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Tonnes per Centimetre Immersion (TPC)

TPC = waterplane area × water density ÷ 100. The quick hydrostatic derivative every mate uses to convert a planned cargo mass into a draft change.

StabilityHydrostatics
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Formula, assumptions, and limits

TPC=Awρ100\text{TPC} = \frac{A_w \cdot \rho}{100}
SymbolMeaningUnit
AwA_wWaterplane area
ρ\rhoWater densityt/m³
TPCTPCTonnes per centimetre immersiont/cm

Source: Derrett & Barrass - *Ship Stability for Masters and Mates* Ch.6; SNAME - Principles of Naval Architecture Vol I

In short

Compute TPC from waterplane area and water density - sea, fresh, or brackish dock water.

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