Your activities sound gay as fuck. Just make it a party. Like a club on your boat. Although depending on the length of the trip, you probably want to wait until a couple of them pass out before getting with one or more of them. Otherwise, the dudes'll disappear with a couple chicks, leaving the other ones feeling rejected and bitter. Play them all off each other, then wait until a couple fall off, then make your selection. And don't think "activities", just think "party" and go from there.
Bring everything imaginable. Alcohol, glowsticks, music, disco ball, drugs, whatever. And pace yourself.