Pedal powered tinny

Discussion in 'Boat Design' started by biggest_kid, Feb 14, 2013.

  1. biggest_kid
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    biggest_kid Junior Member

    Hey guys.

    I recently invested in a bowfishing kit for my compound bow, and am also a very keen rod-and-reel fisherman and so thought it was about time i got myself a boat. However im on a very limited budget, and will be for the next couple of years due to me starting university very soon. Im also a fitness freak, a bit of an eco-warrior and aspiring handy-man. So due to all this i thought id try my hand at creating/building a pedal powered boat. I have read through plenty of other discussions surrounding this subject on these and many other boating forums/websites, but they all seem to be for racing/relaxation oriented pedal powered water craft.

    So what im looking for is a boat that i can take fishing and bow fishing. It needs to be:
    - Stable so that when i stand up with my bow i can aim easily and be steady - Big enough to deter/protect me from crocodiles(a big threat up here in rivers and around the headlands of North Queensland, Australia)
    - Fast enough to be worth the effort of building in the first place(though speed isn't a huge concern of mine)
    - Have some storage space
    - Be able to carry at least 2 people
    - Be cheap!

    Now i have been doing some research and thought using a twisted chain drive system like this one on Recumbents would probably be the easiest and most efficient propulsion system for the money spent. Would you guys agree? I could probably get most of the parts needed from scrapyards/garage sales/friends for cheap. I was thinking of attaching/mounting this to a small flat-bottom punt similar to this one. My thinking behind this was that the small size of the boat should be relatively easy to move through the water with pedal power, and the flat bottom should mean a relatively stable bow-fishing and fishing platform. What are your thoughts on this?

    One last thing to mention before i go. I remember reading somewhere that the fastest pedal powered boats incorporate a prop that is not suspended in the water under the boat but instead mounted on the back of the boat in the air like a fan-boat kind of setup. I cant remember where i read this or how old the article was though, so if this is no longer true, or never was true in the first place, id very much like to know. If this is true a setup like this would help me get into the shallows for bow fishing as the prop would not hit anything in the water or get tangled in reeds or stuck in sand/mud.

    As you can see i have done some initial research into this, but thought i would ask some more knowledgeable people before going out and spending any money and time on this. Thoughts and corrections on anything i have said would be much appreciated.
     
  2. Submarine Tom

    Submarine Tom Previous Member

    A large, stable, inexpensive, used canoe with two paddles and PFD's would meet the highest number of requirements mentioned above.
     
  3. portacruise
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    portacruise Senior Member

    Yes, I also agree with Tom that a used canoe would be the best approach. Stability for steady shots can be increased by using one or two outriggers. If you can find a way to make them retractable on the fly, that would increase your speed when retracted and not in shooting mode. The punt pictured has a lot of drag and would not be suitable for human power. If you want something even bigger, with more load carrying and great stability, lashing 2 canoes together to make a pontoon would still fall within the HP paddling limits.

    Porta

     
  4. biggest_kid
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    biggest_kid Junior Member

    Forgot to mention, im a cycling enthusiast, so pedal power is my preferred mode of propulsion. But thanks for the input anyway. (Will consider paddle power if pedal power is ultimately unsuitable)

    So you think a punt would just be too cumbersome to use with pedal power portacruise? What about a smaller, sleeker model of punt?
     
  5. portacruise
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    portacruise Senior Member

    You put a double emphasis of being on a budget and something cheap. There are plenty of unused canoes around that fit with that. The motor on the back of that punt looks like maybe 25HP, whereas human power will only give you 0.2HP sustained and maybe 0.5HP peak for a few seconds! A sleeker model of punt would have to be shaped like a rowing shell, kayak, or canoe just to reach around 4 knots sustained. If you are ONLY floating down rivers and not fighting back upstream, then a raft shape like a punt would work...

    Porta

     
  6. Submarine Tom

    Submarine Tom Previous Member

    If one guy is sitting on the sole, the other should be able to stand no problem.
     
  7. messabout
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    messabout Senior Member

    But he did mention those wicked crocodiles. Some of them will be even bigger than the canoe and more than merely menacing.

    I think that a garvey, punt, or scow, designed for displacement mode, would be better suited for defense against those huge and scary beasts. A paddle wheel pedal powered system would work and be cheap to build. It would make the boat shallow draft, human powered, and simple to build from salvaged parts. The only drawback to a paddle wheel is noise. Alright it is not as efficient as an immersed prop but will be more efficient with human power than an air prop.

    I'd want to use a Gilmer belt rather than a chain drive. A used timing belt from an automobile can be had probably for free. Find one from an engine such as a V6 so that it will be long enough. (a Mazda 3.0 for example) Subaru urges the mechanic to replace the idler pulleys when the timing belt is changed. They are beautifully made and still have plenty of useful life when replaced.

    Also a bicycle could be the source of some of the parts. In that case the chain drive might be the thing to use, The wheels could be the basis for the paddle wheel. The bearings are there already. The peadals crank and sprocket is there.If you can find a derelict bike then most of the difficult parts are there for not much money.
     
  8. Submarine Tom

    Submarine Tom Previous Member

    You could just bolt the front forks onto an embedded axle on the floor and have the back tire turn the axle of the paddle wheel(s).

    A rudder off the brake levers is a great idea from WaveBike or just have the paddlers steer.

    I'd still just go with two or three paddles and people, those gators wont bother you...
     
  9. biggest_kid
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    biggest_kid Junior Member

    Messabout what about an immersed pedal powered prop? Would that be more efficient on a displacement-type craft than a paddle wheel system? Because i think i could pull off either one, would rather have the most efficient one though. What speed/equivalent HP do you think i could achieve with this setup on a small punt designed for displacement?

    And Submarine Tom, our crocodiles are a lot larger and very much more aggresive and territorial then your alligators (or so the experts say, ive never actually seen a gator in real life). They have actually been known to mistake canooes and kayaks for other crocodiles invading their territory and so ramming into them, flipping their occupants into the water... a situation id quite like to avoid haha.
     
  10. kerosene
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    kerosene Senior Member

    prop would be much better but there are no commercial systems I know of. I have seen one - you can probably find it in the "human powered" thread, but that was not cheap.

    Building your own is not that cheap either as good angle drives are pricey and budget options fail quickly.
     
  11. Jeremy Harris
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    Jeremy Harris Senior Member

    I remember being told by a ranger (before going canoeing in the Everglades) that alligators usually think canoes are other alligators, and (because they can be cannibalistic) alligators tend to move away from what they think are bigger alligators. If crocs behave in a similar way, then I'd guess you want to be sure that your boat looks bigger than the biggest croc you're likely to ever encounter.

    There's a very long pedal boat thread here: http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html that will have buried in it everything you could possibly want to know about pedal power. The summaries above are pretty good.

    If it were me, then I think I'd be looking at either trying to get hold of a really big and beamy canoe or lashing a couple together to make a catamaran. The latter would be slower and need more power, but would give you a more stable platform.

    When it comes to propulsion then you have to trade practicality and performance, and that depends almost entirely on things like cost, area you're going to use the boat, complexity, ease of transport etc. For pedal power efficiency is the most important factor. You're working with a tiny amount of power, maybe 0.2hp continuous, 0.5hp peak.

    You can make an efficient paddle wheel, but it will be 5 or 6ft in diameter (at least), be relatively heavy, add a fair bit of windage and be cumbersome to transport. It will let you run in shallow water though and will be relatively free from weed fouling problems.

    You can make an efficient air propeller, but that will be even bigger than an efficient paddle wheel, and have similar disadvantages and advantages. You'll probably need a prop around 6 to 8ft in diameter to give good efficiency at the low speed a boat like this is going to run at.

    The thread linked to has a lot of information on water props, and generally these can give you 80% plus efficiency (perhaps around the same, or slightly better, than either an air prop or a big paddle wheel), but the prop needs to be fairly big (around 12 to 15" diameter) and you need a means to lift and lower it to deal with obstructions and fouling. If weed is likely to be a problem, then you probably need folding blades to shed the stuff before it wraps around the prop.

    Two canoes strapped together (or maybe an old Hobie cat or similar), with a fishing platform, seat and hole in the bridge deck for a retractable prop drive seems a good option. Take a look at the flexible shaft drives in the linked thread, as they are pretty easy to make and would probably work fine on a boat like this.

    Finally, remember this boat isn't going to go anywhere fast. Plan on going at maybe 3 to 4 kts and you should be happy. If you have visions of doing 10kts plus, then forget pedal power, as you're just not going to do that with this type of boat.
     
  12. portacruise
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    portacruise Senior Member

    What is the smallest punt that would not be attacked by crocks? If you make a pontoon from two Aluminum canoes, I doubt the teeth would penetrate or gain much purchase on the hulls. The pontoon would perhaps present a bigger footprint that wouldn't be attacked, and the luster and metal vibrations would make it clear that it is not other crocs. Unless they are really hostile enough to use brute force to cause a structural failure, you should be fine. Another possibility would be to electrify the hull with high voltage low amps to make things uncomfortable but not lethal even to fish if they get within a meter or so... I've heard that the old style hand crank phone ringers found at army surplus can be used for this... Hmm, too bad it is illegal to take fish in the US by shocking, would be more productive than a bow :), but no sport....

    Porta


     
  13. biggest_kid
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    biggest_kid Junior Member

    Ok on that note i have decided to instead just save up and invest in a small punt.

    But what determines how stable a boat will be? Is it beam width? Whether it is a flat-bottom hull or not? How long it is? Or is it a combination of all or none of these? So i guess what im asking is what should i really focus on when trying to decide how stable a boat will be?

    Thanks,
    big
     
  14. Jeremy Harris
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    Jeremy Harris Senior Member

    In very simple terms, the beamier the boat the more stable. It isn't as simple as that, though, as it also depends on the overall length and the hull shape, too. A flat bottomed hull will have good initial stability (it'll feel stable when you get in and over a small range of angles of heel).

    The problem is that if you increase the beam and stick to a fairly short boat with a flat bottom, then the power you'll need to make it go at a given displacement speed increases. For a pedal powered boat this creates a problem, and it's why reasonably efficient pedal powered boats have long and slender hulls.

    You can get the same stability as a wide beam boat by having a catamaran, yet not incur too much of a resistance penalty. Catamarans are less efficient at low speeds than a slender monohull of the same displacement, but are significantly better than a broad beam punt.

    You can certainly fit pedal power to a fairly wide punt, but the performance won't be great and you may find it just takes too much effort to move it around at the sort of speed you may want to go. Probably not a problem when actually fishing, but might be a problem getting out and back to your fishing spot.

    Might be worth looking around to see if you can pick up an old beach cat cheaply. I've seen these being practically given away when the rig and sails are shot. Add a platform across the hulls, with a seat and I reckon you could have a pretty cheap and fairly easy to propel boat that would be nice and stable. Tiny Turnip has a pedal powered boat like this, see here: http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-26.html#post295399
     

  15. portacruise
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    portacruise Senior Member

    Are you saving for a motorized punt, or still going with pedals? Will you have rough water at any point of travel or is all travel in a protected area?

    What is your stability goal, as there are different types of stability? Is it to hold steady in chop vs. smooth surface so that you can make good shots with your bow? Or is it to intimidate crocs, or to have a lot of walk around room (to shoot in any direction) or room for cargo?

    There is self righting stability for example. If crossing heavy seas or with heavy cargo, beam width works against a smooth ride and the danger of flip over/quick steering response, at the storm extreme, etc. A keel and narrow beam design might be more important.

    Somewhere on the list archives there is a detailed discussion on the various types of stability. Maybe a detailed search will turn something up.

    Hope this helps.

    Porta


     
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