Multiple Gear Boat w/ Propeller

Discussion in 'Boat Design' started by Pedaler, Jun 8, 2009.

  1. Pedaler
    Joined: Jun 2009
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    Pedaler Junior Member

    I have this idea, and I've googled around and searched this forum quite a bit. The concept of utilizing gears, like on a mountain bike seems to be left out in mostly every pedal-powered boat project.

    I'm not in the market for the most speed and efficiency exactly, but I do want my boat to go considerably faster than by just rowing, so as not to defeat the purpose of the whole ordeal.

    In short, from what I imagine it to look like right now. It is my old regular 18 speed mountain bike: [​IMG],
    with the front wheel taken off and the forks mounted on the middle of the floor of my flat bottom boat: [​IMG]

    Now from what I've learned in this forum by searching is that I will need some sort of right angle converter (don't know what it's called) like this: [​IMG] that will take the spinning motion of the back wheel and bend it 90 degrees so that it can be transferred through a metal rod on the end of which is a propeller.

    I wish I could use the back wheel so that I could keep the inertia from it spinning after I stop pedaling, but I realize that that would make things quite a bit more complex.

    I found that the idea is partially existant in a product called the Shuttle Bike: http://www.gizmag.com/go/2505/gallery/.

    As I understand, the back wheel is disconnected from the gearbox and does not spin. The gears are capable of still being used on the water. The only thing that bothers me is why such a small, double-bladed propeller? If I can start out on first gear, I would be able to get the boat moving with a huge, thick, powerful propeller and switch gears on to increase speed.

    For the information, I am on a tight budget, in the understanding that I don't intend to spend much money on the parts for this. I intend to salvage an old bicycle, use materials that I can find in mine or my buddies' garages and not impair my row boat's ability to swim normally again. I simply need the first push of guidance and outlay of how the project should be built.
     
  2. Guest625101138

    Guest625101138 Previous Member

    Huge, thick, powerful propeller requires huge, heavy powerful engine to operate in its efficient range.

    Even the most powerful humans cannot outperform a modern electric motor that weighs 150 grams plus a few kilograms of battery to power it. A small internal combustion engine around 500 grams and a few litres of fuel will also outperform any human.

    To get the best from a human you want an efficient propeller and this will have the longest, thinnest blades that are capable of withstanding the small forces involved in most human powered boats.

    If you are a world class athlete with very strong lower body and not highly developed upper body - say a sprint cyclist, you could get the boat to plane if you set everything up for maximum efficiency. In this case gears might offer some benefit as the boat will go through different operating regimes - from displacement to planing mode. A world class athlete could only sustain planing mode for a few seconds though.

    Joe Average will not be able to get the boat to plane so is condemned to displacement mode and there is little value in having gears. There may be rare occasions when operating in strong head winds that you would like to use a lower gear if available. I doubt that you will operate that boat in the ocean where you need to contend with large swells that might afford some advantage to constantly changing gears.

    Rick W
     
  3. Rangerspeedboat
    Joined: Apr 2009
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    Rangerspeedboat Senior Member

    I have always wanted to use mountian bike gears on a go cart. On a boat works too.

    I would get a smaller lighter boat, row with that you'll go fast and excersise.

    When rowing your working your upper body, thats what you want to work on because that shows. If your going to pedal a bike have it on land so you can get some speed.
     
  4. Pedaler
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    Pedaler Junior Member

    Hah, thanks for the advice Rangerspeedboat, but my whole purpose for this project is to use "the most powerful muscles of the body, the legs" to propel my boat. I'm not looking for the most efficiency as I know I lost that bet when deciding to use my flat bottom boat; and building muscles isn't really the goal here. I work out apart from this.

    Rick, that's some knowledgeable...knowledge! I still don't quite understand however why gears wouldn't be so useful. Would it not work as it does in cars and bikes on the road? Start out with gear 1 to break the potential energy barrier, and then ease yourself into higher speeds by changing gears?
    Check this video out: http://www.youtube.com/watch?v=vPCDFEbJWqU. At around 1:08, you can see the swedish boat with 2 pedalers who actually do plane. And their boat won the race. Though I'm not looking to plane on my boat, I do want maximum possible, (but reasonable) speed. I am confined to using just my Huffy Stone Mountain Cheap bike and the 10 or 12 foot flat bottom boat I have. I know, I know; it's not exactly the high end gear that you guys like using, it's more like redneck project utilizing garbage from the shed.

    At any rate, the main part, the actual mounting of the bike and adapting the spinning power of either the gears or the wheel through to the rod which holds the propeller is the first and most important step. Then I would be able to experiment between propeller styles and sizes to see what fits me most.

    I can sort of fathom how I would mount the bicycle, but the most difficult part for me at this point is the conversion of the actual power that comes out of the gearbox to the rod that spins and propels the propeller. Keep in mind that I need to be able to switch gears and the output of the functional "transmission" of the bicycle needs to be used to propel the boat. I'm even finding it hard to explain myself properly because of my lack of terminology in the subject matter.
     
  5. Guest625101138

    Guest625101138 Previous Member

    That boat is on foils. Foils are 2 to 3 times more efficient than a planing hull so require much less effort to fly. A planing surface is a very inefficient foil.

    I am one of the few people who race pedal boats against other forms of human powered craft. My V11 design is the current 24 hour distance record holder. I have done considerable research and development to get the best from human power on water.

    There is quite a lot of detail on this thread:
    http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-20.html
    The latest pictures are of V14.

    Probably the best set up for your prop using a single gearbox would be a curved shaft off the transom unless you want to punch a hole in the bottom for a shaft tube. The later could be done with some nice engineering but I always try to avoid hull penetrations.

    Rick W
     
  6. Pedaler
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    Pedaler Junior Member

    So is there never a time when you're pedaling on your single-speed boat and you reach a certain RPM (or should I say pedal per minute) when you wished you could just switch to the next gear so that you wouldn't have to pedal so fast to go the same, or an even faster speed?

    I guess I'm still confused about it because as I see it, when you're stuck with one gear on the boat, it's like being stuck on those older single speed bikes. It's about on gear 10 always, so you can't really go uphill on it, and if you're going on a straight road or downhill, you can't pedal any faster, but there is still room for speed because on a speed bike, you could go as far as gear 18 or 21.

    And could you please elaborate a little more on the mechanism used to transfer the rotating motion from the gears all the way to the propeller.
     
  7. Guest625101138

    Guest625101138 Previous Member

    I design my drive system and prop so everything is tuned to my sustainable power level. This is 130W. My preferred cadence is 70 to 75rpm. In calm conditions I can get 11kph with 130W.

    If I want to go faster I pedal faster and the leg forces go up. My maximum power level is around 120rpm using 175mm cranks. The gym machines I use are limited to 630W so this is the highest I have seen but it is very close to my maximum output. A sprint cyclist might get to 1500W or more.

    If I want to ease up I pedal slower. The forces get lower.

    The reason you have gears on a bike are to accelerate and to go up hills. I can get my prop to suck air and spin without load at zero speed. In fact if I want to accelerate quickly I have to get sufficient boat speed before I can really apply force. In a race I can outpace paddlers to 14kph which is near the top speed for most of them. It only takes a second or two to reach that speed - would be wasteful fiddling with gears.

    Most water does not have big hills where gearing is beneficial on a bike.

    This picture shows the curved spring steel shaft I commonly use on boats:
    http://www.boatdesign.net/forums/at...texas-water-safari-v11j_prop_curved_shaft.jpg

    Some have tried freewheeling props so they can stop spinning but then you lose the ability to go in reverse and this is extremely useful on the water. Without a freewheeling hub you might find changing gears a bit more complicated. Relying on a spring take-up on the chain will also limit the ability to apply power in reverse.

    There have been rare times when I would have liked a lower gear when pushing into strong headwinds for hours on end. My knees start to give up before the rest of my body due to the load on the legs.

    Rick W
     
  8. Pedaler
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    Pedaler Junior Member

    Trasmission, by definition uses the mechanics advantage that provides a speed-torque conversion. The numbers you are telling me about what you do at the gym and on the boat don't really speak to me as I'm not in the boating business (yet). But when you reach that 120rpm maximum, what if you had multiple gears and you switched to the next gear? What exactly would happen to the speed of the boat and to your fatigue?
     
  9. Guest625101138

    Guest625101138 Previous Member

    The 120rpm is not my maximum cadence. I can comfortably spin 175mm cranks to 140rpm. Some using 145mm cranks spin over 200rpm.

    If was sprinting at 120rpm and changed to a higher gear the forces on my legs would be too great and I would loose speed rapidly. It is the same sort of situation you would find in your car if you were climbing a hill and you shifted up rather than down. The speed would collapse. You have exceeded the torque capacity of the engine.

    Rick W
     
  10. Pedaler
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    Pedaler Junior Member

    Well then, in that case, could I still utilize the old mountain bike with all its gears in place even though I might have realized that I don't really need so many gears on a boat? I just don't have a single-speed bike to salvage.

    Now that we've passed the gears question, as I imagine the part that I will most likely have to pay for is that right angle converter. What is it called properly and where is it mounted on the bike so that I will be able to reverse?
    I noticed from the other thread that they go for several hundred dollars. Are there not MUCH cheaper alternatives?
     
  11. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "...Foils are 2 to 3 times more efficient than a planing hull..", what kind of foil, what kind of hull, what displacement what speed what aspect ratio what chord etc etc?? Reference, or just the usual numbers plucked from thin air???

    Pedaler
    The reason why narrow tip propellers are shown to be efficient in smooth water trials is that the thrust requirement is low, since a high proportion of the total load on a propeller blade is carried by the tip; therefore local breakdown of flow may occur.

    So, it depends on how much thrust you can deliver not at the gears of you bike, but at the propeller, and how much thrust, or drag there is, required from you boat for certain speeds. Then how to deliver that thrust through the speed range.
     
  12. Guest625101138

    Guest625101138 Previous Member

    The simplest way to use the bike is to just have a straight chain run from the chainring on the cranks to the input shaft of the gearbox. Anything involving a normal hub will preclude reverse and I expect this will be a serious nuisance.

    You will have to be careful how the bike frame is mounted because there is a need to consider stability in a boat. If you sit up high and get a few waves you will end up very wet under the boat rather than on top. There are some pedal boats operating with high seating positions but they are either very stable catamarans or dynamically stabilised narrow hulls with slow speed or emergency outriggers that are deployable.

    You might be lucky and jag a cheap box on Ebay. I know a couple of people who have picked up new or near new boxes for a fraction of their original cost. The Mitrpak are probably the best value and they are lower cost than many.

    Rick W
     
  13. Guest625101138

    Guest625101138 Previous Member

    There are cheaper alternatives but none are as good as the precision cut spiral bevel gears with ball bearing supported shafts.

    I have not tried the open nylon gears shown here:
    http://www.teausa.net/admin/uploads/TEAUSARightAngleDrives.pdf
    The 15mm shaft size will handle your power. The 12mm shaft would be marginal.

    Another very cheap option for doing some mucking about is a right angle drill attachment like this:
    http://www.made-in-china.com/image/...l-Attachment-with-Keyless-Chuck-ST-RAD01-.jpg
    They can be picked up for under $10 in most hardwares. It will last about 5 minutes but costs little. They are difficult to mount and you can get them to last a little longer if you stiffen up the case by encapsulating. I know of one older fellow who used one for more than a year without breaking it.

    Some of the little electric grinders have nice gears and these can be set up to work for a period. They often wear out brushes and it is not worth replacing the brushes so they get thrown out.

    The cheap solution would allow you to do a proof of concept just to gain an idea of what it feels like. Take a paddle so that when it fails you can get back to shore easily.


    Rick W
     
  14. Pedaler
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    Pedaler Junior Member

    Thanks for the help. I've found a Mitrpak, but it's the MITRPAK T081. Do you know if that would suit my needs? If it won't work out with it, then where exactly would I get the cheaper right angle solutions? I imagine mounting the drill attachments would indeed be quite difficult.
     

  15. Rangerspeedboat
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    Rangerspeedboat Senior Member

    Just had a really simple solution come to mind. A paddle wheel boat.

    Have 2 sidewheels powered by your bike which the sprocket from the rear wheel just going to the paddles. You can change gears and all that, it might be more efficient than having gears on a prop.

    Or your bike powering a set of oars, which would basicly be the same thing.
     
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