Draft Survey Quantity Calculator

Work out draft survey quantity instantly with clear inputs, formula shown and shareable results.

About Draft Survey Quantity Calculator

A draft survey measures cargo by weighing the ship: displacement after loading minus displacement before, corrected for dock water density and adjusted for any change in bunkers, fresh water and stores. It is the accepted method for bulk cargoes where weighing ashore is impractical.

Formula

Draft survey

Cargo = (final - initial displacement) x density correction - change in deductibles

Worked example

With the default values below, Draft Survey Quantity Calculator returns Cargo quantity loaded of 29,142.90. Change any input above and every figure here is recalculated in your browser.

Inputs used

Displacement before loading: 12,400 t
Displacement after loading: 41,800 t
Change in bunkers, water and stores: 85 t
Dock water density: 1.019 t/m³

Results

Cargo quantity loaded: 29,142.90 t
Gross displacement difference: 29,400.00 t
Density correction applied: -172.10 t
Implied load per hour over 24 h: 1,214.29 t/h

Step by step

1Values used
2Draft survey
3Cargo quantity loaded= 29,142.90 t
4Gross displacement difference= 29,400.00 t
5Density correction applied= -172.10 t
6Implied load per hour over 24 h= 1,214.29 t/h

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

How accurate is a draft survey?

Typically 0.3-0.5% on a full cargo when carried out carefully in calm water. Trim, list, hog and sag corrections all matter.

Why correct for dock water density?

The hydrostatic tables assume 1.025 t/m3. Brackish or fresh dock water changes the mass represented by the same displaced volume.