They are available for all sizes. i have seen them ot shows with decent size boats on them. I have one for my sea-doo. It works pretty good and the design has gotten better over the years. i got mine in 98. i still pull ot out everynight with the davit. water wsahes up the back pretty easily. i have the e-z port. there are also the black cubes that bolt together, but i heard that theyre not good in rough water.
hope that helps