I could add a few stories about fun afloat, but suffice to say there's just something about being on the water with someone you like a lot.
One thing I really like about boats is that for some reason a lot of women lose all modesty once they step aboard. It can be a truly beautiful thing, even if you're in the look but no touch zone.
Edit to add: OK, I can't resist. There is nothing, truly nothing, like sex in a mayan hammock on the foredeck....or having her boat's tiller in your hand while she's got your tiller.......or like the look on your gf's face when her mother, who is also a live aboard, starts going on about how she likes one particular boat because it has great "v-berth leverage" on the ceiling. Lastly, there's nothing like the need to be extra extra quiet because the whole boat is full of family while you're both in the aft cabin and in the mood. It adds that special "sneaking around" factor.
Boat sex is great!