When sealed up properly brackets definitely float and add bouyancy. There is a formula for calculating the exact amount of bouyancy. I heard somewhere that a 30" bracket has 70# bouyancy. Problem is, bouyancy is not evident if the bracket is mounted high out of the water. It certainly does not float like a piece of cork. In the water sealed off all by itself it would float motor end down with only the top 10" or so above the water line.(best guess) On my 20 the bracket adds bouyancy in heavy seas or coming off plane when it really gets dunked. I believe mine is about neutral in weight with the 500 lb motor hung on the back, boat at mooring. The manufacturers of the brackets can custom make anything your heart desires. There is a lot of conjecture about the correct mounting height for the bracket. I have done the bracket retrofit now on two boats less than 22' long. Stainless Marine gives a neat template to put on the transom, I have found their recommendation right on the money, their bracket raises the mounting height in relation to the keel to account for the water rising back up some 36" behind the boat where the lower unit meets the water. As far as a 30" shaft length, I don't like the idea, the less weight the better on a bracket. I like the jack-plate idea just fine and would recommend a smaller setback as has already been mentioned. 18" setback plus 6" for the jack plate would work nicely. My .04, adjusted for inflation
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