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F1 Tunnel hull as an airboat?

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F1 Tunnel hull as an airboat?

Old 10-15-2014, 03:59 AM
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Jeremy_H
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Default F1 Tunnel hull as an airboat?

Just a curiosity enquiry really. I've another paint job come in and it's making me wonder about using such a hull as an airboat. This one is 44" hull length, I'll measure the beam and take some photos of the important bits to help.

But, has anyone considered one of these?
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Old 10-15-2014, 04:43 AM
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The Dumas Big Swamp Buggy is a type of tunnel hull airboat and has been around for a long time. It's downfall is not having enough downforce on the bow to keep it planted as well as having a high CG. It tends to flip easy. With an outboard it would have a much lower CG and the thrust would be transferred to the bow much better than what an air prop can do. At least in my eyes anyway. I have a BSB and the previous owner added a sheet of polycarbonate to the bottom to turn it into a flat bottom instead of the tunnel type and that was said to run a lot better.
Old 10-15-2014, 05:20 AM
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arcdude
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Doesn't look too wide in the beam, so I'd have to agree the CG would be high. By the same token with the air engine in the back I'd think the down force on the bow may be quite manageable. If one had access to a hull to give it a go, it may be worth giving it a shot.
Old 10-15-2014, 06:49 AM
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Even with adequate downforce on the bow, what is going to make it unstable is the air getting under the hull. Unless your pond or lake is glass smooth, the bow will bounce some and this is where it's gonna want to lift. I'm not saying it won't work because anything can be made to work with enough time and resources. It's just not practical. Besides the BSB, has anyone ever seen a tunnel hull or catamaran type airboat that was very successful? Not many that I've seen. Closest reliable hydro airboat that's been successful has been the outrigger and even they are very picky to get setup just right.

Jeremy - I say try it and see what happens. If you can make it work reliably and run well, you'll have a decent following as airboat builders are always looking for something new. At least IMO anyway.
Old 10-15-2014, 09:08 AM
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arcdude
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Another option Jerry is to add venting similar to what your doing on the twin model to limit lift, may be worth a shot
Old 10-16-2014, 03:50 PM
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Cool. If the rain holds off tomorrow I'll take some daylight pics of it to show the key elements. It's beam may be greater than it looks in that bad image above tbh, we'll see what you think when I show a top view. It's a 1/4 scale boat so a fair size, expected to run a 26-30cc outboard gas engine.
Old 10-16-2014, 05:20 PM
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arcdude
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You know Jerry the hull may not be too bad, I just measured my old scratch built hydro at 21.5" x 44" and it was estimated to have gone 70 mph and I had no bad characteristics in running it. It was only set up with a straight turn fin and at that time I installed one on each sponson. Although I didn't do extensive testing with the model it performed better than I could have hoped so I wouldn't be too quick to dismiss the tunnel or a hydro style hull without giving it a go and in fact it may entice others to try different models themselves should they see a few successful models. Cheers

One item of note is all models that I've experimented with have had the engine behind the sponson's so that is certain to make a difference in the running ability of a given model.

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Old 10-19-2014, 12:25 PM
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Jeremy_H
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Here you go, some pics to contemplate:

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Old 10-19-2014, 07:29 PM
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That is a sleek looking hull Jerry! Off the top, I'd consider the engine towards the back but not right at the back and possibly vent holes to prevent lifting too much. The tricky part I think is to find the right point where the bow is light but not flighty. What is needed is a test bed consisting of the bottom half of the hull and the engine on rails to slide fore and aft and adjustable venting to determine running ability. Only one way to find out m8!

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