Will this work..or is it too big?

I've decided to build an airboat in my spare time. I plan on building it out of 9mm plywood all round, and powering it with an OS 25 LA engine. If I stuck to these plans, would it A)work well, and B)be powered well enough by the 25 LA to get some decent speeds out of it when using a 9x6 propeller?

At the moment I'm wondering if 5" is too much for the height, and maybe I'd be better off building it a bit lower?
Also, is 9mm a bit drastic - would 3mm or 6mm plywood be best?

Thanks,
Marc.

I'm not familiar with your engine, but it'll need to very powerfull if you build the hull out of 9mm ply!

Three mm poplar ply is very light, cover the bottom with a light glass cloth and epoxy, paint the rest, that should be enough.

Regards, Jan.

Thanks.
Here's a link to the engine: OS 25 LA.

Also, what's a light glass cloth?

Thanks,
Marc.

In the US this is available from the LHS, and is usually 2 oz/sq yd woven fiberglass cloth. He's right, 9mm is way too heavy. 3mm would be plenty for a .25LA, and even 1.5mm is not too light if you used 3mm frames. What are the dimensions of the boat? Airboats with that power level are usually in the 600-700 mm range.

Bottom is 8" wide so about 232mm. Top is double that so about 464mm. Length of the bottom is 24" so about 696mm, length of top is 29" so about 823mm.

What do you mean by frames?

Thanks,
Marc.

Prope,
Frames are simply the interior framework for your hull. As to size of your airboat, if you are building the "swamp" style, a ratio of 1.5:1 is about right. some use 1.6:1. 5" is kinda tall for your hull. 1.5" to 2" is more common. Tapered sides will help your boat slide when cornering and help prevent rollovers. Hope you find this helpful. You can find lots of help over at R/C Airboats as well as here in this forum. Best to ya!!
Gordy

Thanks
One last question, you say a ratio of 1.5:1 is about right for the size, but a ratio of what to size?

Thanks,
Marc.

Edit: Is 24" too long for the bottom and is 8" too wide for the bottom, bearing in mind the engine size?

Prope,
I really should refer you to someone with more extensive experience as far as the right size for your engine. I feel you are about right but would prefer that you verify with someone else. I don't want to tell you wrong. .Why don't you check with the guys at Airboat World or maybe someone will help out in this forum. All that ratio means is that your boat should be 1.5 times long as it is wide.Hope this helps. Best to ya!!
Gordy

Prope,
Will it 'work'? Sure. Is it going to be the fastest thing on the water? Nope. BUT, it should survive almost anything! LOL 'Fast' is a combination of the least weight, the most power, with the least friction. Very easy to define, but very difficult to 'get there'...
- 'Doc

"A butterfly built to government specifications is called a 'bum'. It don't work." - P.M.L.

Here's my opinion on your drawing.

5" is way too thick for the boat. !.5"-2" foam would be best. 5" will give you a higher COG.
I would aslo icrease the rake. Make it 6" back from the bow.

I''ve never built a .25 before....If I were to build one, I would make it 22" long by 10-11" across the bottom.

Thanks LtDoc & dadaddyro [8D]

I've had a rethink and have now decided to go for a bigger engine, most likely the 46 LA.
Haljmac PM'd me about some plans he has for a .40 sized boat so I've asked him to send me them.

Thanks,
Marc.

P.s. What's a rake?[&:]

My pleasure to help!

Rake is the angle of the bow section; from the bottom to the tip of the front.