Admiralty Coefficient & Speed-Power Tool Ship Power, Speed & Performance Curve

Admiralty Coefficient • Speed-Power Curve • Displacement Scaling • Fitted Exponent • MCR • Power Margin • Fouling / Weather • Efficiency Chain

Admiralty Coefficient & Speed-Power Tool Ship Power, Speed & Performance Curve

Estimate propulsion power, speed and comparative ship performance using the traditional Admiralty coefficient, then move beyond the cubic-law shortcut with a fitted multi-point speed-power curve. Simple mode calculates AC, target power and predicted speed at available power. Advanced normalizes operating or trial points for displacement, fits the speed-power exponent, compares cubic and fitted models, applies operational margins, screens MCR/reserve, converts the selected power basis through the propulsion-efficiency chain and builds a full performance curve.

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Need measured operating points, fitted exponent, MCR reserve or efficiency-chain analysis? Click Advanced above.Admiralty coefficient is a comparative screening relation, not a full resistance or corrected sea-trial analysis.

Fast8 primary inputs

Core modelΔ²⁄³ × V³ / P

OutputPower, speed & reserve

Reference Vessel / Condition

Reference displacementmetric tonnes.

Reference speedknots.

Reference propulsion powerkW on the selected basis.

Power basisKeep the same basis when comparing AC values.

Target Condition

Target displacement

Target speed

Power margin% added to clean Admiralty estimate.

Available propulsion powerkW on the same selected basis.

Performance Model & Power Basis

Curve model

Performance power basis

Reference displacementt for point normalization.

Installed / available powerkW on selected basis.

Operational power limit% of entered available power.

Required power reserve% of operational-limit power left unused.

Transmission efficiencyBrake → shaft, %.

Overall propulsive efficiencyShaft → effective, %.

SFOC for fuel screeng/kWh on brake-equivalent power.

Target Operating Condition

Target displacement

Target speed

AC scatter review threshold% coefficient of variation.

Sea / weather power margin

Fouling / roughness power margin

Other propulsion margin

Curve minimum speed

Curve maximum speed

Curve step

Speed-Power Observation Register

Enter corrected or otherwise comparable points on one consistent power basis. Each included point is normalized to the reference displacement using traditional Δ²⁄³ scaling before fitting ln(P) versus ln(V).

Use	Speed kn	Power kW	Displacement t

Performance / Data Quality Checks

Power basis consistentAll points use the selected brake/shaft/effective basis. Speed basis comparableTrial/operating speeds are corrected or appropriate for the comparison. Displacements verifiedEach observation has the applicable displacement. Environmental effects reviewedWind, waves, current, depth, water properties and trim are not silently mixed. Hull / propeller condition reviewedFouling and roughness state are understood. Operating mode comparablePropeller pitch/rpm and propulsion configuration are comparable. Target near observed regimeLarge speed/displacement extrapolation is separately justified. Installed-power limit verifiedMCR/SMCR or operational limit uses the same power basis.

Performance limitation: Admiralty coefficient is a comparative/estimating relation, not a complete resistance prediction or ITTC/ISO speed-trial correction. Current ITTC speed/power analysis separately corrects measured trials for wind, waves, current, shallow water, water temperature/salinity, displacement and trim. Use corrected trial/model-test or validated fleet data for contractual or engineering decisions.

Method basis: ITTC defines Admiralty coefficient as Δ²⁄³V³/P, where Δ is displacement, V speed and P a corresponding power. The numerical AC depends on units and power definition, so this tool fixes displacement in metric tonnes, speed in knots and power in kW and labels the power basis. Advanced fitting normalizes points to the chosen reference displacement, then fits P = kVⁿ in log space. ITTC 2024 guidance is used to frame data-quality limitations only; this tool does not claim to perform ITTC trial corrections.

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