Hydrofoil assisted or full flying kayak

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

  1. Canoemaker
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    Canoemaker Junior Member

    The goal of the project is to design and build a kayak and hydrofoil system that would enable sustained long distance 1h+ paddling at 7.5-8.5 knots .Current top of the line distance kayaks and fit paddlers average more or less round 6.5kn for 1h+ races on flat water.The design is ment to be usable for most regular paddler not just top paddlers like the high speed foilkayak

    The kayak design is a rough modification of one of my racing open category kayaks.Hypotetical design has 3 steps to further reduce wetted surface while being foil assisted .with foils providing roughly 30,50 or 70kg of lift for a boat normaly displacing 85kg ,in different configurations. The design concept opens up number of questions :
    -does foil assisted hull reduce drag enough for considerable gain?
    -how does it compare to foil borne ?
    -does the hull in the water reduce the need for foil controls?
    -what kind of foil section would be best for such low speed application?
     

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  2. Doug Lord
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    Doug Lord Flight Ready

    Tom Speer once said that the wetted surface needs to be reduced by four times the plan view area of the hydrofoils in order for the foils to "pay" for themselves with "foil assist". His comments in this thread: http://www.boatdesign.net/forums/sailboats/foil-assist-small-large-monohulls-9732.html
    Sounds like an interesting project.
    You might want to look at this thread: http://www.boatdesign.net/forums/sailboats/stepped-planing-hulls-small-sailboats-7145.html
    and the "Midship Interceptor" is interesting(and easy to experiment with):
     

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  3. Canoemaker
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    Canoemaker Junior Member

    foil assist

    With steps the wetted surface would come down from cca 1,75m2 to 0,55m2 + the foils ,if 70kg of foil lift is provided. So we could reduce the wetted surface close to 10x the foil surfaces(probably cca 0,1-0,12m2) or 8x without using steps
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Your concept of using foils and steps together is interesting-Eugene Clement has done some pioneering work in that area. Could you illustrate what you mean by "steps"?
     
  5. Canoemaker
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    Canoemaker Junior Member

    steps

    Steps are of similar concept as in powerboats and prevent water going along the hull and hugging it longer than needed .So as the boat draft is reduced the steps help cutting the wetted surface ,but otherwise create drag in all other conditions.
    On the sketches you see underwater hull cut abruptly ,that is because of the step that enables water release.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Thanks-I'm familiar with steps on powerboats. I was interested in exactly how you would implement them at such a low speed and why you thought multiple steps would be required.
    Here is a proboat article on Clements mods to Plums theory on hulls using a very small single step.

    http://www.proboat-digital.com/proboat/200510/?pg=168
     
  7. Canoemaker
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    Canoemaker Junior Member

    steps

    i am aware that they are more than likely not needed and/or of enough benefit to be worth the trouble.It is just an experiment ,un like power boats where you are stepping a rather flat surface here i have rockered and round surface that is easy for water to follow even above waterline so just a possible remedy to cut wetted surface. 2-3 steps to compensate for some displacment wariation as kayaks pump up and down while paddling.
     
  8. Canoemaker
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    Canoemaker Junior Member

    steps

    i am aware that they are more than likely not needed and/or of enough benefit to be worth the trouble.It is just an experiment ,un like power boats where you are stepping a rather flat surface here i have rockered and round surface that is easy for water to follow even above waterline so just a possible remedy to cut wetted surface. 2-3 steps to compensate for some draft variation as kayaks pump up and down while paddling.
     
  9. Guest625101138

    Guest625101138 Previous Member

    The break even for displacement versus foiling for a lightweight person, say 70kg, will be around 300W if paddling. It is around 250W if pedalling.


    In all the conditions I have looked at, foil assist is not as good as full foiling.

    An individual has to be quite fit to sustain 300W for 1 hour. The flyak gets toward the elite end of paddlers and I think this has restricted its acceptance.

    Also do not underestimate the problem of weed and other litter. It only takes a tiny piece of weed to destroy the operation of a foil.

    Rick W
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Rick, what do you think of the idea of combining a step or steps with foils for a relatively specific speed?
     
  11. Guest625101138

    Guest625101138 Previous Member

    Doug
    I have thought about a series of steps with the aim of reducing drag. I mean maybe 50 steps down the hull so they are short relative to width. If it had merit it would not benefit from foil assist. In effect it becomes a planing hull with higher lift to drag than a conventional single surface planing hull.

    Rick
     
  12. Canoemaker
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    Canoemaker Junior Member

    foiling

    foil assisted (hull still in the water) option is considered only if the gain to be had is big enough ,you know most people when they hear something foiling think 15-20knots ,but you know kayaks are not like that on a longer distance race 1 knot speed advantage over 6.5-7 kn kayaks would not only be race winning advantage but race dominating one even with a bit lesser paddler. So for me a foil assist that would gain more than 1 knot with reasonable handling properties is already something worth considering. Full foiling even tough is more efficient is sort of all or nothing concept and the problem sustaining flight is not so much in power but constant powering of the boat over 1h+ time.
    To put things in perspective the kayak designs i make are already at the edge of the design for open category racing ,optimised for endurance racing so faster than Surfskis or K1 on flat water over 1h and only as stable as top surfskis,so with new designs we are only able to get small drag reductions as they are already close to optimal ,and only really work well within small margins off design displacment ,in K1 sprint kayaks the margins are even smaller so now you can see for the first time different hull not only for paddler weights(boats are made in s,m,ml,xl,xxl sizes) but for the first time for different course lenghts so a 200-500m design is not the same as the one for 1000m
     
  13. Guest625101138

    Guest625101138 Previous Member

    A well designed pedal boat will achieve 6.5kts with 150W. This level is achievable for average trained cyclist for much longer than 1 hour.

    The break even for a pedal boat to go to foils for a 70kg rider is around 7.5kts. This requires 250W. This is getting to good level of fitness for a 1 hour duration.

    Paddling is not as efficient as pedalling plus there is speed variation with paddling so I expect the break even to be higher; more like 300W.

    The lowest drag hull for a single 70kg person in the 6.5 to 7 knot range has a beam around 220mm. You cannot make a kayak this narrow so it will not be the lowest drag hull.

    The pictured boat is optimised for 6.5kts and achieved this with 150W on the cranks. The 47yo rider covered 245km in 24 hours and also managed 109km in a 10 hour training session. The shape shows you what the lowest drag hull looks like.

    I do not believe all avenues to reduce skin friction have been explored so hull steps might be worth trying. But you would need a lot of them to get a potential advantage. I cannot see any foil assist providing benefit for a shallow draft boat that is not length constrained. It is full flight or nothing. It would be optimised for about 8kts.

    There are various options to go faster.
    1. Make a stabilised monohull to match the power level with paddling. There may be benefit in using small foils for roll control rather than just floats.
    2. Make a pedal powered stabilised monohull to match power. With the pedaling it is easy enough to move weight slightly to have the outriggers doing no more than skimming occasionally.
    3. If you can sustain more than 250W for the duration of the race then you could consider going to a pedalled foiler.
    4. If you can sustain over 300W for the race duration then a paddled foiler could be beneficial.
    5. If there is a length constraint then foiler might have an advantage at lower power level than 300W.

    Anything with underwater appendages suffer the risk of fouling. In practice I have found that methods to avoid fouling are essential to good performance. I do not know how this can be easily incorporated in foils.

    Rick W
     

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  14. Canoemaker
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    Canoemaker Junior Member

    power

    All valid points .
    But i have to disagree with ideas for an ideal design .
    We have been working on various designs ,and i have to say that at certain point the design of a long slim boat just turns unpractical ,suddenly you are designing a 7+m long and 22cm wide hull that can with additional(not with equal power) just go maybe 1knot faster in short races than a 5,2 m long x 40 wide K1 kayak .
    A single seat rowing skiff ,just tops a K1 sprint boat ,while having more power due to rower using legs more and long paddles and having a much longer and slimer hull ,that is unstable for anything else but rowing,but the gain is small ,hull un-practicaly large ,with lots of wetted surface and heavy definetly not something for car toping. You have the same problem with pedal powered boats ,you might have more power in your legs and a slimer ama suported hull but in practical terms ,you end up having a heavy boat ,that is inherently unstable,also imposible to stabilise with your body weight and i would be suprised if the boat could easly outrun surfskis in 1-2 h competition even more so in any other condition but flat water definetly not on open sea where amas would induce additional drag much of the time.
    But that is a different story what i am aiming for is a kayak.So power is limited also hulls longer than 6m with waterline width of waterlines under 36cm wide are not proving beneficial ,a 30cm waterline hull ends up offering drag reductions only at lower end of the speed scale while wetted surface bites back later.
    Look at the picture what you see are a kayak and a narrower outrigger canoe ,kayak has 70cm shorter waterline and 10 cm wider waterline than an outrigger canoe , kayak has more drag but also more propulsive power so it can outrun the canoe,but that is no real comparison like pedal powered boat is not comparable.,on the other hand the new kayak in design is only 20 cm shorter in waterline and 6cm wider at the waterline than the Oc-1 but much faster,even if you have the same amount of power the canoe it only more efficient in lower speed region as wetted surface of narrower hull bites back(and i am not even looking at the ama) ,It is just that design is not universal ,we designed the oc-1 for lower speeds and for good preformace catching & surfing the waves
     

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  15. Guest625101138

    Guest625101138 Previous Member

    I thought you were looking at ways to go faster in medium duration events.

    The fastest is a stabilised monohull with pedal driven prop drive. A prop drive has substantially higher efficiency than a paddle. The thrust is continuous so the speed is steady. This is similar to the advantage a kayak has over an OC1. A pedal boat will give away about 7kg in weight to a kayak but this is made up in the improvement in efficiency. A good prop drive has overall efficiency of 84% compared with around 70% for a paddler with good technique. Windage on a pedal boat is actually less because there is now upper paddle being forced through the air at about twice boat speed.

    The length for lowest drag does not start reducing till above 7 to 8kts depending on pilot weight. At 8kts for 95kg boat it is 7.2m. For 10 knots the lowest drag hull for 95kg displacement is 6.1m. So has got shorter but it is higher than the speeds you are chasing.

    Car-topping a 7m boat is not particularly difficult.

    A fully enclosed hull with flat deck is an inherently strong shape. It can be built very light. It does not have the cockpit opening that weakens the basic structure. The black boat pictured above has a total weight of 18kg and is 7.2m long.

    On a pedal boat the thrust is almost continuous so it is possible to balance a slender hull. The force is not varying widely in amplitude and is not applied on different sides of the boat as occurs with a kayak.

    Pedal boats hold current sprint record of 18.5kts and current 24hr distance record of 245km. Neither of these records were established by elite athletes.

    The advantage of pedal power is proven. Foils are proven in sprinting power levels but not in any foil assist mode on a human powered craft. Foil assist can be beneficial in hulls operating at much higher Froude number than a kayak but I have not been able to determine any benefit for human power. In fact there is a a drag hump rather than any gradual reduction in drag in the cases I have examined.

    Rick W
     
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