[Bushwacker]

Ask Capt. Lloyd about the need for flotation tanks! He had a 140 Zuke 4S (420 lbs) on a 20 cc with a stainless marine bracket with a very small flotation tank. He went to a lot of trouble to build a big tank around it to improve static trim!

Even if you use a 300 lb motor, if you put it 17-21 inches further behind the boat, self bailing will probably be marginal. When you move weight aft, it shifts the boat CG aft . . . just basic physics. You'll need a flotation bracket if you want to have any hope of a self bailing cockpit with a 400lb+ motor. The Hermco bracket on my boat with 30" setback, has the most flotation of any bracket on the market, and with the 429 lb E-Tec, it's just barely self bailing! If the pockets above the scuppers on your boat are more than about 1.5" deep, you have a raised deck model (think they raised the deck in about 74 or 75) which will be a little better, but with no flotation tank, it'll still do exactly what Fr. Frank says!

Another thing you need to consider is that when you're up on plane, that flotation tank isn't doing anything to compensate for the aft shift in CG! It will adversely affect (increase) min planing speed, and that's a big deal in a 20 if you want to ride comfortably and avoid going airborne in rough seas! I had to add a Doelfin and go to a 4 blade stern lifting prop to get my min planing speed back down to the 12-13 mph range I previously had with the old 300 lb V-4 with no bracket! Although brackets provide more room in the boat, improve performance and offer the safety benefit of a closed transom, the balance issue with the newer heavier motors is a potential downside you need to be aware of!