You are correct to be concerned, paint is heavy. If the paint is a new type VOC compliant paint, it's mostly solids(a lot of it is metal and metalic oxides). There should a couple of lines on the can or the website that tell you what percentage that goes into the air. (look for the one that gives the percentage by weight)

The only numbers that I know for weight of paint are:

F14 - 2 coats white IMRON ~1.5 Kg

Factory repaint Marstrom Tornado ~6 lbs.

Now if you want to look really cool and save some weight, I saw a really odd tool last summer at a show. It was a paint roller that would make your car look just like carbon fiber. Roll on the carbon fiber with thin coat of black paint, cover it with a UV resistant clear coat, and you are ready to go.
(for those who are challenged, this is a joke. I think your boat would look better if you let a 1st grader finger paint it)