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Propeller Unbalance Calculator
Calculate permissible propeller unbalance, centrifugal force, eccentricity, and per-blade allowance per ISO 21940. Essential for marine shaft vibration control.
Results
Permissible Propeller Unbalance (ISO 21940)
The permissible unbalance for a propeller is calculated using the same ISO 21940-11 formula used for all rotating machinery:
Where G is the balance grade (mm/s), m is propeller mass (kg), and ω = 2π·n/60 is angular velocity (rad/s).
Centrifugal Force from Unbalance
The centrifugal force generated by unbalance at operating speed:
- U — unbalance (g·mm)
- ω — angular velocity (rad/s)
- F — centrifugal force (N)
Per-Blade Allowance
For symmetrical propellers, the total permissible unbalance is divided equally among all blades:
Typical Balance Grades for Propellers
| Grade | Application |
|---|---|
| G40 | Slow-speed workboat propellers, non-critical |
| G16 | Standard marine propellers, cargo vessels |
| G6.3 | High-speed craft, navy vessels, passenger ferries |
| G2.5 | Precision propellers, low-noise submarines |
Practical Example
Given: Mass = 500 kg, Speed = 300 RPM, Grade = G16, 4 blades
ω = 2π × 300 / 60 = 31.42 rad/s
Uper = 16 × 500 × 1000 / 31.42 = 254,620 g·mm
Eccentricity = 16 × 1000 / 31.42 = 509.2 μm
F = 254,620 / 1,000,000 × 31.42² = 251.5 N
Per blade: 254,620 / 4 = 63,655 g·mm
⚠️ Note: Marine propellers operate in harsh conditions. Fouling, blade damage, and cavitation erosion can alter balance over time. Periodic vibration monitoring is recommended to detect developing unbalance.
Professional field balancing instruments for marine propellers, shafts, and rotating machinery. Achieve ISO 21940-11 compliance on-site.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
