Porpoising boat... but why come?

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FlPitBoss
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Joined: Tue Jan 12, 2021 7:02 am

Porpoising boat... but why come?

Post by FlPitBoss »

All excited to buy my first palm beach hull. SBC 327 with a 1.9-1 gear box. Full sheet of poly. When cruising 15-20 mph or so, no problem. The rear sits down in the water enough to ride smooth but not optimal airboat riding. Can’t slide or do anything fun. When I speed up to 25-30 it wants to porpoise like a mofo. No choice but to use the tab. Then it brings the nose down. When turning, there’s no slide. More of a dig and spray from the front. Not so fun to constantly have to play with the trim tab. Don’t want to rely on the trim tab.
What’s causing the porpoising?
Could it be the angle of the engine?
Could it maybe need center stringers pushed down in the rear-middle?
Please help!
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unforgiven11B
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Re: Porpoising boat... but why come?

Post by unforgiven11B »

Could be numerous things causing it or a combination of. There’s pages and pages of information on the topic on this forum on just about every style of hull/set up. Properly tuned hull will not need a trim tab. I’d hit the search block and read up your answer is in there.

SWAMPHUNTER45
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Re: Porpoising boat... but why come?

Post by SWAMPHUNTER45 »

PitBoss when you report the boat will not slide for you is this occurring in deep water? Have you tried running it in water less than 8 inches deep and what were your observations ?

FlPitBoss
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Re: Porpoising boat... but why come?

Post by FlPitBoss »

When cruising in deep water, I’m going good enough to slide but I’ve got too much trim tab and it’s nosed down. I’ve run in grass and shallow water. Less tab used and yes it will drift a bit. Rather flooded in the glades at the moment though.

unforgiven11B
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Re: Porpoising boat... but why come?

Post by unforgiven11B »

How the bottom? Take a string or long straight edge and check the bottom for any hooks. If it’s straight it’s more than likely engine angle or weight distribution. If bottom is straight, and the cranks level with stringers, adjust rear of engine an 1/8 at a time and see if you find a sweet spot Or move batteries and fuel tank.

RYPiii
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Re: Porpoising boat... but why come?

Post by RYPiii »

unforgiven11B wrote:
Sun Jan 17, 2021 1:38 pm
How the bottom? Take a string or long straight edge and check the bottom for any hooks. If it’s straight it’s more than likely engine angle or weight distribution. If bottom is straight, and the cranks level with stringers, adjust rear of engine an 1/8 at a time and see if you find a sweet spot Or move batteries and fuel tank.
appreciate that. going to have to build a rig to be able to suspend it so i can check the flatness of the bottom.

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