Here are a few nautical terms I heard years ago.

The devil to pay – The devil is the word they use for the last board on a ships hull that is never under water. This board tends to shrink and it must be caulked from time to time since it requires being hung over the side and is a difficult job, the term has become associated with difficult situations.

Between the devil and the deep blue sea – another version of the above.

Let the cat out of the bag – Before hearing this, when I heard this expression I always pictured an angry cat popping out of a bag that it did not wish to be in. It actually refers to the cat of nine tails, a whip that was used to administer punishment to miscreant crew members,and was stored in a burlap bag. Hence, when somebody screws up and causes crew member punishment they have let the cat out of the bag.

Mind your p’s and q’s – I always figured this had to do with the similarity between the two letters. Actually, it refers to sailors going on shore leave and drinking rum that was served in pints and quarts. The bars were notorious for padding bar bills, so the sailors were cautioned to mind their P&Q’s or in other words keep track of how much they had consumed.

I think one or two of those might have other origins. I’m pretty sure “saved by the bell” is a boxing term.