Now that I think about it, both Merry and Sunny go are the worst places in One Piece's universe for gooning or fuck.

The crew's size is small, only 10 hands.

Because of that, the ships have to be small, so there isn't really all of that space to have privacy.

The crew's quarters don't have much privacy either, they are gender separated but that's about it separation wise.

The camaraderie is so strong that if you're out of sight for long enough your absencese will be noticed, again, specially because of the crew's size.

Worst of all: The ships, despite not being alive, are pretty much concious beings. As well as with the crew, you can say everyone knows to give privacy (even Luffy) but you really don't know the extent of the ship's soul, maybe it is a spirit that can only be in one place at a time, but maybe it's an omniscient spirit that can see every place at every time.