swell—An undulating motion of the water, always felt at sea after a gale.
tack—To tack in sailing is to change the course of a vessel from one direction or tack to another by bringing her head to the wind and letting the wind fill her sails on the other side, the object being to progress against the wind.
taffrail—The sternmost rail of a vessel, that is, the rail around the stern.
tarpaulin—A waterproofed canvas. Formerly it was waterproofed by the application of tar.
telltale—An inverted compass, generally mounted on the ceiling of the captain’s cabin. Thus, without going on deck, or even without lifting his head from his pillow, the captain can check up the course the helmsman is steering.
tender—A small vessel employed to attend a larger one.
tholes or thole pins—Pegs fitted into holes in a boat’s gunwale and between which oars are placed when rowing.
throat—That part of a gaff that is next to the mast, and the adjoining corner of the sail.
throat halyard—The rope that elevates the throat.
thwart—Athwart means across, and in a boat the seats are called the thwarts, because they are placed athwart or across the boat.