Ratio for peddle power to prop

Discussion in 'Boat Design' started by jmproject, Jun 15, 2016.

  1. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    I am building a pontoon boat and will be peddle powered via a old bike frame and a right angle gear. I hope to make and use the 16 inch props that Rick has given pictures for in this forum. It will be for one person and the pontoons are foam covered in cloth/epoxy. Most of the info that I have used to design the boat has come from this forum. Thanks! Since I don't plan to have multiple gears I need to know the best ratio for the peddle cog to the prop. My right angle gear is 1:1. Would multiple gears be a good addition to the design?
     
  2. whitepointer23

    whitepointer23 Previous Member

    Depends how many skiers you are going to tow. :D
     
  3. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    None. Just using it for pleasure riding
     
  4. Tiny Turnip
    Joined: Mar 2008
    Posts: 666
    Likes: 131, Points: 43, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Hi JM
    the ratio will depend on the size and pitch of the prop, and the level of ability and fitness of the 'engine' but 1:6 pedal : prop is a norm, and would be okay with a 16 inch 2 blade prop, unless the pitch is extreme.
    Many pedal boats use 2 blade model aircraft props.

    Multiple gears are not necessary on a pedal boat; spinning the prop fast at low boat speed will create turbulence rather than drawing the boat forward through the water.

    Experienced cyclists like a cadence of around 90 rpm, casual users more like 60-80 rpm. My pedal catamaran has 2 identical 1:6 seacycle drives, one with a 16" prop, and one with a 12" prop. It is most comfortable if my keen cyclist mate pedals the 12" prop at a higher speed, and unfit me pedals slowly at the 16" prop.
     
  5. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    Thanks for the information. I think I have a choice for a 4:1 sprocket or a 6:1 sprocket. Since we are only fishing and pleasure riding would not the 1:6 be a little difficult with a 16 inch two blade prop. We are not in shape!
     
  6. Tiny Turnip
    Joined: Mar 2008
    Posts: 666
    Likes: 131, Points: 43, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    I would go with 1:6 pedal to prop. You will be pedalling more slowly to maintain a particular prop and boat speed, which will be more comfortable. As you get fitter, you will be able to maintain a higher speed.

    It doesn't help to think about when you are starting off riding a bike, and you use low gears and change up. What happens in practice on the water is you start pedalling at a speed which is comfortable, and keep pedalling at that speed. The prop starts to propel the boat forward, but 'spills' some of the pedalling effort in creating turbulence. (This would be like spinning the wheel on the bike, which is highly unlikely to happen) Gradually the boat speed increases, and the prop works more efficiently; however the resistance to the boat moving through the water is increasing as well. There will come a point when all your pedalling effort is taken in overcoming resistance (wetted surface, wave resistance) and there is no power left over to accelerate the boat; you’ve reached top speed.

    The length, slenderness, shape, weight and windage of your boat design will all have a very significant effect on speed and efficiency.
     
  7. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    Thanks so much tiny turnip. That is great information and makes a lot of sense. I am in the process of designing the pontoons. Some on this forum have said it is best to have long and slinder then some have said to go wide and shorter. I always thought long and slinder made more sense. What do you think. Unfortunately I have found very information on pontoon design unless you are looking at a pontoon platform boat. Any resource would be helpful.
     
  8. Tiny Turnip
    Joined: Mar 2008
    Posts: 666
    Likes: 131, Points: 43, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    *Definitely* go long and slender. As you go longer, the speed at which wave resistance kicks in increases. It's usually the wave resistance that really limits the top speed If I recall correctly, its worth going up to about 24 ft long with human power, before the amount of drag you have from wetted surface counteracts the benefits.

    Here's a link to Rick Willoughby's pages; http://www.rickwill.bigpondhosting.com/ Rick is the op for the pedal powered boats thread, and probably knows as much or more than anyone else on the subject. Check out his V11 for skinniness. The main hull is only 9 inches wide.

    Here's a video of my own boat, based on Dart 18 hulls, built with Rick W's advice. Very happy with it, apart from it being damn heavy, and no fun to pull up the beach.

     
  9. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    RicKS website is very helpful. I sure like the looks of your pontoons. Would it be possible to get some good pictures you your pontoons ,out of the water along with measurements? I think yours would fit my needs.
     
  10. philSweet
    Joined: May 2008
    Posts: 2,298
    Likes: 166, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The limiting factor here will be the torque capacity of the gearbox. Particularly in the event you jam the prop with debris or hit bottom. The higher gearing saves you a lot of weight and expense in the gearbox. Since you already have a 1:1 box, look at big, recumbent bike chain rings such as 78:13 or so. You may have issues with overhung load rating also. So you might want to go even larger, like 90:15. A human can make about as much torque as a small block chevy, and I'm guessing you aren't using a turbo 350 tranny on your boat. Limiting crank length is also worth looking into. Think womens small mountain bike crank.
     
  11. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    The right angle gear was piece of surplus that turned a small seam turbine. It will certainly with stand this kind of torque. Unfortunately it ia 1:1. Thus far I have not been able to find a bike peddle with more than 42 teeth. I know I can get a smaller gear to fit the right angle gear with about 9 teeth. That would give me close to 1:5. Where would I find a gear larger than 42?
     
  12. philSweet
    Joined: May 2008
    Posts: 2,298
    Likes: 166, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Any bike shop, online or store front. You can get rings up to about 100 teeth, but you need to match spiders and offsets. Best to take the crank to a bike shop if you aren't familiar with the stuff. You want to avoid 9 and 10 tooth sprockets if you can. They simply don't work very well. 11 tooth is ok, 12 would be better. On a road bike, you might carry a 10T for occasional downhill blasts, but they wear out very quickly and are hard on the chain as well. You need to look at the overhung load rating of the tranny. There will be a minimum radius that lets you get max torque without an overhung overload. If this tranny was not designed for a sprocket drive, but a shaft input, it might not work well at all. You may need to add an outboard bearing to take the chain load.
     
  13. jmproject
    Joined: Jun 2016
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mechanicsville, VA

    jmproject Junior Member

    Thanks for that info. I did see on Ebay a few 50+ teeth. I think you are right in that the larger the diameter of the sprocket, attached to the right angle gear, the better it would be. I think for the way I want to use this craft, that a 1:5 would be a good ratio sice I will be turning a 16 inch prop. If I used a 52 teeth on the peddle then I could use a 10 or 11 on the small gear. My problem is that I know very little about bike sprockets and chain and do not have a bike shop close enough to visit. Any setups that you might suggest would be very helpful. I am sure I could then buy it on line. Or Find someone to send me the set up for a price(used would be find). I will be needing two of these since I am making two craft.
     

  14. Tiny Turnip
    Joined: Mar 2008
    Posts: 666
    Likes: 131, Points: 43, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Hi JM

    My hulls are from a dart 18 catamaran - the original design. I picked an old one up for £500 including rig and trailer in the UK. I don't know how widespread they are in the states.

    A google image search will yield many pictures of the hulls

    Here are drawings of the hulls :

    [​IMG]

    From a rather good article about the evolution of catamran design:

    http://sailingtrivia.ravenyachts.fr/2013/08/the-evolution-of-sailing-multihulls.html

    A very straightforward rectangular section hull in ply with taped seams will do very well. The length and skinniness are the thing.
     
Loading...
Similar Threads
  1. thenavalarch
    Replies:
    1
    Views:
    326
  2. RyanBravada
    Replies:
    5
    Views:
    661
  3. wesley Sherman
    Replies:
    12
    Views:
    863
  4. thenavalarch
    Replies:
    0
    Views:
    341
  5. mustafaumu sarac
    Replies:
    4
    Views:
    824
  6. misanthropicexplore
    Replies:
    14
    Views:
    1,584
  7. ryanonthebeach
    Replies:
    41
    Views:
    2,648
  8. Ali Golshani
    Replies:
    0
    Views:
    595
  9. ToMeK
    Replies:
    2
    Views:
    798
  10. ElHurrecan
    Replies:
    5
    Views:
    1,811
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.