Call them blue water capable then, that's what matters.
I think that what matters is what the OP means by "blue water capable." If he just wants a boat that is able to make it, a 15' rowboat will do the trick. After all, it has been done. If he wants a boat that will keep him and his crew comfortable on an ocean passage, that's a whole different matter. Then the question becomes, what exactly does he consider "comfortable"?
Only the OP can really determine what he means by the question. As it is, it is much too vague.