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Weird boat with weird propulsion system(in a good way)


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Has to do with RPM/torque and efficiency. A regular outboard prop for example isn’t the greatest setup in terms of efficiency because there is a big compromise putting the exhaust through the hub.  

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That's a model airplane prop, which are dead cheap and available in just about and diameter and pitch you could imagine. They are also close to perfect for human powered boats, but would be better with more twist as the RPM's are far slower than an airplane.

That video makes it look fun to pedal a boat. Not so fun in reality.

Here's more on systems used in the R2AK: https://gougeon32.blogspot.com/2018/08/pedal-drives-on-2018-r2ak-boats.html

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11 minutes ago, Russell Brown said:

That's a model airplane prop, which are dead cheap and available in just about and diameter and pitch you could imagine. They are also close to perfect for human powered boats, but would be better with more twist as the RPM's are far slower than an airplane.

That video makes it look fun to pedal a boat. Not so fun in reality.

Here's more on systems used in the R2AK: https://gougeon32.blogspot.com/2018/08/pedal-drives-on-2018-r2ak-boats.html

We used the same on an electric crew coach launch prototype a bunch of years back.  Worked well. 

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Except Russell's knees look too bent and his leg never really straightens out.

It's like sitting on a bike with a too low seat. You find it very tiring very quickly. That's why your knees suffered I'm guessing. 

Or you're just old!

 

 

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1 hour ago, Zonker said:

Except Russell's knees look too bent and his leg never really straightens out.

It's like sitting on a bike with a too low seat. You find it very tiring very quickly. That's why your knees suffered I'm guessing. 

Or you're just old!

 

 

Had to put my wife on a trike after several vodka related crashes on her 2 wheel bikes. On the trike you can adjust the boom length and seat position to fit the individual riding it. You want to not quite have your legs fully extended at the bottom of the stroke. Too far away or too close will wreck your knees. 

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8 hours ago, eliboat said:

Has to do with RPM/torque and efficiency. A regular outboard prop for example isn’t the greatest setup in terms of efficiency because there is a big compromise putting the exhaust through the hub.  

Russel hinted at it pretty well, but think glider versus SR71 wing profiles. The same concept applies to props. Those big high aspect blades he uses are great for peddling speeds, but would be utterly worthless at the speeds an outboard would spin them. Same goes the other way. 
 

P.s.  the exhaust through the hub is pretty harmless. The sacrifice in hub size is 99% to hold gears that won’t tear themselves apart. 

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7 hours ago, Zonker said:

Except Russell's knees look too bent and his leg never really straightens out.

It's like sitting on a bike with a too low seat. You find it very tiring very quickly. That's why your knees suffered I'm guessing. 

Or you're just old!

 

 

Just old enough to get my Covid shot, thank you very much, and old enough to not recover from shit like pedaling a 2000 pound boat long distances. Actually, I think I did have the geometry right, and could adjust it with cushions, but my cadence was too slow. That's what screwed my knees. I had the right prop onboard, but kept the "motor sailing" prop on because it seemed okay. It wasn't. I got Trench Foot too. Wasn't walking so good for a while.

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Actually pedal to prop propulsion has been done a fair bit in races like the British and Tasmanian 3 Peaks race!

As they usually had 3 sailors and 2 runners, most boats stuck what was basically 2 x tandem bikes (up to 4 cyclists at a time) on the stern.  The drive was a long shaft on a uni joint so it could be raised/lowered.  Also ran through a gear system,  

Some boats did experiment with a straight through drive and pedals running along the cockpit floor with ply sitting between the seats for normal sailing.

Most of these were 35ft+ older race yachts and most could pedal at up to 5 knots!!

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