Trim is the difference between the aft draft and the fore draft: Trim = Aft Draft − Fore Draft. A positive value means the ship is trimmed by the stern (deeper aft), which is normal for most laden ships. A negative value means trimmed by the head (deeper forward).

TPC (Tonnes Per Centimetre Immersion) is the mass needed to change the mean draft by 1 cm. It is read from the ship's hydrostatic tables at the current displacement. Typical values range from 10–15 t/cm for small vessels to 100+ t/cm for VLCCs.

What is LCF and why does it matter?

LCF (Longitudinal Centre of Flotation) is the pivot point of the waterplane — the point about which the vessel trims when mass is added, removed, or shifted longitudinally. It is measured from the keel perpendicular (usually aft). When cargo is shifted, the change of trim is distributed to fore and aft as a lever problem about LCF.

What is GML (or BML) and how does it relate to COT?

GML (Metacentric Height, longitudinal) governs the moment to change trim by 1 cm: MCT1cm = (Δ × GML) / (100 × LBP). This tool uses the standard formula COT (cm) = (W × d) / MCT1cm, which can also be expressed as COT = (W × d × 100 × LBP) / (Δ × GML). You can enter MCT1cm directly if it is available from hydrostatic tables.

How are new drafts calculated after a cargo shift?

Change of trim (COT) is divided between fore and aft as: Change at Aft = COT × (LCF / LBP); Change at Fore = COT − Change at Aft. The signs depend on whether the shift is forward or aft. These corrections are added algebraically to the original drafts.

What is the difference between shifting and loading/discharging cargo?

Shifting cargo changes trim only — displacement and mean draft stay constant. Loading or discharging cargo changes both displacement and trim. This tool handles the cargo shift case. For loading/discharging, combine a rise/sinkage calculation (W/TPC) with a trim correction.

Ship Trim Calculator

Enter fore and aft drafts, MCT1cm, LCF, and cargo shift details to calculate trim, change of trim, and new drafts.

Current Drafts

Fore Draft (m)

Aft Draft (m)

Hydrostatic Data

LBP (m)

LCF from AP (m)

MCT1cm Input Method

MCT1cm (t·m/cm)

Cargo Shift (optional)

Leave blank to compute trim only from current drafts.

Cargo Mass (t)

Longitudinal Shift (m)

Positive = toward bow, negative = toward stern.

Enter fore/aft drafts and hydrostatic data, then click Calculate Trim.

Change of Trim & New Drafts

MCT1cm

—

t·m / cm

Trimming Moment

—

t·m

Change of Trim

— cm

Change at Aft: — cm

Change at Fore: — cm

Draft	Before	Change	After
Fore	—	—	—
Aft	—	—	—
Trim	—	—	—

Key Formulas

Trim = Aft Draft − Fore Draft

Mean Draft = (Fore + Aft) / 2

MCT1cm = (Δ × GML) / (100 × LBP)

Trimming Moment = W × d

COT (cm) = Trimming Moment / MCT1cm

Change at Aft = COT × (LCF / LBP)

Change at Fore = COT − Change at Aft

Δ = displacement (t), GML = longitudinal metacentric height (m), W = cargo mass (t), d = shift distance (m), LCF measured from AP.

Summary

Ship trim is the difference between aft and fore drafts. When cargo is shifted longitudinally, the change of trim (COT) equals the trimming moment divided by the moment to change trim by 1 cm (MCT1cm). COT distributes to the fore and aft as a function of LCF position relative to LBP. This tool computes current trim, MCT1cm (if GML is given), COT from a cargo shift, and the resulting new drafts.

How it works

Enter the fore (forward) draft and aft draft from the ship's draft marks.
Enter MCT1cm directly, or calculate it from displacement, longitudinal metacentric height, and LBP.
Enter LBP (Length Between Perpendiculars) and LCF (Longitudinal Centre of Flotation) from the keel forward.
Optionally enter cargo mass and longitudinal shift distance to compute change of trim.
The tool computes current trim, change of trim (COT), and new fore/aft drafts after the shift.

Use cases

Determine a vessel's current trim from draft readings before departure.
Calculate the effect of shifting ballast or cargo on fore and aft drafts.
Verify that drafts after a cargo shift remain within load line limits.
Support stability calculations during cargo planning on bulk carriers and tankers.
Check trim corrections needed to achieve even keel or a specified trim.
Assist officers and cadets with naval architecture coursework on trim problems.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu