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This post was ignored too porta.

There seems little to no interest in our difference of opinion.

So be it.

 

Sorry Tom, I'm always playing "catch up" on here because I'm round the other side of the planet (around 7 hours from you, for example). It means I do occasionally miss posts when there's been a flurry of what is, to me, overnight activity, especially if, as happened yesterday, I'm only on line for an hour or so..

My concern with the submerged pod idea is the added wetted area when you're trying to accelerate the boat to foil-borne speed. You'd have the foil, pod and part of the hull all producing viscous drag right at the point on the prop efficiency curve where there's not too much thrust available (assuming the prop is sized/geared/pitched for best efficiency at cruise speed.

Maybe it could be made to work, but I think the only way to find out might be to do some large scale (or maybe full scale) model testing, as I think trying to simulate resistance is going to be tough, because of the relatively complex interactions between the hull, submerged pod and foils as the depth of immersion changes.

Laddering makes some sense, and looking at the way Decavititor performed I think it might work, although they adopted a retracting large area foil, it seems, in order to overcome the mismatch in foil area with speed problem.

I'm sure T foils would be the most efficient, and suspect that the approach that Doug Lord pointed out (as used on the Flyak) of having them autostabilise as a consequence of their interaction with the near-surface might be a reasonable compromise, although such a scheme might increase drag from surface wavemaking (I'm reasonably sure the Flyak foils are close enough to the surface for this to be a potential problem).

Overall I'm inclined to agree with Dennis and suggest that the hydrofoil debate has pretty much run its course, plus the sun's shining here this morning, so as soon as it warms up a bit I'm off to lay up the internal epoxy/glass on the new boat............

 

It's now 3:30 am my time and I'm still up! ...... and been thinking about this tandem pedal system on a proa and got an idea! All this gazing at these weird bi/tri/quad-cycle contraptions seems to have sparked some ideas. that pic of the back to back tandem bike was inspiration and I could do it that way or face each other (for hundreds of miles?) which would shorten my "common drive chain". With the take-apart travel bike mods I've seen I can adapt that kind of thinking to convert my prop power platform on the boat to a road worthy tandem bike to tow the boat. The details aren't there yet but I got a direction! (and on a shunting proa which way is forward again?) Anyway, I got both sets of pedals driving the same drive shaft and the shaft will rotate to either side depending on which direction I want the thrust. Who mentioned that quick release drive shaft option? Yeah, cool! Now I got to come up with one? Hummm......

 

Pedal powered boat

I once saw a pedal powered cat, it was small 1 man vessel and propulsion was pedal power to a plane propellor, was quite ingenious,and funny to watch.

 

Yes, some good ideas, Tom.

But now it comes time for a working model to prove that it works at 70 watts, exceeding the speed of an equivalent displacement boat. It's just too close to call without a working model, but even if it does succeed,there has to be a significant difference compared to displacement type. Wouldn't the liabilities of a foil limit the use to very ideal conditions, or racing situations? These and some other comments were also not addressed, as the focus became multi horsepower vehicles that have succeeded....

Porta

 

Yes, I use quick release and surface piercing options on my flex shafts. You can study a quick release hex mechanism used with cordless drills to get the idea, just push-pull, no tools needed...

Porta

 

thanks porta! and thanks to everyone else too! All the answers are already out there, I just got to pick and choose the ones that will work for my applications. Nothing that I'm doing is all together different, just put together in a way that hadn't yet been done before (to my knowledge anyway). it was closing on 6 am when I actually tried to go to sleep ...... I got a shelf with my models on it in perfect view of my bed .......

 

Jeremy and Porta,

Thanks for your posts.

My thought was to design the max prop efficiency for "lift off" velocity as once achieved, cadence can be eased and efficiency is not so critical to maintain foil flight.

I believe the added buoyancy would outweigh the increased wetted area penalty of the pod. Length to beam should be 5.5 or 6.0 to 1 and three diameters depth must be maintained to eliminate surface wave drag.

The added energy is available for transition and would be very short term.

I would argue closer to 100 watts sustained is available at the prop for the average person assuming 80% overall mechanical efficiency.

I think air resistance could be reduced with a cowling and improved performance would come from an air prop.

The sun is shining here too so that combined with a lack of interest in this particular thread direction, I'm off.

 

By way of contrast, the sun is now too low in the sky to give any meaningful warmth here, and I'm keeping my fingers and toes crossed that the epoxy I laid up today goes off..........................

 

This graph here illustrates it perfectly.



L/D ratios from 8 onwards are very good..from L/D ratios of 10 onwards are excellent.

Wave-making resistance is also proportional to beam. L/B ratios from 10+ are ok, from 15 are very good. L/B ratios from 20 and above are excellent. The trend follows very much that of the L/D ratios.

 

It is becasue you already have a separate thread devoted to it here: http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/hyswas-anyone-42222.html

 

No. Beam squared.

 

There is always one who picks up the missing little bit in the upper right hand corner of the term....geeessss!!

 

Just to rub it in...
At high Froude numbers wavemaking resistance is proportional to the waterplane area.

 

That is an electric hydrofoil model (90 cm) with huge contests limitations.

This is something completely different.

But thanks for at least responding.