Sonironi... don't sweat it. Like Cris said above, just tell him it's your time of the month. (or as I like to say: "my friend of the month is here") Hahaha... As soon as you tell him that, he should understand. If it's someone elses boat you don't want to feel like a burden for having to dock so you can change your tampon. And if you guys own your own boat then give it a try on your light days.