help needed

Airboats with smaller powerplants.
Noel Dunne
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help needed

Postby Noel Dunne » Sat May 21, 2016 4:59 am

Hi Folks I am new here
I built a mini airboat, loosely based on the Lake Buggy design. I ended up with a10ftx5ft glassed over plywood sigle seat hull with 20hp Honda engine and 42insx24 prop. My problem is that she is digging in at the stern and creating a big wake.I have moved the seat forward to alter the trim and this improved performance at low revs but when i open throttle she slows down and digs in at stern
The engine is mounted with shaft parallel to hull. If I pitch the angle down slightly will provide some lift and improve the trim. Any help welcome
Regards Noel


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glades cat
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Re: help needed

Postby glades cat » Sat May 21, 2016 6:40 am

It sounds like your boat is trying to plane but doesn't have enough power/thrust to get over the hump.
Try running in shallow or marsh areas instead of deep water.
Video what you described, for better feedback.
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Deano
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Re: help needed

Postby Deano » Sat May 21, 2016 8:13 am

I agree with everything Glades Cat posted. To specifically answer your question:

IF you have enough power, AND you have the correct prop, AND your weight is properly distributed, AND by "pitching the angle down" you mean lowering the prop end of the engine, THEN the answer would be yes . . . doing so would help it to not 'squat' as much.

If you search, you should find a build thread for a similar mini that may offer you some useful 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."
- Carl Sagan

Noel Dunne
Southern Airboat Member
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Joined: Fri May 20, 2016 2:12 pm

Re: help needed

Postby Noel Dunne » Sun May 22, 2016 6:46 am

Good morning guys and thank you for the replies
I am a complete novice with airboats and being based on the Shannon in Ireland there is no local knowledge that I can tap into. I think that I have plenty of power for such a small light boat judging by the size of the wave that I am creating but I may be wrong.
If I tilt the prop down at a slight angle would anybody guess by how much would be a good starting point. I will video the results and put on next post

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Deano
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Re: help needed

Postby Deano » Sun May 22, 2016 8:49 am

Typically, when adjusting the angle of thrust, flat fender washers are used
as spacers so that adding and removing them allows for small angular changes.

You want the initial angle of thrust to be parallel with the bottom. This should translate into the prop shaft being parallel with the stringers. Once you get it close, from there 2 or 3 washers is a big adjustment.

Lowering the rear (prop end) of the engine, will lower the bow.
This is the direction you would go to relieve the squatting that you now have.

Raising the rear (prop end) of the engine will raise the bow.
In your case this would compound your problem. If it starts porpoising, you've lifted the bow to far.
"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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