Paddle vs. Pedal?

[KalleA]

Reading about Greg Kolodziejzyk's 24 hour world record got me thinking. Greg K covered some 245 km in a pedal/prop boat vs. Carter Johnson's previous record of 242 km in a surfski kayak, i.e. virtually identical performance. I would have expected the pedal/prop boat to be more decidedly faster and I wonder what the differences between the two concepts really are, adjusted for weather and engine differences?

I hope someone with real know how will pitch in, and this is just an attempt to outline some issues for comparison (most quantifications I have gathered from this amazing forum, so apologies if I've gotten them wrong and credit to Rick W if they're right):

1. Biomechanical efficiency
I gather paddling and pedaling are pretty similar at around 26 %?

2. Mechanical losses
0 % for paddelling and 3 to 4 % for pedals.

3. Propulsion efficiency
72 % assuming an excellent paddler (?) and 87 - 88 % for the prop.

4. Concept specific drag
I guess the propshaft produces some drag? Does the side mounted prop result in any turning motion that needs to be trimmed/counter steered?

5. Aerodynamic drag
The more upright paddling position as well as the paddle moving through the air should be a relative disadvantage for the kayak, but perhaps miniscule at the speeds and weather conditions in question?

6. Hull shape. My initial thoughts were that the pedal concept should allow for a longer, sleeker, more efficient hull than the surfski, but perhaps this is cancelled out by the outriggers?

Not sure what I might have missed and/or gotten wrong, but it would seem to me that the pedal/prop concept should be more superior to the kayak than the 3 km difference indicates, and that differences in engine capacity and specific weather conditions would explain that?

Cheers

[Guest625101138]

Reading about Greg Kolodziejzyk's 24 hour world record got me thinking. Greg K covered some 245 km in a pedal/prop boat vs. Carter Johnson's previous record of 242 km in a surfski kayak, i.e. virtually identical performance. I would have expected the pedal/prop boat to be more decidedly faster and I wonder what the differences between the two concepts really are, adjusted for weather and engine differences?

I hope someone with real know how will pitch in, and this is just an attempt to outline some issues for comparison (most quantifications I have gathered from this amazing forum, so apologies if I've gotten them wrong and credit to Rick W if they're right):

1. Biomechanical efficiency
I gather paddling and pedaling are pretty similar at around 26 %? That is what the data tells us. Rowing is about 22% as a matter of interest but better for anaerobic state as more muscles involved.

2. Mechanical losses
0 % for paddelling and 3 to 4 % for pedals. 4% is good. Do not know if it is possible to get below this.

3. Propulsion efficiency
72 % assuming an excellent paddler (?) and 87 - 88 % for the prop. Both figures are at the top end. Greg's prop was around 86%.

4. Concept specific drag
I guess the propshaft produces some drag? Does the side mounted prop result in any turning motion that needs to be trimmed/counter steered? You can trim out the prop torque and offset thrust from the side-mounted prop. In fact the prop rotation torque is set up to counter the offset weight of the gearbox. Just happens to ballance out at 12kph - the design speed. At lower speed you can trim by moving body slightly or presetting the outriggers for very slight initial roll. You know when this is right and is part of the tuning exercise.

5. Aerodynamic drag
The more upright paddling position as well as the paddle moving through the air should be a relative disadvantage for the kayak, but perhaps miniscule at the speeds and weather conditions in question? A kayak has less body windage but Carter's the surf ski would be similar to Greg. In stronger wind the paddle is at a distinct disadvantage. As you note this is from forcing the upper blade at roughly twice hull speed through the air. Greg trialed fairing but it made no benefit in low wind conditions. The fairing was not ideal shape though. These records will not be bettered in windy conditions.

6. Hull shape. My initial thoughts were that the pedal concept should allow for a longer, sleeker, more efficient hull than the surfski, but perhaps this is cancelled out by the outriggers? The hull Greg used was optimised for 12kph with his body weight. Absolutely no compromise. The surf-skis require some inherent stability as there is no outriggers for stability hence they have higher hull drag. The outriggers need to be carefully trimmed so they just kiss the surface. They contribute little to drag unless the pilot loses concentration and allows one to load heavily. I expect paddling efficiently on a surf ski would be more demanding than keeping the boat in trim when pedaling. Things like a side breeze can be annoying because you need to shift weight quite a lot to counter.

Not sure what I might have missed and/or gotten wrong, but it would seem to me that the pedal/prop concept should be more superior to the kayak than the 3 km difference indicates, and that differences in engine capacity and specific weather conditions would explain that?

Cheers

One factor that is somewhat elusive is water temperature. Whitefish Lake gets frozen I believe and I expect was cooler than California. Choosing early autumn for Greg's run was considered to give the best water temperature for the location but warmer water would be better.

Another subtly is the shaft. Greg used a 1/4" (6.34mm) shaft. The ideal is more like 8mm. What this means is that Greg had to train muscles and concentrate to cycle. The thicker shaft provides significantly higher torsional rigidity (4th power of dia) and takes less concentration to keep smooth prop operation.

Greg feels age does not make much difference in these events but I understand Greg has quite a number of years on Carter.

Greg had an outrigger loose in the morning light but does not know how long it had been flopping about. He suspects it was for a number of hours and you can see how he fell off through the night. Always hard to know without more engine data during the run to pinpoint any specific boat problem.

I am highly biased here but I feel an average of 11kph would be achievable with a younger trained pilot. I guess time will tell. On the other hand I believe Carter feels he could do better than Greg has already achieved. For now Greg is the benchmark. Greg's average output for the run was about 110W. If you look at what world class cyclists can sustain over 24 hour runs then it is more like 200W. Put this into a boat designed for that power and the result would be over 13kph - 312km in 24 hours. Then you have to ask how close is Carter to a world class athlete.

I cannot see how a paddled craft could do better than a pedalled boat. The only advantage of a paddled boat is that it can be built lighter because there is no drive to worry about. The best possible pedal boat would carry a 3 to 4kg disadvantage in this regard. However it means any recumbent cyclist can get on the boat and immediately feel at home. It takes many years of training to achieve the paddling efficiency of a good kayaker. Every stroke has to be done with precision. This is much more difficult task than just rolling the legs over.

Rick W

[jehardiman]

Rick points out most of the tradeoffs between pedal-prop and paddling, and like him, I believe that in a long distance event, the prop has an advantage. He also points out, correctly I believe, that long term power is limited by muscle mass oxigenation. i.e. the legs are stronger, but they use more oxygen and waste more energy just because of thier mass so in the end it is a near wash. In HP submarines, it was easy to go anaerobic with either arms or legs only.

The only place where paddled-oared may have it over pedal-prop is in short sprints. This is beacuse the effective thrust is immediate and ameaniable to "over speeding". FWIW. props are not the end-all for propulsion, there are situations where paddle-wheel, air props, and cyclic rowers have thier usefulness.

[sigurd]

Hi, jehardiman,

can you elaborate on the advantages and disadvantages of paddlewheels and air props please? And, what is cyclic rowing?

[Guest625101138]

....

The only place where paddled-oared may have it over pedal-prop is in short sprints. This is beacuse the effective thrust is immediate and ameaniable to "over speeding". FWIW. props are not the end-all for propulsion, there are situations where paddle-wheel, air props, and cyclic rowers have thier usefulness.

John
I am reasonably confident that the prop will accelerate faster. I can easily outaccelerate a kayaker. Rowing might be a bit harder but still think the prop would be better. So a 100m drag race would see a prop in front.

The olympic 2000m events would make an interesting comparison for rowing and pedal. Greg could hold 15kph over 1000m and I know a young rider who can hold 16kph over 1000m on my boat. This is getting into rowing scull territory.

The numbers show a boat optimised for an olympic sprint cyclist over 2000m would outperform an olympic rowing scull. It would be an interesting comparison.

The fastest human powered boat was pedal powered and prop driven. It achieved close to twice the speed of a rowing scull but only for 100m.

Rick W

[KalleA]

1. Biomechanical efficiency
I gather paddling and pedaling are pretty similar at around 26 %? That is what the data tells us. Rowing is about 22% as a matter of interest but better for anaerobic state as more muscles involved.

What produces the 4% disadvantage of rowing? Does it relate to the return stroke and returning the body to the forward position (assuming a sliding seat configuration)? Does this take into account the oscillation (boat bobbing longitudally as a result of the moving centre of gravity) induced work, i.e. that the sliding back and forth involves some horisontal movement as well? If so, is there any data on differences in biomechanical efficiency between sliding seat and sliding rigger configurations?

I remember from somewhere that the propulsion efficiency of rowing is around 64-65 % on flat water, deterioring significantly when it gets choppy. Can one assume that the prop has a slight advantage over the paddle in rougher seas?

On the topic of biomechanical efficiency: what is the efficiency of a swing arm system with a top mounted pivot? In your Pedal Povered Boat thread (Post #80) you mention that the efficiency is higher than for a crank - do you have a number/estimate of by how much?

What sort of mechanical losses can one expect in the roller clutches?

In addition to the nice motion, I can imagine other potential advantages of the swing arm solution:

- Feet/legs are lower down = lower COG.

- The lower foot position might generally be good for the body hydraulics (?) and or allow for a more reclined position whilst still having the pump above the feet = further lowering of COG and possibly better aerodynamics

- As the configuration is narrower at the top, a more aerodynamic fairing might be possible (?)

One factor that is somewhat elusive is water temperature. Whitefish Lake gets frozen I believe and I expect was cooler than California. Choosing early autumn for Greg's run was considered to give the best water temperature for the location but warmer water would be better.

Then again, the higher oxygen content of the cooler air should be good for the engine...

All in all, it seems that you have come a very long way in optimising the pedal/prop concept. Where do you see potential for further improvement?

Cheers

[jehardiman]

John
I am reasonably confident that the prop will accelerate faster. I can easily outaccelerate a kayaker. Rowing might be a bit harder but still think the prop would be better. So a 100m drag race would see a prop in front.



Unless you are talk about a large wheel, the paddler has it all over a wheel. When we looked at setting the submreged speed record through a trap, we did some measurments and investigations because we had so much mass to accelerate. A 0.8M dia CR prop set turned by a professional cyclist generated 200 lbs thust at bollard, but it quickly droped off as speed was gained. A paddler with a optimized (~0.6 m^2 CF) paddle generated approximately 300 lbs, but maintaind that thrust until thier arms could not move fast enough.

That is the real issue. Basically, the thrust of a paddle or oar is maintained until the biomechanics of the lever cannot keep up, because the thrust of the blade is effectively equal to the drag of the hull. For a wheel, thrust is only proportional to J, which for human propulsion can use gearing to optimize delivered power.

[jehardiman]

Hi, jehardiman,

can you elaborate on the advantages and disadvantages of paddlewheels and air props please? And, what is cyclic rowing?

To be very efficient, HPV marine props must be large and thin. This leads to several major problems, draft, tip speed, and bending moment being the most common. As I have said, we used a 0.8m CR set , and other fast subs used wheels at least 0.5m or better. A 1m wide, 1.5m paddle wheel could replace these props with only a draft of ~0.1m, and an 2-3m air prop (which has the same problems as a marine prop BTW, see MIT's Decavitator HPV) could have even less draft. All propulsion systems have advantages and disadvantages, you need to get the best one that suits your needs.

A cyclic rowing machine is like FrontRower and some other more obscure designs that use a fixed seat and leg/arm power to operate a rowing, sculling (oscillating foil like the Hobie Mirage system or Scripps SubDUDE HPV), or paddleing system.

[sigurd]

Thanks. Curious why Decavitator uses air prop and Rick W. and most others use water props.
The SubDude device sounds interesting. Got pics?

[KalleA]

A cyclic rowing machine is like FrontRower and some other more obscure designs that use a fixed seat and leg/arm power to operate a rowing, sculling (oscillating foil like the Hobie Mirage system or Scripps SubDUDE HPV), or paddleing system.

Looked up the FrontRower. What an interesting solution:

http://www.frontrower.com/aboutfrontrower.htm
http://www.patentstorm.us/patents/5685750/fulltext.html

http://img242.imageshack.us/img242/3268/bestfrontrowerpic2b.jpg (http://www.imagehosting.com/)

http://img242.imageshack.us/img242/8914/shakeclipimage0010013.jpg (http://www.imagehosting.com/)

Does anyone here have any hands-on experience with, or qualified thoughts about, the FrontRower?

Surely, a pedal/prop will be more efficient, but the FrontRower raises some thoughts:

1. Biomechanics
It could be more efficient than a sliding seat rowing setup since the body, like on a sliding rigger, does not move back and forth. Leg power is transmitted directly (not through back/arms/hands) via a nice top pivoted swing arm action. For anaerobic sprints, one can still use the combined power of both arms and legs. So, without knowing the specific ins-and-outs of the FrontRower, it might have some advantages over traditional rowing?

It just strikes me that there might be a biomechanical component related to the forward vs. backward facing rowing position: constantly twisting your neck! I HATE this about my single sculler - you're constantly turning your head and still not 100 % sure where you're heading and when you'll decapitate some poor swimmer or ram into something... One of many reasons for looking into pedalboats.

2. Mechanics
There are a few cables, pulleys and return springs involved, so I'm guessing some mechanical losses, 1 - 2 %?
It seems as if most forces acting on the chassis would be straight tension and compression, but still, given the dynamic loads, the wooden structure might be less than ideal?

3. Propulsion
In flat water, probably similar to the 64 per cent of traditional rowing, but I can imagine that it suffers even more in rough seas, given the automatic lifting and feathering of the oars? It took me a while to undestand how this works btw, but it's really pretty nifty and clever.

4. Other
The FrontRower seems to have similar ease-of-use qualities as the pedal/prop - not too much technique, just pedal away.

I like the way you can drop the whole FrontRower assembly into an existing hull (like a narrow rowing boat or a canoe) with apparent ease of installation. Does something similar exist as a concept or a commercial product in the pedal/prop world? i.e. an adjustable seat/frame/pedal/prop assembly that one could bolt onto, say, a canoe? I guess an added complication compared to the FrontRower is that one would need some steering arrangement as well.


Anyway, thanx for the heads-up, certainly interesting and different.

Cheers

[Guest625101138]

What produces the 4% disadvantage of rowing? Does it relate to the return stroke and returning the body to the forward position (assuming a sliding seat configuration)? Does this take into account the oscillation (boat bobbing longitudally as a result of the moving centre of gravity) induced work, i.e. that the sliding back and forth involves some horisontal movement as well? If so, is there any data on differences in biomechanical efficiency between sliding seat and sliding rigger configurations? These comparisons were done on static machines. The rowing was with sliding seat. The speed fluctuation of theboat is another penalty for the scull. The sliding rigger was banned because it was viewed as giving an unfair advantage. The fastest bicycle has registered 140kph on the flat. It is recumbent of course but you do not get these in olympic competition.

I remember from somewhere that the propulsion efficiency of rowing is around 64-65 % on flat water, deterioring significantly when it gets choppy. Can one assume that the prop has a slight advantage over the paddle in rougher seas? Mike Lampi in his 20ft cadance can do reasonably well against kayaks and OC1s but rowing sculls normally outperform him until the seas picks up. He has a video of him catching a rowing scull in quite heavy weather. Sculls do not like rough water. The day Greg got his test ocean boat 20 miles offshore a rower in an ocean rowing boat could not make way. Pedal is much better for power application in wet weather. Basically the same reason props replaced paddle wheels on ocean ships.

On the topic of biomechanical efficiency: what is the efficiency of a swing arm system with a top mounted pivot? In your Pedal Povered Boat thread (Post #80) you mention that the efficiency is higher than for a crank - do you have a number/estimate of by how much? Just turning the cranks over costs about 10W more than the swing arms. I do not know how it works out once you begin to develop real power. I have not had both types of drives on the same hull. One of the issues is the lack of rotating momentum with a prop. That is why you need a shaft with acceptable torsional rigidity. The pedal feel is very mushy. I did calculations on this and you need to work with RMS power to get good answers if the shaft is not stiff.

What sort of mechanical losses can one expect in the roller clutches? The losses are very low. The clutches have negligible take-up angle. Once the wire is pinned to the rollers it does not slip. I expect it would be higher efficiency than a chain if it is not reeved through a large number of pulleys. I stopped working with these when my colleage in the US passed away.
In addition to the nice motion, I can imagine other potential advantages of the swing arm solution:

- Feet/legs are lower down = lower COG.

- The lower foot position might generally be good for the body hydraulics (?) and or allow for a more reclined position whilst still having the pump above the feet = further lowering of COG and possibly better aerodynamics

- As the configuration is narrower at the top, a more aerodynamic fairing might be possible (?)

There are bikes that use swing arms but have not enjoyed strong market support. Gearing may be one problem. The other is setting the system up to work over a range of speed. The reason being that you need some initial tension in the system. If it is more than required you are wasting power in the reeving. If it is too little the wite can go slack as you pedal faster. You cannot pull back on the pedals so clips do not make sense. I used semi-shoes that held my feet at the right height but they pulled out of the shoe if I tried to pull back.


Then again, the higher oxygen content of the cooler air should be good for the engine...

All in all, it seems that you have come a very long way in optimising the pedal/prop concept. Where do you see potential for further improvement?

Cheers

I now have lighter and stiffer frame than Greg used. It is made from factory produced CF tube.

Greg did not use the dipping rudders I now use. Once you get used to these they lower power by 2 to 3 watts.

Viscous drag is the major loss. There are surface finishes and other surface treatments that can lower this. This is an area I have not explored seriously. If you had very deep water it would be possible to used submerged buoyancy effectively. This has potential to dramatically reduce surface area and thereby reduce viscous drag.

A rider capable of holding 200W could sustain flight on foils at around 14kph. I looked at this very closely for Greg but it was beyond his sustainable power level. At 150W there was no benefit and his sustained level is even somewhat below this.

Rick W

[KalleA]

I now have lighter and stiffer frame than Greg used. It is made from factory produced CF tube.

I was looking at my carbon rowing oars recently, wondering if they would not be a material source for making a frame...

Greg did not use the dipping rudders I now use. Once you get used to these they lower power by 2 to 3 watts.

Still surfing and searching around the forum, and just found the dipping rudders. Interesting stuff. What is your view on integrated rudders (like Epic and Mirage use on their kayaks)?

http://img257.imageshack.us/img257/9332/pmiragerudder.jpg (http://www.imagehosting.com/)


A rider capable of holding 200W could sustain flight on foils at around 14kph. I looked at this very closely for Greg but it was beyond his sustainable power level. At 150W there was no benefit and his sustained level is even somewhat below this.Rick W

You addressed something that was just on my mind. I used to be decent cyclist in my youth, but 200W sustained is quite a bit and certainly well beyond me these days. Still, for a hybrid with a very modest electrical engine this could be cool.

Cheers

[Guest625101138]

.....

Still surfing and searching around the forum, and just found the dipping rudders. Interesting stuff. What is your view on integrated rudders (like Epic and Mirage use on their kayaks)?

.....

I expect these have merit. Definitely worth considering as a trimming rudder at least.

Rick

[KalleA]

Rick,

sorry for swamping you with questions, but you are such an amazing source of knowledge and information. I feel like a kid in a candy store!

On the topic of biomechanical efficiency: what is the efficiency of a swing arm system with a top mounted pivot? In your Pedal Povered Boat thread (Post #80) you mention that the efficiency is higher than for a crank - do you have a number/estimate of by how much? Just turning the cranks over costs about 10W more than the swing arms. I do not know how it works out once you begin to develop real power. I have not had both types of drives on the same hull. One of the issues is the lack of rotating momentum with a prop. That is why you need a shaft with acceptable torsional rigidity. The pedal feel is very mushy. I did calculations on this and you need to work with RMS power to get good answers if the shaft is not stiff.

What sort of mechanical losses can one expect in the roller clutches? The losses are very low. The clutches have negligible take-up angle. Once the wire is pinned to the rollers it does not slip. I expect it would be higher efficiency than a chain if it is not reeved through a large number of pulleys. I stopped working with these when my colleage in the US passed away.

I guess this is the ZRower concept?
http://www.forwardface.com/

http://img440.imageshack.us/img440/4928/lu200401.gif (http://www.imagehosting.com/)

Wondered why this had gone quiet. Sorry to learn about the inventor's demise.

I must admit that I haven't quite figured out how the reeving really works, but am I correct in assuming that the prop is only turned during the power stroke and freewheels during the "return stroke"? If so, using swing arms rather than the original rowing setup, could one imagine a solution with two reeving setups in tandem, each connected to one of the swing arms, and set up 180 degrees apart?

Not sure if this would work for the reeving system, but top pivoted swing arms w. roller cams ought to work for driving a normal chain and box transmission to a prop, right? A bit like this:

http://img58.imageshack.us/img58/4295/alenaxcloseup.th.jpg (http://img58.imageshack.us/img58/4295/alenaxcloseup.jpg)

If the motion is more biodynamically efficient and the rolling clutches have negligible losses, could this have some merit in a "normal" transmission, or am I missing something?

Cheers

[KalleA]

The sliding rigger was banned because it was viewed as giving an unfair advantage. The fastest bicycle has registered 140kph on the flat. It is recumbent of course but you do not get these in olympic competition.

Yeah, I remember that the sliding rigger was totally dominating the sliding seat boats in the early 80's. I believe FISA banned it because of the costs of re-fitting all rowing boats with sliding riggers in order to stay competitive. Perhaps the right decision from a sporting perspective, but it appears to have had a handicapping impact on all rowing boats. How often do you see sliding riggers compared to sliding seats on non-regulated and recreational boats? Almost never, I would say. And for no good reason, as the sliding rigger is clearly superior.

If anyone is interested, this is an interesting take on the sliding rigger:
http://www.rocat.co.uk/boat/rigger.htm

Cheers

P.S. Re. your reference to the fastest bicycle, part of my interest in PPB's stems from having two friends who always argue the rowing scull vs. kayak debate - one is a former Olympic class sculler and the other a former international K1 kayaker. It would be fun if their argument regarding the fastest HPB could be settled and demonstrated by an old cyclist...

[markdrela]

A major advantage of circular pedaling is that it is a forced motion, in which the kinematics or motion paths of all the major mechanical and body masses are fully constrained by the mechanism. Such forced motion conserves kinetic energy, so that nearly all muscle force power ends up in the drive shaft, the only losses being mechanical friction in the gears and bearings.

In contrast, paddling, sculling, rowing, etc. are free motion, where the mass motions are determined by the athlete. In this case the athlete must dissipate some kinetic energy on each stroke in order to reverse the motion to start a new stroke cycle. The braking is typically done by the muscles in "brake" mode, where they exert a contractile force while extending.

One can directly compare the power loss of free and forced motion having roughly the same kinematics:
1) Free motion: Make rapid pedaling circles "in air" while lying on your back, or sitting on a stationary bike with your feet ahead of or behind the pedals. It's quite tiring, because your muscles are constantly exerting positive and negative work to accelerate and decelerate each leg over each pedal cycle. But the negative work is 100% lost as heat, since muscles do not have a regenerative braking system.
2) Forced motion: Now hook your feet to the stationary bike pedals without a chain. Pedaling at the same RPM is now almost effortless, because the cranks are doing all the motion reversals, not your muscles.

The siding-seat rowing or sculling system is a sort of halfway solution where only some of the motion is forced, but not all. The sliding seat also reduces the mass which is oscillated, which is always better with free motion (with forced motion, how much mass is being oscillated doesn't really matter).

The sliding seat could be made nearly 100% forced by incorporating a flywheel which would would absorb and provide the power to do the motion reversals. I think such a system would blow away all current rowing records, but it would most likely be quickly banned to prevent a complexity and $ arms race.

[KalleA]

A major advantage of circular pedaling is that it is a forced motion, in which the kinematics or motion paths of all the major mechanical and body masses are fully constrained by the mechanism. Such forced motion conserves kinetic energy, so that nearly all muscle force power ends up in the drive shaft, the only losses being mechanical friction in the gears and bearings.

In contrast, paddling, sculling, rowing, etc. are free motion, where the mass motions are determined by the athlete. In this case the athlete must dissipate some kinetic energy on each stroke in order to reverse the motion to start a new stroke cycle. The braking is typically done by the muscles in "brake" mode, where they exert a contractile force while extending.

One can directly compare the power loss of free and forced motion having roughly the same kinematics:
1) Free motion: Make rapid pedaling circles "in air" while lying on your back, or sitting on a stationary bike with your feet ahead of or behind the pedals. It's quite tiring, because your muscles are constantly exerting positive and negative work to accelerate and decelerate each leg over each pedal cycle. But the negative work is 100% lost as heat, since muscles do not have a regenerative braking system.
2) Forced motion: Now hook your feet to the stationary bike pedals without a chain. Pedaling at the same RPM is now almost effortless, because the cranks are doing all the motion reversals, not your muscles.

The siding-seat rowing or sculling system is a sort of halfway solution where only some of the motion is forced, but not all. The sliding seat also reduces the mass which is oscillated, which is always better with free motion (with forced motion, how much mass is being oscillated doesn't really matter).

The sliding seat could be made nearly 100% forced by incorporating a flywheel which would would absorb and provide the power to do the motion reversals. I think such a system would blow away all current rowing records, but it would most likely be quickly banned to prevent a complexity and $ arms race.

Sounds right. Wish I had paid more attention in mechanics class.

Thinking of rotating pedals vs. top pivoted swing arms (which would both be forced motions, right?): is there a relevance of continous motion (pedalling the crank) vs. accellerating/decellerating motion (pushing the swing arm in a pendulum motion)?

Cheers

[markdrela]

Thinking of rotating pedals vs. top pivoted swing arms (which would both be forced motions, right?): is there a relevance of continous motion (pedalling the crank) vs. accellerating/decellerating motion (pushing the swing arm in a pendulum motion)? Oscillating motion in itself isn't necessarily bad. For example, the thighs oscillate during pedaling. It's only bad if the oscillating motion must be enforced by "eccentric" (or negative) muscle work.

There's a simple mental test to determine whether a power motion is forced or free:
Imagine that the athlete goes completely limp for a few seconds, and the mechanism becomes frictionless and subjected to vacuum so there are no aero/hydro loads.
If the mechanisms keeps running in the same cyclic way (as pedaling would), then it's of the forced-motion type.
If the mechanism bangs against a stop or flails about in some way (as rowing, paddling, running, etc all would), then the mechanism is of the free-motion type.

As I mentioned before, there are partially free/forced systems. Also, some systems are "forced" by gravity or spring forces, even though they appear to be mechanically "free". For example, a classical cross-country skier must reverse his arm and leg motions repeatedly (free motion -- bad). But by letting the legs and arms swing like pendulums, some of this reversal is done by gravity rather than by muscle brake forces. This gravity-forced motion produces a rather large power savings for the skier. If the oscillating motion is close to the natural pendulum frequency, nearly all the muscle braking forces can be eliminated.

I don't see such gravity forcing being usable for paddling or rowing. However, one could imagine putting a spring behind the rower so that his upper body motion is stopped and reversed by the spring rather than by his muscles. Another spring or springs could do the same for the oar, perhaps installed in the oarlock. By tuning the stiffness of these springs, the power savings might be quite substantial.

[KalleA]

Oscillating motion in itself isn't necessarily bad. For example, the thighs oscillate during pedaling. It's only bad if the oscillating motion must be enforced by "eccentric" (or negative) muscle work.

There's a simple mental test to determine whether a power motion is forced or free:
Imagine that the athlete goes completely limp for a few seconds, and the mechanism becomes frictionless and subjected to vacuum so there are no aero/hydro loads.
If the mechanisms keeps running in the same cyclic way (as pedaling would), then it's of the forced-motion type.
If the mechanism bangs against a stop or flails about in some way (as rowing, paddling, running, etc all would), then the mechanism is of the free-motion type.

As I mentioned before, there are partially free/forced systems. Also, some systems are "forced" by gravity or spring forces, even though they appear to be mechanically "free". For example, a classical cross-country skier must reverse his arm and leg motions repeatedly (free motion -- bad). But by letting the legs and arms swing like pendulums, some of this reversal is done by gravity rather than by muscle brake forces. This gravity-forced motion produces a rather large power savings for the skier. If the oscillating motion is close to the natural pendulum frequency, nearly all the muscle braking forces can be eliminated.

I don't see such gravity forcing being usable for paddling or rowing. However, one could imagine putting a spring behind the rower so that his upper body motion is stopped and reversed by the spring rather than by his muscles. Another spring or springs could do the same for the oar, perhaps installed in the oarlock. By tuning the stiffness of these springs, the power savings might be quite substantial.

OK, let me just check that I get this:

- for a pendulum swing arm setup, top pivoting must be the way to go since it uses gravity for some of the reversal?

- augumenting a top pivoting setup with return springs would further improve the efficiency, potentially resulting in a fully forced motion?

- the FrontRower discussed above might actually have some real biodynamic advantages over conventional rowing with its fixed seat, top pivoting swing arms and spring assisted return stroke?

Cheers and thanx for the lessons

[Guest625101138]

I must admit that I haven't quite figured out how the reeving really works, but am I correct in assuming that the prop is only turned during the power stroke and freewheels during the "return stroke"? If so, using swing arms rather than the original rowing setup, could one imagine a solution with two reeving setups in tandem, each connected to one of the swing arms, and set up 180 degrees apart?

Not sure if this would work for the reeving system, but top pivoted swing arms w. roller cams ought to work for driving a normal chain and box transmission to a prop, right? A bit like this:


If the motion is more biodynamically efficient and the rolling clutches have negligible losses, could this have some merit in a "normal" transmission, or am I missing something?

Cheers

The swing arm system that I proposed to Warren Loomis, and he supplied the parts, has two rollers meaning it is being pulsed almost constantly. There is a small period during the arm reversal when it freewheels. Initial testing that Warren did showed it was slightly more efficient than his sliding rigger set up with the long power stroke and long coast.

There are pictures and video of my test frame that might give you a better idea of the reeving for the swing arms in the Pedal boat thread.

Clearly someone thought enough about the swing arm system to try it on a bike. I do not know anyone who has tried this bike but I could imagine gear changing being a disadvantage to a standard system. Greg did not believe it was more efficient than cycling and he has looked into some of these things.

The critical part of the design is to link the two arms via the pull cord so you get an enforced motion or simple harmonic motion. I did a dynamic model of the legs and swing arms to optimise the geometry. It is a very pleasant motion for a relaxed pace and I am reasonably confident can be set up to be more efficient than cycling.

One of the reasons I stopped testing my system was the lack of reverse and I had a bad experience with weed fouling the prop. Took me about 15 minutes to get to shore to clean the weed from the prop.

Rick W

[jehardiman]

FWIW, SubHuman III was built with a "stair-stepper" Bi-directional drive that used over-running clutches to drive a counter-rotating prop set. This drive type was selected for enevlope considerations because it has significant advantages over a rotory crank set. SubHuman II used an elipitical sproket set for the dead space problem, but needed a 30" diameter , 3000# hydrodynamic mass hull to fit it in, SubHuman III was able to get the hull down to 26" and about 1300# hydrodynamic mass.

I'll see if I can find some pictures. Additional, I have pictures of almost all HPV submarines from the first 3 ('89, 91, & '93) international sub races.

[sigurd]

Would love to see all those pics.

[Village_Idiot]

4. Concept specific drag
I guess the propshaft produces some drag? Does the side mounted prop result in any turning motion that needs to be trimmed/counter steered?


This makes me wonder about the drag of a paddle or oar when being pulled through the water. You know, the great void left on the lee side of the paddle that tries to suck the paddle as well as water back in to fill the void?

Have there been any design concepts on paddles or oars to minimize this drag? Perhaps a teardrop-shaped bubble on the backside of the paddle? Of course, this would turn it into a "one-way" or unidirectional paddle, which may not be a good design in applicability.

[KalleA]

FWIW, SubHuman III was built with a "stair-stepper" Bi-directional drive that used over-running clutches to drive a counter-rotating prop set. This drive type was selected for enevlope considerations because it has significant advantages over a rotory crank set.

It would be interesting to see some pictures or drawings of this. Did you make any estimates regarding biodynamical and mechanical efficiencies of this setup?

Cheers

[Guest625101138]

This makes me wonder about the drag of a paddle or oar when being pulled through the water. You know, the great void left on the lee side of the paddle that tries to suck the paddle as well as water back in to fill the void?

Have there been any design concepts on paddles or oars to minimize this drag? Perhaps a teardrop-shaped bubble on the backside of the paddle? Of course, this would turn it into a "one-way" or unidirectional paddle, which may not be a good design in applicability.

Kayak paddles are cupped. The aim of any paddle is to grip the water so the relative velocity through the water is very low.

Rick W

[Village_Idiot]

Kayak paddles are cupped. The aim of any paddle is to grip the water so the relative velocity through the water is very low.

Rick W

True about the low velocity, once you are up to speed. However, I was also thinking in terms of paddles on a paddlewheeler...

[jehardiman]

True about the low velocity, once you are up to speed. However, I was also thinking in terms of paddles on a paddlewheeler...

High efficiency paddle wheel blades are cupped also. In order for a "paddle" blade (or oar or anything to else for that matter) to generate "force" it must be 1) attempting move at some relative velocity to the water, 2) have a significant area perpendicular to the relative direction of motion, and 3) change the speed and direction of the water. A prop or a paddle that is not "slipping" relative to the water generates no thrust. A "cupped" propeller, oar, or paddle generates more thrust because the apparent velocity off the edge generates a larger relative velocity change (i.e. 1-0=1 but 1-(-1)=2).

See the pelton wheel diagram below:

http://members.tripod.com/hydrodocs_1/pelton3.gif

[markdrela]

High efficiency paddle wheel blades are cupped also. In order for a "paddle" blade (or oar or anything to else for that matter) to generate "force" it must be 1) attempting move at some relative velocity to the water, 2) have a significant area perpendicular to the relative direction of motion, and 3) change the speed and direction of the water. True. A propeller also has some "slip" in the water. This is also known as "induced velocity" or "self-induction" velocity. In each case, this slip implies a maximum possible efficiency that the device can achieve, known as Froude efficiency:
eff_Froude = 1 / (1 + v_slip/V)
The attached plot compares this for an ideal prop and an ideal paddle (for CD=1). The prop is vastly superior for the same disk area. Both curves asymptote to 1, but the paddle asymptotes extremely slowly, which means it must be huge to be efficient.
The paddle can be improved by increasing its CD by cupping, but that's just the same as increasing the area a bit.

The prop has an additional loss from blade-airfoil profile drag that the paddle does not, but even with this it's still better than any paddle of reasonable size.