Trim is the difference between the forward and aft drafts, showing whether a ship floats deeper by the head or by the stern. It is set by the longitudinal position of weights relative to the centre of flotation, the point about which the ship trims.

MCTC is the moment to change trim one centimetre, a hydrostatic value in tonne-metres per centimetre. The change of trim in centimetres equals the trimming moment, the weight times its distance from the centre of flotation, divided by MCTC.

How is list angle calculated?

Moving or loading a weight off the centreline shifts the centre of gravity sideways. The list angle satisfies tan(list) equals the heeling arm divided by GM, where the heeling arm is weight times transverse distance divided by displacement. This tool uses that relation.

What is the centre of flotation?

The centre of flotation is the centroid of the waterplane, the longitudinal pivot about which a ship changes trim. A weight added exactly at the centre of flotation changes draft evenly with no trim, while the same weight further forward or aft produces trim.

Does this give the final drafts?

It gives the change of trim and the list from a single weight operation, not absolute drafts. Apply the trim change to your current drafts, splitting it forward and aft about the centre of flotation, and use the list to check angle of loll and deck-edge immersion limits.

Ship Trim & List Calculator

During cargo work the duty officer must know how each lift changes the ship’s attitude before committing to it. This calculator takes the standard hydrostatic parameters and a weight’s longitudinal and transverse offsets to return the change of trim and the resulting list — the two numbers that keep a vessel safe and within draft limits at the berth.

How it works

Trim change comes from the longitudinal trimming moment divided by MCTC, while list comes from the transverse heeling arm against GM:

trimming moment   = weight × longitudinal distance from CoF
change of trim    = trimming moment / MCTC        (centimetres)
heeling arm       = weight × transverse distance / displacement
tan(list)         = heeling arm / GM
list angle        = atan(heeling arm / GM)        (degrees)

A weight placed forward of the centre of flotation trims the ship by the head; aft of it, by the stern. A weight off the centreline heels the ship toward that side until the righting moment from GM balances the heeling moment.

Example and tips

Loading 200 tonnes 30 m forward of the centre of flotation with an MCTC of 180 tonne-metres per centimetre gives a trimming moment of 6000 t·m and a change of trim of 6000 / 180 ≈ 33 cm by the head. If that same weight sits 4 m off the centreline on a 20,000-tonne displacement with GM 1.2 m, the heeling arm is 200 × 4 / 20,000 = 0.04 m and the list is atan(0.04 / 1.2) ≈ 1.9°. Keep GM positive and realistic — a small GM produces a large list for the same offset, so verify stability data before trusting a tight angle.