Pedal Powered Boats

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Could be a great idea. "Foil assist" is being used on many small and large sailboats to great effect. The idea is to use vertical lift to reduce hull wetted surface but not eliminate it like a full flying foiler. To work, the design must be very carefully done but is certainly worth looking into in detail.

 

Hi, Tom:

Yes, probably most on this list are active people that do some kind of exercise, and would adapt quickly to the bicycling skills required for 130 watts. No offense, but this number may be high for females because of lower muscle mass. Also "regular" joes which tend toward being sedentary and obese in the USA would have to train for quite a while before pushing a 'foil.

A young, large, athletic, man like Rhinox is probably capable of more than you would think (post#1380):

http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-92.html

Thanks for your contributions, Tom. No disrespect meant, JMHO.

Porta

 

Porta,

Thanks for your response.

Where I was going with this was: with a few design modifications like a buoyany bulb, single strut design and lighter/smarter building, your challenge could be met.

However, what I'm seeing now from our dialogue is a difference of opinion in "the average joe". With that in mind I think you are very likely correct and that I am most certainly wrong (mark the time and date down on your calendar, I rarely admit that!).

I'm going to continue my design endeavour out of curiousity. I'm 200 pounds and of fair fitness (although that is a highly subjective measuring estimate).

Thanks for your politeness and objectivity.

 

You're forgetting that for a "rubber" hydrofoil at the design stage, the power required will roughly scale with the total weight. Since smaller people tend to have larger power/weight ratios (as evidenced by the typical bike racing climbing specialist), they are better suited for powering a hydrofoil.

Once the hydrofoil is built, the required power scales disproportionately with total weight, roughly as weight^1.5 (assuming deep submergence, with weak Froude number effects). So the power/weight ratio scales as

P / W_pilot ~ (W_pilot + W_boat)^1.5 / W_pilot

which has a minimum at W_pilot = 2 * W_boat
So the "optimum" pilot weighs only twice as much as the boat, which will be a rather small person. And this is on top of the inherent advantage in available power/weight for small people.

We found this to be the case with the 50 lb Decavitator. A fit 110 lb woman could pretty easily get it onto the foil, while fit 180 lb guys had a lot of difficulty.

 

Markdrela,

From my work with accomplished athletes I have found, pound for pound, women are often stonger than men. There is evidence of this in some research of muscle fiber.

What do you mean by a "rubber" hydrofoil?

 

Mark and Tom:

Thanks for the information, appears considerably more energy than I thought is being exerted in just keeping a 'foil up.
Are we looking for endurance at the same power to weight when considering extended 'foil use, and does it track?

Do you think perhaps where P/W is the same, performance becomes sports specific? Olympic competition records are dominated by men in equivalent sports. Interesting to think that women might dominate if there was an olympic 'foil event....

Porta

 

Porta and Mark,

I didn't word that very well. Of course men are "stronger" than women of the same weight, generally speaking.

What I meant was some of their muscle groups can be stronger pound for pound. Often leg and buttocks muscle has been found to display this characteristic.

Some time ago I reviewed research that supported the idea and of course now I have no recollection where, so take it simply as my opinion and we'll leave it at that.

Performance is definitely sport specific.

 

The short answer is that elite male cyclists have significantly greater power/weight than elite women cyclists -- that's just a biological fact. The shorter the event the greater the disparity. I've heard that women may be faster in ultra-ultra-marathons, but AFAIK this is hearsay, and it's not relevant to HP hydrofoils in any case.

 

One whose geometry is still free to vary in the design phase, i.e. before it's actually built.

For example, a rubber fully-submerged hydrofoil wing can decrease in size as the design speed is increased.
An existing fully-submerged hydrofoil wing obviously has a fixed size at any speed.

 

Some info here:
http://www.boatdesign.net/forums/sailboats/new-high-performance-monofoilers-25366.html
posts #62-68

The short answer is that using a hydrofoil only makes sense above ~10-12 mph (4.5-5.5 m/s), depending on the pilot weight. Buoyancy is better for lower speeds.
This assumes near-optimum hulls, wings, props, etc. If you make lousy hulls but good wings and props, then the break-even speed will be lower, and vice-versa.

 

Harry:

Here's something that looks like fun and new I found while surfing. Cross posted from the modern paddlewheels discussion. Not an attractive way to demonstrate IMHO, but I wonder how efficient the mechanism is....

http://www.youtube.com/watch?v=HFS1ZJ2x41s&feature=related

Tin:

I always liked the inflatable microcats from way back. They won some events at the hpb annual competitions many years ago. Too bad someone else didn't pick up the line when the company went belly up....

Porta

 

Best shape for prop fairings?

I've been curious about what the most efficient shape of prop fairings on say, a model plane prop used on a HPB? The pics I've seen from a distance on Rick's, Coach's and McDenny's spinners seem to show they are somewhat different. The props are not identical though...

-Should the prop fairing just cover prop hub or be larger or smaller?
-Should they be more or less elongated compared to standard model prop spinners?
-Is a front fairing more important than a rear?
-Should the shape approximate that of a standard model prop spinner or be more cone shaped?
-Is there a significant gain from using both a front and rear spinner compared to a single and should the shapes for both be about the same?
-Is there a significant gain with fairings despite the increase in water resistance from the increased surface area?
-Does an unfilled cavity between front and rear fairings diminish the benefits significantly?

Thanks,

Porta

 

I've worked on the basis (and may be wrong) that there needs to be a smooth pressure recovery from the prop hub to the free stream aft of the prop, and that this needs to be similar to the spinner shape used on pusher prop aircraft (like this: http://www.berkut13.com/ntxspinner.htm).

I've tried to do this for my props, like this one (please excuse the rough paint job - it's a work in progress!):

 

Jeremy:

Thanks for the info and pic. Really like your propulsion setup. You also answered a question about putting a spinner on a folding prop, which I was pondering.

I haven't been able to measure much difference based on real time watts draw when using an unteathered flex shaft and 10" to 12" diameter RC props. But I was using a pair of styrofoam fishing floats, fore and aft of the prop for spinners.

Porta

 

Hello Porta!

The cross section should be minimized, but size depends on the biggest cross section needed to fit all mechanical components within.

A standard spinner is optimized for use in air, but the only rule is, that the water must be capable of following the curve. For instance, a blunt nosecone from a plane is not suitable for the rear of a prop used in water. Here you would require something elongated instead. The water would create a lot of drag in the blunt section

If you compare that to a car (5-doors model), the cross section is reducing to the backside, ending with a sharp edge, where the flow can separate without too much drag, resulting in a CW of 0.3 compared to the maximum cross section.

Speed also plays a big role. For low speeds, the shape of a water drop is best. for higher speeds, the optimal form is the "Sears–Haack" body. This form is elongated at both sides and used for supersonic aircraft.

Both are important, but I think that the rear one is more important because water will divide by itself because of pressure builtup. Also look at cars here. The front side has less account for CW than the rear side.

The form of the whole drive should have the form of the natural flow of the water. If you have the prop at the front, a blunt nose will perform better and in the rear, a cone shape more likely.

See above.

A faired drive has a CW of about 0.05, which means the drag is reducing by 95% compared to using a square tube of the same thickness. The biplanes where using thin wires for stiffening the wings. They soon went out of service, as a thick but aerodynamic wing had a lot less resistance than some of this only millimeters thick wires. The form drag plays a bigger part here than surface drag.

Any cavity is producing drag, unless you fill it with air. My racing boat (4.7m sail boat) had a sword with initially trapezoidal shape, as I wanted to sail and not to sand it in shape of a water drop. The speed was instantly reduced to 4 knots and a lot of vibrations came from it. After sanding it into form, the speed can go up to 20 knots now.

This is a very good example for how much a good fairing can do.

Hope I could help you a little bit,
Andreas