It's one of those things that is so easy to control, and can really make the difference between a great vacation and a living nightmare.
Dengue and Chikungunya ain't going away. The carriers are there year-round. And it's nasty stuff.
Just spray yourself. With a DEET based spray (at least 15%). Spray yourself when going ashore after sunset, and take some spray with you during the day, just in case.
Spray yourself at night on the boat if you're moored close to shore, or if it's a perfectly still night.
If you're worried about DEET, worry about it when you get home. And have a great vacation.