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

Name: Ship Trim Calculator
Availability: InStock
Author: Nham Vu

Enter fore and aft drafts, TPC, 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