Pedal Powered Boats

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

  1. Guest625101138

    Guest625101138 Previous Member

    Thought it would be a good idea to start a thread on pedal powered boats. Aim is to cover design, development and operation of pedal powered boats.

    A little more specific than human powered boats. The hulls often have a lot of similarity with canoes, kayaks, sculls and other rowing boats that rely on arm power or both legs and arms. This thread is essentially aimed at leg powered boats but any contribution welcome.

    So as fuel prices go north and we examine the options to reduce oil demand the pedal powered craft offers an interesting alternative to have fun in boats on the water rather than just sitting at a mooring.

    A place for lurkers from more specific HPB forums to contribute and provide insight on boating matters at the low power, high efficiency end of the scale.

    For starters I have attached a video of me doing a slow pass in Mike Lampi's Cadence on Lake Union near Seattle. I have also attached the performance data from a couple of hours in the boat. At agressive cruising of 150bpm the boat holds around 10kph. Top speed achieved in a sprint is 16.8kph. There was a bit of slop when this was achieved so the aging engine might nudge 17kph in smooth water.

    Attached Files:

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  2. Guest625101138

    Guest625101138 Previous Member

  3. ASM
    Joined: Sep 2005
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    ASM Senior Member

    Nice thought, how about utilizing a very small electric motor in the shaft as additional power up or a as a generator when doing slow spped, to power up a battery in order to have that extra umph when you have wind or waves when going home ? (maybe aided by a little solar panel ?) That is also the main purpose of these electric assust bikes we have overhere, to get 70+'s over a bridge.....
  4. Guest625101138

    Guest625101138 Previous Member

    These boats are as many and varied as the mind can contemplate. The things that I have found that suit my purpose are:

    1. The most important feature for me is relaxed exercise. I can sit at home on an exercise machine but it is nowhere near as rewarding as being on the water. I could get out on the roads in a recumbent bike but then I have to be constantly alert for traffic. Australia does not have the cycle tracks or wide road verges that some places have.

    2. Safety is a feature. I would not use a boat that can sink if swamped or holed. I do not want to be easily rolled in beam seas. I need to be able to easily uncleat pedals if am rolled and be able to right the boat from the water.

    3. A boat that performs well is highly desirable. I work hard on efficiency to get the most out of the 1951 vintage engine. It is a bit of a thrill for an old codger to leave fit young men on surfskis and kayaks in my wake. Also fun to have the sailing fleet chase me around a course. It is nice to nudge 18kph in a sprint. Most onlookers cannot believe what they see when you can outpace a small planing dinghy.

    4. Weight is the most important feature for ease of handling and also benefits performance. My design objective is to keep boat weight below 20kg. I do not have many frills. Even selective about the amount of water and nibbles I carry.

    5. Length up to 24ft is tolerable for car topping and storage. I think 5m would be considerably more practical but going down to this length impairs performance. I am also working on an inflatable version that can be carried as luggage when I travel on business.

    So the variations on the theme of pedal boats is endless. After trying it for a few years I am surprised how few people have actually explored the possibilities.
    Kirk likes this.
  5. ASM
    Joined: Sep 2005
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    ASM Senior Member

    I am intrigued by the human pedal powered desigs you made as seen on your website. And you are right, why do people not use this more often as an excersize gadget ? Since I am also interested in bikes and cycling in general (basically I a interested in all that moves from an design/engineering point of view) I came acroos a shft driven bycicle.. would this be a good tool to incorporate into a pedal powered boat ? no chain, no grease, less maintenance and they claim lifetime warranty....

  6. Guest625101138

    Guest625101138 Previous Member

    The appendage drag on a pedal boat can be significant. The most efficient arrangement I have developed uses a 1/4" spring steel shaft hanging off a right angle gearbox driving the prop. The shaft does not need any other support providing it is pushing but I normally use a tiny strut to allow me to go in reverse. The attached photo shows the shaft unsupported and this works very well.

    I calculate losses down to as little as 0.25W and work to eliminate them.

    OK - so the problem with the cycle drive shaft is that you need a large spinner on the prop to shroud the gear. This comes at a significant cost in extra drag. There are other more efficient ways to eliminate the chain.

    Mitrpak are sponsoring Greg K. in his various boats and I have been working with them on a purpose built drive leg that incorporates two of their boxes.
    This shows the product range and an idea of costs:

    I have also attached a photo showing a drive leg I made that uses a small gearbox underwater and one at the top with a chain reduction. This could be engineered into a simpler arrangement but again highlights the need to keep the underwater bits small.

    It is no accident that the fastest pedal powered boat used an air propeller.

    Attached Files:

  7. Guest625101138

    Guest625101138 Previous Member

    Here are a couple more options for chainless drives. These are used in conjunction with curved shafts driving on the centreline of the hull.

    Attached Files:

  8. ASM
    Joined: Sep 2005
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    ASM Senior Member

    I see your points... I was just thinking of the shaft + gear system as a deletion of the chain drive (though people claim that the chain is far more efficient (98%)), then, because one can change the angle of the shaft going to the 'wheel' , you can have a down shaft into the drive leg you made and thus having the prop underneath your seat area.... I am thinking in a more 'overall' usage, not top speeds but good speeds for an fittness tool, less maintenance, no grease, userfriendly. Would a 'gearbox' like a bycicle Shimano 8 speed unit be any beneficial by the way on a pedal boat ? And.... one could the incorporate an small electric motor in that hub (250 Watt).... so you have hybrid human power !
  9. ASM
    Joined: Sep 2005
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    ASM Senior Member

    See attached sketch what I mean...

    Attached Files:

  10. Guest625101138

    Guest625101138 Previous Member

    I looked at the cycle gear drive a while ago and cannot recall what turned me off it. Maybe the ratio at the cranks was not high enough!

    One of the things I like is to readily inspect the prop. This means having it beside the hull so it is easily visible or in a lift-out well. These are the two ideas I pursue now.

    Generally gearing is not required but if you are pushing strong winds or have had a long hard day there is some advantage in altering gearing. If you spin fast, say around 90rpm with standard cranks, then you work less efficiently aerobically but the leg muscles last longer. You find most long distance cyclist spin around the 90rpm. I personally like 75 to 80rpm but start to taper after about 4 hours due to muscles giving out.
    Kirk likes this.
  11. Guest625101138

    Guest625101138 Previous Member

    Every gear and bearing comes at a cost in terms of both dollars and losses. I try to keep the component count low.
  12. kayakn
    Joined: Feb 2008
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    Location: Virginia

    kayakn Junior Member

    do a google search for the "decavitator", i am looking forward to building one before the next 4th of july. it goes 19 knots and is powered by a bicycle and an airplane propeller on a catamaran hull.
    Kirk likes this.
  13. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I like the trailing (somewhat freely) hanging long shaft as in your boat. However - isn't even slight shaft angle a big problem for efficiency loss and vibration with hi aspect props?

    It would seem that horizontal shaft would be quite important
  14. Guest625101138

    Guest625101138 Previous Member

    The prop is self stabilising it just aligns itself perpendicular to the flow so it is always at peak efficiency and no induced vibration due to misalignment. The shaft curves and is spring steel so there are no losses in the shaft.

    The attached video shows an unsupported prop as the boat turns. Watch for the silver flashes of the blades toward the back of the boat. You can see how it moves in and out from the hull to align with the flow. It does this in the vertical direction as well. As soon as the prop starts to turn it lifts to align itself.

    I have not found anyone who believes this unless they actually see it. Hard to believe a 1/4" unsupported shaft can swing a 14" prop pushing a 24ft boat at 10 knots.

    Attached Files:

  15. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Thanks for starting a very interesting thread.

    Of course, the design of the hull will depend a lot on the type of race. In a simple endurance race where steady speed is the key, one type of hull will be optimal. In a Tour de France type of event, with long steady periods punctuated by sprints, a different hull might be preferable.

    The attached graphs show the predicted squat and resistance of two rowing shells (lightweight men single sculls): total displacement approx 87kgs; length approx 8.0m, draft approx 0.09m.

    The resistance coefficients are non-dimensionalised using the 2/3 power of displacement volume: e.g.

    C_W = R_W/[1/2 rho U^2 D^(2/3)].

    where R_W is the wave resistance (in Newtons), D is the displacement volume (m^3), U is the hull speed (in m/sec), and rho is the density of water (1000 kg/m^3).

    The graph of squat shows the movement of the bow and the stern for the two hulls. In the graph, dzb is the change in position of the bow: dzs is the same for the stern. Positive values mean the bow (or stern) rises out of the water.

    It can be seen that Hull 2 trims much more than Hull 1 for speeds greater than about 3 m/sec, i.e. the bow rises further out of the water, and the stern digs in deeper.

    The effect of squat on the displacement of the two candidate hulls is shown in the bottom plot of Figure 1. (The graph shows the ratio of the dynamic displacement to the static value.)

    Here it can be seen that the dynamic displacement of Hull 2 is about 9% greater than the static value at speeds of about 4 m/sec. Therefore, if designing for speeds of around 4 m/sec, it might be worthwhile using a displacement that is a little larger than the static value. Once over the hump speed, the (dynamic) displacement starts decreasing again.

    The effect of squat on resistance components is shown in Figure 2. The thin curves are for the hulls in their static attitude. The thick lines are for the hulls in their squatted attitudes.

    At speeds of about 4m/sec the differences between predictions of total resistance, with and without squat, are about 3.5%.

    Do you have the offsets and principal dimensions of a representative hull that we can use for benchmarking purposes? Or are there just too many different types? (I'm not that interested in the sidehulls of multihulls at the moment. Ideally, they should only come into play when the vessel heels.)

    All the best,
    Last edited: Mar 27, 2015
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