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

Engine kW, Shaft RPM, IACS M68 Diameter, Torsional Stress, Gearbox Rating, Coupling Capacity & Future Uprate Margin

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

Turn propulsion power and rpm into the torque every drivetrain component must carry. Screen traditional propulsion-shaft diameter against IACS UR M68, calculate hollow-shaft torsional stress, compare gearbox input / output torque and service factor, test coupling continuous and peak torque, model transient and derated operating cases, identify the weakest component, and estimate how much additional shaft power the existing train can accept before a shaft, gearbox or coupling becomes the limiting item.

Propulsion Power & Reduction Gear

Mechanical sizing should normally use the approved maximum power the train can actually receive. Do not use an overridable EPL / ShaPoLi setting to justify smaller mechanical components unless the approved design basis specifically allows it.

Prime mover / propulsion type

Engines / motors feeding this shaft

Rated power per prime mover, kW

Rated prime-mover speed, rpm

Gear ratio, engine rpm : shaft rpm

Gearbox mechanical efficiency% from gearbox input power to output shaft.

Mechanical design power basis

Permanent approved power limit% of installed MCR.

Overridable EPL / ShaPoLi currently set% of MCR. Operational information only unless permanently approved as mechanical design basis.

Normal service power% of mechanical design power.

Annual propulsion hours

Main-engine SFOC for loss valuationg/kWh.

Fuel priceSelected currency / tonne.

Propulsion Shaft & IACS M68 Screen

Shaft type

Material family

Specified minimum tensile strength, N/mm²

Existing shaft outside diameter, mm

Shaft bore diameter, mm

M68 shaft design feature

Static torsional stress screening limit, MPaEditable owner / designer screen. Not an IACS M68 yield or fatigue approval value.

Calculated / measured alternating torsional stress, MPa

TV assessment shaft speed, rpm

Transient peak torque multiplierEditable crash-astern / rapid manoeuvring / transient screening multiplier.

Gearbox Ratings

Gearbox continuous power rating, kW

Gearbox continuous input torque rating, kN·m

Gearbox continuous output torque rating, kN·m

Gearbox peak output torque rating, kN·m

Minimum desired continuous service factor

Maximum gearbox input speed, rpm

Flexible / Rigid Coupling Ratings

Coupling continuous torque rating, kN·m

Coupling peak torque rating, kN·m

Minimum desired coupling service factor

Coupling / bolts / hub approved for reverse torque

Advanced Operating-Case Register

Use this to compare continuous, derated, one-engine, low-rpm high-torque and transient cases. Enter shaft rpm directly so unusual CPP, hybrid, clutch or manoeuvring conditions are not forced onto a propeller-law assumption.

Case	Power % design	Shaft rpm	Torque multiplier	Hours/year

Engineering Readiness

Approved shafting calculation availableClass / designer shaft diameter and connection details are available for comparison with the M68 screen. Torsional vibration analysis verifiedNormal, relevant transient and one-cylinder-misfiring cases have been assessed where applicable. Gearbox maker rating sheet confirmedContinuous and peak torque ratings reflect the exact ratio, duty and application factor. Coupling rating / bolt basis confirmedContinuous, peak, reverse torque and misalignment limitations match the installed coupling. Shaft alignment / bearing loads checkedAft bearing contact, alignment, thermal offsets and bearing loads are verified separately from torsional strength. Power-limitation documentation reconciledMCR, permanent derating, EPL / ShaPoLi and propeller design power are consistent across approved files.

Propulsion-shaft screening only: This tool is not a class-approved shafting design, gear-tooth rating, bearing-load analysis, shaft-alignment calculation, coupling-bolt calculation, fatigue analysis, torsional-vibration analysis, transient dynamic simulation, propeller hydrodynamic model or OEM guarantee. IACS UR M68 applies to traditional straight propulsion shafts and explicitly does not cover gearing shafts, engine crankshafts, motor / generator rotor shafts and several other special designs. Use the applicable class rules and maker ratings for final approval.

Reference basis: Torque conversion uses T = 9,550 × P / n for kW and rpm. The optional shaft-diameter and torsional-vibration screens follow the published IACS UR M68 Rev.3 framework for traditional propulsion shafts, including installation factor F, design-feature factors k and cK, material-strength limits and size factor cD. M68 requires the complete dynamic shafting system and relevant operating conditions to be considered and is not a gearbox-shaft rule. DNV's current rules also treat shaft alignment and propulsion-shaft bearing performance as separate design checks. Power-limited vessels should keep approved propulsion-power documentation aligned with the mechanical design basis. IACS Unified Requirements · DNV Rules & Standards.

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