a mark-boat in sailing or rowing matches.

An iron-shod pole used for mooring a punt, or serving as a mark for competitors in aquatic sports. Also attributive and figurative.

a boat moored or otherwise fixed to serve as a starting-point or mark for racing boats; also, a fixed boat to which other boats may be moored.

a mark on a racing course towards which boats sail into the wind.

a boat used as a turn-mark in yacht-racing.

a buoy or boat round which yachts turn in racing.