Ship Trim Calculator

This ship trim calculator computes a vessel's initial static trim and dynamic longitudinal changes resulting from shifting on-board weights. Proper trim analysis ensures safety, structural integrity, and optimal hydrodynamic fuel efficiency.

Imperial (ft / long tons) Metric (m / tonnes)
1. Initial Floating Drafts
Measured in Feet (ft).
Measured in Feet (ft).
2. Vessel Characteristics
Measured in Feet (ft).
Distance from Aft Perpendicular (ft).
Measured in ft-tons/inch.
3. Optional Weight Shift Adjustment
Weight in Long Tons.
Distance in Feet (ft).

Visualizing Longitudinal Trim Orientations

Vessel Trim Diagrams showing Trim by Bow and Trim by Stern profiles

Understanding Ship Trim Dynamics

In naval architecture, **Trim** describes the operational longitudinal balance of a ship. It is calculated explicitly as the mathematical variance between the draft readings at the stern (Aft perpendicular) and the bow (Forward perpendicular).

Trim Classifications

  • Even Keel: Forward draft exactly matches Aft draft. Ideal configuration for baseline hull efficiency across structural components.
  • Trim by the Stern: Aft draft is deeper than Forward draft. Typically preferred slightly on merchant ships to ensure complete propeller and rudder immersion.
  • Trim by the Head (Bow): Forward draft is deeper than Aft draft. This configuration degrades steering responsiveness, limits speed, and increases structural wave impact stresses.

The Mechanics of a Weight Shift

Shifting items longitudinally alters the trimming moment without modifying overall displacements. The formula relies upon identifying your vessel's Center of Flotation (LCF)—the central rotational point about which the ship tips like a seesaw. If a weight moves forward, the bow lowers, and the stern rises symmetrically relative to its distance metrics from LCF.