p>Marine machinery generates several categories of vibration, each arising from a different physical mechanism.<\/p>\n\n    <h4>By Excitation Source<\/h4>\n\n    <ul>\n        <li><strong>Free vibration<\/strong> \u2014 the system oscillates at its natural frequency after a transient excitation (startup, shutdown, impact).<\/li>\n        <li><strong>Forced vibration<\/strong> \u2014 continuous excitation at a frequency related to rotational speed, blade count, or electrical supply. The majority of steady-state vibration is forced.<\/li>\n        <li><strong>Self-excited vibration<\/strong> \u2014 the machinery creates its own excitation through an internal feedback mechanism: oil whirl in journal bearings, aerodynamic flutter, stick-slip friction.<\/li>\n        <li><strong>Parametric vibration<\/strong> \u2014 system stiffness or damping varies periodically, pumping energy into the response. A cracked gear tooth that changes mesh stiffness once per revolution is a typical example.<\/li>\n    <\/ul>\n\n    <h4>By Relationship to Speed<\/h4>\n\n    <ul>\n        <li><strong>Synchronous (order-related)<\/strong> \u2014 frequency is an integer or simple rational multiple of shaft speed. Unbalance (1\u00d7), misalignment (2\u00d7), and looseness (many harmonics) belong here.<\/li>\n        <li><strong>Asynchronous<\/strong> \u2014 frequency is not an integer multiple of shaft speed. Bearing defect frequencies, electrical line-frequency harmonics, and belt-slip vibration fall in this category.<\/li>\n    <\/ul>\n\n    <h4>By Direction<\/h4>\n\n    <p><strong>Radial<\/strong> vibration (perpendicular to the shaft) dominates in most rotating equipment and is the first direction measured. <strong>Axial<\/strong> vibration (parallel to the shaft) flags thrust-bearing problems, coupling issues, and aerodynamic forces. <strong>Torsional<\/strong> vibration (twisting about the shaft axis) requires specialised sensors and is mainly tracked on long propulsion trains where torsional resonance can be destructive.<\/p>\n\n    <h4>Natural Frequencies and Resonance<\/h4>\n\n    <p>Every mechanical system has natural frequencies determined by its mass, stiffness, and damping. When an excitation frequency approaches a natural frequency the response is amplified \u2014 sometimes by a factor of 10 or more. In rotating machinery these coincidences are called <a href=\"https:\/\/vibromera.eu\/glossary\/critical-speed\/\">critical speeds<\/a>.<\/p>\n\n    <div class=\"mrn-callout mrn-warn\">\n        <div class=\"mrn-callout-title\">Design rule<\/div>\n        <p>Operating speed should be separated from all identified critical speeds by at least 15\u201320&nbsp;%. Running persistently within this margin risks resonance-driven fatigue and rapid failure.<\/p>\n    <\/div>\n\n    <h4>Vibration Sources<\/h4>\n\n    <p><strong>Mechanical<\/strong> \u2014 unbalance, misalignment, bearing defects, looseness, gear problems, shaft bow. Frequencies typically relate to shaft speed and component geometry.<\/p>\n\n    <p><strong>Electromagnetic<\/strong> \u2014 rotor-bar defects, stator eccentricity, supply-voltage imbalance. Frequencies concentrate around twice the line frequency (100 Hz for 50 Hz supply, 120 Hz for 60 Hz) and its multiples.<\/p>\n\n    <p><strong>Hydraulic \/ aerodynamic<\/strong> \u2014 blade-passing, cavitation, turbulence, recirculation. Blade-passing frequency equals the number of blades multiplied by rotational frequency; cavitation produces broadband random noise concentrated above 1\u20132 kHz.<\/p>\n\n    <h3 id=\"s2-3\">2.3 Units and Standards<\/h3>\n\n    <p>Vibration measurements use both linear and logarithmic (decibel) scales. The decibel form compresses wide dynamic ranges and emphasises relative changes:<\/p>\n\n    <div class=\"mrn-formula\">\n        dB = 20 \u00b7 log\u2081\u2080(measured value \/ reference value)\n    <\/div>\n\n    <p>Reference values are standardised in ISO 1683: 10\u207b\u2079 m\/s (1 nm\/s) for velocity and 10\u207b\u2076 m\/s\u00b2 (1 \u03bcm\/s\u00b2) for acceleration. Always state the reference when reporting levels in decibels.<\/p>\n\n    <h4>ISO 20816 (formerly ISO 10816) \u2014 Vibration on Non-Rotating Parts<\/h4>\n\n    <p>The <strong>ISO 10816<\/strong> series was historically the most widely used framework for evaluating machinery vibration measured on non-rotating parts (bearing housings). It is being superseded by the <strong>ISO 20816<\/strong> series: ISO 20816-1:2016 replaced both ISO 10816-1 and ISO 7919-1, and <a href=\"https:\/\/vibromera.eu\/glossary\/iso-20816-3\/\">ISO 20816-3:2022<\/a> replaced ISO 10816-3 for industrial machinery rated above 15 kW. The four-zone evaluation logic (A through D) remains the same in both series; the numerical limits depend on machine group and support class.<\/p>\n\n    <p>The table below shows <em>example<\/em> zone boundaries for one specific classification (ISO 10816-3 \/ ISO 20816-3, Group 2 machines 15\u2013300 kW, rigid support). These values are not universal \u2014 always consult the part of the standard that applies to your machine type, power range, and mounting.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Zone<\/th>\n                    <th>Condition<\/th>\n                    <th>Velocity RMS (Group 2, rigid support)<\/th>\n                    <th>Guidance<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>A<\/strong><\/td>\n                    <td>Good<\/td>\n                    <td>up to 1.4 mm\/s<\/td>\n                    <td>Newly commissioned or recently maintained<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>B<\/strong><\/td>\n                    <td>Acceptable<\/td>\n                    <td>1.4 \u2013 2.8 mm\/s<\/td>\n                    <td>Unrestricted long-term operation<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>C<\/strong><\/td>\n                    <td>Unsatisfactory<\/td>\n                    <td>2.8 \u2013 4.5 mm\/s<\/td>\n                    <td>Limited-duration operation; plan remedial work<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>D<\/strong><\/td>\n                    <td>Unacceptable<\/td>\n                    <td>&gt; 4.5 mm\/s<\/td>\n                    <td>Damage likely; immediate action<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Marine and Machine-Specific Standards<\/h4>\n\n    <p>Beyond the general machinery series, several standards address ships and specific machine types directly:<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Standard<\/th>\n                    <th>Scope<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>ISO 20283-2<\/strong><\/td>\n                    <td>Measurement of vibration on ships \u2014 structural vibration of the hull and superstructure<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 20283-3<\/strong><\/td>\n                    <td>Pre-installation vibration measurement of shipboard equipment<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 20283-4<\/strong><\/td>\n                    <td>Measurement and evaluation of vibration of the ship propulsion machinery<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 20283-5<\/strong><\/td>\n                    <td>Vibration with regard to habitability on passenger and merchant ships (crew and passenger comfort)<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 10816-6<\/strong><\/td>\n                    <td>Reciprocating machines with power ratings above 100 kW \u2014 marine diesel engines fall in this category<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 8528-9<\/strong><\/td>\n                    <td>Vibration measurement and evaluation of reciprocating-engine generating sets<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>ISO 7919 series<\/strong><\/td>\n                    <td>Shaft vibration measured on rotating shafts with proximity probes (its parts are progressively merged into ISO 20816)<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>API 610<\/strong><\/td>\n                    <td>Centrifugal pumps \u2014 vibration acceptance criteria used in offshore and cargo-handling applications<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Machine Groups and Support Classes<\/h4>\n\n    <p>Under the ISO 10816-3 \/ ISO 20816-3 framework the primary groups for industrial machinery are: <strong>Group 1<\/strong> \u2014 large machines rated above 300 kW and up to 50 MW; <strong>Group 2<\/strong> \u2014 medium machines rated 15\u2013300 kW. Separate provisions exist for pumps depending on whether the driver is integrated or external. Limits are further split by support stiffness.<\/p>\n\n    <p>A support system is considered <em>rigid<\/em> when the lowest natural frequency of the machine-plus-foundation assembly is well above the principal excitation frequency \u2014 a common practical guideline is at least 25&nbsp;% above. <em>Flexible<\/em> supports have their lowest natural frequency below the excitation frequency, which amplifies housing vibration and is assigned more lenient acceptance limits. The distinction should be verified by measurement (impact test) rather than assumed from construction appearance alone \u2014 this matters on ships, where resiliently mounted machinery is common.<\/p>\n\n    <h4>Measurement Points<\/h4>\n\n    <p>Standards prescribe measurement on bearing housings, as close to the load zone as practical, in three directions: horizontal radial, vertical radial, and axial (usually at the drive-end bearing only). Measurements should be taken under stable operating conditions \u2014 rated speed and representative load \u2014 and averaged over a period long enough to capture any cyclic variation.<\/p>\n\n    <div class=\"mrn-callout mrn-warn\">\n        <div class=\"mrn-callout-title\">Shipboard caveat<\/div>\n        <p>Vessel motion, sea state, and cargo loading can influence vibration readings. Good practice includes logging these conditions alongside every measurement and filtering or flagging data collected in rough weather.<\/p>\n    <\/div>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 3 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s3\">\n    <h2>3. The Marine Operating Environment<\/h2>\n    <p class=\"mrn-lead\">What makes vibration work on a ship different from the same work in a factory \u2014 variable speeds, a flexible steel foundation that floats, and a propeller at the end of the shaft line.<\/p>\n\n    <h3 id=\"s3-1\">3.1 Variable Speed and Load<\/h3>\n\n    <p>Unlike most industrial plant, marine propulsion machinery rarely sits at one speed. Main engines follow bridge orders, generators pick up and shed electrical load, and vessels with controllable-pitch propellers change load at constant shaft speed. For diagnostics this has two consequences:<\/p>\n\n    <ul>\n        <li><strong>Spectra smear.<\/strong> A conventional FFT taken while speed drifts spreads each rotational component over several frequency bins. Order tracking \u2014 resampling the signal against a tachometer reference \u2014 keeps speed-related peaks sharp regardless of drift.<\/li>\n        <li><strong>Baselines must be condition-tagged.<\/strong> A reading taken at 85&nbsp;% MCR in calm water is not comparable with one taken at 50&nbsp;% load in a seaway. Every stored measurement should carry speed, load, and sea-state metadata, and trends should compare like with like.<\/li>\n    <\/ul>\n\n    <h3 id=\"s3-2\">3.2 Propeller Blade-Rate Excitation and Hull Resonances<\/h3>\n\n    <p>The propeller is one of the strongest periodic exciters on the vessel. Each blade passing through the non-uniform wake field behind the hull generates a pressure pulse, producing vibration at the <strong>blade-passing frequency<\/strong> (blade rate) and its harmonics:<\/p>\n\n    <div class=\"mrn-formula\">\n        BPF = Z \u00b7 n \/ 60<br>\n        Z \u2014 number of blades &nbsp;|&nbsp; n \u2014 shaft speed in r\/min &nbsp;|&nbsp; BPF in Hz\n    <\/div>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Worked example<\/div>\n        <p>A four-blade propeller turning at 120 r\/min: shaft frequency = 120\/60 = 2 Hz; BPF = 4 \u00d7 2 = <strong>8 Hz<\/strong>, with harmonics at 16 Hz, 24 Hz, and so on. These low frequencies fall exactly in the range of hull-girder and deckhouse natural frequencies.<\/p>\n    <\/div>\n\n    <p>Because the hull is a large, relatively flexible welded structure, blade-rate excitation can couple into hull-girder bending modes, local panel modes, and deckhouse modes. Symptoms range from crew discomfort in the accommodation to cracked pipe supports and fatigue in local structure. ISO 20283-2 governs the measurement of this structural vibration; ISO 20283-5 sets the framework for evaluating habitability. Remedies include propeller redesign or repair (blade damage increases wake-induced excitation), changing the number of blades, structural stiffening, and avoiding prolonged operation at resonant shaft speeds.<\/p>\n\n    <div class=\"mrn-callout mrn-warn\">\n        <div class=\"mrn-callout-title\">Diagnostic pitfall<\/div>\n        <p>Elevated blade-rate vibration measured on an aft-ship machine is not necessarily that machine's fault. Always check whether the frequency matches propeller blade rate before condemning a pump or motor mounted on a vibrating foundation.<\/p>\n    <\/div>\n\n    <h3 id=\"s3-3\">3.3 Shaft Lines and Torsional Vibration<\/h3>\n\n    <p>A ship's shaft line \u2014 main engine or gearbox, intermediate shafts, stern-tube bearing, propeller \u2014 is a long, heavy rotor system whose alignment depends on the hull around it. Hull deflection changes with cargo loading, ballast condition, and temperature, so a shaft line aligned perfectly in dry dock can run misaligned at sea. Symptoms include elevated 1\u00d7 and 2\u00d7 vibration at intermediate bearings, stern-tube bearing overheating, and uneven wear-down readings.<\/p>\n\n    <p>Long shaft lines driven by diesel engines are also prone to <strong>torsional vibration<\/strong>. Engine firing orders excite torsional natural frequencies of the crankshaft\u2013shaft-line system; where a significant torsional critical falls inside the operating range, a <em>barred speed range<\/em> is defined in which continuous operation is prohibited. Torsional vibration is largely invisible to ordinary casing-mounted accelerometers \u2014 it requires dedicated instruments (torsiographs, strain gauges, encoder-based twist measurement). ISO 20283-4 covers the measurement and evaluation of propulsion-machinery vibration.<\/p>\n\n    <h3 id=\"s3-4\">3.4 Classification Societies and Environmental Factors<\/h3>\n\n    <p>Classification societies (DNV, Lloyd's Register, Bureau Veritas, ABS, and others) publish machinery and vibration guidance and offer condition-monitoring class notations under which an approved, auditable monitoring programme can substitute for parts of the fixed-interval survey regime. The specific requirements differ between societies and change over time, so the applicable rules should always be checked with the vessel's own class \u2014 but the common thread is that data quality, documented procedures, and analyst competence must be demonstrable.<\/p>\n\n    <p>Finally, the marine environment itself works against the measurement chain: salt-laden air corrodes connectors, engine-room temperatures cycle widely, and washdown areas demand appropriately protected sensors and cabling. Environmental ratings, stainless hardware, and disciplined cable maintenance are not luxuries \u2014 a corroded connector produces intermittent signals that imitate machine faults.<\/p>\n<\/section>\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 4 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s4\">\n    <h2>4. Measurement Methods and Sensors<\/h2>\n    <p class=\"mrn-lead\">Sensor selection, mounting, signal conditioning, and the practical realities of collecting good vibration data on board a ship.<\/p>\n\n    <h3 id=\"s4-1\">4.1 Measurement Principles<\/h3>\n\n    <h4>Kinematic vs. Dynamic<\/h4>\n    <p>Most vibration sensors measure <em>motion<\/em> only \u2014 displacement, velocity, or acceleration \u2014 without quantifying the force that produces it. This is kinematic measurement. Dynamic measurement combines motion and force data, typically through paired accelerometers and force transducers, and is used mainly in controlled test-bench situations such as modal analysis or transfer-function measurements.<\/p>\n\n    <h4>Absolute vs. Relative<\/h4>\n    <p><strong>Absolute vibration<\/strong> is the motion of a point relative to an inertial reference frame. An accelerometer bolted to a bearing housing gives an absolute casing vibration measurement. <strong>Relative vibration<\/strong> is the motion between two parts \u2014 typically the shaft and the bearing housing. Proximity probes provide this and are standard on large turbomachinery where shaft orbit information is needed.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Type<\/th>\n                    <th>Best for<\/th>\n                    <th>Limitations<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Absolute (accelerometer, velocity sensor)<\/td>\n                    <td>General machinery, auxiliary equipment, structural vibration<\/td>\n                    <td>Cannot directly reveal shaft motion inside the bearing<\/td>\n                <\/tr>\n                <tr>\n                    <td>Relative (proximity probe)<\/td>\n                    <td>Large turbomachinery, journal bearings, critical shafts<\/td>\n                    <td>Expensive installation, requires shaft access<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Contact vs. Non-Contact<\/h4>\n    <p>Contact sensors (accelerometers, velocity pickups, strain gauges) are physically attached to the vibrating surface. They offer high sensitivity, broad bandwidth, and well-established procedures. Non-contact sensors (eddy-current probes, laser vibrometers) measure from a distance and are essential for rotating surfaces, high-temperature zones, and locations where mass loading by a contact sensor would alter the measurement.<\/p>\n\n    <h3 id=\"s4-2\">4.2 Sensor Technologies<\/h3>\n\n    <h4>Piezoelectric Accelerometers<\/h4>\n    <p>The workhorse of marine vibration measurement. A piezoelectric element (quartz or ceramic) generates electric charge proportional to applied force. Internal electronics (IEPE \/ ICP standard) convert this to a low-impedance voltage signal that travels reliably over long cables in noisy engine-room environments.<\/p>\n\n    <div class=\"mrn-kv\">\n        <div class=\"mrn-kv-card\">\n            <div class=\"mrn-kv-label\">Typical bandwidth<\/div>\n            <div class=\"mrn-kv-value\">1 Hz \u2013 10 kHz<\/div>\n        <\/div>\n        <div class=\"mrn-kv-card\">\n            <div class=\"mrn-kv-label\">Sensitivity<\/div>\n            <div class=\"mrn-kv-value\">10 \u2013 100 mV\/g<\/div>\n        <\/div>\n        <div class=\"mrn-kv-card\">\n            <div class=\"mrn-kv-label\">Operating temperature<\/div>\n            <div class=\"mrn-kv-value\">\u221250 to +120 \u00b0C<\/div>\n        <\/div>\n        <div class=\"mrn-kv-card\">\n            <div class=\"mrn-kv-label\">Mass<\/div>\n            <div class=\"mrn-kv-value\">5 \u2013 50 g<\/div>\n        <\/div>\n    <\/div>\n\n    <p>High-frequency models (up to 50 kHz, lower sensitivity) are used for early bearing-defect detection. High-sensitivity models (100\u20131000 mV\/g, bandwidth to ~5 kHz) are chosen for low-level vibration in precision machinery.<\/p>\n\n    <h4>MEMS Accelerometers<\/h4>\n    <p>Micro-electromechanical accelerometers are smaller, cheaper, and consume less power than piezoelectric units. They have become viable for permanent monitoring of non-critical machinery and wireless sensor networks. Bandwidth and dynamic range have improved substantially in recent years, though piezoelectric sensors still lead in high-frequency performance.<\/p>\n\n    <h4>Velocity Sensors (Seismic Transducers)<\/h4>\n    <p>A suspended magnetic mass moves relative to a coil, generating a voltage proportional to velocity. These sensors require no external power, have robust construction, and give a direct velocity output \u2014 convenient for ISO 20816 \/ legacy ISO 10816 evaluation without integration. Drawbacks include limited low-frequency response (typically above 10 Hz), temperature sensitivity, and relatively large size.<\/p>\n\n    <h4>Proximity Probes (Eddy-Current Sensors)<\/h4>\n    <p>A high-frequency oscillator creates an electromagnetic field at the probe tip. Eddy currents in the nearby conductive shaft surface alter the impedance, and electronics convert the change to a DC voltage proportional to gap distance. Two probes mounted at 90\u00b0 on each bearing provide X-Y shaft position data for orbit analysis. Resolution is on the order of 0.1 \u03bcm, and the probe has DC response (it can track slow static displacements as well as dynamic vibration).<\/p>\n\n    <div class=\"mrn-callout mrn-info\">\n        <div class=\"mrn-callout-title\">Application note<\/div>\n        <p>Proximity probes are standard on large main turbines, turbochargers, and reduction-gear shafts. They are almost never used for auxiliary machinery \u2014 the installation cost is too high relative to the equipment value.<\/p>\n    <\/div>\n\n    <h3 id=\"s4-3\">4.3 Mounting and Calibration<\/h3>\n\n    <h4>Mounting Methods<\/h4>\n    <p>The way a sensor is attached to the machine determines the upper usable frequency. Each method introduces a mounting resonance above which the measurement is unreliable.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Method<\/th>\n                    <th>Usable Upper Frequency<\/th>\n                    <th>Notes<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Threaded stud<\/td>\n                    <td>Up to sensor limit (often &gt; 10 kHz)<\/td>\n                    <td>Best accuracy; permanent or semi-permanent<\/td>\n                <\/tr>\n                <tr>\n                    <td>Thin adhesive layer<\/td>\n                    <td>~5\u20137 kHz<\/td>\n                    <td>Good for temporary campaigns<\/td>\n                <\/tr>\n                <tr>\n                    <td>Magnetic mount<\/td>\n                    <td>~2\u20133 kHz<\/td>\n                    <td>Quick; ferromagnetic surfaces only<\/td>\n                <\/tr>\n                <tr>\n                    <td>Hand-held probe<\/td>\n                    <td>~1 kHz<\/td>\n                    <td>Screening only; poor repeatability<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <div class=\"mrn-callout mrn-warn\">\n        <div class=\"mrn-callout-title\">Common error<\/div>\n        <p>Using a magnetic mount for bearing envelope analysis (which relies on frequencies above 2\u20133 kHz) will produce misleading results. A stud or thin adhesive mount is required.<\/p>\n    <\/div>\n\n    <h4>Signal Conditioning<\/h4>\n    <p>IEPE sensors need a constant-current power supply (typically 2\u20134 mA at 18\u201328 V DC). The data acquisition front-end normally provides this. Charge-mode sensors require a separate charge amplifier. In either case the signal path should use shielded, low-noise cables, and cable runs should be kept as short as practical to minimise electromagnetic pickup from engine-room power cables.<\/p>\n\n    <h4>Calibration<\/h4>\n    <p>Sensors and channels should be checked against a traceable reference at least once a year \u2014 more often in harsh marine environments. A portable calibration exciter producing a known acceleration at a known frequency (commonly 10 m\/s\u00b2 at 159.15 Hz) is the standard field tool. Back-to-back comparison with a reference accelerometer gives higher confidence and can be done aboard.<\/p>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 5 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s5\">\n    <h2>5. Signal Analysis<\/h2>\n    <p class=\"mrn-lead\">From raw vibration waveform to diagnostic conclusions \u2014 the signal-processing chain that makes fault identification possible.<\/p>\n\n    <h3 id=\"s5-1\">5.1 Signal Types<\/h3>\n\n    <p>Understanding what kind of signal your machine produces determines which analysis techniques will extract useful information.<\/p>\n\n    <h4>Periodic and Harmonic Signals<\/h4>\n    <p>A pure sinusoid at a single frequency is the simplest case (rare in practice). Most rotating machinery produces <em>polyharmonic<\/em> signals \u2014 a fundamental frequency plus its integer multiples. A four-stroke diesel produces firing-order harmonics; a gear train produces mesh frequency and its harmonics.<\/p>\n\n    <h4>Modulated Signals<\/h4>\n    <p><strong>Amplitude modulation (AM)<\/strong> \u2014 the signal envelope varies periodically. A bearing inner-race defect that passes through the load zone once per revolution creates AM of the high-frequency impact response at the shaft speed. <strong>Frequency modulation (FM)<\/strong> \u2014 the instantaneous frequency varies. Speed fluctuation from a reciprocating compressor is a common source.<\/p>\n\n    <div class=\"mrn-formula\">\n        AM: &nbsp; x(t) = A \u00b7 [1 + m \u00b7 cos(2\u03c0\u00b7f<sub>mod<\/sub>\u00b7t)] \u00b7 cos(2\u03c0\u00b7f<sub>carrier<\/sub>\u00b7t)<br>\n        m \u2014 modulation depth &nbsp;|&nbsp; f<sub>mod<\/sub> \u2014 modulation frequency &nbsp;|&nbsp; f<sub>carrier<\/sub> \u2014 carrier frequency\n    <\/div>\n\n    <h4>Impulsive and Transient Signals<\/h4>\n    <p>Short-duration, high-amplitude events that excite multiple resonances simultaneously. Rolling-element bearing defects, gear-tooth chips, and loose fasteners all produce impulsive vibration. Characteristic features: high crest factor, broad frequency content, rapid decay, and periodic repetition at the defect frequency.<\/p>\n\n    <h4>Random Signals<\/h4>\n    <p>Turbulent flow, cavitation, and advanced surface degradation produce vibration with no dominant periodic component. Statistically it is characterised by its power spectral density (PSD) rather than by individual frequency peaks.<\/p>\n\n    <h3 id=\"s5-2\">5.2 Time Domain and Frequency Domain<\/h3>\n\n    <h4>Time-Domain Analysis<\/h4>\n    <p>Examining the raw waveform reveals information that spectral analysis can obscure: impact timing, modulation patterns, asymmetry (truncation, clipping), and the presence of transient events. Statistical parameters calculated from the waveform \u2014 RMS, crest factor, kurtosis, skewness \u2014 quantify signal character and are often the first indicators of bearing deterioration.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Parameter<\/th>\n                    <th>What It Detects<\/th>\n                    <th>Typical Guide Value (healthy)<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>RMS<\/strong><\/td>\n                    <td>Overall energy<\/td>\n                    <td>Machine-specific (see ISO zone limits)<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Crest factor<\/strong><\/td>\n                    <td>Impulsive content<\/td>\n                    <td>\u2248 3 \u2013 4 (trend matters more than the absolute value)<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Kurtosis<\/strong><\/td>\n                    <td>Peakedness \/ impact rate<\/td>\n                    <td>\u2248 3.0 (Gaussian baseline)<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Skewness<\/strong><\/td>\n                    <td>Waveform asymmetry<\/td>\n                    <td>\u2248 0 (symmetric)<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <p>Kurtosis is especially valuable for bearing diagnostics. A healthy bearing produces roughly Gaussian vibration (kurtosis \u2248 3). Developing defects drive kurtosis well above 4 \u2014 sometimes above 10 \u2014 long before overall RMS rises enough to trigger an alarm.<\/p>\n\n    <h4>Frequency-Domain Analysis (FFT)<\/h4>\n\n    <p>The Fast Fourier Transform converts a time record into a frequency spectrum, revealing which frequencies carry the most energy. This is the primary diagnostic tool because different fault types produce vibration at different, predictable frequencies.<\/p>\n\n    <div class=\"mrn-formula\">\n        X(k) = \u03a3<sub>n=0<\/sub><sup>N\u22121<\/sup> x(n) \u00b7 e<sup>\u2212j2\u03c0kn\/N<\/sup>\n    <\/div>\n\n    <h4>Key DSP Considerations<\/h4>\n\n    <p><strong>Sampling rate<\/strong> must exceed twice the highest frequency of interest (Nyquist criterion). Anti-aliasing filters attenuate everything above the Nyquist frequency before digitisation. A practical rule: sample at 2.56 \u00d7 the analysis bandwidth (to allow for filter roll-off).<\/p>\n\n    <p><strong>Frequency resolution<\/strong> = 1 \/ T, where T is the record length. To separate two close frequencies you need a longer record. For marine applications where speed varies slightly, order tracking (resampling synchronised to a tachometer pulse) maintains constant resolution in the order domain regardless of speed drift.<\/p>\n\n    <p><strong>Windowing<\/strong> suppresses spectral leakage caused by finite record length. Hanning is the general-purpose default; flat-top gives the best amplitude accuracy (important when comparing to absolute limits); rectangular is appropriate only for truly transient signals.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Window<\/th>\n                    <th>Frequency Resolution<\/th>\n                    <th>Amplitude Accuracy<\/th>\n                    <th>Use Case<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Rectangular<\/td>\n                    <td>Best<\/td>\n                    <td>Moderate<\/td>\n                    <td>Transient \/ impact<\/td>\n                <\/tr>\n                <tr>\n                    <td>Hanning<\/td>\n                    <td>Good<\/td>\n                    <td>Good<\/td>\n                    <td>General purpose<\/td>\n                <\/tr>\n                <tr>\n                    <td>Flat-top<\/td>\n                    <td>Poor<\/td>\n                    <td>Best<\/td>\n                    <td>Calibration, amplitude checks<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h3 id=\"s5-3\">5.3 Advanced Techniques<\/h3>\n\n    <h4>Envelope Analysis (Amplitude Demodulation)<\/h4>\n    <p>The method of choice for rolling-element bearing diagnostics. Steps: (1) band-pass filter around a structural resonance excited by bearing impacts (typically 2\u20138 kHz), (2) extract the amplitude envelope via Hilbert transform or rectification + low-pass filter, (3) compute the FFT of the envelope. <a href=\"https:\/\/vibromera.eu\/glossary\/bearing-fault-frequencies\/\">Bearing defect frequencies<\/a> (BPFO, BPFI, BSF, FTF) then appear as distinct peaks in the envelope spectrum, clearly separated from shaft-speed harmonics and other sources.<\/p>\n\n    <h4>Cepstrum Analysis<\/h4>\n    <p>The cepstrum is the inverse FFT of the log-magnitude spectrum. It detects periodic patterns <em>within<\/em> the frequency spectrum \u2014 exactly what sidebands around gear-mesh frequency or harmonic families from looseness produce. The technique is less intuitive than direct FFT but excels when multiple sideband families overlap.<\/p>\n\n    <div class=\"mrn-formula\">\n        Cepstrum = IFFT( log |FFT(x(t))| )\n    <\/div>\n\n    <h4>Order Tracking<\/h4>\n    <p>For variable-speed machinery (common on vessels with variable-frequency drives or during manoeuvring), conventional FFT smears speed-related peaks. Order tracking resamples the time signal using a tachometer or speed reference, converting the analysis from the frequency domain to the order domain. Each order corresponds to a fixed multiple of shaft speed.<\/p>\n\n    <h4>Coherence Function<\/h4>\n    <p>Measures the linear relationship between two signals as a function of frequency. Coherence close to 1.0 at a given frequency means the vibration at the response point is predominantly caused by the excitation at the reference point. Useful for isolating transmission paths, verifying measurement quality, and assessing how much of a machine's vibration is transmitted to nearby structures \u2014 or, on a ship, how much of the \"machine's\" vibration actually arrives from the propeller through the hull.<\/p>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 6 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s6\">\n    <h2>6. Condition Monitoring Programmes<\/h2>\n    <p class=\"mrn-lead\">Building and running a shipboard vibration monitoring programme \u2014 from acceptance testing through trend analysis.<\/p>\n\n    <h3 id=\"s6-1\">6.1 Acceptance Testing<\/h3>\n\n    <p>Vibration acceptance testing establishes that newly installed or overhauled equipment meets its design specification before entering service. For marine equipment this is typically done in stages: factory acceptance test (FAT) at the manufacturer \u2014 ISO 20283-3 covers pre-installation vibration measurement of shipboard equipment \u2014 harbour acceptance test (HAT) after installation aboard, and sea trial at full load.<\/p>\n\n    <h4>What Acceptance Testing Catches<\/h4>\n    <ul>\n        <li>Residual unbalance exceeding the specified <a href=\"https:\/\/vibromera.eu\/glossary\/iso-21940-11\/\">ISO 21940-11<\/a> (formerly ISO 1940-1) balance quality grade<\/li>\n        <li>Soft foot \u2014 one or more mounting feet not in proper contact with the foundation<\/li>\n        <li>Coupling misalignment introduced during installation<\/li>\n        <li>Piping strain transmitted to pump or compressor flanges<\/li>\n        <li>Foundation resonances that coincide with operating speed or propeller blade rate<\/li>\n    <\/ul>\n\n    <p>Measurements during acceptance testing become the baseline for future condition monitoring. They should be taken at several load levels (typically 25&nbsp;%, 50&nbsp;%, 75&nbsp;%, 100&nbsp;%) and documented with operating parameters (speed, load, temperatures, sea state).<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Break-in example<\/div>\n        <p>A newly installed cargo pump showed 4.2 mm\/s RMS immediately after commissioning. Over 100 hours of service the reading settled to 2.1 mm\/s as bearing surfaces conformed and clearances stabilised. Without acceptance testing the initial high reading might have triggered an unnecessary investigation.<\/p>\n    <\/div>\n\n    <h3 id=\"s6-2\">6.2 Monitoring Systems<\/h3>\n\n    <h4>Portable (Route-Based) Systems<\/h4>\n    <p>A technician walks a pre-defined route through the engine room, collecting data at each tagged measurement point using a handheld data collector. Software on a shore or office PC stores, trends, and analyses the data. This is the most cost-effective approach for auxiliary machinery where continuous monitoring is not justified.<\/p>\n\n    <h4>Permanent (On-Line) Systems<\/h4>\n    <p>Sensors are permanently installed on critical equipment and wired to a central data acquisition system. Measurements are taken automatically at scheduled intervals or continuously. Alarms trigger when thresholds are exceeded. Main engines, generators, propulsion motors, and reduction gears are typical candidates.<\/p>\n\n    <h4>Hybrid Approach<\/h4>\n    <p>Most modern fleets combine both. Continuous monitoring covers the 10\u201315 most critical machines. Route-based portable measurements cover 50\u2013200 auxiliary items on a weekly to quarterly cycle. Unified software merges both datasets into a single database.<\/p>\n\n    <h4>A Practical Starting Point<\/h4>\n\n    <p>The table below is a typical starting matrix for a merchant vessel. It is deliberately generic \u2014 criticality analysis, class requirements, and maker's instructions take precedence for any specific ship.<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Equipment<\/th>\n                    <th>What to Measure<\/th>\n                    <th>Where<\/th>\n                    <th>Typical Interval<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td><strong>Main propulsion engine<\/strong><\/td>\n                    <td>Broadband velocity, selective spectra; torsional monitoring per class requirements<\/td>\n                    <td>Main bearings \/ frame, thrust bearing, turbocharger casings<\/td>\n                    <td>Continuous or weekly route<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Shaft line<\/strong><\/td>\n                    <td>Broadband velocity + 1\u00d7\/2\u00d7 components; bearing temperatures<\/td>\n                    <td>Intermediate shaft bearings, stern-tube area<\/td>\n                    <td>Continuous or monthly<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Diesel generators<\/strong><\/td>\n                    <td>Broadband velocity (ISO 8528-9 framework), spectra on alternator bearings<\/td>\n                    <td>Engine frame, alternator drive-end and non-drive-end bearings<\/td>\n                    <td>Weekly \u2013 monthly<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Sea-water \/ fresh-water pumps<\/strong><\/td>\n                    <td>Velocity spectra + bearing envelope<\/td>\n                    <td>Pump and motor bearing housings, 2\u20133 directions<\/td>\n                    <td>Monthly<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Engine-room fans, blowers<\/strong><\/td>\n                    <td>Broadband velocity + 1\u00d7 (unbalance builds up from deposits)<\/td>\n                    <td>Fan and motor bearings<\/td>\n                    <td>Monthly \u2013 quarterly<\/td>\n                <\/tr>\n                <tr>\n                    <td><strong>Compressors, purifiers, separators<\/strong><\/td>\n                    <td>Velocity spectra + high-frequency bearing parameters<\/td>\n                    <td>Bearing housings per maker's drawing<\/td>\n                    <td>Monthly<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Database and Hierarchy<\/h4>\n    <p>The monitoring database organises equipment in a tree: vessel \u2192 department (engine, deck, electrical) \u2192 system (propulsion, auxiliary cooling, fire-fighting) \u2192 machine \u2192 component \u2192 measurement point. Each point has defined sensor type, direction, units, alarm levels, and analysis settings. Good hierarchy design makes fleet-wide benchmarking and reporting practical.<\/p>\n\n    <h3 id=\"s6-3\">6.3 Alarm Levels and Trend Analysis<\/h3>\n\n    <h4>Setting Alarm Levels<\/h4>\n    <p>There are three common approaches, and they can be combined.<\/p>\n\n    <ul>\n        <li><strong>Standards-based<\/strong> \u2014 use ISO 20816 (formerly ISO 10816) or API zone boundaries directly. Simple but one-size-fits-all.<\/li>\n        <li><strong>Statistical<\/strong> \u2014 set the alert at baseline mean + 2\u20133 standard deviations, the danger threshold at mean + 4\u20136 \u03c3. Tailored to each machine but requires sufficient baseline data.<\/li>\n        <li><strong>Experience-based<\/strong> \u2014 derived from the analyst's knowledge of a specific machine type. Often the most effective for unusual or very old equipment not covered well by generic standards.<\/li>\n    <\/ul>\n\n    <div class=\"mrn-callout mrn-warn\">\n        <div class=\"mrn-callout-title\">Avoid alarm fatigue<\/div>\n        <p>On a ship with hundreds of measurement points, poorly calibrated alarms generate dozens of false positives per route. Crews learn to ignore them. Invest time in proper baseline collection and alarm-level tuning \u2014 it is the single highest-leverage activity in a new programme.<\/p>\n    <\/div>\n\n    <h4>Trend Analysis<\/h4>\n    <p>Plotting a parameter over time reveals developing faults before they reach alarm levels. Trending works for overall RMS, individual frequency components, statistical parameters (crest factor, kurtosis), and envelope-derived metrics. The slope of the trend line \u2014 and especially any sudden change in slope \u2014 is the primary decision driver.<\/p>\n\n    <p>Methods range from simple visual inspection of time-series plots to statistical process control (CUSUM, EWMA) and regression-based remaining-useful-life models. For critical machinery, combining multiple trended parameters in a single \"health index\" provides a more robust picture than any one parameter alone.<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Trend success story<\/div>\n        <p>A main-engine cooling pump showed a steady month-on-month increase in outer-race defect-frequency amplitude over six months. Bearing replacement was scheduled during a routine port call, preventing an unplanned failure that would have required diverting the vessel.<\/p>\n    <\/div>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 7 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s7\">\n    <h2>7. Fault Detection and Identification<\/h2>\n    <p class=\"mrn-lead\">Translating spectral peaks, waveform shapes, and statistical parameters into specific fault diagnoses.<\/p>\n\n    <h3 id=\"s7-1\">7.1 Rolling-Element Bearing Diagnostics<\/h3>\n\n    <p>Rolling-element bearings are the most commonly monitored component in marine vibration programmes. Each defect location produces a distinct <a href=\"https:\/\/vibromera.eu\/glossary\/bearing-fault-frequencies\/\">characteristic frequency<\/a> determined by bearing geometry and shaft speed.<\/p>\n\n    <h4>Defect Frequencies<\/h4>\n\n    <div class=\"mrn-formula\">\n        BPFO = (N\/2) \u00b7 f<sub>shaft<\/sub> \u00b7 (1 \u2212 d\/D \u00b7 cos \u03c6)<br>\n        BPFI = (N\/2) \u00b7 f<sub>shaft<\/sub> \u00b7 (1 + d\/D \u00b7 cos \u03c6)<br>\n        BSF &nbsp;= (D\/2d) \u00b7 f<sub>shaft<\/sub> \u00b7 [1 \u2212 (d\/D \u00b7 cos \u03c6)\u00b2]<br>\n        FTF &nbsp;= (1\/2) \u00b7 f<sub>shaft<\/sub> \u00b7 (1 \u2212 d\/D \u00b7 cos \u03c6)<br>\n        <br>\n        N \u2014 number of rolling elements &nbsp;|&nbsp; d \u2014 element diameter<br>\n        D \u2014 pitch diameter &nbsp;|&nbsp; \u03c6 \u2014 contact angle &nbsp;|&nbsp; f<sub>shaft<\/sub> \u2014 shaft frequency\n    <\/div>\n\n    <p>The outer-race frequency is always the lower of the two race frequencies (BPFO \u2248 0.4 \u00b7 N \u00b7 f<sub>shaft<\/sub> as a rough rule) and the inner-race frequency the higher (BPFI \u2248 0.6 \u00b7 N \u00b7 f<sub>shaft<\/sub>); together they sum to N \u00b7 f<sub>shaft<\/sub> \u2014 a convenient sanity check.<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Worked example<\/div>\n        <p>Deep-groove ball bearing with 9 balls, d = 12.7 mm, D = 58.5 mm, \u03c6 \u2248 0\u00b0, running at 1&nbsp;750 r\/min (f<sub>shaft<\/sub> = 29.17 Hz):<br>\n        BPFO \u2248 4.5 \u00d7 29.17 \u00d7 (1 \u2212 0.217) \u2248 <strong>103 Hz<\/strong> \u00b7 BPFI \u2248 4.5 \u00d7 29.17 \u00d7 (1 + 0.217) \u2248 <strong>160 Hz<\/strong> \u00b7 BSF \u2248 <strong>64 Hz<\/strong> \u00b7 FTF \u2248 <strong>11.4 Hz<\/strong><br>\n        Check: BPFO + BPFI = 103 + 160 \u2248 262.5 Hz = 9 \u00d7 29.17 Hz \u2713<\/p>\n    <\/div>\n\n    <h4>Fault Progression Stages<\/h4>\n\n    <ol class=\"mrn-stages\">\n        <li><strong>Onset<\/strong> \u2014 subtle increase in the high-frequency noise floor (ultrasonic band, &gt; 20 kHz). No discrete peaks yet. Detectable only with specialised high-frequency techniques (acoustic emission, spike energy).<\/li>\n        <li><strong>Discrete defect frequencies appear<\/strong> \u2014 bearing-characteristic frequencies (BPFO, BPFI, etc.) become visible in the envelope spectrum or high-frequency-band acceleration spectrum.<\/li>\n        <li><strong>Harmonics and sidebands develop<\/strong> \u2014 defect-frequency harmonics grow; modulation sidebands at shaft speed appear around bearing frequencies.<\/li>\n        <li><strong>Broadening and increase<\/strong> \u2014 the noise floor rises in the bearing-frequency band; overall acceleration and velocity RMS begin to climb; crest factor may start to decrease as random content grows.<\/li>\n        <li><strong>Advanced damage<\/strong> \u2014 broadband random vibration dominates; displacement levels rise; temperatures increase; audible noise. Failure is imminent.<\/li>\n    <\/ol>\n\n    <h4>Envelope Analysis in Practice<\/h4>\n    <p>Band-pass filter the raw acceleration signal in the 2\u20138 kHz range (or around the highest bearing-excited resonance \u2014 identify it from an impact test or from the spectrum itself). Compute the Hilbert-transform envelope. FFT the envelope. If you see peaks at BPFO, BPFI, BSF, or FTF (and their harmonics), you have a positive bearing-defect identification.<\/p>\n\n    <h3 id=\"s7-2\">7.2 Gear Faults and Shaft Problems<\/h3>\n\n    <h4>Gear Diagnostics<\/h4>\n    <p>The fundamental gear-mesh frequency (GMF) equals the number of teeth multiplied by shaft rotational frequency. A healthy gear produces a clean mesh peak with low sidebands. Developing problems manifest as increased mesh amplitude, growing sidebands spaced at the shaft frequency of the damaged gear, and eventually generation of higher harmonics of GMF.<\/p>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Gear example<\/div>\n        <p>23-tooth pinion at 1&nbsp;200 r\/min (20 Hz) meshing with a 67-tooth wheel (6.87 Hz). GMF = 23 \u00d7 20 = 460 Hz. Sidebands at 460 \u00b1 20 Hz indicate a developing pinion defect; sidebands at 460 \u00b1 6.87 Hz point to the wheel.<\/p>\n    <\/div>\n\n    <h4>Shaft and Coupling Problems<\/h4>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Fault<\/th>\n                    <th>Dominant Frequency<\/th>\n                    <th>Key Indicators<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Mass unbalance<\/td>\n                    <td>1\u00d7 shaft speed<\/td>\n                    <td>Radial vibration; stable phase; amplitude \u221d speed\u00b2<\/td>\n                <\/tr>\n                <tr>\n                    <td>Parallel misalignment<\/td>\n                    <td>2\u00d7 (+ 1\u00d7, 3\u00d7)<\/td>\n                    <td>High radial vibration; 180\u00b0 phase shift across coupling<\/td>\n                <\/tr>\n                <tr>\n                    <td>Angular misalignment<\/td>\n                    <td>1\u00d7 and 2\u00d7<\/td>\n                    <td>High axial vibration at coupling<\/td>\n                <\/tr>\n                <tr>\n                    <td>Bent shaft<\/td>\n                    <td>1\u00d7 and 2\u00d7<\/td>\n                    <td>High 1\u00d7 axial; 180\u00b0 phase between bearings<\/td>\n                <\/tr>\n                <tr>\n                    <td>Mechanical looseness<\/td>\n                    <td>Many harmonics of 1\u00d7<\/td>\n                    <td>Subharmonics (0.5\u00d7); unstable phase; directional<\/td>\n                <\/tr>\n                <tr>\n                    <td>Rotor rub<\/td>\n                    <td>Fractional harmonics<\/td>\n                    <td>0.5\u00d7, 1.5\u00d7, 2.5\u00d7 etc.; truncated waveform<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Impeller \/ Flow-Related Problems<\/h4>\n    <p>Blade-passing frequency (BPF) = number of blades \u00d7 shaft frequency. Elevated BPF and its harmonics indicate impeller damage, diffuser\u2013impeller gap issues, or inlet flow distortion. Cavitation produces broadband high-frequency noise \u2014 a \"crackling\" sound signature above 2 kHz with high kurtosis. Recirculation at low flow creates low-frequency random instability. On ships, remember that the propeller itself produces blade-rate vibration that propagates through the structure (see Section 3.2).<\/p>\n\n    <h3 id=\"s7-3\">7.3 Severity Assessment and Prognosis<\/h3>\n\n    <p>Detecting a fault is only half the job. The maintenance team needs to know <em>how fast<\/em> the fault is progressing and <em>how long<\/em> the machine can continue to operate safely.<\/p>\n\n    <h4>Severity Metrics<\/h4>\n    <ul>\n        <li>Amplitude of the defect-frequency peak relative to its baseline value<\/li>\n        <li>Rate of change of that amplitude (slope of the trend)<\/li>\n        <li>Number and strength of harmonics and sidebands<\/li>\n        <li>Crest factor and kurtosis progression<\/li>\n        <li>Overall velocity or acceleration RMS relative to ISO zone boundaries<\/li>\n    <\/ul>\n\n    <h4>Prognostic Methods<\/h4>\n    <p>Simple trending with linear or exponential extrapolation gives a rough remaining-life estimate. More sophisticated approaches include physics-based degradation models (e.g., spalling propagation under Hertzian stress) and data-driven models trained on run-to-failure datasets. In either case, predictions should carry explicit confidence intervals \u2014 a point estimate of \"42 days remaining\" is much less useful than \"30\u201360 days at 90&nbsp;% confidence\".<\/p>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Severity Level<\/th>\n                    <th>Recommended Action<\/th>\n                    <th>Typical Timeframe<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Good<\/td>\n                    <td>Continue normal monitoring<\/td>\n                    <td>Next scheduled measurement<\/td>\n                <\/tr>\n                <tr>\n                    <td>Early fault<\/td>\n                    <td>Increase monitoring frequency<\/td>\n                    <td>Weekly \u2192 bi-weekly<\/td>\n                <\/tr>\n                <tr>\n                    <td>Developing<\/td>\n                    <td>Plan maintenance intervention<\/td>\n                    <td>Next port call or planned downtime<\/td>\n                <\/tr>\n                <tr>\n                    <td>Advanced<\/td>\n                    <td>Schedule repair as soon as possible<\/td>\n                    <td>Within 1\u20132 weeks<\/td>\n                <\/tr>\n                <tr>\n                    <td>Critical<\/td>\n                    <td>Reduce load or shut down; emergency repair<\/td>\n                    <td>Immediate<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n<\/section>\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 8 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s8\">\n    <h2>8. Alignment and Balancing<\/h2>\n    <p class=\"mrn-lead\">The two corrective actions that eliminate the largest share of vibration problems on marine rotating equipment.<\/p>\n\n    <h3 id=\"s8-1\">8.1 Shaft Alignment<\/h3>\n\n    <p>Misalignment between coupled shafts is one of the top three vibration causes in marine machinery (alongside unbalance and bearing wear). It creates excessive forces on bearings, seals, and couplings, and produces a characteristic vibration signature dominated by 2\u00d7 shaft speed.<\/p>\n\n    <h4>Misalignment Types<\/h4>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Type<\/th>\n                    <th>Dominant Vibration<\/th>\n                    <th>Direction<\/th>\n                    <th>Phase Signature<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr>\n                    <td>Parallel (offset)<\/td>\n                    <td>2\u00d7 RPM<\/td>\n                    <td>Radial<\/td>\n                    <td>180\u00b0 shift across coupling in radial direction<\/td>\n                <\/tr>\n                <tr>\n                    <td>Angular<\/td>\n                    <td>1\u00d7 and 2\u00d7 RPM<\/td>\n                    <td>Axial<\/td>\n                    <td>180\u00b0 shift across coupling in axial direction<\/td>\n                <\/tr>\n                <tr>\n                    <td>Combined<\/td>\n                    <td>1\u00d7 + 2\u00d7 + higher<\/td>\n                    <td>All<\/td>\n                    <td>Complex; requires multi-point measurement<\/td>\n                <\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <h4>Static vs. Dynamic Alignment<\/h4>\n    <p>Static alignment is measured when the machine is cold and at rest. Dynamic (operating) alignment can differ substantially because of thermal growth, foundation deflection under load, and piping forces that develop with temperature and pressure. A diesel generator, for instance, may grow 1\u20132 mm vertically at the coupling centre when the engine reaches operating temperature. On ships there is an extra layer: hull deflection with cargo and ballast condition changes shaft-line alignment between the laden and ballast voyage.<\/p>\n\n    <div class=\"mrn-formula\">\n        Thermal growth: &nbsp; \u0394L = L \u00b7 \u03b1 \u00b7 \u0394T<br>\n        Example: 2 m steel shaft height, \u03b1 = 12 \u00d7 10\u207b\u2076 \/\u00b0C, \u0394T = 50 \u00b0C \u2192 \u0394L = 1.2 mm upward\n    <\/div>\n\n    <p>Laser alignment systems calculate cold offsets to compensate for expected thermal growth, so that alignment is correct at operating temperature rather than at ambient.<\/p>\n\n    <h4>Soft Foot<\/h4>\n    <p>If one or more machine feet do not contact the foundation properly, tightening the hold-down bolt distorts the frame, shifts bearing alignment, and changes vibration characteristics in a load-dependent way. Detecting soft foot is the first step before any alignment procedure: loosen each bolt in turn and measure movement with a dial indicator or laser system. Correct with precision shims.<\/p>\n\n    <h3 id=\"s8-2\">8.2 Balancing Theory<\/h3>\n\n    <p>Mass unbalance creates a centrifugal force that rotates with the shaft, producing vibration at 1\u00d7 RPM. The force is proportional to \u03c9\u00b2, so a rotor that vibrates moderately at low speed may be destructive at high speed.<\/p>\n\n    <div class=\"mrn-formula\">\n        Unbalance force: &nbsp; F = m \u00b7 r \u00b7 \u03c9\u00b2<br>\n        m \u2014 unbalance mass &nbsp;|&nbsp; r \u2014 radius &nbsp;|&nbsp; \u03c9 \u2014 angular velocity\n    <\/div>\n\n    <h4>Unbalance Types<\/h4>\n    <ul>\n        <li><strong>Static<\/strong> \u2014 a single heavy spot; the rotor would settle with the heavy side down on knife edges. One correction plane is sufficient.<\/li>\n        <li><strong>Couple<\/strong> \u2014 two equal masses 180\u00b0 apart in different axial planes. No static imbalance, but the rotor wobbles during rotation. Two correction planes required.<\/li>\n        <li><strong>Dynamic<\/strong> \u2014 the general case: combination of static and couple. Always requires two-plane correction for full elimination.<\/li>\n    <\/ul>\n\n    <h4>Balance Quality \u2014 ISO 21940-11 (formerly ISO 1940-1)<\/h4>\n    <p><a href=\"https:\/\/vibromera.eu\/glossary\/iso-21940-11\/\">ISO 21940-11<\/a> defines permissible residual unbalance as a function of rotor mass and service speed, expressed as a balance quality grade G. The grade value equals the product e<sub>per<\/sub> \u00b7 \u03c9 in mm\/s, where e<sub>per<\/sub> is the permissible specific unbalance (displacement of the centre of mass from the shaft axis) and \u03c9 the angular velocity at service speed. In practical units:<\/p>\n\n    <div class=\"mrn-formula\">\n        e<sub>per<\/sub> [g\u00b7mm\/kg] = 9549 \u00b7 G \/ n &nbsp;&nbsp;&nbsp; U<sub>per<\/sub> [g\u00b7mm] = e<sub>per<\/sub> \u00b7 m<sub>rotor<\/sub> [kg]<br>\n        G \u2014 balance quality grade [mm\/s] &nbsp;|&nbsp; n \u2014 service speed [r\/min]\n    <\/div>\n\n    <div class=\"mrn-tablewrap\">\n        <table>\n            <thead>\n                <tr>\n                    <th>Grade<\/th>\n                    <th>e<sub>per<\/sub>\u00b7\u03c9 (mm\/s)<\/th>\n                    <th>Typical Application (ISO 21940-11, Table 1)<\/th>\n                <\/tr>\n            <\/thead>\n            <tbody>\n                <tr><td>G 0.4<\/td><td>0.4<\/td><td>Gyroscopes, spindles and drives of high-precision systems<\/td><\/tr>\n                <tr><td>G 1.0<\/td><td>1.0<\/td><td>Audio\/video drives, grinding-machine drives<\/td><\/tr>\n                <tr><td>G 2.5<\/td><td>2.5<\/td><td>Compressors, gas and steam turbines, electric motors above 950 r\/min<\/td><\/tr>\n                <tr><td>G 6.3<\/td><td>6.3<\/td><td>General machinery: pumps, fans, gears, electric motors, turbochargers, water turbines<\/td><\/tr>\n                <tr><td>G 16<\/td><td>16<\/td><td>Drive shafts (cardan and propeller shafts), agricultural machinery, crushers<\/td><\/tr>\n                <tr><td>G 250 \u2013 G 4000<\/td><td>250 \u2013 4000<\/td><td>Crankshaft drives of large, slow marine diesel engines (grade depends on mounting and inherent balance)<\/td><\/tr>\n            <\/tbody>\n        <\/table>\n    <\/div>\n\n    <div class=\"mrn-callout mrn-ex\">\n        <div class=\"mrn-callout-title\">Worked example<\/div>\n        <p>Sea-water pump rotor, mass 120 kg, service speed 2&nbsp;950 r\/min, specified grade G 6.3:<br>\n        e<sub>per<\/sub> = 9549 \u00d7 6.3 \/ 2950 \u2248 <strong>20.4 g\u00b7mm\/kg<\/strong> \u2192 U<sub>per<\/sub> = 20.4 \u00d7 120 \u2248 <strong>2&nbsp;450 g\u00b7mm<\/strong>.<br>\n        At a correction radius of 200 mm this corresponds to a residual mass of 2450 \/ 200 \u2248 <strong>12.2 g<\/strong> \u2014 the total allowed, typically split between two correction planes.<\/p>\n    <\/div>\n\n    <h3 id=\"s8-3\">8.3 Field Balancing<\/h3>\n\n    <p>Field balancing corrects unbalance in the machine's own bearings and supports, under real operating conditions. This is almost always preferable to removing a rotor for shop balancing when the unbalance is due to in-service fouling, erosion, or thermal distortion rather than manufacturing defect.<\/p>\n\n    <h4>Single-Plane Procedure (Influence-Coefficient Method)<\/h4>\n\n    <ol class=\"mrn-stages\">\n        <li>Measure initial vibration amplitude and phase at 1\u00d7 RPM (reference run).<\/li>\n        <li>Attach a known trial mass at a known angular position on the rotor.<\/li>\n        <li>Run the machine and measure vibration again (trial run).<\/li>\n        <li>Calculate the influence coefficient: how much vibration change one unit of mass at that radius produces.<\/li>\n        <li>Calculate the correction mass and angle that will drive vibration to zero (vector arithmetic).<\/li>\n        <li>Remove the trial mass, install the correction mass, verify with a final run.<\/li>\n    <\/ol>\n\n    <p>Two-plane balancing follows the same logic but solves a 2\u00d72 system of influence coefficients, allowing simultaneous correction of static and couple components.<\/p>\n\n    <div class=\"mrn-cta\">\n        <div class=\"mrn-cta-body\">\n            <h4>Balanset-1A \u2014 Portable Balancing and Vibration Analysis<\/h4>\n            <p>Vibromera's Balanset-1A is a portable instrument for single-plane and two-plane field balancing with built-in vibration measurement and FFT spectrum analysis: vibration velocity 0.2\u201380 mm\/s RMS, frequency range 5\u20131000 Hz, laser tachometer 250\u201390&nbsp;000 r\/min, powered over USB from a laptop. It is used on fans, pumps, centrifuges, separators, shafts, and other rotating equipment in marine and industrial environments.<\/p>\n        <\/div>\n        <a class=\"mrn-cta-btn\" href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Learn more<\/a>\n    <\/div>\n\n    <h4>Marine-Specific Challenges<\/h4>\n    <ul>\n        <li><strong>Vessel motion<\/strong> \u2014 background vibration from waves and engine can mask the 1\u00d7 signal. Mitigation: measurement averaging over many revolutions, scheduling for calm conditions or in port.<\/li>\n        <li><strong>Limited access<\/strong> \u2014 correction planes may be inside enclosures. Pre-planning and custom weight-attachment methods are often required.<\/li>\n        <li><strong>Thermal effects<\/strong> \u2014 machines balanced cold may develop additional unbalance at operating temperature due to differential expansion. Ideally, verify balance at normal operating temperature.<\/li>\n    <\/ul>\n\n    <h3 id=\"s8-4\">8.4 Other Vibration Reduction Approaches<\/h3>\n\n    <p>When balancing and alignment do not bring vibration to acceptable levels, several other techniques are available.<\/p>\n\n    <h4>Source Modification<\/h4>\n    <p>Redesign or modify the component to reduce the excitation force \u2014 for example, optimising impeller\u2013diffuser gap in a pump, improving manufacturing tolerances, or selecting an operating speed further from a critical speed.<\/p>\n\n    <h4>Stiffness and Damping Changes<\/h4>\n    <p>Reinforcing a foundation shifts its natural frequency away from the excitation frequency. Adding damping (constrained-layer treatments, viscoelastic mounts) reduces the amplification at resonance. Both approaches can be applied post-installation, though foundation reinforcement in a ship is constrained by structural weight limits.<\/p>\n\n    <h4>Vibration Isolation<\/h4>\n    <p>Resilient mounts (rubber, spring, air) decouple the machine from the hull structure. Isolation becomes effective when the excitation frequency exceeds roughly \u221a2 \u00d7 the mount natural frequency. Marine isolators must also resist loads from vessel motion and tolerate corrosive atmospheres.<\/p>\n\n    <h4>Tuned Absorbers and Dampers<\/h4>\n    <p>A tuned mass damper (TMD) \u2014 a small secondary mass-spring system tuned to the problem frequency \u2014 absorbs energy from the primary structure at that specific frequency. Effective for narrow-band problems such as a deck resonance excited by a generator or by propeller blade rate. The drawback is that each TMD addresses only one frequency.<\/p>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 9 \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s9\">\n    <h2>9. Emerging Technologies<\/h2>\n    <p class=\"mrn-lead\">Where marine vibration diagnostics is heading \u2014 wireless sensors, edge computing, machine learning, and the path toward autonomous maintenance.<\/p>\n\n    <h3 id=\"s9-1\">9.1 AI and Machine Learning<\/h3>\n\n    <p>Machine learning is shifting vibration diagnostics from manually defined rule sets toward data-driven pattern recognition. The most immediate applications are automated fault classification and remaining-useful-life prediction.<\/p>\n\n    <h4>Classification<\/h4>\n    <p>Convolutional neural networks (CNNs) trained on labelled vibration datasets can classify bearing, gear, unbalance, and misalignment faults with accuracy comparable to experienced analysts \u2014 provided the training data covers the actual operating conditions. Transfer learning and domain adaptation address the common problem of limited labelled marine data by starting from models trained on industrial datasets and fine-tuning with shipboard data.<\/p>\n\n    <h4>Anomaly Detection<\/h4>\n    <p>Autoencoders and variational autoencoders learn a compressed representation of normal vibration. When a new measurement falls outside the learned distribution the system flags it as anomalous \u2014 without needing prior examples of every possible fault type. This is particularly valuable for rare failure modes.<\/p>\n\n    <h4>Digital Twins<\/h4>\n    <p>A digital twin is a physics-based or hybrid model of a machine that runs in parallel with the real one, continuously updated with sensor data. Deviations between model predictions and real measurements indicate changing internal conditions. Digital twins enable scenario simulation (\"what if we increase speed by 5&nbsp;%?\") and more reliable prognosis because they incorporate physics rather than relying solely on statistical extrapolation.<\/p>\n\n    <h3 id=\"s9-2\">9.2 Wireless Sensors and Edge Computing<\/h3>\n\n    <p>Wireless vibration sensors have matured to the point where battery life exceeds five years, communication reliability is sufficient for non-safety-critical monitoring, and on-board processing allows the sensor to compute statistical parameters locally, transmitting only summaries and alarms rather than raw waveforms. This drastically reduces installation cost \u2014 no cabling, no conduit, no junction boxes \u2014 and makes it economical to monitor hundreds of auxiliary machines that were previously unmonitored.<\/p>\n\n    <p>Edge computing places processing power at or near the sensor, enabling real-time alarm generation, local FFT, and even neural-network inference without relying on a shore-side cloud connection. This is important for vessels that spend days or weeks with limited satellite bandwidth.<\/p>\n\n    <h3 id=\"s9-3\">9.3 Autonomous Diagnostics and Integration<\/h3>\n\n    <p>The long-term trajectory points toward systems that detect, diagnose, and act with minimal human intervention:<\/p>\n\n    <ul>\n        <li><strong>Self-calibrating sensors<\/strong> that verify their own health and compensate for drift.<\/li>\n        <li><strong>Automatic fault diagnosis<\/strong> integrated with the vessel's planned maintenance system \u2014 a bearing-defect detection automatically generates a work order, checks spare-parts inventory, and suggests a maintenance window.<\/li>\n        <li><strong>Fleet-level analytics<\/strong> \u2014 comparing the same equipment type across an entire fleet identifies systemic problems (a bad batch of bearings, a design-related resonance) that single-vessel monitoring would miss.<\/li>\n        <li><strong>Multi-parameter fusion<\/strong> \u2014 combining vibration, oil analysis, thermography, and performance data in a single health index provides more reliable condition assessment than any single technique alone.<\/li>\n    <\/ul>\n\n    <div class=\"mrn-callout mrn-info\">\n        <div class=\"mrn-callout-title\">Regulatory note<\/div>\n        <p>Classification societies (DNV, Lloyd's Register, Bureau Veritas, ABS) maintain rules and class notations that recognise condition-based maintenance as an alternative to fixed-interval surveys. Robust, auditable vibration monitoring programmes are becoming a regulatory enabler, not just a cost-saving tool.<\/p>\n    <\/div>\n\n    <h4>Preparing for Adoption<\/h4>\n    <p>Technology alone is not sufficient. Successful adoption requires workforce development (data-literacy training for engineers accustomed to wrenches, not algorithms), cybersecurity planning (connected monitoring systems are an attack surface), and a phased approach \u2014 pilot on a few vessels, prove the value, then scale.<\/p>\n<\/section>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 SECTION 10 \u2014 FAQ \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<section id=\"s10\" class=\"mrn-faq\">\n    <h2>10. Frequently Asked Questions<\/h2>\n    <p class=\"mrn-lead\">Short answers to the questions marine engineers ask most often about vibration diagnostics.<\/p>\n\n    <details>\n        <summary>Which ISO standards apply to vibration of marine machinery?<\/summary>\n        <div>\n            <p>The general framework is the ISO 20816 series (formerly ISO 10816) for vibration measured on non-rotating parts. Ship-specific measurement is covered by the ISO 20283 series: Part 2 for structural vibration, Part 3 for pre-installation testing of shipboard equipment, Part 4 for propulsion machinery, and Part 5 for habitability. Reciprocating machines above 100 kW \u2014 including marine diesel engines \u2014 fall under ISO 10816-6, and generating sets under ISO 8528-9. Rotor balance quality is specified in ISO 21940-11 (formerly ISO 1940-1).<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>What vibration level is acceptable for a shipboard pump or motor?<\/summary>\n        <div>\n            <p>It depends on the machine's power rating and mounting. As one example, for a medium machine (15\u2013300 kW) on rigid supports under ISO 10816-3 \/ ISO 20816-3, up to 1.4 mm\/s RMS is zone A (good), 1.4\u20132.8 mm\/s is zone B (acceptable for unrestricted long-term operation), 2.8\u20134.5 mm\/s is zone C (plan remedial work), and above 4.5 mm\/s is zone D (risk of damage). Larger machines and flexibly mounted machines have higher limits \u2014 always check the group and support class that actually apply.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>How is the blade-passing frequency of a propeller calculated?<\/summary>\n        <div>\n            <p>Multiply the number of blades by the shaft speed in revolutions per second: BPF = Z \u00d7 n \/ 60, with n in r\/min. A four-blade propeller at 120 r\/min gives 4 \u00d7 2 = 8 Hz, with harmonics at 16 and 24 Hz. These low frequencies can excite hull and deckhouse resonances, so elevated blade-rate vibration on aft-ship machinery does not necessarily indicate a fault in that machine.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>Can a rotor be balanced on board without dismantling it?<\/summary>\n        <div>\n            <p>Yes \u2014 this is field balancing. Using a portable instrument with vibration sensors and a tachometer, the influence-coefficient method needs only a reference run and one trial run per correction plane to compute the correction mass and angle. It corrects the rotor in its own bearings under real operating conditions, which is usually preferable to shop balancing when unbalance is caused by in-service fouling, erosion, or blade damage.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>How often should vibration measurements be taken on ship machinery?<\/summary>\n        <div>\n            <p>Critical propulsion and power-generation machinery is typically monitored continuously or on a weekly route; auxiliary pumps, fans, compressors, and separators monthly to quarterly. The interval should shorten as soon as a parameter starts trending upward \u2014 a machine in \"early fault\" state deserves weekly or even continuous attention until the fault is understood.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>What is the difference between ISO 10816 and ISO 20816?<\/summary>\n        <div>\n            <p>ISO 20816 is the successor series that progressively replaces both ISO 10816 (vibration on non-rotating parts) and ISO 7919 (shaft vibration), combining them in one framework. ISO 20816-1:2016 replaced ISO 10816-1 and ISO 7919-1; ISO 20816-3:2022 replaced ISO 10816-3. The four-zone evaluation concept (A\u2013D) is unchanged; references in older documentation to ISO 10816 zone values generally remain usable, but new specifications should cite ISO 20816.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>Do sea state and vessel motion affect vibration readings?<\/summary>\n        <div>\n            <p>Yes. Wave-induced hull vibration, slamming, and load changes raise background levels, particularly at low frequencies. Good practice is to log sea state, speed, and load with every measurement, take routine readings under repeatable conditions (calm water, steady load) where possible, and flag or exclude data collected in heavy weather from trend analysis.<\/p>\n        <\/div>\n    <\/details>\n\n    <details>\n        <summary>Which sensor should be used for engine-room measurements?<\/summary>\n        <div>\n            <p>An IEPE piezoelectric accelerometer is the default choice: robust, broadband (typically 1 Hz\u201310 kHz), and tolerant of long cable runs in electrically noisy environments. Use stud or adhesive mounting for bearing diagnostics above 2\u20133 kHz; magnetic mounts are acceptable for broadband velocity readings. Proximity probes are reserved for journal-bearing turbomachinery where shaft-relative motion matters.<\/p>\n        <\/div>\n    <\/details>\n<\/section>\n\n<\/main>\n<\/div>\n\n<!-- \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 FOOTER \u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550 -->\n<footer class=\"mrn-footer\">\n    <div class=\"mrn-footer-inner\">\n        <h2>Summary<\/h2>\n        <p>Vibration diagnostics is the primary condition-monitoring technique for rotating marine equipment. It covers the full lifecycle \u2014 from acceptance testing through routine monitoring to end-of-life prognosis \u2014 and its effectiveness depends on proper sensor selection, disciplined data collection, and competent analysis. As AI, wireless sensors, and digital twins enter the maritime space, the technique is becoming more automated and more integrated with vessel management systems, but the underlying physics and engineering judgement remain essential.<\/p>\n        <p>\n            <a href=\"https:\/\/vibromera.eu\/\">vibromera.eu<\/a> &nbsp;\u00b7&nbsp;\n            <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> &nbsp;\u00b7&nbsp;\n            <a href=\"https:\/\/www.youtube.com\/@vibromera\" target=\"_blank\" rel=\"noopener\">YouTube<\/a>\n        <\/p>\n    <\/div>\n<\/footer>\n\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Which ISO standards apply to vibration of marine machinery?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"The general framework is the ISO 20816 series (formerly ISO 10816) for vibration measured on non-rotating parts. Ship-specific measurement is covered by the ISO 20283 series: Part 2 for structural vibration, Part 3 for pre-installation testing of shipboard equipment, Part 4 for propulsion machinery, and Part 5 for habitability. Reciprocating machines above 100 kW, including marine diesel engines, fall under ISO 10816-6, and generating sets under ISO 8528-9. Rotor balance quality is specified in ISO 21940-11 (formerly ISO 1940-1).\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What vibration level is acceptable for a shipboard pump or motor?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"It depends on the machine's power rating and mounting. 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Vibromera Engineering Team \u00b7 Standards: ISO 20816 \u00b7 ISO 20283 \u00b7 ISO 21940-11 At a glance What: vibration-based [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ai_generated_summary":"","footnotes":""},"categories":[54],"tags":[],"class_list":["post-6285","post","type-post","status-publish","format-standard","hentry","category-content"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/posts\/6285","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/comments?post=6285"}],"version-history":[{"count":4,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/posts\/6285\/revisions"}],"predecessor-version":[{"id":102227,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/posts\/6285\/revisions\/102227"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/media?parent=6285"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/categories?post=6285"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/pa\/wp-json\/wp\/v2\/tags?post=6285"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}