Pedal Powered Boats

Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Scheny
    The wave interference hull is only 2.6m long, shouldn't be hard to build or take very long. Everyone will have their comments or opinions on the boat, build it and put it to the test!
    What sort of drive system are you thinking of using?

    Ian
     
  2. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member


    I've just done a very rough a ready resistance estimate, just using viscous drag and assuming long narrow canoe-like hulls. It's good enough as a starting point, I think. The rough plot is below and probably errs on the side of being overly pessimistic (it may well be out by 10 - 20%, a Michlet run would tell you more, but probably isn't worth the effort at this stage).

    The thrust figures below are based on the approximate hull resistance at each speed, and are in Newtons (sorry, I'm in metric-land!).

    The 16 x 12 prop gives (thrust, rpm, power, efficiency):

    4 kts = 30 N, 514 rpm, 87 W, 71%
    5 kts = 46 N, 642 rpm, 166 W, 71%
    6 kts = 63 N, 767 rpm, 272 W, 71.5%

    The 16 x 16 prop gives (thrust, rpm, power, efficiency):

    4kts = 30 N, 373 rpm, 83 W, 74.6%
    5 kts = 46 N, 466 rpm, 159 W, 74.7%
    6 kts = 63 N,558 rpm, 260 W, 74.8%

    Based on these figures I'd go for the 16 x 16, at least initially, and gear it so that you can spin it to around 600 rpm maximum and see how you go.

    Hope this helps.
     

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  3. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    GMR:

    Coach Dave uses very large electric RC props and his videos seem to show good speed on a large HPB.... He posted that awhile back, maybe a search will turn something up. Some electric APC props seem to be more efficient than their pattern type....

    Porta

     
  4. GMR
    Joined: Sep 2011
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    Location: Nova Scotia

    GMR Junior Member

    Hi Porta,
    Thanks for the heads up, I will look back through Coach Dave's posts and see what I can find. I will buy from the electric side of the RC prop selection.

    Jeremy,
    That is a huge help and I will start out with that prop and the suggested gearing. I am supposed to be in metric land too but I have feet in both systems. It will be really interesting to see how these numbers work out. The speed and rpm will be easy to measure but I am not sure yet how I will measure the power. I thought I might be able to use displacement of a spring loaded idler on the chain and calibrate it with a torque wrench. If nothing else that would give me a relative indication, which may actually be more valuable when comparing props and gearing.
    Cheers,
    Glen
     
  5. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Glen, my cat has two sea cycle units side by side. I bought both 12inch and 16 inch props (identical pitch) and the only practical difference it makes is not to the top speed, cruising speed, acceleration, just the comfortable cadence, i.e, as we spend 99% of the time at an 'all day cruise' speed, the seacycle unit with the 12 inch prop on runs at a higher cadence, which tends to suit practiced cyclists better.
     

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  6. GMR
    Joined: Sep 2011
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    Location: Nova Scotia

    GMR Junior Member

    Hi there TT,
    You've had the SeaCycle drives for a while now, what is your impression? The boat looks amazing with that background. If you were to set out for an all day cruise in quiet conditions as shown in the picture, what sort of speed would you expect to be doing? That would help me make a realistic judgement on how far I might get on a similar day. When out in my seakayak I have often wished that I could reduce my paddle area so that I could keep a comfortable cadence while grinding slowly into strong winds. I am planning on using a triple crank on the cat that has been resting in the basement for a while, and putting a (front)derailler on the drive line would be easy. A locking chain tensioner would retain the reverse capability while allowing gear changes. This would also allow me to gear down to go up the front of huge waves and gear up to zoom down the back side!! Other than the last point, do you think this would be a useful option? The cat will be a cruiser while the mono hull version I am hoping to keep lighter and somewhat faster.

    Cheers, Glen
     
  7. Jeremy Harris
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    Jeremy Harris Senior Member

    IIRC, the Seacycle drives have a 1:6 ratio, so for a pedal cadence of 60 to 80 the output shaft rpm would be 360 to 480. If you are happy spinning at, say, 100 then the prop would be spinning at 600 rpm.

    I cycle most days, but am far from being an athletic biker, and, in common with a fair few "leisure cyclists" I'm not happy spinning over about 80. My understanding is that serious cyclists prefer to spin faster than this, but try as I might I'm firmly in the "I'd rather push harder and slower" camp, even though I know it's less efficient! If you're already a fit cyclist, used to a more efficient, higher pedal cadence, then I'd say gear for that. If you're not quite so fit, then you may be more comfortable, at least at first, with gearing for a lower cadence. If you build in the ability to change the ratio then you can adjust this later.

    I doubt changing gear is worth the complexity, TBH, as the prop rpm, and hence pedal cadence difference between the fastest and slowest boat speed, unlike a bike, isn't very great.
     
  8. GMR
    Joined: Sep 2011
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    GMR Junior Member

    I ride about 8000 kilometers a year. Half of that commuting 85 kilometer round trip to work at 100 cadence on an upright bike. And the other half for fun on recumbents, (lowracers mostly) at around 90 to 95 cadence. I don't really have a feel for how this will be on a boat but I am getting the impression that cadence is a smaller part of the equation than some other factors involved in the design. When people see my bikes they always ask "how do you ride that thing??" and "how many speeds does it have?" So other than bragging rights it may not be worth it to add this flexibility to the cat. More things for the salt water to get at.....
     
  9. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Glen
    Putting in a system to change gears while pedalling isn't necassary as there aren't any hills on the water. It would be making your setup a lot more complex than it needs to be. What I have done to alter my gear ratio is to change over the bike gear at the 90 deg 1:2 ratio gearbox. The setup has a 52 tooth chainring connected to a 14 tooth gear at the gearbox, this gives me 1:7.4. At first I was using a 15 tooth gear which was 1:6.9 ratio, this felt a bit light. I can go higher with a 13 tooth gear at 1:8 but this might be too heavy. Changing the ratio this way is easier and cheaper than changing props, Rick made the coupling for me. The end unscrews and the gear is fixed into place, the gears are available from any bike shop.

    Ian
     

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  10. GMR
    Joined: Sep 2011
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    GMR Junior Member

    Yeah.....you're right of course......darn!
     
  11. GMR
    Joined: Sep 2011
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    GMR Junior Member

    I do like the idea of the folding prop to reduce drag when you stop pedaling. This cat will see a number of different power sources. It will at some point be outfitted to use a sail and a parasail kite or traction kite. I will probably pull the prop up for these but will need to add a dagger board or similar device for these options. Generally a very predictable on shore breeze here starting around 11 am, so pedal out in the calm morning and use the wind to get home in the afternoon. I'll get the package operational before I start looking at folding props.
     
  12. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    GMR:

    Another advantage of folding props is that it reduces the need for a freewheeling device with large, heavy props. These would tend to keep pedals spinning when you coast, requiring that you keep feet engaged for safety. You get easy reverse with a folding prop and that would be more challenging with a freewheel...

    Porta

     
  13. Submarine Tom

    Submarine Tom Previous Member

    Another subjective result of spinning faster (higher cadence) is the flywheel effect. Of course the hardware but also the feet and legs of the engine. This will not be apparent to those uncomfortable at higher RPM's, but once mastered, it is a real bonus.
    The result is a smoother power delivery, vastly reducing pulsating from the power stroke of the legs.
     
  14. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Hi Glenn
    I'm pretty happy with the seacycle drives, with a couple of caveats. I bought factory recon units, still not particularly cheap, but they are fairly robust and efficient - twisted chain in a wet sump. The chain tensioning and clamping rings need a bit of technique, it is easy to over tension and the drive will temporarily seize under hard pedalling. Also, it is easy to over tighten the clamping rings on the axle and pop them off their proper seating. I also bought the yokes, which support the units. They are fine, but are not totally rigid when pedalling - they twist slightly.
    The boat will do around 4 knots in all day mode, and about 5.2 flat out. The hull characteristics mean that the wave resistance starts to kick in between 4 and 5 knots, and then requires a huge amount of power to accelerate the boat. (for reference, my co-engine Paul is a club cyclist, and is out with the club or competing 3 times a week.) The trip in the picture we did 15 miles and a lunch stop in 4 hours.

    The difference in our fitness and cycling strength shows in sprint speed, but becomes much less relevant at cruising speeds.

    The gearing is 1:6. I would quite agree that changeable gears would have no practical advantage, just give you different cadences.

    The boat is relatively heavy (dart 18 hulls, plywood deck) but very low windage, which is pretty key, I think, under the very low power available from human engines. It is, of course, wet. We've played out in a F6 in the reasonably sheltered bay. I wouldn't consider anything stronger, or more exposed.

    Incidentally, I splashed out on a couple of Trice recumbent mesh seats, and they're great.
     

  15. GMR
    Joined: Sep 2011
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    Location: Nova Scotia

    GMR Junior Member

    TT
    The hulls without fittings, rudders, paint etc were 38 pounds each. I have not weighed the other pieces of frame etc yet. Your cat is a wet ride eh? I'm sure mine will be too so I am not going to powder coat the sections of the frame that determine the platform height off the water until I have had it out in some chop. Guess it's another balancing act between windage and wet. I don't know the theoretical speed at which the wave interference becomes an issue on this cat.
    Actually Porta I had forgotten that small detail about free wheeling and might have had a rude surprise thank you! Too deep into the bike world I guess....I was looking at sites today (Hobby Lobby for one) that sell replacement CF blades for folding RC props. I would probably machine my own center and as you say, try and hide the blades.
    Glen
     
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