Trim And Stability Calculator

Work out trim and stability instantly with clear inputs, formula shown and shareable results.

About Trim And Stability Calculator

Metacentric height GM is the distance between the centre of gravity and the metacentre, KM minus KG, reduced by the free surface correction for partly filled tanks. Righting moment at small angles is displacement times GM times sin(heel), so GM is the single number that decides whether a ship is stiff, tender or unsafe.

Formula

Metacentric height

GM = KM - KG - free surface correction; righting moment = displacement x GM x sin(heel)

Worked example

With the default values below, Trim And Stability Calculator returns Effective metacentric height (GM fluid) of 1.15. Change any input above and every figure here is recalculated in your browser.

Inputs used

Displacement: 8,200 t
Height of transverse metacentre (KM): 8.4 m
Height of centre of gravity (KG): 7.1 m
Free surface correction: 0.15 m

Results

Effective metacentric height (GM fluid): 1.15 m
Solid GM: 1.30 m
Righting moment at 10 degrees heel: 1,638 t·m
Stability assessment: Comfortable range

Step by step

1Values used
2Metacentric height
3Effective metacentric height (GM fluid)= 1.15 m
4Solid GM= 1.30 m
5Righting moment at 10 degrees heel= 1,638 t·m
6Stability assessment= Comfortable range

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

What is a minimum GM?

Most codes require at least 0.15 m of fluid GM in all conditions, and many operators keep 0.3-0.5 m for comfort and margin.

Why does free surface reduce stability?

Liquid in a partly filled tank shifts to the low side as the ship heels, moving the centre of gravity and effectively raising KG.