Human Powered Boat

[mackid068]

Oh, maybe you'd want a seatbelt...if you need to have the vessel self right....cause we don't want you conking your head on the canopy in heavy seas and going unconcious. it's kind of an ignoble death.

[mattotoole]

Originally Posted by cyclops

The chain and sprockets are wear prone. Calculate # of hours you need them to run EFFICIENTLY and run the exact same parts 4 X as long in a accelerated test with a electric motor turning a prop in large tank that allows loading everything. 10 X as fast should be safe for wear and heating of parts.

Just look at a typical bicycle scenario. Since the motor is the same, so is the load.

Even in gritty road conditions, bicycle chains and sprockets can last 20,000 miles or more if kept clean and lubricated. Assuming a typical average 15 MPH speed in hilly country, this gives 1333 hours. However, the main enemy of chains and sprockets is road dirt, which shouldn't be present in a boat. So as long as the chain is kept clean and lubricated, it should last many thousands of hours. Note that timing chains in automobiles usually outlast the cylinder bores, rings, and valves. This is because they're shielded from dirt and run in an oil bath.

Bicycle chains generally do not break except while shifting under high load, such as when caught in too high a gear on a steep hill. A boat drivetrain would not be subjected to this condition. However, carrying a chain tool and a few extra links isn't a bad idea, as when riding a bicycle.

Modern "bushingless" bicycle chains do not last as long as the older bushing type. This is because they're designed to be laterally flexible, to work with today's 8, 9, and 10 speed gear clusters (for a total of 30 gears). The pins and rollers fit loosely, don't retain lubricant as well, and let dirt in more easily. The older type are still available though. Older chainrings and cogs may be more durable too. They're thicker because they lack the sculpted teeth designed to make shifting easier.

[cyclops]

www.mcmaster.com has information and sells roller chain and sprockets of all types in small amounts with master and 1/2 links. They are a industrial supply house for any size order.-------Their catalogue is 3,300 pages and most is shipped the same day with actual shipping cost only.

[Sean Herron]

Hello...

Do what you know - do what you understand - do what you have access to - do what your friend who has a machine shop knows - the friend with a machine shop who will modify off the shelf components for beer money - do what you can afford - do what you can engineer and replace on your own - stick to your plan - don't get side tracked by others and go for it...

Cheers...

SH.

[mackid068]

What about money, now?

[tspeer]

Consider looking at model airplane propellers. You may find something readily available with the right diameter and pitch-diameter ratio. They are cheap enough to buy several sizes with which to experiment.

Consider also that you will need to power the craft when it is being pitched and rolled, perhaps violently. Both the ski trainer and stair stepper depend on one's weight to keep in place. If rotated so you're in a recumbent position, you still have to maintain the force, but it doesn't do much for you in terms of propulsion. A skiing motion would require that you raise your foot against gravity each time to begin a new stroke - very tiring.

Have you been cycling recently? Modern cycling pedals and shoes clip the feet in so they are captive - a good feature if you're being tossed about. They also make it possible to deliver power throughout the stroke. You don't just push on the pedal, you also pull up on it as well as push tangentially at the top and bottom of the stroke. By gearing down and spinning, you deliver a much smoother, continuous power stroke than alternating big pushes like you do when standing in the pedals. I think the former is more suited to the cruising endurance task while the latter is better for short bursts of high torque, like climbing a hill. When recumbent, one foot counterbalances the other, so there's not much difference from a vertical sitting posture.

If you're not an active cyclist now, you might want to start - both for training and to learn about the new technology.

[Skippy]

tspeer: A skiing motion would require that you raise your foot against gravity each time to begin a new stroke - very tiring. ... Have you been cycling recently?

I think I mentioned the "Nordic Trak" earlier, I agree with Tom on the skiing part. What I really had in mind was the arm levers. That's also relevant if SG isn't a cyclist, and it's the reason I mentioned the rowing machine. SG, what works best for you? Leg exercise or upper body? Or in between? It depends on the individual.

[markdrela]

I have a number of comments and suggestions here.

I'll echo Tom's suggestion of a model airplane prop. The best ones by far are APC propellers: www.apcprop.com . Almost everything else is really crude by comparison.

I'd go with simple pedalling. Long-term power production is determined primarily by cardiovascular output and biomechanical efficiency. Muscle mass doesn't matter much in this case, and so an added arm power system is just useless claptrap. For biomechanical efficiency, it's hard to beat pedalling. Rowing is less efficient because it wasted power in muscle-forced motion reversals. In pedalling, the pedal cranks passively reverse foot and leg motion with no energy required from the cyclist.

Sizing the prop diameter will require a good estimate of the anticipated power, and especially the speed. A well-trained touring cyclist will typically put out 2 Watts per kilogram of body mass almost all day, given enough food and water. A good bike racer can put out 3W/kg for very long times. In a shorter-duration bike race of a few hours this might be more like 4-5W/kg.

In any case, the minimum prop radius R should be chosen such that the thrust coefficient based on boat speed V is no more than about 0.5 or so.
Tc = Thrust / (0.5 rho V^2 pi R^2 ) < 0.5
Having Tc < 0.4 or Tc < 0.3 would be even better, but may give an impractically large prop. The reason for limiting Tc is that it determines the maximum or "Froude" efficiency, which is roughly analogous to induced drag on a wing.
eta_prop < 2 / [ sqrt(1 + Tc) + 1 ]
So setting Tc < 0.5 implies eta_prop < 0.90 which is acceptable. Additional swirl and profile losses should give an overall prop efficiency of
eta_prop = 0.70 to 0.75
in these sizes. The thrust can be estimated from the available power, boat speed, and prop and gearing efficiency.
Thrust = Drag = eta_prop * eta_gear * Power / V
Some iteration will be required.

Forget the air prop. Try sizing the prop with the Tc criterion using air density -- it will be huge. The air prop worked well on the Decavitator because it was a hydrofoil and a sprint machine. Going fast allows using a smaller prop.

Once the prop diameter is chosen, the next step is to select a pitch. For a cruising type prop, I would use a somewhat large Pitch/Diameter ratio of at least 0.8 to 1.0, since this is likely to give the best profile efficiency. Acceleration will suffer, but so what.

The pitch quoted for APC props is the true aerodynamic pitch (I verified this by wind tunnel tests). The zero-load rpm is therefore
RPM_0 = 60 * V / Pitch (V in meters/s, Pitch in meters)
The operating RPM will typically be about 20% larger than RPM_0.
RPM = 1.2 * RPM_0

Knowing the prop RPM, and picking a reasonable pedal rpm of 60-80, fixes the required pedal to prop gearing. My guess is that at least 1:4 to 1:6 will be required. A fixed ratio makes sense, since the impedance match between prop and cyclist will still be nearly ideal for a wide range of power, pedal RPM, and boat speed.

For transmission, I'd use the following setup, which has worked out well in several HPBs:
* Large custom chainring with small sprocket gives the overall required gear ratio.
* Sprocket drives a hard-stainless shaft about 5/32" to 3/16" diameter via a 1:1 90-degree gearbox.
* Shaft goes diagonally down and back though a stuffing box, and flexes to horizontal through a big arc to the prop.
* The end of the shaft is held just in front of the prop, by a simple journal bearing at the end of a thin strut.

The advantages of such a drive system are:
No gears, chains, or sprockets under the water.
Gear ratio is easy to change by swapping sprockets.
Absolutely minimal amount of wetted area added under the hull.
Drag of round shaft is acceptable because it's at a shallow angle to the flow.

[tspeer]

When I rode in RAGBRAI ([The Des Moines] Register's Annual Great Bicycle Ride Across Iowa), I was impressed by a gal I saw riding a hand-cranked bike. She had a friend with her riding a regular bike. I'd stop in a town for lunch, and about the time I'd be getting ready to leave they'd be just pulling in. They weren't all that far behind me. Day after day.

So you can look to cycling technology for arm power, too. But I think there'd be a lot of other things you'd be doing with your arms on a trip like that while your legs churned away. Like holding on. Or navigating. Or fixing meals. Or repairs. It might be useful to have a fold-out hand crank for when you needed max effort, say, penetrating into wind and current to get into the lee of an island. But I think the legs are best for power and the arms for everything else. A couple of arm handles continually swishing back and forth right next to you is going to get really inconvenient after a while.

[Jake Frith]

This is a fascinating post. It touches on a number of concepts that I have toyed with for some time.

I have always wondered whether a rowing machine connected to a flywheel (and if necessary a self feathering prop) would be more efficient than just rowing in a boat that was big enough to make the weight of the flywheel and mechanism less of an issue.

If you consider the rowing stroke with oars as performed in a sliding seat boat, the first part of the stroke which begins with the blades angled out at 45 degrees (optimally in a river scull) is forcing the blades outwards from the hull. The last part of the stroke (which optimally in a river scull ends with the blades at 37 degrees) is forcing the blades towards the hull. (Going past this is inefficient and referred to as 'pinching' the boat). The only decent part of the stroke is the short bit in the middle when the oars are perpendicular to the hull.

Imagine a very thin but large flywheel mounted inside a hydrodynamically profiled keel on an ocean rowing boat. the flywheel would provide inertia for the recovery phase of the stroke, but also if the boat design had the usual ocean rowing boat turtle decks fore and aft, the self righting would be spectacularly efficient (Providing the flywheel didn't fall out of its bearings when upside down!). The big twin bladed prop could be fitted to the back end of this keel case, although the gearbox would have to be mounted above the keel as there would not be space within it. The belt driving the flywheel could go round the edge of the flywheel to keep the keel as thin and hydrodynamically efficient as possible. I expect the keel case would be best in cast aluminium in two halves bolted together with a gasket in between. It would almost certainly have a lump either side in the middle, outside, to accomodate the bearings inside. Being the lowest part of the boat, this keel case will fill with water, however carefully this is protected against. Having even a smooth flywheel turning in water would be inefficient, even more so when it gets up to the level of the bearings in the middle of the flywheel, as it would do very quickly at sea. I would address this by running a thin tube down the inside to the bottom and sitting a small float switch and pump in one of the redundant bottom corners of the case. This could possibly be run off the boat's solar supply, or could even be a mechanical bilge pump operating continuously off the rowing machine. The alternative would be to completely encapsulate the flywheel in its case and run it in oil, just like the leg of an outboard motor.

Of course you could go to all these lengths and the added weight and mechanical losses render it less efficient than a pair of oars, but you would have the satisfaction of inventing something new.

There is a step that could be made in ocean rowing though before anybody tries the idea detailed above. Nobody to my knowledge has put a sliding rigger system in an ocean rowing boat. The sliding rigger is proven to be faster in river rowing boats: it was banned for competition by FISA in about 1980 as it was deemed 'unfair' on the poorer coutries who could not afford to invest in the technology. Some argue that the efficiency gains are simply because it removes much of the pitching fore and aft, as the main centre of body gravity remains static but I think it must also be much more efficient in converting leg power to boat drive at the catch. As a rower, I spend a great deal of time strengthening the lower back muscles that convert the leg drive at the catch to the pull on the handles, but a sliding rigger boat with plenty of support behind the back would convert this force more efficiently than even the greatest rower could in a conventional unsupported sliding seat. The way I think of it is imagining wanting to push a car out of a garage. The conventional set up is like fitting a rope and handle to the car and using the legs anchored to something stationary on the ground, pulling the car out of the garage from the front. The sliding rigger method would be like putting your back against the back wall of the garage and your feet against the car boot and pushing it out against the solid anchor point of the wall. I am sure that the second option would accelerate the mass more rapidly for a given athlete, and therefore wish somebody would just put a sliding rigger system in an ocean rowing boat.

Another point raised by the thread: Mick Bird did not row round the world, he got a long way round though. Nobody to my knowledge has yet. I dream about being the first person to row round the world, although so do several others! I would seek to use one of the technologies mentioned above, and possibly one that I am working on at the moment that unfortunately due to the nature of intellectual property rights I cannot share. For the time being my adventures are very much more local. Please visit www.southamptonrowing.org to see my latest.

[markdrela]

I was impressed by a gal I saw riding a hand-cranked bike. She had a friend with her riding a regular bike. I'd stop in a town for lunch, and about the time I'd be getting ready to leave they'd be just pulling in. They weren't all that far behind me. Day after day.

Yep. This is evidence that long-term aerobic power is primarily a function of the heart/lung system, not the muscle mass involved.

[markdrela]

Originally Posted by Jake Frith

If you consider the rowing stroke with oars as performed in a sliding seat boat, the first part of the stroke which begins with the blades angled out at 45 degrees (optimally in a river scull) is forcing the blades outwards from the hull. The last part of the stroke (which optimally in a river scull ends with the blades at 37 degrees) is forcing the blades towards the hull. (Going past this is inefficient and referred to as 'pinching' the boat). The only decent part of the stroke is the short bit in the middle when the oars are perpendicular to the hull.

I have to disagree violently here.

The oar on a crew boat is more of a lift device (e.g. prop blade) than a drag device (e.g. paddlewheel blade). RIght after the catch, the oar is advancing into the water and has dynamic lift, with its tip edge acting as the leading edge. It can be viewed as a laterally-translating prop blade with a very high pitch, or pehaps as a skate being pushed sideways. If the oar's L/D is decent, the oar is quite efficient in this condition, despite the "bad" angle.

As the stroke progresses, the oar's angle of attack increases, reaching 90 degrees in the middle of the stroke. The oar is a pure drag device in this condition, and it's efficiency depends entirely on the slip velocity. But this drag condition doesn't last long.

During the second half of the stroke the oar again acts as a wing, but with the blade's tip edge now being the trailing edge. If the L/D is good, the efficiency will be quite good even if the oar "pinches" the boat.

Much of the drag on the oar in the lifting phases is induced drag, so an efficient oar needs more "span", or width perpendicular to the shaft, and less "chord", or width parallel to the shaft. If you look at the evolution of oar blade shapes, this is pretty much how they've gone -- from long and skinny to more square. The ideal oar blade would be a high aspect ratio wing, forming a "T" on the end of the shaft. The airfoil must be reversible, like on a proa keel. Obviously, such an oar would be a real handful for the rower, so it's not used.

[cyclops]

O K. Leg power it is. Shaft drive it is. Prop size --to be trial and error. Prop survival in a storm? Fixed and is also a built in sea anchor without the danger of opening topside to deploy? How do we prevent the prop from overreving in a storm when the wind is pushing the boat? Safety OSHA? Is a perfectly balanced crank assembly needed? Rudder to be to be in front of the propellor to keep propwash most efficent? Prop and rudder to look similar to a Nuke sub? With the streamlined tail cone around the prop?-----------------Hey, how does he get fresh air in this boat that is totaly enclosed like a torpedo during a storm without taking in water also?

[mackid068]

What about stability? If you get beam waves, would you roll? So, certainly don't do a torpedoesque hull, have a flat bottom or a round bottom with a significant keel.

[cyclops]

Words, torpedo and sub, are for reference not design use.