porpoiseing

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David-Keen
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porpoiseing

Post by David-Keen » Sat Mar 30, 2019 9:17 pm

Alright guys have a few questions..... Can you take the back of the motor up to help with a porpoiseing problem or does the back of the motor need to go down. It is a 13ft river master hull with a sbc dd on it no Polly just slick bottom. Someone please help driving me crazy
Can get up on plane and it starts

unforgiven11B
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Re: porpoiseing

Post by unforgiven11B » Sat Mar 30, 2019 10:08 pm

There can be much more to it than raising or lowering the engine. Use the search. Have you checked the bottom for straightness? Is engine level with stringers? Or is it already high or low Could be a hook in the hull. If you just start messing with engine angle you could be chasing your tail.

barhopper
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Re: porpoiseing

Post by barhopper » Sun Mar 31, 2019 6:23 am

To answer you question raising the back of the motor would pick up the nose of the boat. Lowering it would push the nose down and could possibly help your issue. A lot of good points were brought up in the previous post.

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John Fenner
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Re: porpoiseing

Post by John Fenner » Sun Mar 31, 2019 7:21 am

Search porpoising or hop, I and many others have tackled this in many different times, ignore the string theories, a solid straightedge is the only way to find the rock, 9 times out of 10 it is the back lip bent up.
I never finish anyth,,,.

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Deano
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Re: porpoiseing

Post by Deano » Sun Mar 31, 2019 10:53 am

Motor rear mounts being moved up/down will raise the bow up/down and will work as hoped,
AS LONG AS the bottom is straight and true, and the stringers are straight and strong.
This is the easiest adjustment to make to determine if the other parameters are or are not the problem.

The second post in this thread expands on that exact adjustment and the differences it makes:
https://southernairboat.com/phpBB3/view ... 0&p=276752

Shimming the engine mounts with fender washers is one way to dial it in.
Adjust it for the best results according to the above thread.
If it still porpoises, then the bottom/stringers and/or the fore/aft weight placement should next be held suspect.
Bottom/stringers is a different can of worms, but there is a lot of info here.

The other thing, in your case is weight placement fore and aft. It is a DD correct?
How far is your prop from the transom? With a V8 CM in that hull you may well need it a little further forward than normal.
In this case being a front driver may help because the forward ballast will help offset the weight imbalance. Is it, or isn't it?

John evidently didn't realize that you have a 'glass hull. Bending and restoring 'the lip' is not an option for you in this case.

Leveraging this new info and understanding may well solve your problem, if not report your results and we can go from there.
"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

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