Butt at sea does indeed refer to the part a sailor sits on but that terminology in the English language may very well have come from the usages we are about discuss and not the other way around.
By and large a butt is the terminal end of something. The most usual reference being a plank of wood. The Sailor’s Word Book describes butt as “the joining of two timbers or planks endways.” In other words the planks butt up against one another and are in no way overlapped. This is common carpentry in shipbuilding with the pressure of the ship’s planking holding the ends tight against one another to form seams which would then be caulked. In very large ships, men-of-war and the like, these butt ends are bolted to one another as their separation could potentially create a gushing leak which would in turn be difficult to repair. The instance of two planks coming apart in such a manner is known as springing or springing a butt from whence the more familiar landsman’s phrase “springing a leak”.
Butt-and-butt is the name for the kind of joinery that causes two butt ends to meet but not overlap. The opposite type is said to hook a butt, meaning overlap, and is sometimes called hook-scarph. Interestingly, the butt end of a plank in the language of ship’s carpentry is the same as its butt head.
A butt might also refer to the terminus of a firearm. The butt of a blunderbuss or musket is the part tucked against the musketeer’s shoulder when firing. There are also butt-shafts in archery. These are arrows, known in Medieval times as butt-bolts, which have a heavy tip but no barb and were used by peasants exclusively for target practice – “shooting a butt” – or to stun small game such as rabbits. Anyone familiar with the story of Robin Hood will recall that part of his initial trouble with the Sheriff of Nottingham was being discovered with hind barbs (for killing deer) rather than butt-bolts. These weapons marked him as a poacher of the King’s elk.
Buttock is also a familiar term at sea and, since ships are generally thought of as female, it should surprise no one that the word often refers to the back end of a vessel. A fine buttock shows well as she sails away, and does not drag her down. A lumpy or wide buttock is a sad failure of the dockyard and the ship’s carpenter will labor tirelessly to correct such a problem. No one likes a lumpy buttock, after all.
Though it has nothing to do with the end, terminus, or behind of anything, I’ll include this interesting and very old English sailor’s term. To make buttons is a saying that probably originated on or before Elizabeth I’s seadogs and refers to a person being suddenly anxious. It may be an early way of describing what modern psychology would call a “panic attack”. The phrase has nothing to do with butts, but it’s curious all the same.
And there I shall end, and get up off my butt to fetch a mug of grog. Join me, Brethren?
Header: Ship’s planking via nps.gov