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Hydrofoil Boat RC (experimental)

by wersy, published

Hydrofoil Boat RC (experimental) by wersy Apr 18, 2014
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I still couldn't use the full power of my motor on the enlarged motorboat. http://www.thingiverse.com/thing:284692
My intention now was to lift the bow to avoid the huge bow wave and also lift the stern so it does not dip so deep.
So maybe a hydrofoil would achieve it. I choosed the profile NACA 63-412 which is common for sailboats like the Moth. At front I took the brigde from the two hulled boat http://www.thingiverse.com/thing:286848 at back I designed a new mount.

The test have shown that it is very tricky to find the right balance between the pitch of each wing, the right speed and the optimize CG.
On the first try you can see how it behaves (00:36 - 00:40). As soon it became fast and lift, the propeller don't gets enough water anymore. Then it suddenly slows down till the propeller reaches the water again. It makes it several times.
Then with some changes it run better.
At the end I tried without the front wing. The stern still kept up but the bow throw a big wave and went steep upwards again.
And better choose flat water without waves and where you can go in - very specially if you drive it as wild as I tried ;-)

All boats I designed have a displacement hull. This type runs best with its hull speed. The longer it is the more speed it will make. If you try to go over the hull speed you need relatively much more power. Additionally its driving behavior is then unfavorable. The bow lifts up and throws high spray water - partly also in the boat.

So take it as a suggestion and make something really good! :-)


Wing mounts
Layer hight: 0.3 mm
Width: 0.5 mm
Infill: 0.5
Solid layer: 2 on bottom and top

Layer hight: 0.3 mm
Width: 0.5 mm
Infill: 0.1
Solid layer: 4 on bottom and top

There are M2 holes to fasten the mounts to the hull with screws M2x5 mm.
I recommend to put metal strips between the screws and the hull to protect the hull from penetration. For this I used brass strips 6 x 48 x 0.2 mm.

All remaing parts you can take from:
http://www.thingiverse.com/thing:284692 (motor boat enlarged)
http://www.thingiverse.com/thing:272132 (motor boat)

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Neat. If you ever revisit the idea, should try one with a leading skimmer that controls the front plane angle. Since your test area is calm and smooth water, shouldn't need to worry about a damper either. It's a pretty simple mechanism too, more or less a small water-ski on a lever in front that pivots the front plane. Given the size and boat's ballast load, I'd suspect you could also get away with using more symetrical lower lift foils.

And of course changing to a jet pump, waterproof motor, or V-drive could help with the thrust angle. Just figure out a way to keep it in line with the rear plane.

Thank you for the tips.
Your thoughts are pellucid, so I will have them in mind if I make another attempt.

The problem is you are trying to use a hull that is not designed for planing, In reality you want the boat out of the water as much as possible without flipping, the more of it out of the water , the less drag you have slowing you down. This hull would be more suitable for moderate speeds. A hull with a deeper v-shape and chines would be much more stable at high speeds and plane well. Take a look here http://www.google.com/imgres?imgurl=http%3A%2F%2Fwww.airmar.com%2Fblog%2Fmilford%2Fwp-content%2Fuploads%2F2012%2F06%2Fhull-line.jpg&imgrefurl=http%3A%2F%2Fwww.airmar.com%2Fblog%2Fpage%2F4%2F&h=2592&w=1944&tbnid=g7dfz7AoeHIVIM%3A&zoom=1&docid=IGf6-Kp4F4xmaM&ei=ccVbU7jyAcHCywHnu4HoBA&tbm=isch&client=firefox-a&ved=0CJkBEDMoPDA8&iact=rc&uact=3&dur=386&page=4&start=56&ndsp=21http://www.google.com/imgres?i... the chines and ledge on the hull help keep it on plane and stable while on plane.

Yes I know what you mean. Finally I added a v-shaped stern part and this is really fast now.

Speed Boat RC (experimental)
by wersy

You should experiment with curved or shallow V shaped foils. These will help greatly both with stability and "fly height" regulation.
These shapes cause more of the foil to exit the water flow as speed (power) increases, reducing lift and causing the system to be self regulating. The shapes also cause the lift to have vectors that are angled to the hull making the boat more laterally stable.
Looks good, keep experimenting.

Thank you for your advice and encouragement.
The wing is already v-shaped with an 150° angle and the stability is very good.
But I must disappoint, in the next time I won't continue experimenting on boats.
Finally I must finish my second airplane now...

Seems like you may need to lower the engine on the boat so it's deeper into the water? Or I just don't understand the project.. Found it on http://Hackaday.comHackaday.com

It is not possible to lower the Motor because it is not water tight. But in principle you are absolutely right. At least the propeller should be lower. This needs a different transmission and would require a completely different design.
My aim was to replace or add - with littleeffort - only parts of a base model and see how far I come. It is clear that this can't be
always quite successful, especially if one try to morph a displacement hull to a speed boat ;-)
But today I made a little test of my very last version - and this is really fast :-)
It will coming soon...

Should have added this in my other reply... Maybe you could figure out a way to have the current driveshaft turn a small wheel, and then use the small wheel with a belt to turn a larger wheel that powers the propeller? I read on another one of your projects that the speed was an issue.. That would slow it down too.

A belt in the water will generate additionally water drag. A cardan joint would be better.

I feel like lowering the propeller wouldn't be too difficult, especially since you have a 3d printer (or so it appears). It's a pretty interesting project and if i had some free-time I'd love to build something similar..

In principle it is not a problem, but as I mentioned before, it would require a completely different design. I wanted to see how far I come using only one design by adding or changing little modifications.
And yes, I have my own designed small Wersybot. For me, it is the best of all :-) I even printed my airplane with it.
Though it is a very interesting project, I will end boat designing now for a longer time. But I would love to see what you are going to build.