Drawing a line in the sand and the term "crossing the line", may have come from the serious nature of rituals performed by Vikings on behalf of Neptune when crossing the equator. Sever tests were administered to the uninitiated Vikings at equator crossing to prove suitability as a seaman.
It was customary to place a piece of toast in hot toddies and mulled wine popular with seamen. Hence the term Drinking a Toast
Mind your P's and Q's means be on your best behavior. When these vessels were operated, the term referred to Pints and Quarts consumed at taverns on credit.
Today, the term carry on means proceed with what you were doing. It originally was an order to put up all canvas the ship could handle given conditions
The term blue Monday came from a tradition of tallying misdeeds during the week and flogging the men on the following Monday.
The man on the bow likely has releaved himself as this is the position most suited. Typically a freyed line would be used for toilet paper the line being dropped into the sea for cleaning.
On board ships, Red for Port and Green for Starboard was at the discretion of the Captain, like almost everything else, until 1848.
The original meaning of the term Deep Six referred to minutes not fathoms. Pearl divers of Ceyolon could remain submerged for as long as 6 minutes. Otters in the Pacific Northwest have been observed similarly, though the average dive is about 30 seconds.
Hand-me-Downs originally referred to clothing hung on hooks high above where sailors might reach them. This was because uniforms were not provided by Captains for crew. Crew, even if military, were required to obtain clothing by what ever means felt appropriate. Hence, shop keepers, preferred to climb a ladder and had down clothing to customers.
British sailors who murdered one of their own aboard ship were subject Swift Justice. They were tied to the weighted corp
Young George Washington, father of the US Nation, was determined to join the Navy and visited Waterfront bars hoping to be taken by a press gang. Unfortunately his parents made certain that he would be recognized as from an influential family and hence George remained a landluber.
The expression Paint the Town Red, may have come from boat decks that were painted red so that the uninitiated would not notice blood spilled during battle, and loose enthusiasm for doing their duty.