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. . . but the concensus here is that less is ok- why is that?
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The concensus is less WEIGHT is ok! Power can be whatever your wallet can afford! The 20' hulls were designed for motors that weighed ~ 300 lbs, so if you shift the CG way aft by hanging a 500 lb motor on the transom (or, even worse, move it further aft on a bracket) it WON'T RIDE like it's supposed to, and min planing speed will be in the low 20's instead of the low teens!
Most folks don't seem to realize how much more efficient the SeaCraft hull is compared to almost any other boat, so they don't NEED all the power you're used to seeing on other similarly sized boats. Carl Moesly got ~45 mph out of the early 21's (which are HUGE 21' boats) with just two 100 hp I-6 Mercs!
The 23's seem to run fine with a single 225, and the 20' hull will run fine with a light 85 hp motor. Ran mine for over 30 years with a 115 with no complaints, especially regarding the soft ride. In fact, the 20 will start to go airborne in seas over 3' above 20 kts, so if you run offshore a lot, you won't be using a lot of power. IMHO anything over 150 hp on the 20 is overkill! Maybe I'm spoiled because the E-Tec is a VERY strong 150 (actually 165 hp at prop), but I almost NEVER use all that power! The boat gets on plane easily at about 45% throttle (the I-Command gage displays throttle position sensor reading) and optimum cruise is about 37% with a very heavy Bahamas-cruising type load. Although it will run almost 50 with a light load, I rarely run more than 30-35 and generally cruise at 25-28 mph.
Another factor that reduces a SeaCraft's power requirement is the relatively light hull weight compared to other boats of similar strength. The early Moesly and Potter models were built like aircraft, with balsa cored soles and decks, with very tall and stiff stringers that were relatively thin but installed about half way through the layup and finally bonded to the inner liner, essentially creating 4 very stiff I-beams between the cockpit sole and the bottom. (Ask the guys who have pulled out the inner liner just how tough these boats are!) Hope this answers your question!