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Jul 22, 2008, 07:31 AM
Proud to eat Kraut ;-)
Julez's Avatar
Thread OP
Build Log

Cool DIY Airboat!


Normally, I do airplanes, but recently, my buddys and me go to the canal every now and then to hang out and chill a little. Each one of us built a little boat for this, and I built an airboat.

The hull consists of blue strofoam. It is 50cm long, 40cm wide, and 6cm thick. It is nicely rounded at the front and at the sides, and covered with a piece of plastic film normally used for truck livery.

The center piece of the back is the mounting plate. It consists of 3mm plywood, coated with 163g/m glass fibre and red dyed resin.
The rudders and the RC box lid are made from the same material.

On the mounting plate, there are 2 booms made of 10*10mm square aluminium pipe, carrying the rudders at the end. The rudders have 3mm music wire pivots, which were glued in a slot before the glass fiber was laminated on them. There is a normal rudder horn on one rudder, and they are connected with a wire going through two lugs.

At the center of the mounting plate, there is a rectangular piece of 2mm aluminium, with a milled mounting aid, which goes into the 10*10mm square aluminium pipe carrying the motor. The motor is a Turnigy aerodrive XP, SK series. It pulls around 15-20A on a 9*6" propeller. It gets barely warm, even when constantly driving full throttle. It was protected against corrosion with lots of silicon spray.

The servo is fixed with the metal parts of a luster terminal, and 2 M3 screws coming through the mounting plate from the bottom.

The RC box carries the reciever, a Plush 25A ESC from Hobbycity, a large aluminium heatsink, and a 4s A123 pack.
It is made from 3mm Plywood "painted" with resin inside and out. The lid has hinges made of M4 aluminium bolts normally used as rudder horns for large composite gliders. 1.5mm nails serve as pivots.
Foam rubber strips normally used to cushion the fuselage, when a wing is mounted, are used as seals.
The large heatsink is made from a L- shaped piece of 2mm Aluminium, which I got from my uncle when I was a kid. Yes, I kept it that long
I removed the ESC from its shrink wrap, and took away the little aluminium plate heatsink. I bent the main capacitor a little to the side, so thet the FETs can rest flush with the aluminium surface of the large heatsink. I drilled 6 holes into it, so that I can thread zip ties through it, which are used to press the ESC against the heatsink. The silicon thermal transfer pad, which was between the FETs and the stock heatsink, was also used when the new heatsink was attached. The large heatsink is velcro'd on the side wall of the RC box. I was very careful to make the cable feed-through at the rear part of the RC box water-tight. Therefore, I glued 2mm sockets into the top part, in which the cables to the motor are inserted using 2mm gold plugs.
The main contact bridge used the 3.5mm gold contacts that originally came with the motor. The antenna was lead through a piece of brass pipe.
The bay for the RX box was cut into the foam by electrically heating a piece of 1mm music wire, which was bent into the appropriate shape.

The driving caracter of this contraption is fun and very exciting
I had to add little aluminium fins at the bottom to improve stability. It works good right now, but I will increase the length to about 30cm, and see what happens.
Edit: I now mounted fins 30cm long and 1.5cm high. For each fin, I glued 3 strong wooden dowels into the styrofoam. Thin screws are driven through the fins into the dowels.

The boat's speed is satisfying, and its a blast to jump over waves, and have the water splash all around and through the propeller.

The built was definitely worth it. I hope I can also use it in the snow, when the winter comes.




Due to some questions, here are the detailed dimensions:

Lenght: 50cm
Width: 40cm
Heigth: 6cm

Aluminium Fins:
Length: 30cm
Heigth: 1.5cm

Twin Rudders:
Distance in between: 16.5cm
Height: 16cm
Length at top: 10cm
Length at bottom: 14cm
Distance leading edge <--> pivot point: 3cm
Distance pivot point <--> transom: 11.5cm

Distance shaft <--> boat deck: 11.5cm
Last edited by Julez; Sep 02, 2009 at 05:53 AM.
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Jul 22, 2008, 12:34 PM
Grumpa Tom
Kmot's Avatar
Looks pretty cool. Very nice for a home design!
Jul 23, 2008, 06:35 AM
Is life for real?
pkboo's Avatar
Nice built Julian, it does look like it can use some more "nose" but still cool AB. Boo
Jul 24, 2008, 07:01 AM
Proud to eat Kraut ;-)
Julez's Avatar
Thread OP

You mean, it should be longer?
I tried different designs some time ago, and I found this one produces the most lift at the nose. If the fuselage is narrower, it is more difficult to get "air under the boat".
I will go to the canal again today, and hopefully get a video
Jul 24, 2008, 12:31 PM
Is life for real?
pkboo's Avatar
I'm sorry yes no offense. I could be wrong but the proportion just looks a little off, maybe you can bring the rudders in a bit see what it does, a vid would be cool and prove me totally wrong I'm still saying it's a nice clean cut built and I wouldn't be able to built that clean cut Boo
Jul 25, 2008, 07:10 AM
Proud to eat Kraut ;-)
Julez's Avatar
Thread OP
No problem at all, constructive critizism is always welcome
I just figured, that, while a wider fuselage may create more lift at the nose, a longer fuselage has a longer lever arm, so they might be equally effective.
Yeah, when I have a little free time, I will test this theory with a new fuselage.
I have installed longer fins at the bottom, 30cm.
Now I can turn at any radius, and if I slam the rudder @ full speed, the front edge digs into the water, spraying a lot into the propeller, which leads to cool sound effects
I noticed, that wind and waveheigth have an influence. The less both is, the cleaner the boat drives.
Jan 11, 2009, 11:25 AM
Proud to eat Kraut ;-)
Julez's Avatar
Thread OP

Today I was driving in the snow with a friend!
This thing is a blast!
It can get quite fast, and one can do cool things like jumping over ground irregularities.
A video is uploading at the moment.


Last edited by Julez; Jan 11, 2009 at 11:34 AM.
Jan 11, 2009, 11:29 AM
Grumpa Tom
Kmot's Avatar
Oh, how fun! Do you have an area of flat ice to do a speed run on?
Jan 11, 2009, 11:42 AM
Proud to eat Kraut ;-)
Julez's Avatar
Thread OP
No, it snowed before the ice was thick enough.
But it gets fast enough on flat snow to tumble over backwards due to lift at the front.
Like this.

Well, here is my video:

Heizboot im Schnee (2 min 52 sec)

Some cool stunts in the last half.
Jan 11, 2009, 07:37 PM
Grumpa Tom
Kmot's Avatar
Wow, it really takes a pounding out there! But it looks like most excellent fun!
Jan 12, 2009, 01:47 AM
Taking care of the pond.
That's cool, takes a licking and keeps on ticking!!!
Jan 12, 2009, 09:35 AM
Retired for now
Way to go Julez. That sled is terrific. Can't beieve how it takes such punishment and comes back for more. Great job there. You either have one very nice front yard or a super frozen over lake to play in. Pete
Jan 12, 2009, 09:37 AM
Retired for now
Originally Posted by Kmot
Wow, it really takes a pounding out there! But it looks like most excellent fun!
kmot I see your english vocabulary is getting primed for what might sound like Chinese pending your trip to the Old Country. Ha!AHHHHH SOOOO! Pete
Jan 12, 2009, 01:16 PM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
Nice thing about airboats,... they go anywhere.
Fun video thanks
Jun 11, 2009, 08:39 AM
Registered User
bitmaniac's Avatar
Thank you Julez for the updated (measurement) infos

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