NATARAJAST-05
The draft survey
Learning outcomes & permitted supports
- Take six drafts to the quarter mean — and say why midships carries the weight of six
- Enter a hydrostatic table and read Δ, TPC, MCTC and LCF at your draft
- Apply the first and second trim corrections with their signs reasoned, not memorised
- Correct the table's salt-water world to the dock water the hydrometer actually reads
- Deduct everything that is not cargo, and defend the cargo figure to a chief mate
Supports in this lab: Calculator. MV NATARAJA training hull with a real hydrostatic table (waterplane and LCF move with draft — that is why the corrections exist). Scenarios constructed from a true cargo the engine knows; your survey's error is shown. Golden 840/840.
MV NATARAJA (training hull) — a survey from six numbers
The surveyor reads six drafts, opens the ship's hydrostatic table, and weighs the ship with the sea. Every figure below is live from the readings; press New ship for another.
| 1 · Means F · M · A | 7.783 · 8.683 · 9.583 m (P/S averaged — list cancels) |
|---|---|
| 2 · Trim | 1.800 m by the stern · hull hogged 0.00 cm |
| 3 · Quarter mean (F + A + 6M)/8 | 8.683 m |
| 4 · Table at that draft | Δ 22260.4 t · TPC 27.28 · MCTC 290.8 · LCF 3.31 m abaft of midships |
| 5 · First trim correction | +116.0 t — the layer between the mean draft and the draft where she PIVOTS (at F) |
| 6 · Second trim correction | +3.41 t (Nemoto — always additive; MCTC changes across the trim) |
| 7 · Density correction | −502.2 t — dock water ρ 1.002, table cast for 1.025 |
| 8 · True displacement | 21877.6 t |
| 9 · Deductibles | ballast 650 + FW 300 + fuel 500 + stores/constant 325 = 1775.0 t |
| 10 · Light ship | 4200 t |
| CARGO ABOARD | 15902.6 t |
The hydrostatic table — and why the corrections exist
The table is cast for standard salt water at level trim. The ship you survey is trimmed and floating in something else — the corrections walk from the table's world to hers. Watch LCF move aft as she sinks: that movement is the first trim correction's whole reason.
| draft (m) | Δ (t) | TPC | MCTC | LCF from midships |
|---|---|---|---|---|
| 4.0 | 9900.4 | 25.51 | 277.0 | 1.20 abaft |
| 5.0 | 12470.1 | 25.89 | 279.9 | 1.65 abaft |
| 6.0 | 15077.8 | 26.27 | 282.9 | 2.10 abaft |
| 7.0 | 17723.4 | 26.65 | 285.8 | 2.55 abaft |
| 8.0 | 20406.8 | 27.02 | 288.8 | 3.00 abaft |
| 9.0 | 23128.2 | 27.40 | 291.7 | 3.45 abaft |
| 10.0 | 25887.4 | 27.78 | 294.7 | 3.90 abaft |