# Need your thoughts- Hobie Trifoiler/Dared Kiteboat/Self Design Frankenstien

Discussion in 'Boat Design' started by LeeDesign, Jul 11, 2018.

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### LeeDesignJunior Member

Hello all,

New user and long time lurker here. These days I am in the midst of a design project, taking the size and layout of the DARED kiteboat:

and combining it with a Hobie Trifoiler inspired foiling system:

Here is my first question, but first a little background information. Instead of an adjustable trailing edge on the foil I am intending to rotate the entire body of the foil to actively adjust angle of attack, dumping or adding lift as needed to actively adjust for heeling, wave action and speed.

-So how much angle of attack is enough, in general, when it comes to hydrofoils?

Currently, whilst cruising at speed the foil axis is at 0 degrees 12 inches below the surface of the water, with the hull flying in the air another 12 inches above the water. When the hull comes to rest on the water (either due to a wave, heeling action, or attempting to get up to speed to rise up on the foils) the angle of attack is adjusted to 20 degrees. As the hull rises and the foil nearly breaches the surface of the water, its angle of attack is adjusted to -34 degrees. Here is a bit of a diagram to illustrate my meaning if it wasn't clear, using a generic airfoil.

What are your thoughts on this, readers? Are these angle of attacks too much, too little? It seems to me that the positive angle of attack is too much, that it would provide much more life than would ever be needed to get its portion of a 200 lb boat and rider out of the water. Also it would cause unneeded drag as the boat accelerates from rest in an attempt to get up on the foil in the first place.

Ill add my other question later.

Thanks!

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Welcome to the forum! Why Hobie "feelers" instead of wand controlled flaps? I'd say that the angle of incidence you show is waay too much...
For what its worth Dr. Sam Bradfields foilers were set up like this:
1) when sitting in the water before starting to move the static waterline was close to parallel to the flight waterline after takeoff.
2) The mainfoils were set up with a +2.5 degree angle of incidence relative to the static waterline. The rudder foil set at zero degrees relative to the static waterline. The two mainfoils were designed to carry 80% of the load together(at takeoff) and the rudder foil 20%. Rudder foil loading was about half of the mainfoil loading.
3) As the boat began to move the wands would cause the flaps on the main foil to go down 25-30 degrees depending on the amount of righting moment required from the foils. The rudder trailing foil did not need a wand or any other adjustment while flying-some boats used a manual adjustment of the rudder foil to fine tune trim.
4) The two forward mainfoils and the rudder foil were symmetrical sections because they had to not only lift up, but had to pull down as well. Symmetrical section on the rudder foil. This is directly parallel to what you're trying to do. His boats were not kiteboats but the dual independent wands acting on flaps on the forward foils supplied all of the righting moment for the boat automatically.
Good Luck!

This simply illustrates how you can determine the change in AOA of a foil with the flap down. The angles shown in this illustration are not relevant to a hydrofoil. To compare the Bradfield foil set up with an all moving foil draw out a foil with a + 2.5 degree angle of incidence. Drop the flap(say 30% of chord) 30 degrees. Connect a line as shown in the illustration from the leading edge of the foil to the tip of the down flap. Measure the resulting angle against the straight line you used to get the +2.5 degree AOI("relative wind" in the illustration) :

Last edited: Jul 11, 2018
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### LeeDesignJunior Member

Hey Doug, I was hoping I might get your attention Im not too familiar with Dr. Sam Bradfield, I will have to do some research into him. As far as the feeler thing goes, I just showed the trifioler as a very visible example of an active foil control system. I am actually intending to use a kind of wand system, but one that is small section of the hull to fold down, pivoting from somewhere near the nose. Kind of similar to this:

From project.kiteboat.com. They are using a 'shell' of the hull that folds up against the hull when the hull is at rest/heeled. My idea is a 'slice' out of the main hull that provides the same function.
Also, this thing being small, I expect it to see some rough treatment both in storage and use, so I feel a wand/feeler system that folds up into the hull would be an advantage over a delicate wand system external to the hull.

And the reason for going with adjusting the whole foil as opposed to trailing flaps is the simplicity of it. My composite construction skills would probably be up to the challenge of the internal pivots/ flexible flaps needed for such a system, but this project is to be a proof of concept/ rapid prototype. A solid (although foam filled) foil with a single central pivot would be easier for now.

Are there any advantages you think I would be missing out on going with this type of system over a trailing flap?

Anyways, thank you very much for point #4. It simplifies things very much and eliminates one of my next questions, at least partially. ( What foil section to use) It reduces the options to a elongated hydrodynamic teardrop. That being said, what foil section would you advise? At least as far as a height to length ratio. Some quick google research shows the Moth uses a NACA 0012 at about a 12% H/L ratio. I see no reason why the same wouldn't work for me?

Now, I'm not too sure i am conceptualizing your points 1,2,3. Let me throw together a bit of a simplified diagram to see if I'm there, and maybe even clean up my own models to show the point at which my overall design currently sits.

Thanks!

Lee

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You'll have to do research on the foil section-Bradfields proprietary sections were 12% T/C(thickness/chord) ratio. Greg Ketterman was a fan of an all moving foil but the problem with them could be if you hit something-then the whole system gets screwed up whereas a daggerboard and a foil with a wand controlled flap can handle a bit more contact w/o total destruction. Ketterman believes that the Hobie Trifoiler was faster than Bradfields Rave because the Rave used (vertically mounted)T-foils that can have more drag than the Trifoilers inward pointing "L" foils. Otherwise, I personally don't like something sticking out in front of the boat but your proposed system would be a bit better in that respect.

Bradfields 40' SKAT -the largest boat to ever use dual independent wand systems to provide RM and lift.

Kettermans all-moving inward pointing "L" foil. He actually built a version of the trifoiler with the foils pointing outboard and found that it was significantly slower:

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### LeeDesignJunior Member

Here you go, a roughed out model of my intended design. Its shown with the front wand at the approximate cruising height, giving the foil a neutral/2.5 deg angle of attack. The control linkages are not shown here, nor are the rear two wands, but you can imagine where they will go I think?

Any obvious errors so far, keeping in mind its a rough concept? Thoughts, opinions?

Edit: The muscular manikin depicted is 6', length overall is 6', width is 5' while maximum buoyancy sits around 240 lbs (will probably need to go up)

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It's not necessarily an error but I think a kiteboat-especially a small one- might work better with a conventional "aircraft" configuration rather than a canard configuration. You would only need two wands-with the aft trailing foil working automatically following the main foils. What's your rationale for this configuration?
Regardless of the configuration you'll need to pay very close attention to the distance between the forward and aft foils which needs to be(probably) more than what you show.

Another aircraft configuration kiteboat similar to the one above:

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### LeeDesignJunior Member

Hey Doug,

That kiteboat is pretty damn cool, eh?

Anyways, I assume your talking about the configuration of 1 float in front, 2 in the rear, when you refer to canard config. ( I just hadnt thought of applying the term canard to it) Originally I had assumed that all 3 foils would work best with each having a control wand. With this thought in mind, I thought of the steering: putting the steering in the rear would mean a complex linkage between rudder and wand. (The wand would be stationary on the center hull, while the rudder would be pivoting) Putting the steering on the front float, the whole float would turn for steering, essentially allowing a static relationship between rudder and wand even though the rudder is turning. Does that make sense? I dont think im explaining it well.

But with the current configuration with 1 in the front, I am having a hard time connecting the wand to the foil. Basically the frame gets in the way. So it may be that the layout of 2 in the front, 1 in the rear may be better. But can you really get away with having a static foil on the rear and only having active adjustments on the front 2? This seems to me that you would have issues with the rear foil popping out of the water as you gain speed?

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Well, numerous foilers including both kitefoilers in this thread use the "aircraft configuration" with a single rudder t-foil. That single rudder foil is called a "trailing foil" and it automatically follows the lead of the wand controlled forward foils. The AOI settings and loading I mentioned in #2 are critical, however. The rudder t-foil can have manual(while flying) trim adjustment but it is not necessary. All the foils should have adjustable angle of incidence while on the beach. The rudder foil provides about 20% of the lift at takeoff and on a normal foiler automatically will begin to pull down at a certain speed if required.
The rudder foil is 100% automatic providing the mainfoil/rudder foil set up is very close to what I mentioned in#2.
I suggest you go with proven technology for your first prototype and don't try to re-invent the wheel until you have substantial foil experience. Build a quick proto- as similar to the kitefoilers above as possible- that you can use to learn with and go from there. Nothing beats learning while doing.

Wand foiler animation:

Last edited: Jul 12, 2018 at 8:59 PM
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### LeeDesignJunior Member

Back to the drawing boards, just a bit. Thats ok, its easier when the board is digital eh?

So ive been giving your information alot of consideration and come to the conclusion that your right. Firstly, the distance between front and read foils needs to be greater. In aircraft, when the tail and wing are too closely coupled you end up having alot of oscillations, which the pilot attempts to correct. In a boat it would be the wands trying to do the correction, but i think some similarities would be found here. Solution: lengthen the distance between front and rear foils.

Secondly, the layout of 2 front-1 rear versus the 1 front-2 rear configuration; If you can get away with the rear foil having no active control via wand, then it would be a much simpler system to go with 2 front-1 rear.

Conclusion: I need to model a skinny main hull with 2 small outriggers. Somewhat similar to a outrigger race canoe i think, except symmetrical of course. Kinda like this:

Though this is much too long, the pilots seat needs to be moved towards the rear, and perhaps bias the outriggers towards the front. And add hydrofoils + control systems. What do you think?

Anyways Im going to get back to the modeling. I see there's been 13osomething views. Wheres everyone else at?

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I think you should copy ,as close as possible, the K2-just to start with. Wands don't have to be as far forward* as they are on K2 but the main foils need to lift 80% of the load changing automatically (and most importantly) to: lift from the kite should be 80% on the forward foils, 20% on the rudder foil(like the K2).

This is the wand system on Bradfields 18' Osprey. Similar position on the Rave, Whisper Cat and 40' Skat. There are some who believe that placing the wand way forward is faster but there are major advantages to the Bradfield and Whisper systems particularly on a kiteboat, in my opinion:

Wand System on the Whisper:

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### LeeDesignJunior Member

Thats an interesting configuration on the Whisper. Why have they chosen to locate the wants behind the active foils? It seems too me that by the time they react its too late, the wave has passed, hull has buried, or the foil has breached.

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The theory is that with mid-ship wands(on the Whisper) the wands hit the water in line with the longitudinal CG of the boat so that they work strictly for altitude control w/o inputs from pitch attitude-pitch being controlled by the rudder T-foil.
PS-if you want to read more about mid-ship wands vs forward wands go here:
High Performance MPX Foil/Self-righting Trimaran-The Test Model https://www.boatdesign.net/threads/high-performance-mpx-foil-self-righting-trimaran-the-test-model.36058/page-163

See post 2436 for Tom Speer on why forward wands work and,

post 2440 for Ron Price (designer of Whisper and F101) on why mid-ship wands work.

Last edited: Jul 15, 2018 at 9:08 PM
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### MurphyLawJunior Member

This is what I am going to build but using 2 solid wing-sails, I am going to use inertial sensors and an SBC to control the foil flaps. The problem with this particular design is you cant align the fuselage/body with the apparent wind..well it has no fuselage. If you look at the Sail Rocket the floats and foils can rotate about the vertical axis so the fuselage/body can point directly into apparent wind therefore presenting the smallest air resistance. The foils and floats point in the direction of travel but everything else points directly into the apparent wind. I'm not sure why people are still messing about with wands when every cell phone had inertial sensors that are good enough to control a hydrofoil, I have a super dooper model designed for drones and missiles that not only gives basic readings of inertia but it has a maths computer built in and will give degrees offset. Another strategy I have and am keen to try is to use LIDAR from autonomous vehicles to map the sea ahead, you could map 50m ahead of the boat and auopilot the steering as well as the foils to steer the path that is the least resistance through the waves. Another untried method is to use LIDAR to sense the wind patterns, it is sensitive enough to read the frequency of ripples on the water surface so it could be possible for a computer to sense where the wind is strongest in an area and sail the best course automatically. If you take a 4 motor drone and mount it on a boat and have 4 hydrofoils instead of sending power to the motor to increase speed you send to another motor that increase lift on that foil. VOILA you have a self leveling hydrofoil system.

Last edited: Jul 16, 2018 at 6:19 PM
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### LeeDesignJunior Member

Im not too sure about all that, sounds more complicated than i could manage myself. But a bit simpler and more realistic for me would be to use some kind of non contact electronic measuring system like ultrasonic, laser, infrared, etc, to measure the distance between hull and water. Then use that measurement to control the hydrofoil surfaces via stepper motor. I kinda like that idea cuz it would eliminate the wands altogether. However its been my experience that electronics are finicky, especially on a boat. One short or malfunction, especially at speed, would result in a spectacular crash. Thats my thought on it anyways.

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### MurphyLawJunior Member

Don't listen to the electrics and water mob, how many drones out there that cost a few hundred dollars that can remain on position in crazy wind ? Last time i tried controlling one of those things manually it was a LOT more sensitive and finnicky than controlling the balance on a boat. The term LIDAR is used as a catchall for a combination of lasers/infrared/cameras etc to measure distance, you could go it alone or you could just take one of the many LIDAR DIY projects out there and adapt for sailing. I am going to use 4 foils and 4 motor drone technology to get a working boat, then I am going to replace different hardware/software with stuff more suited to sailing. Whether the boat crashes when the software hangs up or whether the car crashes when the software hangs up are the same, worse for the car, which is why they tend to use a combination of lasers/infrared/magnetic/camera to measure the distance. I think stuff developed for cars/drones will probably be more robust than stuff for sailing. For a start what the car sees could be tarmac,concrete,plastic,steel,grass soil etc while what a boat is looking at will either be water or something to avoid, a very simple decision.

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