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Stability & CargoPage 4 of 12

Final draft from TPC: everything that comes on board sinks her

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Final draft from TPC: the cargo and the bunkers together sink her bodily by w ÷ TPCThe ship's side with a magnified mean-draft scale. Present mean draft 15.62 m. Coming on board: cargo 6150 t + bunkers 850 t = 7000 t. Sinkage = 7000 ÷ TPC 98.5 = 71.07 cm = 0.711 m, so the water climbs the side, level, to the final mean draft 15.62 + 0.711 = 16.33 m. The TPI of 250.2 tons per inch is not used.15.415.615.816.016.216.416.6present 15.62 mfinal 16.33 m+ cargo 6150 t+ bunkers 850 tw = 7000 t÷ TPC 98.5 t/cm= 71.07 cm sinkageTPI 250.2 tons/inper inch — not used15.62 + 0.711 = 16.33 mmean draft on completion 16.33 mShip's side · mean draft scale magnified · sinkage to scale

The rule

  • TPC is the weight that sinks her one centimetre bodily at this draft; read it from the hydrostatic table at the present mean draft — for a large change, at the mean of the present and final drafts.
  • w is every weight that comes on board during the stay: cargo and bunkers together. Weight discharged or pumped out is subtracted.
  • Sinkage = w ÷ TPC, in centimetres; divide by 100 for metres and add it to the present mean draft.
  • Use the TPC column. TPI is tonnes per inch, about 2.54 times larger, and has no place in a sum worked in centimetres.

Formula

  • Sinkage (cm) = w ÷ TPC
  • Final mean draft = present mean draft + sinkage ÷ 100

Worked example

Present mean draft15.62 m
Cargo still to load6150 t
Bunkers to be taken alongside850 t
TPC from the hydrostatic table98.5 t/cm
TPI from the same table250.2 tons/in
  1. w = 6150 + 850 = 7000 t
  2. Sinkage = 7000 ÷ 98.5 = 71.07 cm = 0.711 m
  3. Final mean draft = 15.62 + 0.711 = 16.33 m

Answer16.33 m

Common mistake

Counting the 6150 t of cargo and forgetting the 850 t of bunkers: 15.62 + 6150 ÷ 98.5 ÷ 100 = 16.24 m.

The draft does not care what a tonne is for: fuel taken alongside sinks her exactly as cargo does, and the 850 t left out are 8.63 cm that the marks will show and the plan does not.