Quote:
Originally Posted by Chaser
. . . I'm repowering with a 135 or 150 4 stroke (I know it's heavy I'm going to deal with it). Originally I thought moving the fuel tank forward was a good way to balance the weight of the heavier outboard. But then I though that would change the trim depending on the amount of fuel in the boat... So I think I am going to put the new tank right over the CG and shift the console a little bit forward . . .
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Don't know about Potter, but Moesly always centered fuel tank on the CG so trim wouldn't change as you burned off gas. (With over 13,000 hrs flight time in WWII, most of it flying cargo, he understood the importance of CG location better than most!) Probably safe to assume Potter did the same thing.
So to begin with, assume the original CG was at center of fuel tank, with a 300 LB MOTOR that the 20' hull was originally designed for! Now you're talking about changing lots of stuff, so I'd look at each change independently and calculate the CG change of each. Going to a 500 lb motor will move CG
AFT, as will installing a lighter deck, console and removing wet foam! Even if the total package is lighter, it still won't float and handle right unless CG is right. I would NEVER accept the performance penalty of ballast when you can move batteries, gas tank, and console forward to get it right. Since people, coolers and gear tend to congregate in the back where ride is softest, and
ALL of your planned changes are moving CG AFT, I'd put that gas tank as far forward as possible! My gut feel is that you're gonna have to move console fwd a fair amount, but before you bolt it down, maybe do a flotation test after you hang motor with pictures of transom/bootstripe to document how level boat sits in water. Then you can move console to see what effect it has. Use trash cans filled with sea water to simulate crew weight. And if you DO still have to add ballast, consider using 20' of chain on your anchor rode . . . makes a HUGE difference in anchor holding power!