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Pedal morphology

Here is a link to a breakdown of some of our family race boat ideas we gave points for creativity: http://www.designwizardry.com/pedalboatrace/index2004.shtml

I thought "Randy's" was coolest but "Long Johns" was always fastest.

 

Looks like fun was had by all!

I reckon the coolest has to be the squirrel cage thing in you post.

Nick

 

Mike Carambat used a flexible shaft from a weedwacker in one of his boats. He said it was quite good at low power but it would wind up at higher power.

This is pertinent to a recent question. Is he still around? I would be interested to know how he describes the sensation pedaling with a shaft like this.

Rick W

 

Yes, if this could be geared up somehow, and the wheel made lightweight and streamlined, might be fast. It depends on water friction for propulsion and goes faster the higher the water friction is. So it uses water drag to go faster instead of fighting it as most streamlined boats attempt to do. But it is fighting displacement with a very short hull "length" which would slow it down. The "hydrocopter" uses a similar principle but is very fast because it rides above the water without displacement being an issue.

Porta

 

Here's something interesting along the lines:

http://www.youtube.com/watch?v=Psyl-AQ0m2A

Porta

 

Vic
It gets back to the Bob Stuart's tracks because the buoyant part needs to be long and slender to reduce wave drag.

One of the interesting things that I never really thought about until Leo Lazauskas provided a paper on it is that hovercraft suffer from wave drag. The efficiency of the craft can be improved by altering the shape of the pressure field for different speeds. Point is; wave drag is an issue even when the craft is not in direct contact with the water.

On the big wheel boat the viscous drag provides the propulsion but the wave drag is a killer. Worse than trying to ride a bike through sand. However turn it into a long slender tube in the form of a continuous track and you would have something much more efficient. It needs to be built.

Rick W

 

Your comment reminded me of this patent that I stumbled on last week. It's a patent for a ship that uses a buoyant track system for propulsion. Practical? I doubt it. Cool? Absolutely!

 

This is one method that could have a dramatic reduction in energy required to move across water.

The minimum drag hull for human power uses about 90% of the power to overcome skin friction. There is only 10% going into making waves. If skin friction could be reduced there would be a huge gain in speed.

If a system could be engineered for bulk carriers it would save vast quantities of fuel.

Rick W

 

Start blowing bubbles under the hull it will dramaticaly reduce friction drag and has already been done on ferries

 

Seriously? I was under the impression that water transportation uses far less fuel per ton than land transportation. What this invention does is essentially turn water transportation into something like land transportation.

I recall seeing pictures of a single ox pulling a barge along a canal. The barge looked large enough to carry the equivalent of what ten two-ox carts would carry.

 

It still is much more efficient than anything else because of the size of loads it can carry otherwise i might bet on the train.

 

Yes land transport is more expensive per tonne. Most of the cost is moving through the air and inability to recover energy downhill.

I have not thought about the break even size with a boat where the rolling friction would cost more than the viscous friction. It might be quite small vessel. Trains go to a lot of effort to reduce rolling drag and windage is lower than road transport. It would be an interesting analysis.

One of the problems with the buoyant belt idea is the air drag on the return strand but it would be much less than the water drag at the current speeds of interest.

Rick W

 

Twist

I'll get Brother Mike's opinion or better get him to join this forum. The big wheel was tried out by me and was very unstable, you sat suspended in the center and it resisted your efforts to "roll" till you were about upside down or going very slowly! I think we discussed making it with outriggers and cutting down the "blade area". Very technical stuff and at our last bonfire we may have decided on competitive gliders Ala-Flugaltoss? Being shot from a bungee launcher, going for distance (man size of course and into lake Pontchartrain). Rules and cost limits still need to be worked out.

 

I had actually wondered about this sort of thing although I had not gone that far. I was thinking more of having a paddle wheel that got rid of the angls and splash problems by being a track. Why not practical? It would have huge efficiency benefits. The "hulls" walk back down the water flow! It gets rid of the inherent problems with paddle wheels as well.

Surely with modern materials this could be done.

 

Surface Piercing?

The only mention I found in this thread about SPP was that weed could be cleared by half-lifting the prop, yet SPP seems to have a lot going for it (might clear weeds for a start!) . Is there any reason why this is not being used?