Ship stopping distance calculator

What this calculates: the deceleration, time to stop, and stopping distance of a ship coasting or reversing to a halt, from hull resistance and hydrodynamic added mass.

What it assumes: calm water, ITTC-1957 friction plus Holtrop–Mennen wave resistance (valid within moderate speed ranges), and no rudder or current effects.

What it ignores: sea state, fouling, loading condition, and propeller-specific reverse-thrust characteristics.

Full derivation and worked physics: Understanding Ship Deceleration.

Vessel Type

Select Vessel Type

Type Characteristics

Typical Cb:

Thrust margin:

Crash stop (full astern):

Parameters

Length Overall (m)

Breadth (m)

Draught (m)

Displacement (tonnes)

Initial Speed (knots)

Scenario

Results

Stopping Performance

Initial Deceleration: m/s²Deceleration (g): gTime to Stop: minDistance: mShip Lengths:

Typical crash stop for Container Ship:

Hydrodynamics Details

Block Coeff:Wetted Surface: m²Froude No:Form Factor:Wave Cw:

Forces & Resistance

Resistance Ct:Drag at V₀: kNTotal Force at V₀: kNAdded Mass:

Debug Information

Speed: m/sEffective mass: tonnesReynolds No:

Important Notes

• Resistance uses the ITTC 1957 friction line and the Holtrop (1984) wave-making regression, both fitted to conventional hull forms

• The typical ranges are crash-stop (full astern) rules of thumb; a coasting ship goes several times further

• Coasting is integrated to 1 knot because quadratic drag alone never brings the ship fully to rest

• Astern thrust is held constant after a fixed reversing delay; real engines ramp up, and the ship veers off its track

• Real stopping distances vary significantly with sea conditions, loading, fouling, and propeller condition

How it works

Ships have no brakes in the automotive sense — they decelerate purely against hydrodynamic resistance, and against reverse propeller thrust if the scenario calls for it. The calculator estimates block coefficient and wetted surface area from the vessel's dimensions, derives a resistance coefficient from Froude and Reynolds numbers, and integrates the resulting force against the ship's effective (added) mass to get deceleration, time, and distance. See thefull post for every equation.