Porpoise

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Brownitsdown
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Porpoise

Post by Brownitsdown »

I have a 12x7 wilcox step decked over 383 2.38 oxbox 80”jr , boat porpoises in deep water when cruising and really bad when floored in deep water, my question is being it’s a step hull Does Lowering the rear of motor push my bow down? Also don’t have much room to lower rear of motor and no I don’t want a trim tab, thanks in advance

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Deano
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Re: Porpoise

Post by Deano »

Brownitsdown wrote:. . . my question is being it’s a step hull does lowering the rear of motor push my bow down?
Also don’t have much room to lower rear of motor and no I don’t want a trim tab
In spite of some things being different with a step hull,
the generality of lowering the rear of the engine to lower the bow does in fact, remain the same.
If it is not possible to lower the rear, raising the front will accomplish the same thing, if that is the easier implemented option.
Needless to say, there are other parameters (other than engine attitude) that could be responsible.
In this particular case, to much weight aft is also be something that could maybe held suspect.
Generally, starting with the easiest corrections first will ultimately simplify the process.

Despite there not being any other option in some cases, I do agree with you about the
desirability of a trim tab, as they are analogous to treating the symptom rather than the cause of the problem.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

Brownitsdown
Southern Airboat Member
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Joined: Sat Nov 21, 2020 5:47 pm

Re: Porpoise

Post by Brownitsdown »

Thanks for the response, the boat had a lyc 0320 on it and never porpoised the sbc gearbox is a fairly heavier so I’m trying to make it work, more than happy with the boat, only when I get on it in deeper water does it porpoise I’m going to raise the front and see how it goes

Swamp Thang
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Re: Porpoise

Post by Swamp Thang »

You might have done it already but putting a straight edge on the bottom fore to aft to check for imperfections such as a hook or bubble is always a good idea, adding that much weight to a hull can exaggerate a bottom issue. Most step hulls don't porpoise much if at all in a straight line, they will hop a little in turns though. I have a very similar setup as yours, Chuck Hawk 12 x 7 383 with 2.88 OX and three 79 inch JR race layup blades. Something else to try even though it goes against the general way of thinking when it comes to fixing a porpoising problem is to raise the rear of the engine with a few washers, it will free up the nose but could make the issue worse. It could be pushing down on the nose too much and then "climbing" back up causing the porpoise to start in deep water. As Deano said some things are different with step hulls. Checking the bottom and things like adding/removing washers or moving weight around are free and easy just remember to only change one thing at a time. where is the fuel tank and does the hull have any jacks?

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