TPC • TPI • MCTC • Waterplane Area • Parallel Sinkage • Trimming Moment • LCF • LCG • Weight Add / Remove / Shift • Final Drafts

TPC, TPI & MCTC Tool Draft Change, Waterplane Area & Trim Moment

Calculate tonnes per centimetre immersion, tons per inch immersion, moment to change trim one centimetre and the resulting forward/aft draft changes from loading, discharge or longitudinal weight movement. Simple mode solves one weight event from hydrostatic geometry. Advanced cross-checks hydrostatic-table values, builds waterplane area from Cwp when required, tracks multiple add/remove/shift events, updates displacement and LCG, models water-density transition, screens final drafts and solves the weight-shift distance needed to reach a target trim.

Figures represent
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Need hydrostatic-table cross-checks, multiple weights, LCG tracking or density transition? Click Advanced above.Simple treats TPC and MCTC as local hydrostatic coefficients and solves one loading/discharge event about the LCF.
HydrostaticsTPC + TPI + MCTC
LoadingParallel sinkage + trim
Draft resultFinal forward & aft drafts

Single Weight Change

m² at the current waterline.
t/m³.
metric tonnes.
m.
m.
t; positive = load, negative = discharge.
m forward from AP. AP = 0, FP = LBP.
m forward from AP.
m at AP.
m at FP.

Hydrostatic Condition & Cross-Check

m².
t/m³.
m, used for Cwp area source.
m.
Awp/(LWL×BWL).
t.
m.
m.
m.
m.
t/cm.
t·m/cm.
% difference for derived-vs-entered review flag.

Draft, LCF / LCG & Density Transition

m; AP = 0, FP = LBP.
m.
m at AP.
m at FP.
t/m³. Set equal to current density to disable density transition.
m, screens the larger of final AP/FP drafts.

Weight Add / Remove / Shift Register

All longitudinal positions are metres forward from AP. Add uses the “To / position” field. Remove uses “From / position”. Shift uses both. Positive trim moment in this tool means bow-down, so the forward draft increases relative to the aft draft.

EventWeight tFrom position mTo / position m

Target Trim Shift Planner

m; positive = bow deeper, negative = stern deeper.
t available for longitudinal relocation after the entered events.

Hydrostatic / Loading Checks

Hydrostatic limitation: TPC and MCTC vary with draft and hull form. These calculations use local/constant hydrostatic coefficients and small-angle trim geometry. For large loading/discharge changes, strong trim changes or significant density transitions, use the ship’s approved hydrostatic/stability data or loading computer at the updated condition and iterate as required. This tool does not replace longitudinal-strength, stability, load-line, draft-survey or loading-computer checks.
Method basis: TPC = ρ × Awp / 100 in metric tonnes per centimetre. TPI is shown as long tons per inch and is converted from metric TPC. MCTC = Δ × GML / (100 × LBP). Net weight change produces parallel sinkage/rise of ΔW/TPC; trimming moment about the LCF produces change of trim = moment/MCTC; the trim change is distributed to AP and FP in proportion to their distances from the LCF.
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