I have a 280 regal with a 10ft beam.Its a big cruiser,twin 5.0lx mercr.,with alphas.weighs around 9-9500 lbs.Factory props are 141/2 x 17 and the boat cruises nicely with them.If it is choppy and I trim the drives up,they cavitate before they trim up much.I know I am not trimming them up too...