What is the word for the distance from the waterline to the main deck of a ship? In other words, the height of the main deck (or gunwale if that has a name) above the water when the ship is at sea.

To understand my motivation, broadly speaking I am interested in the furthest you would fall if you were standing on the main deck and went overboard.

The distance from the waterline to the bottom of the boat is called the draught.

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    - Air Draft is the distance from the water line to the highest point on a ship (including antennas) while it is loaded. Technically, standard draft is the distance a ship can pass over, air draft is the distance a ship can pass under. en.m.wikipedia.org/wiki/Ship_measurements
    – user 66974
    May 31, 2018 at 14:54
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    @user3850720 - Air Draft includes antennas, whereas the OP wants the height excluding masts, antennas, etc. May 31, 2018 at 16:40
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    @Greenonline - yes, and I didn’t post that as an answer, but still worth a post here, I think.
    – user 66974
    May 31, 2018 at 16:43
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    @user3850720 It is helpful, if only to stop people mistakenly posting it as an answer.
    – Simd
    May 31, 2018 at 16:44
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    Could you edit the question to be clearer about what you're actually looking for? Your first two sentences contradict: the first asks (roughly) for the height of the gunwale above the waterline but the second asks for the height of the top of the superstructure above the waterline. In a comment, you say you want the distance somebody would fall if they went overboard but that depends entirely on where they fall from. Jun 1, 2018 at 19:13

2 Answers 2


The word you are looking for is freeboard:

In sailing and boating, a vessel's freeboard is the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship.

Source: Wikipedia

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    where water can enter the boat This is the essential point. All the words used to describe things on boats sound unusual to land-lubbers because they are very precise. The freeboard is how far the water has to come up the side before you start taking on water. The air draft is how much clearance you must have when going under a bridge. The draught is how deep the water must be before you hit the bottom. All the terms have a precise meaning because they have a precise purpose. Jun 1, 2018 at 6:37
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    The question is very explicit about wanting the distance to the top of the hull, not the superstructure - isn't it?
    – Useless
    Jun 1, 2018 at 14:40
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    @Useless Yes exactly. In fact what I really wanted to know was how far you would fall if you went overboard, which is the same thing.
    – Simd
    Jun 1, 2018 at 14:43
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    Well, unless you're falling from a fo'c'sle, poop or other deck raised above the lowest point of of the top of the hull.
    – Useless
    Jun 1, 2018 at 14:49
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    @Useless True. I should say I have completely failed to find this freeboard figure for any navy ship so far despite now knowing the correct term.
    – Simd
    Jun 1, 2018 at 15:14

"the height of the boat when it is in the water excluding masts etc." is not operationally useful. It won't prevent water from entering and it won't prevent the boat from colliding with a bridge. Hitting a mast on a bridge can tilt the boat which could let water in.

Freeboard is all about flooding the ship. It's how high water can come up without water coming onto the deck and entering the ship, so freeboard is defined by the lowest point of entry of water. But that's not what you're asking.

Air draft of course is the ship's height above water, or how low a bridge it can go under. Also not what you're asking.

I think you're looking for "Deck height above water" and I don't think there's a nautical term for that.

  • It's operationally useful if you're not near any bridges.
    – Strawberry
    Jun 2, 2018 at 18:23

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