Terms for sex on a boat?

Fixed.

 

Got to include something about the mast, bow and stern, hull, or coxwain, right?

 

Let's not forget the Sex Pistols' "Friggin in the Riggin'.

 

Docking the Coxwain?

 

I like "Dropping Anchor" even if it sounds like a term for taking a dump over the side of the boat.
"Oral in the coral" was another one we came up with.

In college, I had a friend who had served in the navy on a submarine. When they needed to come to the surface immediately, they'd purge the water from the ballast tanks and pop up like a cork. The term for that also works here -- "emergency blow"

 

Docking Stem to Stern

Coming Home to Port

Trolling in the Weeds

or, simply

Fuckin' on a boat

 

Steamin' Semen

 

Sinkin' the Bismark

 

"Takin the banana boat to tuna town"....[dad from grumpy old men]

 

Crabbing

 

Brilliant four times over!

 

Hooking bait.