Draft or draught: how deep does a boat sit?
Draft—British spelling draught—is the vertical distance from the waterline to the vessel’s deepest immersed point. It indicates how much depth the vessel needs before safety margins are added.
Also called: draught (UK)
Related terms
How it works
Draft is not the same as water depth, freeboard, or under-keel clearance. Under-keel clearance starts with available depth and subtracts the vessel’s actual draft plus appropriate allowances.
Actual draft can change with loading, trim, water density, and vessel condition. Safe planning also considers tide, squat, waves, chart reliability, and a margin suited to the operation.
A measurement, not a privilege
The Navigation Rules also use the narrow category “vessel constrained by her draft”: an International-Rules power-driven vessel severely restricted by available depth and width. It does not mean every deep vessel has right of way, and the category does not exist in the US Inland Rules.
On the water
- A yacht drawing 2 m needs more than 2 m of charted and tidal depth to retain a safe margin.
- Loading stores or fuel can increase draft and change trim.
- Squat can increase effective draft when a vessel moves quickly in shallow or confined water.
Common mistake
A published design draft is not guaranteed to be the boat’s exact draft today. Loading, trim, density, and dynamic effects can all change the real clearance.
Remember it
Draft measures DOWN from the waterline; freeboard measures UP.