Shaft Torsional - 1st Critical Speed
First torsional critical speed of the propulsion shaft - must stay outside the engine's continuous-running band.
1st critical rpm
80rpm
Status
Outside MCR band
Formula, assumptions, and limits
$$\omega_n = \sqrt{K/I}$$
Barred Speed Range (BSR) applied ±10 % around critical rpm - engine not run continuously in BSR. Class rules (IACS UR M68) mandate torsional vibration calculation.
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $I$ | Propeller + shaft polar inertia | kg·m² | rotor dynamics |
| $K$ | Shaft torsional stiffness | N·m/rad | material + geometry |
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