I have a '72, 21 foot, 2200lb. (empty), Starcraft Islander that had a 2.5, which I replaced with a newer 3.0L. With 3-4 fishermen, this thing should have what prop size? The WOT is at least 5000 when I tested it on the water. (console tach max. readable is 5K) I have a 14 by 19 prop now...