“Dog watch” refers to one of two two-hour watches (the first from 2 p.m. to 4 p.m and the second from 4 p.m. to 6 p.m.). Ships' crews were divided into two shifts, the “port watch” and the “starboard watch” each of which served four hours on and four hours off duty. Each four-hour period was also called a “watch” and, of course, each had a name and several nicknames. The 2 p.m. to 6 p.m. watch was split in two in order to stagger the schedule so that the same swabbies didn't have to be on duty for the same times for the entire voyage. After all, nobody likes the “grave yard watch” from midnight till 4 a.m. The origin of the name is unclear. Some say it was named for Sirius, the dog star, which rises at some latitudes and some times of year between 2 and 6 p.m. It may be because the shorter watch allowed sailors to “dodge” the regular watch and “dodge” evolved into “dog” in the same way that “forecastle” became “fo'c's'l.”
But there's also a hatch dog with which to “dog the hatches.” This was simply a locking device to prevent a hatch from blowing or washing open in heavy weather. And there's also “dog's body” which had two meanings in the old British Navy. The first was a meal consisting of dried peas and eggs boiled in a bag. The second was a midshipman or junior officer who had to do work spurned by senior officers.
Then there's cat. The “cat o' nine tails” was multi-stranded leather whip used for punishing offending tars. It was kept in a leather bag, so whenever someone “let the cat out of the bag” it meant that someone was about to get it! On either side of the bow of square-rigged ships there was a “cat head” which was a large protruding timber for “catting” (or securing) the anchor when not in use. Some of these had lions' faces carved in them but which came first – the carving or the name – nobody knows.
A cat boat is shoal-draft, broad beamed sailing vessel with one large gaff-rigged sail. It was developed around 1840 in New York and originally used by commercial fishermen in Long Island Sound and Barnegat Bay but soon became popular as a pleasure boat for summer folk. And a “cat's paw” is a breeze that can be detected by sudden ripples on the water's surface – the sort of thing small boat racers are always on the lookout for.
And last but not least, monkeys! Thirsty sailors were occasionally known to “bleed (or suck) the monkey.” This refers to the practice of drilling a hole in the top of a cask of spirits and inserting a straw – a practice that might well result in the cat coming out of the bag. And when ships came in to the wharf, a “monkey's fist” (or weighted knot) on the end of a light heaving line) was thrown to someone on shore. Then the heavy hawser (mooring rope) would be tied to the end of the heaving line and pulled ashore.
Some of the more colorful nautical lore and legend is purely myth like the “brass monkey” which was allegedly a brass rack for securing cannonballs on deck to keep them from rolling around. In extremely cold weather, the brass would contract more than the iron balls which would tend to fall off and roll. Hence the expression: “cold enough to freeze the balls off a brass monkey.” A comforting thought in these dog days of summer!