Human Powered Boat

Where we are now...
I have worked out a "simple" prop/shaft design that will push a 26' Swampscot/surf dory. It should displace about 1000 lbs. empty and about 2800 ready for sea.
I seek consultants (voulenteers) to help get from design parameters to cutting files. I may be able to ge a break on the cutting now that I work in a shop again...
I'm only talking about an aluminum dory here, flat bottom ( 3/16" ), about 8 or 9" of rocker on each end, bottom plank, side plank each ( 1/8" ) and a transome ( 3/8) only six pieces!
If anyone feels up to the task, their efforts would be appreciated and acknowledged.

 

Firstly, without wanting to get into a discussion of the relative merits of props versus paddlewheels versus oars, the most efficient way of transferring a continuously high level of power from a human body to a rotating shaft is via a conventional foot driven bicycle crank. This has been shown over and over again through the history of the bicycle and other human powered land vehicles, as well as being the choice of projects such as the gossamer albatross. Other mechanisms such as a stair stepping or cross country ski-ing motion are not as efficient, neither is arm power.

As far as the biomechanics go, you can get ideal geometries from technical books about bike geometry, but some basics are that most trained cyclists use an average cadence of around 90 rpm when trying to go fast on level roads for significant periods of time. Sprints, hill climbing and headwinds can change this ideal cadence, but it is probably what you should aim for when doing calculations for your drivetrain.

Crank length is typically 170mm (this is pretty much the standard size) with taller riders using 175 or even 180 mm cranks. Standard bicycle components are extremely reliable and the better ones can be bought with virtually no steel parts, reducing corrosion issues. The chain is an exception, but it may be possible to enclose this and the derailleurs completely.

Using a bicycle mechanism has another advantage for your voyage, it allows you to do extensive training indoors on a stationary bike, or outdoors on a real one. If you are not physically capable of getting up to a level of riding more than 200-300 km per week for several months before your voyage, you are not going to have the physical endurance to do the trip.

 

Andrew;

Having been involved with HPV's for a while, we have found that the cadence need to be lower (~60) because that torque requirements are much higher. Yes, you could gear down and spin faster, but in my experience we have found that this tires the propulsor much faster because so much effort is wasted just moving the legs at the higher cadence (especially if the rider is upright). In this type of endevor think hill climb or stair stepper. The need here is for the maximum torque to be delivered to the shaft which is only turning about 2-3 times the crank speed.

I totally agree however that he should be starting to train now. This is not a sprint, but a slow steady slog.

 

why so much?

 

Possibly so, but I would think that such a low cadence would be extremely fatiguing over a long effort of several days or weeks. Think hill climbing - if you are trying to go up at maximum speed you will push a bigger gear, but you will be unlikely to maintain that effort for a long period of time. What most cyclists will do for a maintained effort up a mountainside where speed is not the issue is get into a granny gear and spin their way to the top.

 

I have to agree with Andrew on the torque question, although I can see how a fairly moderate cadence might be optimal. On a bicycle, you can stand up on the pedals and power your way up a small hill, but when you're climbing a mountain, you have to gear down and ideally pedal about as fast as you would otherwise. With the boat, as long as the prop is turning faster than the pedals, torque is not the problem. The issue is the rider. As jehardiman said, the reason for lower rpm could be inefficiency due to excessive leg motion, or the difference between long-distance cruising at a moderate output level vs. shorter, more intense races. Another issue for racing is acceleration when jockeying for position or breaking out of a pack, which is easier at high rpm, but isn't necessary in distance cruising.

As for cycling vs. rowing, I thought rowing was pretty efficient over the long haul. It seems to me that bicycles operate in high traffic environments, where facing backwards would be dangerous, and that the same might apply in an airborne craft when landing(!). The evenness of pedaling might also be important for a lightweight vehicle moving through the air. But in a boat, the momentum of the rower's body moving forward on each stroke should smooth out the boat's motion. The boat is driven by the prop during the stroke, and by transfer of the rower's momentum between strokes. And finally, here also there's the issue of the rider. One person might have strong legs, whereas another has a strong back and/or arms. So I don't see why rowing couldn't be better than pedaling in some situations.

 

As I said before, I do not have a view as to whether oars or a prop are a more efficient method of propelling the vessel, my comments were purely to do with what was the most effective method of transferring human muscle power to a rotating shaft.

Rowing has the advantage of mechanical simplicity, and possibly manouverability, and certainly there have been many people undertake long passages in rowed vessels going back thousands of years.

The cycling position has proven to be efficient, but the question of whether a human powered propeller driven craft is superior to one driven by oars I will leave to others.

 

I'm still thinking about the prop/rowing machine. Sorry, didn't really make that clear. I still like the distribution of the stress over a lot of muscles, especially with a sliding seat to include legs, back, arms, etc.

 

Just out of curiosity...
Oars or Prop.
I'm thinking of the muscles involved. I've done countless open ocean swims each measured in miles, I walk out of the surf but have a hard time carrying my gear from the beach as my arms ache. I'm talking hours of swimming. Side stroke mostly but the point is I use legs and arms and the arms go first. True, rowing has just as much to do with ones back and mine's been very good to me. I expect years of good use of it.
However I'm not kidding myself, my recovery time isn't what it used to be....

The point: Efficiency.

I ask an opinion. A best guess if you will from anyone who reads this thread.
Which is most efficient?
All things considered, pertaining to propulsion efficiency only.

Oars or Prop.?

 

Let's define efficiency as work completed divided by the power input. Work completed can be distance travelled over time. Power input is the energy expended by the body to either pull on the oars or pedal a propeller.

I think you have to distinguish between calm water and rough water.

In calm water, I personally believe that a rower in a racing shell with sliding seat is very efficient, even though the blades are working only half the time (they are in the water for only half of a complete stroke). In calm water, the complete stroke is quick, even, precise, and the drag on the hull is minimal. I suspect that if you were able to measure the amount of energy the rower is expending, you would find he is quite efficient--gains a great distance with minimal energy output.

A propeller powered boat, I believe, would not be as fast, therefore the distance covered over time would not be too great. I am unsure about the amount of energy expended by a cyclist, I am sure others who are more professional cyclists than I have a better feel for that. But if we say the energy is roughly the same, I think that in calm water, the rowing shell is going to be faster, will cover more distance, than the propeller driven craft. Therefore, the rowing craft is more efficient.

In rough water, the opposite may be true. In rough water, the rowing stroke is messy, the oars are all over the place, there is no grace to the stroke, and it is much more inefficient. The oars are in the water for less time and with shorter strokes. I learned this from Tory Murden who is both an Olympic class rower and an ocean rower. Also, in rough water, the drag of the boat goes way up, speed goes way down. So efficiency is much less.

By comparison, the propeller craft driven by a cyclist will keep the propeller turning more or less constantly, although probably slower, but to my mind it would seem to lose less efficiency than the rower would, thereby bringing the two to a more equal standing as far as efficiency is concerned.

That's my 2 cents worth.

Eric

 

WATER WORLD OF HUMAN POWERED RACING BOATS
more on hull design than prop or oars but its a good read at http://www.hiswasymposium.com/pdf/2004/Leo%20de%20Vries.pdf

 

HPB's...

Hello....

See http://www.swallowboats.com/winsome.htm

http://www.nauticraft.com/models.htm

http://www.pedalboatrace.com/

http://snorlax.lampi.org/mike/cowichan95/cowichan95.html

http://www.humanpoweredboats.com/

http://www.prophish.com/pedalmachine.html

http://www.waterbiking.org/

http://www.ornithopter.org/forum/showthread.php?t=46

 

Here's some more:

Rowing Bikes of the World

Unusual Human Powered Vehicles. "Rowing Sites" is the second section.

Rowingbike

Rowbike


And just for fun,
http://www.watergames.com/easyboat.htm
http://www.ibike.org/images/one-wheelers.jpg (from http://www.ibike.org/library/tech.htm)

 

Thanks to all for the links. Eric, I see what you are saying regarding the definition of efficiency, but lets not forget that a rowing shell will never make a circumnavigation. A row boat might or an HPV might.
What I'm looking at now is 3 gear ratios: 1:1, 1:1.5 and 1:2 which would give me a shaft rpm range of ~50 to 180. Figuring a fully loaded disp. of 2,800 lbs. a shaft size of 5/8" and a hp range of ~.5 to .75, I should be able to hone in on my ideal prop. shape. I plan to make the 2 bladed props out of carbon fiber, and once I have made a few "keepers", I'm going to try 1 or 2 out of 6061 T6 aluminum.


So who thinks props.? And, who thinks oars?

 

Hello Solomon and all...

Here's an alternative transmission system for you - solid state. No chains, belts, whatever. Only two moving parts.

Basically, you pedal a generator, and the power is transmitted by wire to a motor that spins the prop.

This would not be as efficient as the state-of-the-art in bicycle components, but offers some advantages...

Cadence doesn't matter, as power electronics smooth your input.

You can direct your output to charge your onboard batteries rather than spin the prop.

Your batteries can drive the boat, or assist your pedal effort in combination.

Lying on your sea anchor, you can raise a wind generator to charge the batts.

If you anchor in a river current or tidal current, you can let the prop freewheel to charge the batts.

Placement of pedals vs prop offers more flexibility (easier to route wires vs chain/whatever)

Here's a post I wrote a while back with a bit more info (I'm not proposing an air prop for your project, just a bit more info on the idea of power trans via wire):
http://www.boatdesign.net/forums/showthread.php?t=813

I believe you mentioned earlier in this thread that you are carrying batteries, and your reference was to lead-acid?

Check out what Valence has done with lithium:
http://www.valence.com/ucharge.asp

Cheers
Lock Hughes