Pedal Powered Boats

Jeremy and Ad Hoc,

I think inverted T foils, independant surface-wand control of the entire port and starboard wings stabilizing roll, pitch and heave (ride height) and perhaps a submerged pod for mild buoyancy assist (and to house the AoA control mechanisms). The pod could also house the prop although, maybe it should be an air prop...

Laddering could also be employed of course to get on-foil.

 

Isn't the point about v-foils that you need a lot more surface area for the same lift? The lift vector is not straight up, so you have more area to create drag. Laddering does reduce area, but when you have the next ladder at or near the surface they don't produce lift, just drag.

Somebody explain where I misunderstand.

 

In a nutshell, yes.

The "self-stabilizing" effect of the "W" or "VV" type, rather than the pure "V" is very good. But, the penalty is the added drag.

Hence foils for lift on first appearance seems an interesting and reasonable one. But once you begin to look at the mechanics of the system how it will deliver the lift, when and how to control and the dynamic stability coupled with all the parasitic drag, the results look less promising and more challenging.

If you wish to use hydrofoils for lifting the hull totally out of the water, then you must design the whole boat around this concept, rather than have a slender hull and foils as an appendage. This has been tried many many times, none that I know of work. Including 2 of our own. Kavernear Fjellstrand (spelling?) spent over $20m trying to get their 40m catamaran doing just that in the late 90s...it broke the company!

The only route that does work is a hull designed for such a duty with the foils being a part of the whole philosophy, and not an add-on appendage.

 

Have a look at this website, shows human powered hydrofoils.
http://www.human-powered-hydrofoils.com/

Ian

 

If the website wasn't so unstable and kept crashing be fun to watch those.

You can see they have come up with many different ways of trying to solve the stability problem, none really successfully for a long endurance. Good fun on short runs, like the 15 second burst by one. But he looked totally knackered afterwards, and seemed to spend a lot of effort trying to control his running attitude.

The rowing boat is neat, very fast too. Must be related to Steve Redrgave

The 2.2m span on the small canoe, i'm sure he has manoeuvring problems too!

Great way to keep fit on the water though, especially those pump-foils

 

You're absolutely right. I'm not a fan of v-foils but was addressing your question.

Laddering: what you say is true but, that added surface drag is at lower, transitional velocity. Once overcome it facilitates the higher speed, lower drag main foil. So while it make take more energy to get through transition, it is momentary and allows for a lower sustained effort for a greater return.

 

For the first time in this thread a topic I can add advice instead of receiving only.

The major problem with foils in V-shape is "air-sucking". When they pierce surface, air is sucked in the portion below and the wing sort of stalls (water won't follow profile, as air is between). You can only overcome this by using "boundary fences". You can google pics for that.

If you want to decrease drag, you have to make the lift distribution elliptic and account the pressure decrease from the vertical strut having effect on the upper side of the horizontal wing. The Diamond TwinStar has very interesting engine pods (a shape which is getting thinner proportional to underpressure of the surrounding wing) because of this interference drag and a higher angle in the area of the prop, as downwash decreases with the higher flowspeed in this region.

I was a pilot for this plane type and it has many state of the art technologies in aerodynamics used on it. There is a site with good information about all airfoils and their drag: www.worldofkrauss.com

I also have the opinion, that human power is only enough to sustain flight for short distances. The "Flyak" is the only boat which is optimized enough to reach 30kph and as far as I know, it can be used for sprints only. The problem is (as already posted before) to get fast enough, that this tiny wings can produce enough lift.

There is a company building a hydrofoil using a Torqeedo outboard right now. They need 2000W for one person and 4000W for two persons to lift them at a top speed of 30kph. Cruise speed is only as low as a little bit above 20kph. I am afraid, that hydrofoils are not more efficient than a good glider.

 

Here is an example of a 2 person human powered hydrofoil exceeding 34kph so it can be done with a lot less than 4000W http://www.youtube.com/watch?v=RvE6Xd6tgPA

Scheny: by glider do you mean planing hull? I am unaware of any human powered planing hull that can reach these speeds with one or two crew.

I agree that human powered hydrofoils are only suited to sprint distances. It would be possible to make a wing that would work at less power and lower speeds but the increased drag would make it less efficient than an optimised displacement hull.

 

I found their homepage, but it is in german.

www.waterbla.de
http://www.youtube.com/watch?v=Opf1Jn2b3HI

They write, that the driver can have 75kg and the max. payload 160kg. The consumption is 4000W for 35kph, 3200W for 30kph, 2300W for 25kph, 1500W for 20kph, 3200W for 30kph, 1400W for 16kph. The wattage includes the losses in battery, inverter and motor too. The efficiency of the overall drive (wattage to propulsion) is 56%. So for two athletes with a lighter boat and higher efficiency of the men as a motor I think they came very close to the eqvuivalent wattage during the sprint.

16kph is the minimal flying speed at a wing of 0,19m² and canard of 0,04m². The boat in your link is really optimized, but you can't use that for daily use. The wing alone is so fragile, I wonder it lasted until the end of the race.

 

I've worked through some calculations on foil area, section, planform and velocity and it seems that the major problem is that already identified, that a relatively large foil area is needed initially, in order to get the boat up on foils at the the fairly low speed that a hull-borne pedal craft can achieve, but then the foil area needs to be reduced as speed increases (due to reduced drag and near-constant power), to optimise the system for the limited power available.

What's more, it seems that such a craft will also run into propeller efficiency problems; as the speed increases the required prop pitch increases, the prop diameter ideally needs to reduce and the prop rpm needs to increase, in order to continue to get the most out of the limited power available.

The practical problems associated with a pure foil-borne human powered boat seem difficult to overcome, at least for the sort of boat this thread is primarily about. However, I have been wondering if there may be a sort of hybrid design that might offer some benefits. If a long, narrow, hull is used for a pedal powered craft (as many have found to be the best compromise) and if it is of simple rectangular section (again, as Rick and others have found, this offers simple construction with low enough hull resistance) then anything that lifts the hull will reduce wetted area and hence resistance. It seems possible that the small increase in wetted area from a pair of small foils, together with their added induced drag from lift, might still give a small benefit, particularly if the main hull is extremely narrow and relatively deep. This might be worth a bit of exploration by the committed performance pedallers here.

 

wavebike

Here's an oldie with a much more practical fast and simple hull, though I don't care for the upright position: http://www.youtube.com/watch?v=lfazLTtGvJ0

Trading outriggers for draft with a single hull might be a plus in non ideal racing, perhaps more typical rough water conditions.

Porta

 

Jeremy,

Slats and flaps would be ideal but likely too complex.

What about laddering with each wing lifting clear of the water?

Prop design could all be low velocity oriented as speed is not the goal here, it's staying on foil at resonable energy expenditure (i.e. for extended periods).

Perhaps a single strut and mildly buoyant pod with directable thrust (sound familiar?).

 

There are examples of this type of arrangement, but they are limited. The principal limitation is the structural material and hence its size of the hydrofoil. Using fine long slender hulls, 2 side by side, offers the stability. Since if a monohull the reduction in draft, will reduce the restoring moment and become more unstable.

The catamaran types work if the hulls are close together, for structural reasons. But this is not ideal from a resistance point of view alone, of the separation of the hulls. However, for a more pedantry type of speed and the fact the 2 hulls offers the stability element too, it could well be possible. However, the other factor that has prevented success of this type of arrangement in the past is the Lift/Drag ratio of the whole system. The actual gains have been minimal, on the 2 vessels I have been involved with in an attempt to do just this, reduce draft/resistance. The first just didn't produce any benefit at al, the gain = losses, the other increased speed, but not by the amount predicted/calculated, by some 50-60%.

Careful selection of foils, spacing of hulls and a suitable high L/D ratio hull form could offer a solution. But i suspect somewhat limited and over a narrow range of options.

 

If you want to lift off at a reasonably high speed, allowing you to reduce the size of the foil at the low speed design point, you ought to go for the minimum hull resistance. Even Rick when he worked with Greg??? on the 24 hr world record used a circular hull section. They are easy enough to do that I don't see the attraction of the square hull. IMO.

 

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Thats why a "wand" or "feeler" type altitude control system is used on monohull and multihull sailing foilers: Before takeoff the wand is back causing a flap to be max down giving high lift; as the boat rises the wand(surface sensor) reduces the flap down angle until it is at about zero degrees for minimum drag.

altitude contol system animation:

http://www.youtube.com/watch?v=yuFwDm8t3IM