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  1. #1

    Water-foil rudder....Thoughts please!

    Has anyone attempted to use a water rudder/foil for lack of a better term on an outrigger to get up on plane. I've posted a pic to give an idea of what I'm considering......so please feel free to post any thoughts you may have on the idea, Thanks
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  2. #2
    1QwkSport2.5r's Avatar
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    I wouldn't mess with something like that. Wet rudder yes, water/wet foil no. I would expect undesirable handling from something like that though I've not tested anything like that. Just a regular wet rudder only.
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  3. #3
    Yes a few experiments, no evidence of that but I got to point where it was clear that it's a high precision exercise.

    One of the problem of simple foils like you show is that they have persistent lift. Given enough speed they will simply eject your entire rudder out of the water. So what's needed is a form of lift that controls itself somewhat more. You could spent an eternity changing chord length and angle of incidence to get that right, but the optimal region is so tiny it's just not practical, at least I found it so needing tuning every time out . But there is at least one prospect of a solution, and that can be learnt from Hydrofoils.

    Consider a V shaped foil , so the bottom of the V is in the water, if the sides of the V taper from top to bottom in chord the effective surface area decreases as the foil rises in the water, in effect regulating itself. The idea is that the foil optimizes it's running height so that it's the minimum drag with sufficient control, and the degree of lift/drag is directly related to the speed of the boat. This is a far less sensitive way to work with Hydrofoils, and I've often thought it worth pursuing for a rudder.

    Not got to it yet though

  4. #4
    Here, this pic may help:

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  5. #5
    1QwkSport2.5r I have to say I'm a little surprised in your response in light of your current outrigger with adjustable air stabilizer, I have considered the same idea however like you I want to do something a little different. To my understanding the sailing world and high speed boats are being extensively tested and built with foils for faster speeds and efficiency. Don't get me wrong I'm no engineer, just a lowly hack who envisions something in the head and has an over active imagination, sometimes things work out and other times they don't.

    Jeremy_H excellent ideas Thanks, I have scoured the web for hydrofoil ideas for this particular application and found a big fat zero. What I propose is a rudder that will come on plane and run the hull level and provide turning ability at the same time. What I have found with actual foils is they're designed to work under water and not to plane on the surface....hence the challenge. As with the V style you mention It may have a tendency to porpoise side to side should it rise too high, what about a double fork with two legs spread out wouldn't it tend to be more stable? What style did you experiment with?
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    Last edited by arcdude; 01-28-2014 at 08:22 PM.

  6. #6
    1QwkSport2.5r's Avatar
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    That tail wing is really there as a function of looks. I do not suspect it does much or will do much. However, an airfoil and water oil are two different animals. As Jeremy said, the faster you go with a water foil the more lift you get. Novel idea, don't get me wrong. I just don't think it's going to work as you'd want it to unless you can control how much lift you get even as speed increases. The idea behind my outrigger is to get on plane and go fast and not go airborne. I like simple. My rigger floats super well with the crappy sponsons so it should float and go better with good sponsons. I hope.
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  7. #7
    1QwkSport2.5r What I'm considering is kind of a half breed of sorts it will climb up due to the angle of the foil and ride on top of the water as with the rear sponsons on some riggers with approx 2-3 degrees up, the traditional foils are designed to stay under water. I am merely replacing the rear sponsons with the foil so to speak, less weight and less air turbulence, I hope. All in all it should achieve an aircraft running attitude without the bulk and weight. The foil pictured above and please excuse the rudimentary sketch but the lower limbs are on about 2-3 degrees up angle so the faster you go the higher it will lift but without sufficient air surface should ride on the top of the water and basically be incapable of flight due to it's design with only enough wing load area to function in water and not in the air. Although I'm not opposed to a little flight!

  8. #8

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    I did not get as far as testing anything, but I soon will have a platform for doing so. I'm making what I'm calling a Power Module, a single piece engine/radio module that could bolt on top of any hull. My plan it's to fiddle with hull designs once that is available, this could be included in that.

  9. #9
    Btw I meant anything in respect to the V rudder idea. I made foil rudders, based on attachments for outboard motors, but as I indicated I found them very tricky to set up with no in-between pulling the stern down or floating it too much, as it just alters with speed. Mine were mounted a little under the keel height..

  10. #10
    Thanks Jeremy_H What I have in mind is to construct the rigger without rear sponsons and the ultimate goal is to design something that will lift the hull enough to run at a horizontal plane without touching the water, that is why I'm looking at a small foil mid height on the rudder which will run on the surface. Should the attempts fail I will incorporate a method in the build to attach rear sponsons later on if necessary. I'm familiar with the foils your talking about at one time I had a 25 outboard and too much boat to push so I used a bolt on foil and it seemed to help with the running attitude. So far design wise I have the V you mentioned which I like and the fork idea with two prongs and another is just a flat horizontal foil set at about 2-3 degrees to start and see what happens. I realize this is relatively uncharted waters and is probably being met with a great deal of deserved skepticism, and that's o.k. If full size boats can utilize foils to lift an entire boat out of the water certainly a foil of some design can be utilized to lift the back end of a rigger up to run on plane. Could be interesting to say the least, thanks for the input.....much appreciated!

  11. #11
    crispyspa's Avatar
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    Quote Originally Posted by arcdude View Post
    1QwkSport2.5r What I'm considering is kind of a half breed of sorts it will climb up due to the angle of the foil and ride on top of the water as with the rear sponsons on some riggers with approx 2-3 degrees up, the traditional foils are designed to stay under water. I am merely replacing the rear sponsons with the foil so to speak, less weight and less air turbulence, I hope. All in all it should achieve an aircraft running attitude without the bulk and weight. The foil pictured above and please excuse the rudimentary sketch but the lower limbs are on about 2-3 degrees up angle so the faster you go the higher it will lift but without sufficient air surface should ride on the top of the water and basically be incapable of flight due to it's design with only enough wing load area to function in water and not in the air. Although I'm not opposed to a little flight!
    I think your original idea and picture you posted warrant some testing. However one change, leave some rudder below the "wing" so you can still steer when it is on "plane".
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  12. #12
    Hey crispyspa Thanks for the vote much appreciated, really nothing to lose. I can't seem to find anything anywhere indicating the this has been tried on an rc boat. I also noticed in the drawing that the rudder didn't go down below the foil, it was a quick draw just to get some feedback on the idea. I have a 6.5 inch tapered rudder that I plan on using and at this point I figure the sponson height will be approx 1.5 - 2 inches below the tub so the rudder should be long enough.

    Question: does anyone have any suggestions on how I might attach a horizontal aluminum foil to the rudder in a clean fashion?

  13. #13
    1QwkSport2.5r's Avatar
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    Machine it as one piece A), JB Weld B), or TIG weld C). If your rudder was brass you could solder it together. Aluminum doesn't solder well (Alumiweld works but requires annealing the assembly as it gets too soft from brazing). TIG welding is the go-to for aluminum welding but takes immense skill and a very expensive welder to do. JB Weld is your best bet IMO.
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  14. #14
    crispyspa's Avatar
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    "L" brackets and bolts. Use 2-56 SHCS for the horizontal bolts and 2-56 FHCS countersunk into the bottom of the foil or just use the SHCS from the top and tap 2-56 holes in the foil then file off the excess bolt on the "Water side". It would require small holes to be drilled into the rudder, but those could be easily filled with JB weld if it doesn't work.
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  15. #15
    Just for interest. When I found this problem of fussy angle of attack of the foil I drew this. Never made it, but perfectly doable. It presents a smooth profile with a means of quick angle adjustment.The plan was to make the foil by joining two T section extrusions, so the top of the 'T' where shaped as a disc that can be rotated in the rudder blade, a pinch bolt locks it down with little force:

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    In my head I think the plan was to make the rudder blade adjustable too, so it could be moved up and down the rudder stock to adjust the foil's height.I do remember finding that this has to be a rudder and mount that can take the weight of the butt end of the boat, pivots needed thrust washers at least. Proper bearings would be cool.

  16. #16
    Appreciate the input guys! Good suggestions. I will be mulling it around in the old noggin for a while until I can solidify a direction to go in.

    Jeremy_H I had a similar thought to the stress on the rudder and mount which would likely entail building a whole setup to suit the need including beefing up the hull to suit. I did come up with one idea considering this is all experimental and that is to attach the foil under the hull for experiments rather than combining rudder and foil. It would be mounted right at the stern or as close as possible and be constructed in a similar fashion to a rudder with break away bolts ie: tap through the bottom and attach the foil with nylon bolts and attach a small diameter fishing leader or something in the event of a collision with water born livestock. I doodled a quick sketch to show what I'm thinking of and if anyone has any thoughts on the idea please by all means chime in, I'd like to hear some feedback.

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  17. #17
    It would probably be a simpler way to try things. It's just the effect of turning it that'll be missed.

  18. #18
    It might be a better way to go and break it down by first trying a foil to get onto plane and how big and so on and then experiment with the turning which I suspect would be easier than figuring out how big a foil and at what angle of attack would be req'd for the hull weight and so on. I'm stuck on this idea because when I watch videos of outriggers and hydro's they don't fun parallel to the water causing a lot of wake but rather at a slight upward angle, so my thought is if a person removed the air and water friction it can only add up to a whole lotta speed. I realize the design purpose of most hulls is to somewhat trap air under the hull to aide in the lifting process but if a mechanism can be devised to negate the whole exercise one would think it should improve performance. Okay I'm rambling, sorry bout that and Thank you to everyone who has offered their opinions.


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