FENDER - A cushion, placed between marine vessels, or between a marine vessel and a pier, to prevent damage.
FIGURE EIGHT KNOT - A knot in the form of a figure eight, placed in the end of a line to prevent the line from passing through a grommet or a block.
FIGUREHEAD - symbolic image at the head of a traditional sailing marine vessel or early steamer.
FIRE EXTINGUISHER - A device used to suppress fires, usually using water, foam or chemicals.
FLANK - The maximum speed of a marine vessel.
FLARE - The outward curve of a vessel's sides near the bow. A distress signal.
FLOAT PLAN - A plan outlining details about the boat, route, departing and arriving times, persons aboard and other pertinent information.
FLOOD - A incoming current.
FLOORBOARDS - The surface of the cockpit on which the crew stand.
FLUKE - The palm of an anchor.
FOLLOWING SEA - An overtaking sea that comes from astern.
FOOT - The bottom of a sail.
FORE - Towards the bow
FORE-AND-AFT - In a line parallel to the keel.
FOREPEAK - A compartment in the bow of a small marine vessel.
FORWARD - Toward the bow of the marine vessel.
FOXTROT - Letter F in the Marine Radio Alphabet.
FOULED - Any piece of equipment that is jammed or entangled, or dirtied.
FREEBOARD - The minimum vertical distance from the surface of the water to the gunwale.
FURL - To roll or wrap a sail around the mast or spar to which it is attached.