When you write about boats you face a choice. You can explain each term when you use it, or you can assume the reader knows what you think. I personally don't like reading sentences like "We sailed 10nm (19km or 11.5 miles)", so I haven't written any. However, for the benefit of my Mum, here is an overview of the most common nautical terms and units that salt any good tale.

Nautical Mile(nm). If I say mile I mean a nautical one. These are incredibly logical units, which are about 1.15 statute miles or about 1.85km. Why are they logical? Because a nautical mile is the distance described by a minute of arc of latitude. So if you go North from a latitude of 12 deg 00 min N to 12 deg 37 min N you have gone 37nm. Cool huh. This unit makes celestial navigation much easier.

Minute of arc. A sixtieth of a degree.

Knot (kn). A speed of a nautical mile per hour. True Blue goes 7kn flat out, unless we are surfing. Our top speed ever down a wave was 13.8. Almost all cruising boats average 5kn when they go somewhere. Bigger boats are faster but they spend more time stopping to fix things.

Fore, aft, port, startboard. Towards the front, back, left and right of the boat.

Ketch. A sailing boat that has two masts, with the aft one in front of the steering station.

Sheet. A line that holds the bottom back corner- 'clew' of a sail.
Halyard. Pulls the sail up by the 'head'. Spelled many ways.

Mainmast. The front, bigger one on a Ketch.
Mizzen Mast. The one further aft.
Mainsail. The big sail that hangs off the front mast.
Genoa. The big sail that hangs off the forestay. Ours rolls up on a 'Roller Furler' at the pull of a line.
Mizzen Mainsail. The little sail that hangs off the mizzen mast.
Mizzen Staysail. A really cool sail like a Genoa for the Mizzen Mast.
Forestay. The wire that holds the mast forwards and stops it from falling over.
Backstay. I bet you can figure that one out.
Shrouds (upper and lower). Stop it falling over sideways.

That's enough for now, anything else, just try Dictionary.com