Pedal Power or Oar Power - which is more efficient?

you can use legs when rowing with a sliding seat, and sprint kayakers use their legs also to a lesser degree. But legs are not always needed for efficiency, or power. At lower levels of output for long sustained travel, cardiovascular fitness is more critical than strength and power and use of the larger muscle groups. Also, if you are a rower or paddler or wheelchair athlete you may develop large enough muscles in the upper body to efficiently burn whatever oxygen the heart and lungs are able to provide.

As for the curve of the blade, or Greenland paddle versus more vertical paddle, or propeller, again the key thing is to engineer and execute things in such a way that you are pushing the boat across the water more than you are pushing the water past the boat. The other consideration is to minimize transmission losses, whether it is through gear losses, chains, levers, sliding seats, or electrical systems. For human powered boats, depending on the weight and length of the boat, and whether you are sprinting or travelling all day, vertical paddling or rowing, more horizontal paddling or rowing, of a propeller, or perhaps even a paddle wheel in flat water, can all be very efficient or very inefficient depending on how the system is engineered, and the fitness and technique of the person doing the work.

 

Here is another consideration for pedal power:

Cyclists (and motorcyclists, in particular) have long known that chain drive is much more efficient than shafts drive. Yet, many pedal-boat builders strive to use shaft drive because it looks more elegant and offers conveniences for making perpendicular changes in the driveline.

I suggest that for maximum pedaling efficiency, one would sit perpendicular to the long axis of the hull while pedaling a crank with a chain connected directly to the propeller shaft. The chain setup also allows for easier gearing changes as one develops their muscles/cadence/endurance. On the downside, the pedaled must learn to be comfortable facing the gunwale, rather than facing in the direction they are traveling. Large mirrors may help.

 

That is a great idea particularly for boats that might also be sailed, as they tend to be beamier and that seating style is more natural when sailing. You could sit to windward or leeward, but you might have to pedal in reverse from one side of the boat, or have some reversing mechanism. I am not sure you would need to gear up or down very much. A pedalling cadence of 30 to 120 rpm might already match closely with what you want for a propeller. If so, you might not even need a chain but you could pedal directly on the propeller shaft. I think this would be a great idea for a small hybrid daysailer or micro-cruiser.

 

We are talking about important structural, mechanical and handling modifications and complications for an almost negligible difference in terms of speed.

The additional power to the prop due to 3-5% more efficient mechanical transmission can typically give approximately 1% speed increase. At competitive levels it makes difference, because it translates to some 0.1 kt higher max speed. But a recreational boater will hardly ever notice that his cruising speed has increased by some 0.05 kts.

By the way, some interesting info about the mechanical efficiency of commercial bicycle transmissions can be found here: http://www.rohloff.de/en/technology/speedhub/efficiency_measurement/

 

Here's a start.

Man rides bike boat across San Francisco Bay



https://www.youtube.com/watch?v=OqKx7K34D7g#t=12

 

Nope. Consider a motorbike - power travels down a crankshaft, tranny input shaft, idler shaft, output shaft, along a bit of chain, then through the wheel hub which is a shaft. Why all these shafts?

Chain is cheaper, more adaptable, amenable to quick field repairs, benefits from parts standardization, is perhaps a bit lighter, has perhaps a bit more inertia, is self cooling, has versatile damping characteristics, makes a good mechanical fuse, and is well suited to that particular job in terms of geometry and dealing with the torque characteristics of one or two cylinder, lightweight, poorly balanced motors; but it is not necessarily more efficient. But if you replace it with a shaft; then somewhere, you have to add back in all those things listed above that are important. And that can lower the overall efficiency of the system.

There hasn't been a commercially successful chain-driven car or truck for a while now. (1940 Sterling??)

There is a relationship between the amount of power and the distance you are transmitting it that can favor one or the other, but what you said just isn't true as a general rule. Not if you have the freedom to locate the motor more or less as you please. Not if you have some say in the gearing of the transmission - ie the motorbike has a tranny, then a chain, then a final gearing (chain speed/tire speed). The practical limits to the freedom in choosing these ratios has a big impact on overall drive efficiency - its not just about the chain. Design an efficient chain to connect a source and a load. Then look at the gearing you need at both ends of the chain to get it to work. Sometimes it's reasonable, sometimes it's not.

 

Nice boat in the background.

 

The work efficiency of the cycling motion is higher. However you need to efficiently transfer that work into thrust.

"The net work efficiency when rowing was 19% for both groups, experienced and inexperienced: when cycling it was 25% for cyclists and 23% for oarsmen."

Oxygen consumption and metabolic strain in rowing ergometer exercise

http://link.springer.com/article/10.1007/BF02343794

 

I like the Autocanoe concept myself.

Though this looks fun: http://rivertownrevival.com/wp-content/uploads/2013/05/unnamed-amphibious.jpg

With wheels that big the floats should be articulated somehow....

 

And here are some rowing records: http://www.concept2.co.uk/indoor-rowers/racing/records/ultra-distance/world/24-hours

So only one pedalling boat record in over 200 km (245). Several Kayak records are over 200 km, but the best is slightly worse (242).

Rowing record is much better (314 km) and also female, under 19 years male and over 60 years male records are more than 245 km.

Seems like rowing is the clear winner for overall performance, but maybe there haven't been equally good athletes trying the pedalling record.

 

Joakim, that 314km figure is for indoor rowing on a machine.

I cannot find a figure for 24 hour distance record on water for an individual; there's a figure of 342 km for a team of 8....

 

Thanks for the posting.
There are very few racing pedal boats and racers in the entire world, compared to the extremely huge numbers of rower racing boats and rowing racer talent- not a level playing field of comparison. Only one? fairly real solo attempt at 24 hours with a non dedicated, cross trained athlete and purposely built racing boat that I could find. My link did not include rowing records (per your posting) and seemed to imply that pedaling is generally faster, which may not necessarily be true, even for first time riders.

Cheers,

PC

 

Interesting...that would surprise a lot of motorcycle racers, as well as technical editors of motorcycle publications.

Autos don't have chain drive because it likely loses too much efficiency in the bulk size that would be needed to handle the power output of the engine, and (more likely in this day and age) chains require more maintenance than shaft drive, which is a huge "no-no" when you are trying to market and sell vehicles. Same reason more motorcycles have shaft drive now - most people just do not want to deal with chain maintenance. Same reason auto transmissions are so much more prevalent over manual transmissions. Convenience is the trump card nowadays.

 

Like I said, chain, as a component of a motorcycle drive line, can add a lot of tunable features that are hard to tune in a shaft. They form part of an optimized system. They have properties that are well suited to that purpose. But by themselves, they offer no particular advantage in power transmission efficiency. If that was the only thing it offered, it would be a wash.

One of the things that being exploited is some very low loss gearing that happens to fit the need nicely. If you were forced to use a 1:1 sprocket ratio and deliver the same rpm at the load as you had at the source, the way a shaft does, there would not really be any difference in system efficiency worth mentioning. The chain reduction reduces the losses in the tranny gearing more than it increases the losses in itself. My point is that it is the system as a whole, not the chain by itself, that needs to be considered. So a motor cycle needs to get from 10,000 rpm shaft to a 125 mph pavement speed. And a reduction chain happens to fit in the envelope. On a criterium bicycle, you need get from 93 rpm to a 50 mph road speed, and a chain overdrive fits the envelope (coupled with stupidly big 700mm rims with massive aero drag). If you had a better match between engine rpm and over the road speed (think car at 1700 rpm @ 60mph, or Lycoming O-320 driving an airplane propeller (O-320 is 5+liters and 150hp) you don't see chains much. In fact, you hardly ever see them in a 1:1 configuration which is where they are actually at their most efficient.

 

Very good points. Shafts are also very efficient at 1:1 , and you could sit sideways like you were sailing. ;-)