What about "Cold enough to freeze the balls off of a brass monkey".

That one comes from when they used to store cannonballs on the deck, in a brass verticle treelike device that had arms extending out of it. The arms were curved so they could move a bit with the rolling of the ship, so they looked like monkey's arms. Naturally they were brass to minmize corrosion.
The balls actually were nestled into round rings on the end of the arms.
When it got really cold, the rings would shrink more than the balls so the pressure would build up and then something would trigger the release and the balls would pop out of the rings. "Cold enough to freeze the balls......"

"Son of a gun" Refers to days of old when the men who used to operate the cannons on Naval ships were called "Guns".
Well when the ship would sail into town the crew would go out get some liquor and shall we say "local ladies" who might perchance, to visit the ship. Well the cannons were located in cubiholes on the sides of the ships, just big enough to squeeze into.... and nine months later.... a son of a "Gun"

was born.
Now I would like to know the origins of "athwartship". I may have misspelled, but I see a word somewhat like this ocassionally. It's not in my copy of the "Oxford Dictionary".