Pedal Powered Boats

The concept I was considering would not sap much power because the pitch would not project out from the surface of the shaft much. It would run the full length on the shaft. Maybe not even project enough to create much of a reverse flow if any. But I am thinking bits of entangled weed would not be drawn into the prop as much as a straight shaft. This is because weeds would stall as the slightly slippery gentle screw surface vigorously augers them upward. Maybe they would become disentangled enough from the shaft in their attempted move against the flow of water to be blown away. Seems like it should keep some weed away from the prop/ strut area anyway. But I may be wrong with some weed types, where you might just get a stationary buildup along the shaft itself causing drag from remaining wrapped on the shaft instead of being fed down into the prop. Anyway thanks for the comments. Interesting to see you had already considered a foil to help with that issue. V.

Porta

 

Vic
I now understand what you are saying. I think it would work. It would need to go deep enough on the shaft to ensure it was still trapping weed in wave troughs.

Basically it would be a little auger keeping the weed at the surface. There are some plaster insets that might be suitable for the stringy weed that gives me the most problem with the fixed blades.

It may even wind the weed to the side so it does not need to be cleaned off by hand.

Rick

 

Yes, that's the idea. If you study a fixed length solid rod radio antenna with exterior spiral contactor winding of the type that goes on trucks, you can get a better idea of the pitch and configuration of the augered shaft I think is suitable. That's what I will use as a prototype to test the concept. If it works, then just a matter of scaling up to hpb or larger sizes. Fabrication for larger size might be a challenge, though. Either the spiraled auger is machined below shaft diameter level or a helical strip is welded to the shaft to create a slightly raised auger on the shaft surface. V.

Porta

 

I have spent some time recently looking at building a fast pedalboat and one of the first things that struck me was the irony that we are borrowing a drivetrain from a dynamically ballanced bicycle and attaching it to a hull borrowed from a scull or surf ski (which are also dynamically ballanced, as are competetive canoes an kayaks) and are producing craft in which the rider is not able to actively assist in ballancing the craft.

The cost in terms of drag penalty for keels, stable hull forms, proas, tris, and foil systems can be calculated fairly accurately for a specific speed and righting moment, and they are all depressingly large. Has anyone investigated any strategies for dynamic ballancing while pedalling a boat?
- pivoting the seat longitudanally on the hull?
- controlling the pitch on a couple of foils about the size of a butterknife?
- twin surface-piercing props that are set up to counter heeling?

With the cost of stability so high, I looked at getting the rider as low as possible, and it looks to me that if the rider's left heel goes all the way to the bottom of the main hull and you construct a sort of heel-bucket ama to acommodated the the right heel, there is a small savings in drag due to the lower stability required up to a draft of about 100mm.

One other idea regarding drivetrains. The trouble associated with the fact that props slip and bike tires don't has been mentioned several times before. If your prop is operating at 12% slip on average, its really operating over a range of maybe 6 to 16% as the force on the pedal varies through 180 dergees (if anyone has a chart on pedal force for recumbent positions, please post it.) A simple cam and follower could be attached to the chainring to greatly smooth the torque to the prop. I looked at egg-rings and gyros, but the cam seems easiest.

 

Phil
You are making assumptions here. There are a lot of subtleties in a good boat that may not be readily apparent to some.

The outriggers do not need to sit in the water at rest. At speed the boat is dynamically stable or can be. Ideally you could make slight adjustments to allow for wave height but the drag from outriggers that are just clipping the top of waves is very low. Much less than a single outrigger that is carrying some load.

The boats in the attached picture were dynamically stable but not particularly efficient for a number of reasons.

With side mounted prop rotating it the right way you get torque that offsets the weight to the side. It can also be set up to not require any steering input to track straight. It is also possible to shift weight slightly to offset side wind ore any other imbalance.

The idea of using foils for leveling has been thought about but not tested to my knowledge. Would have more drag than surface skimming outriggers.

The counter rotating props have been tested. They are very complex and the losses in the drive cannot be offset by any benefit. It is easier to offset a little weight to counter the torque.

So there is virtually zero cost in achieving stability using twin outriggers. The most significant is windage but this can also be quite low. In fact if you were to compare the loss of power that scullers and racing kayakers lose in keeping the boat stable you would find they are paying a penalty over the twin outriggers. This is particularly evident after long durations. A novice in a tippy boat spends so much energy staying upright that they perform badly. It takes a lot of skill to row or paddle tippy hulls efficiently. If you buy a Flyak you need a weekend training session to learn to keep it upright.

Rick W

 

CAMS HAVE BEEN TRIED ON HPB AND DON'T APPEAR TO OFFER MUCH IF ANY ADVANTAGE.

PORTA

 

The OWC Cadence is a long monohull that can optionally be configured with outriggers. The outriggers can be configured to be several inches above the water.

Without the outriggers the boat is typically dynamically balanced by the pilot leaning and by the thrust from the propeller against the rudder. This can be effective in waves of up to 3 feet, depending on their direction relative to the boat, the speed of the boat and the skills of the pilot.

With the outriggers there are no worries (or very few) about balance in waves of up to 5 or 6 feet, again depending on the direction relative to the boat. The outriggers have little cost, except when one is trying to sprint well above "hull speed".

I find it best if one trains to pedal in circles rather than by pumping the pedals. Smoothing out one's cadence can improve speed by up to 1 mph.

Michael Lampi

 

Ok, I agree, it can be made dynamically stable; and Rick anticipated where I was going with this. I'd very much like to convert some of those subtleties into some numbers or fudge factors. Presumably, even the best hulls have some degree of stability and roll damping built in to them; and a bit of rider input is used to increase its effect. Torquing the prop is possible, but obviously not desireable from a performance standpoint. A correctly located rudder can help to keep the hull beneath one's butt. Does anyone have a recommended starting point for GM for a one man fast pedalboat. Absent further input, I'm guessing something around negative150mm would be manageable for a recumbent setup. I have a feeling it will be more difficult to balance a recumbent setup since shifting bodyweight is not very practical. The pedalboat in the photo can be pushed about undeneath the riders to a much greater extent than is possible on a recumbent setup. The best arrangement I have come up with (on paper) is to use a small controlable foil off to one side. If the foil has a lift to drag of 16 or so, and is set to lift at all times, the decrease in displacement offsets enough of the drag penality to beat the other methods I mentioned previously. (I believe you need a L/D of more than thirty to actually improve performance of this sort of craft with foils). But I still have the fundamental problem of deciding how much stability is needed. I'm not concerned about tipping past five degrees of heel or so. I intend to use the faux tri or faux proa for handling that.

 

Porta, thanks for those two bits of info. There is a good chance I can visit Roanoke in a month or so. I'm planning on a trip to North Carolina. You can just make out the underwater fin arrangement in the last photo of the waterbike. Its pretty big. I'd like to get info on the cam setup. It should relieve leg strain. If it didn't, I'm curious why.

Michael. Familiar with the Cadence from other posts. Wonderful craft. But it is set up for more open water conditions than what I have in mind. It has a much higher degree of form stability. I'm looking at something like a single scull with pedals. Waterline beam about 10 inches.

Darn, just found a serious typo in my first post. The depth of the heel bucket ama should be 4 inches or 100 mm, not 400mm.

 

phil
Where did the 12% slip come from? My boat requires a thrust of 35N to do 11kph and I am spinning a 400mm prop. You can work out the slip but it is a fraction of your figure.

The most important aspect for driveline/pilot biomechanical efficiency is torsional stiffnes in the drive train. Without this there is a lot of lost time pedalling through the deadspot. The RMS power ends up quite a bit higher than the average in this case.

There is benefit if you can spin as opposed to push-push but it is quite slight. This is a matter of training. I can drop my heart rate by about 3bpm by spinning but it takes concentration and the muscles to do it are not well trained. Guys who use recombunts regularly end up quite smooth. The torque fluctuation is still of the order of 40% from peak to trough however the prop slip is quite low.

The main areas to focus on are weight and simplicity. The hull should be designed for lowest drag. You can notice a slight difference if there is some inherent stability but typically my GMT is considerably more negative than you suggest.

Any well that collects water is a real nuisance if your feet are ploughing through it. I stop pedalling if I plough through a wave to try to keep feet dry.

I have found that I save more power with the dipping rudders rather than a permanently submerged rudder that would help with dynamic stability. The smallest submerged rudder I have used uses about 3W. There are a few little tricks in setting up the outriggers for low draft but they cost no more than 1 to 2W once they are sre right and you are sensitive to the hull roll.

Rick W

 

Escargot breeds!

Whilst idly trying to track down what became of Escargot, built to Phil Theil's design for the Environment Agency (UK) by Colin Jones of Southampton, I was delighted to discover that

Gruene-Flotte of Mulheim,

Germany have built a fleet of 5, with a very slight size increase, a custom drive, with two pedal stations to one prop, an auxillary electric drive built into the rudder, plus solar charging, and accommodation for 4. (pretty cosy I should think.) The boats are available for hire, on a stretch of the Ruhr.

I've taken the liberty of babelfishing it. - enjoy the picturesque translation!

A little more information from www.habiter-autrement.org here.

 

Escargot

Tiny Turpin
Boat looks great, wouldn't break any speed records, not that it matters with this boat. The pedal position dosen't look comfortable with nothing to lean on, but that could be easily fixed. Would make a great alternative to a houseboat and probaly could be fitted to a car trailer.

Ian

 

Hi Ian -yes, I'd definitely want a more recumbent position for comfort, but I suppose people do cycle long distances on land with the upright saddle position. I'm sure the windage would be an issue in anything but sheltered waters, with the low power levels pedalling can sustain. Not convinced by the propeller/drive set up either. But it does show the versatility of pedal power - the range from what you and Rick are doing, I guess I'm somewhere in the middle, and Escargot at the other end of the range. I'm still interested in the idea of a 'milder' build of Within for cruising; perhaps inflated a bit for a little more space, sliding hatch/top, but keeping the aerodynamic shape for less wind resistance.

 

Be careful which translation engine you use on the grune flotte website, btw.

Although generally the google translator is better than Babel fish, Google comes out with this rather alarming special offer on the home page!

 

Have been on holidays up the east coast with V14. I have done about 200km on the water. Three runs over 40km and a few others just mucking about but decent distance.

I am very pleased with the folding prop. My best run was on the Nerang River on the Gold Coast. I did a 41km round trip from the Broadwater to Nerang in a bit over 4 hours. Had a little bit of current assist at the start and toward the end but was working well within capacity.

I took attached video of one outrigger while moving at 10kph to show how it occasionally kisses the water. That is all that happens to stay upright when the water is calm.

There is a video clip linked of a somewhat heavier pilot testing the boat on the Logan River:
http://www.youtube.com/watch?v=06zNEAat2lg
In this clip the outriggers are in constant contact due to 10 to 15kg extra load.

Rick W