There's no need to consider a three blade prop for that size boat, the only benefit would be to more quickly spend your boat $$$. A 3 blade is not "better" than a 2 blade, the extra blade is just a way to increase blade crossarea within the diameter permit by space.
He will probably be well served by an inexpensive Matrec two blade folding prop, as used by most 30 footers that have something other than a fixed prop. If he wants to go first class and spend more $$$ he can contact PYI
PYI http://www.pyiinc.com/index.php?section=max-prop&action=main&sn=1 for sizing of a nice MaxProp two blade.