Airboat skipping on water/plane

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
markhexamer
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Airboat skipping on water/plane

Postby markhexamer » Mon Nov 07, 2016 8:43 am

I am very new to air boating please forgive me for any ignorance I have towards this, we all started fresh at one point.

I bought an airboat originally with a Cadillac 1974 472 engine and had to replace it and put a 500 engine. 14' x 7.5' aluminum flat bottom deep hull 6' single blade whirlwind prop carb is a 700. no reduction drive

the problem I am having is once I get on a plane (smooth water) the boat keeps skipping
[youtube]https://youtu.be/elpcX3WdOKI [/youtube]

skipping starts at about 25 seconds into video

I live in the Pan Handle are Navarre Beach Florida any other boaters in the area?

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Deano
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Re: Airboat skipping on water/plane

Postby Deano » Mon Nov 07, 2016 9:03 am

To embed a video, use the [youtube] function like you did, but only put in the youtube
identifier, not the entire address. In this case, putting in elpcX3WdOKI will yield this . . .



What you are experiencing is called porpoising and if the bottom is straight and true, is usually caused by the back (prop) end of the engine being a little to high. You should start with the engine parallel to the stringers. If the bottom has no issues, usually just a little bit up in the back will work the best.

If you can easily drop the back (or raise the front) using a fender washer or two, it is just as easy to do this first as to pursue all the other possibilities. Keep your fingers crossed. . . that may correct it, if not, there is plenty of help here.

This thread explains how changing the engine pitch effects things when the bottom is good:
http://www.southernairboat.com/phpBB3/viewtopic.php?f=85&t=28600

You could additionally, do a search for 'porpoising', 'hooked hull', or 'engine pitch' and find a bunch of info.
"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."
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Bob in Canada
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Re: Airboat skipping on water/plane

Postby Bob in Canada » Fri Dec 02, 2016 5:27 pm

What you're going through is a reoccurring thing with my boat . For me there's a very simple fix . At the bottom of the transom there is a lip that extends out of the bottom rear of the hull . Once or twice a year I bend this lip down just a bit . It sort of acts as a trim tab and keeps the front of the boat running flat and true at speed . Works for me .
I'll try to ad a link it the tool I made to bend the lip .
http://www.southernairboat.com/photopos ... ol/cat/500
14x8 Diamondback , 2.38-1 Stinger , 350 GM Marine , Sensenich 3 Blade "R" prop

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Bob in Canada
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Re: Airboat skipping on water/plane

Postby Bob in Canada » Fri Dec 02, 2016 5:50 pm

I think that link worked .
This hull adjustment lasts a summer or so then from dry loading the lip bends back up a bit and the boat starts to porpoise again . Five minutes of bending it down on the trailer and it runs flat at full speed again . Doesn't take much just a couple of degrees of downward bend . If I don't do this from time to time it will start to hop so bad you'll bounce right off the seats .
:canada:
14x8 Diamondback , 2.38-1 Stinger , 350 GM Marine , Sensenich 3 Blade "R" prop

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john1edwards
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Re: Airboat skipping on water/plane

Postby john1edwards » Sun Dec 04, 2016 5:50 pm


trim tab will fix that.
Just an Orange Engine, Nothing Fancy . Proud to be an American


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Bob in Canada
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Re: Airboat skipping on water/plane

Postby Bob in Canada » Sun Dec 04, 2016 6:01 pm

A trim tab would be good but for me I go over beaver dams , logs , dry load so much I'm sure I'd forget to down and peel it right off .
14x8 Diamondback , 2.38-1 Stinger , 350 GM Marine , Sensenich 3 Blade "R" prop


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