Interesting, and very well done by the look of it.
I'm assuming it's been done to add bouyancy to the stern and help it get up on the plane.
What we need is Cookee, or Adam Y, Biff etc to come along and have an opinion.
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club