Compute change of trim and draft variation using MCT 1 cm and LCF. Sign convention: +TM = trim by stern.
Enter weights (t) and longitudinal arms from midship (m, +aft). TM = Σ(w · x)
Total trim: — m (— cm)
ΔT at AP: — m
ΔT at FP: — m
TA1: — m TF1: — m
Trim describes the longitudinal inclination of a vessel, defined as the difference between the aft draft and forward draft. Accurate trim calculations are essential for assessing propeller immersion, resistance, maneuverability, and compliance with stability criteria.
This Trim Calculator evaluates the change in trim and resulting draft variations using standard naval architecture relationships based on Moment to Change Trim by 1 cm (MCT 1 cm) and the Longitudinal Centre of Flotation (LCF).
When the vessel’s hydrostatic data is available, trim can be calculated directly using the known MCT 1 cm value.
Total trim:
t = TM / MCT
If MCT 1 cm is not directly known, it can be derived from displacement and longitudinal metacentric height.
MCT 1 cm formula:
MCT1cm = 100 · Δ · GML / Lpp
Once the total trim is known, the change in draft at any longitudinal position is proportional to its distance from the LCF.
Draft variation:
ΔT(x) = t · x / Lpp
If initial drafts are provided, the calculator also reports the final forward and aft drafts after trimming.
In practical loading scenarios, trimming moments are generated by moving weights longitudinally. The trimming moment builder allows summation of multiple weights using:
TM = Σ ( w · x )
where w is the weight (t) and x is the longitudinal arm from midship (m).
This calculator assumes small trim angles and linear hydrostatic behavior. For large trim changes or asymmetric hull forms, full hydrostatic recalculation is required.