Dennis44

Just want to say hi, joined the forum because i`ve always been interested in Airboats but here in England there isn`t much info, I had the same problem with modeling dragsters. I want to build a scale airboat, about 30 - 40 inches i guess, i`ve got a new 28cc 2 stroke strimmer engine i`d like to use and i would like to scratch build the hull in ply or alloy.
Any tips, suggestions welcome and if anyone can come up with some plans or drawings it would be appreciated.
Thanks in advance,
Dennis.

Mr Cajun Gator

[link=http://cajungatorairboats.com/id11.html]Basic plans[/link] just scale them up to the size you are wanting. Welcome hope that you get as much enjoyment as most all of us on here are getting from the airboats. good luck on your build.

Dennis44

Thanks for reply, have got plans will post pics as work progresses...............

vamp131

Hi im in SCOTLAND I MADE A FEW BUT VERY HARD TO GET RIGHT SO BOUGHT ONE FROM THE USA ITS GREAT GO,S LIKE STINK THERE ARE PLANES ON HERE SO YOU CAN MAKE YOUR OWN OR GO TO TOWER BUY ONE READY TO FIT AN ENGINE TOO

crispyspa

Vamp......why are you YELLING? LOL

Dennis44

Not too good with forums, might not get it right but have taken some pics of the engine, with and without casing would be interested in what you think. I`ve bought a pair, brand new surplus stock, were destined for a strimmer. They are 28cc and have a centrifugal clutch. Question for you do i keep the clutch or remove it and mount the prop direct to the crankshaft.
Decided on aluminium for the hull, going to fabricate it myself, propose to make it 38 x 18 x 4 ins. using a mix of the designs i`ve seen so far, watch this space............................................. ...
Any comments welcome,
Dennis.

crispyspa

Lose the clutch, aluminum flywheel housing and all the plastic shroud. Remove the vanes from the flywheel and re balance.

You will need a pusher prop and you could upgrade the carb for more power. Looking forward to seeing the build pics and the first video. Keep us posted.

Dennis44

Got the engine down to barebones, clutch off, problem is there is only about 5/8in of crank showing, not enough to fit a prop. Is there anywhere i can get an adaptor or is it a case of having one made ?
I tried a couple of model shops near me and they just ain`t interested, bet if i wanted a complete boat/plane it would be different !!!
If anyone can point me towards a dealer/shop willing to ship to UK would appreciate it, i also need a pusher prop or two.
regards,
Dennis.
p.s. got a cardboard mock-up of the hull ready will post a pic, going to attempt to build it in alloy using "Durafix", i think you call it "Easyweld", if it don`t work then i guess it`s back to plywood.

Dennis44

Put together a cardboard mock-up of my proposed boat and the first thing that jumps out is the apparent "out of scale" appearance,is it just me or have i got the measurements totally wrong. It`s 38 x 18 x 4 and i`ve allowed for a 16 x 8 prop, the engine is 28cc. What would be the max size i could or should, go to, as it is i had intended to use 1.5mm aluminium for the hull will this be thick enough for a larger hull.
Sorry for all the ?`s but i`m on my own over here.
regards,
Dennis.

dadkins

Your scale looks pretty good - I would go about 4 inches wider with angled sides of course, and not quite as thick maybe 1 inch less. Looks good otherwise.

crispyspa

Go with 3" thick and 16" bottom. Angle the sides at a 45 Deg. which would give a total width of 22" wide at the top. If you don't want it that wide, narrow the bottom a tad. Keep in mind though that a long narrow boat will want to bank the corners instead of sliding. It will still slide, just not as easily.

Keep the "drop" in the center of the boat, but extend it through to the transom, this will allow the engine to sit lower for a better CG.

since it will be a pusher, you will probably have a cage....keep this in mind when determining your center of balance. You will most likely have to move the engine forward a bit to compensate.

Dennis44

Thanks for the input, will amend drawings and see how it comes out. Just one point, can`t see how i can lower the engine as i have to allow for the prop to clear the deck unless i reduce the diameter.
I am working on the cage. As it won`t be used for racing, no competition here, i would like to maintain as much as i can the look of the real thing.

crispyspa

Like this.

Dennis44

DOH !!!!!!!!!!!!!!!!!!

crispyspa

.......And that's why we're here, to help out.

500 lb. koolaid man

Dennis44, looks like your project is coming along excellent! Glad to hear! You're doing a great job with scaling. Definitely take crispyspa's advice on hull size and adjust it if necessary for the look you're going for. Looking forward to updates.

Dennis44

Have taken "onboard" tips and suggestions and have come up with what i am looking for. Run out of cardboard so couldn`t make a full size mock-up but have made a couple of 1/20 scale models and it`s looking good, pics attached.
In case it might help someone i have also added my hull plan, it takes one sheet of aluminium and only needs 4 welds to make the hull, also when the bow is formed by bending the sides in it gives it a small slope.
Any comments/suggestions welcome, working on engine mounts at the moment before starting the hull.
regards,
Dennis.

crispyspa

Make the transition from bow to bottom a smooth one and you've got it.

jasperrc

I like the direction you are going and Crispy is a master builder when it comes to gassers so take his advice over mine if I say something contrary to what he says, but I think she looks a little short for the width. What do your overall dimensions look like right now? I think they changed since you started your mock ups.

Dennis44

Hi Jasper,
havn`t started the hull yet, but the final size is coming out at 38 x 26, still time to amend if nessecary. I increased the width but kept the same length and the small card model looks better balanced. Built lots of small mock-ups trying to get the right look, don`t want to cut the metal for the hull until i`m sure, i`ve started on the engine mount as that won`t change.
Dennis.

crispyspa

38 x 26 will most definitely slide in the corners, but having such a short ratio (146%) between length and width might cause the boat to Porpoise. You know, you've seen it, where the bow bounces violently. Other factors contribute too, like engine height and the CB being off. Also, a shorter/wider boat will want to spin out of control more easily.
I guess the lowest ratio that I would go is 170%.....but that's just me.


Thanks for the ego boost Jasper. LOL

Dennis44

hmmmm..........just when i thought i`d cracked it, ok, let me run this by you, where is the ratio taken from ? is it from the deck, which is 38x26 = 146 or from the contact area of the hull with the water which is 25x16 = 156.
Dennis.

crispyspa

I figure the ratio as:

The flat bottom of the boat running all the way from stem to stern....as if the sides are not angled.

Is your bottom 16" wide or 26" wide?

If it is 16" and you have a top deck of 26, then obviously you want the hull 5" thick. Correct? 5" thick hull is too thick IMO. the 45° sides will act a a sail when you do a higher speed sliding corner and flip it over.

A couple of thing you can do to remedy is:
reduce the thickness of the hull and back off the 45° angle to something like 20° and make the bottom of the hull a slight "v" or gently rounded bottom with turn chimes.

Or Like I tend to do, cut back toward the top deck with another 45° angle.

First pic: large sides acted as a sail (4"thick hull)
second pic: reworking helped, but it still wanted to flip.

I hope this helps.

Dennis44

Thanks for that, i understand now, i`ll start over with new plans, watch this space............................................. ..

Dennis44

plans redrawn, alloy bought, break out the compressor and a big hammer and.....................................
early days, lots still to do, get everything right before welding,riveting etc. anyone spots anything way out of line then let me know so i can take another look. got a prop adaptor on order from a machine shop, don`t have a lathe. prop is an m/a 14x7 for starters and see how it goes.
prob be a week or so before i can do any more on it.