Marine Propeller Shaft Torque, Gearbox, Coupling & Power Margin Tool

Shaft Torque, Hollow-Shaft Stress, Gearbox & Coupling Capacity, IACS M68 Screen, Peak Load & Future Uprate Margin

Marine Propeller Shaft Torque, Gearbox, Coupling & Power Margin Tool

Convert shaft power and rpm into the torque carried by the propulsion train. Check hollow-shaft torsional stress, continuous and peak gearbox capacity, coupling torque margin and the weakest power limit. Advanced mode adds prime-mover and reduction-gear reconstruction, IACS UR M68 shaft-diameter screening, torsional-vibration evidence, service-factor checks, operating cases and future uprate analysis.

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Need much more depth? Click Advanced above. Add the prime mover and reduction gear, IACS M68 shaft screen, torsional-vibration evidence, service factors and multiple operating cases.

Shaft Operating Point

Use mechanical power actually transmitted by the shaft at the operating point being checked.

Shaft mechanical power kW transmitted at the shaft-side operating point.

Shaft speed rpm.

Propulsion Shaft

Shaft outside diameter mm at the section being screened.

Shaft bore diameter mm. Enter 0 for a solid shaft.

Allowable static torsional stress MPa. Enter the project, designer or approved screening limit. This is not an IACS universal value.

Gearbox & Coupling Ratings

Gearbox continuous output torque rating kN·m.

Coupling continuous torque rating kN·m.

Transient peak torque multiplier Editable project / OEM screening multiplier applied to current transmitted torque.

Gearbox peak output torque rating kN·m.

Coupling peak torque rating kN·m.

Prime Mover & Reduction Gear

Advanced can reconstruct shaft-side power and rpm from the machinery train instead of using the Simple operating-point values.

Prime mover type

Engines / motors feeding this shaft

Rated power per prime mover kW.

Rated prime-mover speed rpm.

Gear ratio, input rpm : shaft rpm

Gearbox mechanical efficiency % input power delivered to shaft side.

Mechanical design power basis

Permanent approved power limit % of installed MCR.

Current overridable EPL / ShaPoLi setting % of installed MCR. Informational only unless permanently approved as the mechanical design basis.

Normal service power % of mechanical design power.

IACS UR M68 Traditional Shaft Screen

Use only where UR M68 is applicable to the shaft section. It is not a gear shaft, motor rotor, generator rotor, turbine rotor, crankshaft or unprotected seawater-exposed shaft rule.

Shaft section

Material family

Specified minimum tensile strength N/mm². The tool applies the M68 formula-use caps.

M68 installation factor F

M68 shaft design feature

Approved continuous TV stress limit MPa alternating amplitude from the approved torsional-vibration basis for the section and speed checked.

Calculated / measured alternating TV stress MPa alternating amplitude.

TV assessment shaft speed rpm.

Gearbox & Coupling Detail

Gearbox continuous power rating kW.

Gearbox continuous input torque rating kN·m at gearbox input.

Maximum gearbox input speed rpm.

Minimum desired gearbox service factor Project / OEM criterion, not a universal class minimum.

Minimum desired coupling service factor Project / OEM criterion.

Coupling approved for reverse torque

Operating-Case Register

Use shaft rpm directly for low-rpm high-torque, one-engine, hybrid, CPP and manoeuvring cases. Rows sent to Tool Data contain engineering values only, not free-text case names.

Case	Type	Power % design	Shaft rpm	Torque multiplier	Hours/year

Energy & Commercial Context

Annual propulsion hours

Main-engine SFOC g/kWh for indicative gearbox-loss fuel valuation.

Fuel price Selected currency / tonne. Display-only currency selection, no FX conversion.

Engineering Readiness

Approved shafting calculation availableClass / designer shaft section, connection details and design basis are available. Torsional vibration analysis verifiedNormal, relevant transient and misfiring cases are covered where applicable. Gearbox maker rating confirmedPower, input torque, output torque, peak torque, ratio and duty match the exact unit. Coupling / bolt basis confirmedContinuous, peak, reverse torque and misalignment limitations match the installed coupling. Shaft alignment / bearing loads checkedAlignment, thermal offsets, aft-bearing contact and lubrication are assessed separately. Power-limit documentation reconciledMCR, permanent derating, EPL / ShaPoLi and propeller design power use a consistent approved basis.

Screening boundary: this calculator does not replace a class-approved shafting design, gear-tooth load-capacity calculation, coupling-bolt calculation, torsional-vibration analysis, shaft-alignment calculation, bearing-oil-film assessment, transient dynamic simulation or OEM rating sheet. Where the applicable limit is maker-, class-, flag- or project-specific, the tool uses the value you enter.

Reference basis: transmitted torque uses T = 9,550 × P / n for kW and rpm. The Advanced traditional-shaft diameter screen follows IACS UR M68 Rev.3, including the published installation factor F, shaft-feature factor k, bore correction and material-strength formula-use limits. M68 applies to traditional propulsion shafts and excludes several special shaft types including gearing shafts, motor and generator rotor shafts, turbine rotors, crankshafts and unprotected shafts exposed to seawater. IACS UR M56 separately addresses load capacity of qualifying enclosed involute spur and helical marine gears, so this tool compares entered gearbox ratings rather than claiming to reproduce a gear-tooth approval calculation. Shaft alignment and aft-bearing lubrication remain separate engineering checks. IACS UR M68 Rev.3 · IACS UR M56 · DNV shaft alignment

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