Hydrofoil assisted or full flying kayak

Discussion in 'Boat Design' started by Canoemaker, Dec 19, 2009.

  1. Guest625101138

    Guest625101138 Previous Member

    Your foil data is way out. You would deduce from that curve that the boat will be in full flight at 11kph and the drag will be 6N. It implies you could do 11kph with less than 20W. There is an error of the order of 10 times here. Actual foil drag even without allowing for wave drag and strut drag on it will be around 60N. You should check your calculations.

    I have attached the JavaFoil data for the 64412 section with aspect of 10 at Re# 200000 - best L/D is 23. It is not as good as the 5% foil I gave data for. I have attached the data for this foil at the same Re# - best L/D of 31. In practice the thinner foil would need to be slightly longer or wider to provide the same lift so would benefit from this as well because the Re# will be higher or aspect higher.

    The one advantage of the thicker foil is that it is more tolerant to variation in pitch. I expect pitch changes with foil assist will be an issue in all but dead calm but you need to get the best L/D possible if you have any hope of it providing an overall gain.

    Once you get the calculations close you will find the break even will be around 14kph at steady speed. The power level required to sustain this speed is beyond a male of average fitness.

    Rick W
     

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  2. Canoemaker
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    Canoemaker Junior Member

    Nope the hull wouldn't achieve flight before foil produced lift of 87 kg and one drag shows foil only drag and other hull only drag so i don't know where you found i am taking of with 20w of power
    the boat needs 12N less power at 36kg displacment than at 87kg displacment
    base data for foil
    Re 350 000 at 12km/h T=12°C
    Cl = 1.5 (java foil for NACA 63412 ) at 3° angle of attack
    Lift Fy = ro * v^2 * Cl * A / 2
    For 510N
    A = 2 * Fy / (ro * v^2 * Cl) = 2*510/(1000*(12/3.6)^2*1.5) = 0.0612 m2
    span=A/chord = 0.0612/0.12 = 0.51 m
    span = 0.51 m
    Cd = 0.01.
    Fx = ro * v^2 * Cd * A / 2
    Fx = 1000*(12/3.6)^2*0.01 * 0.0612/2 = 3.4 N
    add for the strut ,rough total of 5n
    so we have cca 7N spare
    dSPEED = dDRAG/gradient (at 12km/h)= 7N / (5N/kmh) = 1.4 kmh

    this is very rough calc could be flawed,i am not claiming it is not.If i knew it works i wouldn't ask like most here in the forums,i would just build it.
     
  3. Guest625101138

    Guest625101138 Previous Member

    The Cd for a foil of those dimensions at that Re# is 0.07 not 0.01. A factor of 7 times in the drag will make quite a difference. Again this is making no allowance for strut drag and wave drag. (Where did the 0.01 come from - certainly not JavaFoil?)

    The data in the foiling curve you provided is clearly wrong:
    1. Take a weight of 87kg and go to the lift line. This intercepts at about 11kph.
    2. Now look at the intercept on the drag curve at 11kph. It is 6N.
    3. So the chart is showing that you can get 87kg of lift with 6N of drag at 11kph. This translates to 11/3.6 x 6 = 20W.

    If this was so you would forget the hull and just fly. Anyone could do it all day. I work at higher power output typing than this.

    I also point out that the strut drag and wave drag are significant factors and cannot be ignored. They alone will cost more than 20W at the break even speed.

    Rick W
     
  4. Guest625101138

    Guest625101138 Previous Member

    This thread prompted me to review the commercial progress of the Flyak - the foiling kayak. The site is no longer active so it may be that they have shut up shop.

    These comments from the inventer and commercial designer are interesting:
    Quote
    Not everybody can fly, unfortunately. The big limitation of the Flyak is cardiovascular. “You can’t go very long distances with this craft,” says Fredrik Wenstøp of Pivot, the Oslo firm that formulated the commercial design. “It takes very intense energy for the paddler to keep up on the foils.”

    Rasmussen, too, emphasizes that the Flyak is a highly specialized racing vessel that requires a good deal of skill and endurance from the kayaker: “The total weight of the kayaker and hull dictate the area of the foil pair. Kayakers with a high level of fitness can use smaller foils, and thereby reach higher speeds,” he says. “You could say that the Flyak is like a Formula One car—fast, and just as practical.”
    Unquote

    There is no doubt you could establish an Olympic sport around this boat and it would be much faster than existing sculls or kayaks. However why not set an Olympic class around pedal powered foilers. These would be the ultimate speed machines for human power.

    The problem with this is the vested interest in the existing competitions.

    It is unlikely that the foilers will ever have popular appeal because they need a level of athleticism that takes a lot of training.

    Rick W
     
  5. portacruise
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    portacruise Senior Member

    Here's the video:

    http://www.youtube.com/watch?v=bQRtgEIs--k

    They state 32 Km/hour. Is this faster than pedals? Granted it was done by an elite athlete and over a very short distance.

    Porta

     
  6. Canoemaker
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    Canoemaker Junior Member

    Flyak evolved in to final configuration under Nelo brand but is now sort of a show boat and of only limited production ,as the boat was only for top paddler it was only built with short high speed foils .Think they were runing ca 28-29km/h but idea was that with further development they might reach 32km/h
     
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  7. Guest625101138

    Guest625101138 Previous Member

    Vic
    Decavitator got over 34kph a long time ago. It was highly developed for the time but I am certain that speed could be bettered with a curved shaft water prop and an Olympic class cyclist.

    Rick
     
  8. Guest625101138

    Guest625101138 Previous Member

    I expect there is a message here for you. If the Flyak developers could open the potential market to a wider range of paddlers by getting a benefit from foil assist at lower power level then they would be exploring that avenue.

    Rick W
     
  9. Canoemaker
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    Canoemaker Junior Member

    If you put it that way then propeler driven human powered boats are destined to disapear altogether.100+K kayaks& canoes are sold in US alone yearly VS how many peddal boats.If you think this way there would be no real progress.
    It seems that flyak is almost as fast (with less power )as decavitator while decavitator retracts a low speed foil and has countless hours of MIT research in its development VS a guy in a shed modifying a flatwater boat using of the shelf fastacraft hydrofoils. It the same for your craft you have much more power at your disposal but any gain is negated by loss of active stabilisation and therefore inefficient catamaran or trimaran configuration with rising weted surface that become even more of an issue faster you go.So you might get away with small overall gains but in reality you are using much more power to do it ,sort of like sculls that also have huge amounts of power but small gains and are unpractical package.Your boat is also 2x the weight and over size and can't really be production or user friendly.
    The closet to usable pedal powered boat are hobie kayaks with mirage drive but they also have to trade in gains in propulsion for a barge like stable platform that is not very efficient. But that is not the point we are just bouncing around some ideas that already have practical applications but might or might not be usable for our purpose
     

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  10. Chris Ostlind

    Chris Ostlind Previous Member

    If it's about short track sprinting, then perhaps you are correct with the string of assumptions... but that 100K sales figure does not encompass this foil equipped type of boat any more than would a period at the end of a long paragraph.

    The real magic for pedal/prop craft, whether foiled, or not, is twofold.
    1.) Long distance adventure trips are within one's grasp for a lot less effort.
    2.) A person with a much lower level of fitness can now entertain waterborne outings that were well outside of their potential previously.

    A boat with less effort means that the genre is not limited to elite physical specimens. Now, even out of shape recreationalists can get involved with the sport. When you graph out that potential, the paddled kayak with a lifting foil isn't even in the same league. Then there's the noticeable relative cost issue between easily built pedal systems and much more expensive foils.

    If you want a real take on the leg powered market potential, take a long look at the numbers of Mirage driven boats that go out the door every year. It's positively mind-boggling. I happen to sell boat plans for homebuilders and in the last 15 months, I have seen a distinct rise in the interest level, as well as the sales, of boats designed to accept the Mirage drive.

    Foil equipped boats have a certain coolness factor, to be sure. Their appeal to a small segment of this type of boater is inevitable. But, there are just so many hurdles to jump when looking to engage a niche market with a possible production example. If you don’t intend to go in that direction, then I think that exploring foil-borne kayaks would be fun, as well as engaging technically. If you are looking to market a product commercially, then you'll run smack into the same scenario as is currently being experienced by the Foiling Moth market niche. It looks as if they've pretty much saturated the available market and sales have slowed as a result. Of course, the global economy isn't helping their cause one bit.

    I do hope that you continue to explore your ideas in this regard and that you keep us informed with your progress. You have pushed into an interesting niche in the market. It's one where numbers on paper are only a starting point. You'll have to build and test any number of combinations before the real issues will make themselves known. However you chase this, I really hope that you have fun doing it.
     
  11. Canoemaker
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    Canoemaker Junior Member

    In previous mail i am not debating foil kayaks that are just show boats but kayaks and canoes VS peddal craft, hobbies are numerous but most of them don't have mirage drives.
    The boats we make are in 98% not paddled by athletes but by paddlers i could say in mid-life crisis as i would reckon average age of 40+,sort of similar to group that buys fast racing bicycles that are also sold in thousands but very few to real athletes.
    Its interesting how many kayaks are designed for touring but how few are used that way(i reckon factions of a percent) ,its sort of like 4x4 no one realy needs them but they are really popular.So i wouldn't boast to much off long distance pedal craft.
    This project of foil assist if it could work would resoult only in one or 2 modified boats any way and just for fun.
     
  12. Guest625101138

    Guest625101138 Previous Member

    You have quite a few misconceptions about relative merits of human powered boats. Until you have tried a well designed pedal boat you are not in a position to comment meaningfully but your point of view is not uncommon.

    Pedal boats are gaining in popularity for fishing craft due to hands free aspect. Hobie owners are impressed at how easy the boats move through the water but most have never tried a well designed kayak and are surprised how much faster a kayak is with a good paddler. Their comparison base might be a dinghy or 6ft long sit-on not a racing kayak.

    I operate my boat at 120 to 130W. It is quite a bit lower than what fit paddlers work at because the boat is considerably more efficient. It is a stabilised monohull. The outriggers barely touch the water as you can see in the clip (allow for the clip to download):
    http://www.boatdesign.net/forums/at...08-pedal-powered-boats-v14_outrigger_load.wmv
    In this regard the boat is about 1kph faster for the same power than an OC1 of similar length because the single outrigger carries load and contributes significantly to drag.

    I can apply a lot of power and get above 18kph but I have designed the boat for long duration. My main advantages are the relaxed posture and having hands free. I literally lay down on the job and I can fuel up as I go. There is not much difference between arm power and leg power when the body is aerobically limited. However it is great to know I can get to 10kts if needed.

    The boat sits flat on the ground. Can operate in 150mm deep water. Requires no particular skill to operate. There is no art in keeping it balanced.

    Back to the foils. The lift and drag curves you have are for infinitely wide foils. In your calculations you have made no allowance for the induced drag that results with a foil of finite width. You also need to use data for the Re# you are operating at. As you can see from the curves it makes a big difference to the drag.

    AND, I continue to stress, you need to make reasonable determination of wave drag and strut drag.

    Rick W
     
  13. portacruise
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    portacruise Senior Member

    What kind of time is needed for the learning curve before someone can operate a kayak safely, and with good manuevering skills? Eskimo rolls, special paddles and techniques, etc. Contrast that with the mirage or a prop boat which anyone off the street can work almost instantly. That probably explains why mirage is shaking up the market. But these are more like ONE "hands free" as periodic corrections are required by the rudder.

    Porta




     
  14. Canoemaker
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    Canoemaker Junior Member

    Kayak or canoe can be paddled from the word go by anyone its not any different than Hobie in that respect ,advanced techniqes take more time but that is the same for every sport(how long does it take for some one who never drove a bicycle to learn) and are not essential for most users,eskimo roll even tough it looks difficult can be learned in less than 1 hour
     

  15. sigurd
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    sigurd Pompuous Pangolin

    Hi there, could you assume a length constriction of 3m for a hull, being made for long duration, I dont know, 150 watt is reasonable I deduce from reading this thread. 90kg displacement. Give it a propeller but keep the beam within the "human *** limitation" like a kayak.

    It looks to me as if the boat is less than 4.5m the drag starts rising very fast.
    The L/D at that power and length would be very high, more than any foil according to Rick.

    At 30-50kg however, any displacement hull L/D is much lower, and optimum is shorter. It looks to me like the shortest possible now before drag rises steeply, is around 3m. If one could get about half the weight lifted on foils at L/D 26, like rick mentioned, the remaining displacement L/D might not be very horrible.

    So rick, would you care to see how much faster the 4.5m displacement boat is, compared to the 3m foil assisted?

    Why one would bother with such a short boat, I guess there could be a few reasons. Any way, a slim fast kayak is not the most fun to surf waves with. This foiler would probably fly with only a little help from waves.
    A one kg battery would fly it for an hour if assisted by the human.
    A sail or kite would often enable it to fly.
    Unassisted it would be a dog compared to a 4.5m+ kajak (which could also have retractable foils), how much of a dog is what I would like to know. I think that 3m is faster than 4.5m if foil assisted 50/50 at 150watt. It would also be interesting to know how bad 4.5m is compared to optimum, un-foiled.
    Lastly, I am wondering why the optimum is shorter at high power. I thought wave drag would increase more than friction drag, with speed. And length reduces wave drag. ??
    Thanks for the interesting discussion.
     
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