Pedal Powered Boats

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

  1. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    mono vs cat

    Glen,

    Which is better - an monohull or a cat - Like Ian said, it all depends on how you want to ust the boat. My boat started out as a mono with a single outrigger 8' out from the main hull. http://www.youtube.com/watch?NR=1&v=uAUb47sUdjw That configuration worked nicely and allowed me to position the main hull close to a dock so it is easy for passengers to load/unload. The outrigger has enough bouyancy that I can stand on it without it submerging. The stability comes at a price. The main disadvantage is drag - the additional wetted surface area means more friction. Because the drag is 8' from the center of the main hull it exerts a torque that tends to turn the boat. I went about 65 miles with the boat in that configuration on various boating/camping trips before switching to a stabilized monohull. http://www.youtube.com/watch?v=c_l86SA3i5E I put a video on YouTube because the file is too big for this forum. The boat is very stable. There are 4 of us in the boat plus our food and camping gear. My son is standing up as we get underway and the boat is not rocking. I used a 1/4" stainless steel drive shaft in the first video. The second video shows the carbon fiber drive shaft I made to deliver more power to the prop. The stabilizers are 6" wide and 24' long compared to the main hull which is 2' wide and 28' long. There are two key aspects to the dual stabilizers: 1) the weight of one stabilizer is balanced by the other stabilizer and 2) they are trimmed so that only a small part of the aft section touches in flat water. You can see from the second video that the fore section is up above the water. I have a solo kayak bungeed to each stabilizer to haul them along. When we get to a place that we want to explore in the solo kayaks we launch them from the mother ship like this next video shows. http://www.youtube.com/watch?v=oxwTNn_7OKk You can see how high the fore end of the stabilizers are riding above the water. You can also see how much wake there is from a small recreational kayak carrying one person compared to the mother ship. Toward the end of the video you can see the field expedient repair - I tied 550 cord around the stabilizer because the diagonal strut gave way. Here is a side view (Jr at the pedals) showing how the boat is trimmed with two people and all our camping gear on board. The weight is shifted aft to keep a nose up attitude. I also attached a view facing fore (heading out on a beautiful lake) that shows the trim with 4 people on board. This next photo (no ripple at Mill Creek Falls) shows there is no ripple from the fore end of the stabilzer in flat water. The next photo (outrigger up) shows the same thing. Since I use the boat for touring I added fore and aft holds (Retrieving Lunch from Forward Hold). They are big enough for tents, sleeping bag, small coolers, water bottles, etc.

    Dave
     

    Attached Files:

  2. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    100 miles and still going!

    How long does a drive unit last? Bicycle chains, chain rings, cranks, sprockets, etc. last for 1000s of miles when they are properly maintained. How about your pedal powered boat drive train - can it last 1000 miles? I don't know if mine can so I always take paddles along with us when we head out on the water. We went 28 miles on Lake Jocassee, South Carolina at the beginning of October - the trip that my drive train crossed the 100 mile mark. The picture in my post #1108 on page 74 shows bicycle components (partial frame, bottom bracket, chain ring, cranks, pedals, chain, sprocket) driving a string trimmer gear head. My current gear ratio is 4.75 rotations of an APC20015E prop to one rotation of the cranks. That gear ratio works OK on my 28' boat with 2 to 9 people onboard. So cruising around for 100 miles has worked OK. What about taking it up a notch and going for an all out sprint? We found out when we were 2 miles away from the dock at Lake Jocassee. Check out the "twisted shaft" picture. The twisted piece of metal at the bottom of the picture is the end of a 3/8" stainless steel threaded rod that I ground down to 0.182" square to connect my drive shaft to the string trimmer gear head. During a sprint there was enough torque on the shaft that it exceeded the yield strength of the shaft where it was tapered. At the top of the picture is a Grade 8 3/8" bolt. At the middle of the picture is my improvement - I ground down a Grade 8 bolt to make a tapered section that fits into the coupler in the right side of the picture. I found out that I could go slightly larger (0.205") by angling the corners slightly. The larger area and the higher yield strength steel should be able to handle 5x the torque. I never had that problem before with a 1/4" stainless steel drive shaft because that shaft was too springy. Now that I have a carbon fiber shaft I can deliver way more power to the prop. I am working on other improvements also. I attached a picture "Driveshaft at 33 degrees" showing a severe angle that the carbon fiber shaft makes as it leave the string trimmer gear head. I put it at that angle so the sprocker could be aligned with the bicycle chain ring. When I was using the 1/4" stainless steel shaft it was very flimsy - compliant enough to align with the flow once I got moving. Now with the stiffer carbon fiber shaft I am getting a sidewise force from the shaft deflecting water and a thrust vector since the prop doesn't completely align with with flow. I repositioned the string trimmer gear head to reduce the 33 degrees to 10 degrees and added an idler puller to help twist the chain. The picture "beached rudder & prop" is taken in clear enough water to be able to see the rudder slightly kicked back from hitting the bottom and the prop resting on the bottom. The downward angle is too severe for the carbon fiber shaft. With the 1/4" stainless steel shaft I had to have a strut to keep the shaft down. When I pedal hard the prop would ride up near the surface, ventilate, and I would lose thrust. With the carbon fiber shaft I let the prop be free swimming and it doesn't ride up no matter how hard I pedal. So I reduced the downward angle also. The recumbent seat is also visible in that picture. It is much more comfortable on a long trip than my initial seat shown in post #1108. I like to hang my hydration pack on the back of the seat so I can sip water whenever needed. I attached another picture "rudder recumbent seat drive unit) that gives a closer view of the seat and the rudder fully raised.

    The string trimmer gear head is still working after 100 miles. It was free and already used when I got it off an old broken string trimmer. So I wonder how long it will last. How about angle grinder gears? Does anyone have experience with their longevity in this application? I am looking for a pedal powered drive train that is low price, efficient, light weight, keeps going and going and going . . . In other words it should be like a bicycle - a little bit of maintenance now and then, some adjustments when needed, other than a few flats perhaps - nothing major should wear out or break down for a few 1000 miles.

    Dave
     

    Attached Files:

  3. portacruise
    Joined: Jun 2009
    Posts: 1,475
    Likes: 178, Points: 63, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Coach:

    Thanks for your update and pics! I had some questions/comments on your setup- see the main body of your message.


    Thanks!

    Porta
     
  4. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    carbon fiber drive shaft

    Porta: "Where did you find the carbon fiber shaft (solid or tube?) and what diameter is it? I think you were making a carbon one, last I heard, so what procedure did you use? I am surprised that the APC electric prop has not broken. Rick W. seemed to think that even regular duty gas APC props lost a lot of efficiency because of bending and distortion."


    I started with a 3/8" x 96" pultruded fiberglass rod as form to wrap alternating layers of carbon fiber onto. After 6 layers of CF the outside diameter ended up at 0.642" with 19.9 Nm/Rad compliance. That is stiff enough of a drive shaft with a 4.75 to 1 ratio on a 20x15E prop to give a nice solid feel on the cranks. See the description, diagrams and measurements on page 76 post #1140. Let me know if you have questions, want to see pictures, etc.

    My boat is typically loaded down with people, food, water and camping gear - usually 1000 to 1500 lbs of total displacement. The 20x15E prop seemed to work fine pushing that boat around for the last 35 miles. It has a few minor nicks and scratchs from hitting things underwater but otherwise is holding up OK. The prop cost me about $15 so I decided to give it a try. It should slip less than the 16x16 prop that I was using previously. There are also 26x15E props available but I haven't tried them. The model airplane props are not as efficient as a purpose built prop for a specific speed/RPM/load design point. I'd like to start making my own folding props to gain some efficiency and shed weeds.

    Dave
     
  5. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    Stainless steel drive shaft

    Porta: "I am surprised that 1/4" SS didn't break, even without sprinting. If your design permits, you can use a two piece rigid tube/solid spring flexible steel shaft that is 1/4" electrician's drill shaft at the bottom and it would be considerably stronger."

    I'm guessing that the 16x16 prop was slipping quite a bit and limiting the torque I could apply to the shaft. Now that the carbon fiber shaft is operational the stainless steel shaft is my backup. Paddles are a backup for my backup. :>)

    Dave
     
  6. portacruise
    Joined: Jun 2009
    Posts: 1,475
    Likes: 178, Points: 63, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Thanks, Coach Dave.

    What kind of epoxy did you use and what kind of thinner did you use to get a soak through?

    Porta

     
  7. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    Porta: "What kind of epoxy did you use and what kind of thinner did you use to get a soak through?"

    I am using 635 Thin Epoxy Resin System with 2 to 1 SLOW Epoxy Hardener from http://uscomposites.com/epoxy.html I don't thin it because it is already quite thin. I am usually working with it in hot weather which makes it even thinner. Since I was wetting 4 layers of CF at once I used a metal stud as a trough, put the shaft in a corner of the stud, poured on the epoxy, worked it in with a brush, turned the shaft about 30 degrees, then repeated until it looked like the shaft was thoroughly soaked. Then I slipped on a heat shrink tube. As I heat shrunk the tube excess epoxy squirted out the end. Then I sat the shaft in the Florida sun to "bake". Once it was cured I slit and removed the heat shrink, sanded the shaft, gave it a coat of epoxy then several coats of urethane.

    Dave
     
  8. hpsb
    Joined: Nov 2011
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Nottingham

    hpsb New Member

    Hi,

    I'm part of a team of mechanical engineering students from the University of Nottingham (UK) and we're attempting to design and built a human powered boat.

    We're still in very early stages and I'm very grateful to all those who have posted in this forum as it has already provided us with a huge amount of advice.

    I am currently looking into our options for drive systems and need to be able to justify (preferably quantify) all the design decisions made.

    From what I have read so far, I am leaning toward a twisted chain arrangement, but am struggling to find any data to help me quantify losses associated with twisting the chain. Does anyone know of any sources which might be able to help me with this?

    For interest, we are aiming solely for sprint speed. Our current design thinking is a catamaran driven by two riders, in recumbent position. We will have two hydrofoils, a larger one at the rear and smaller varying pitch foil toward the front. We will have a propeller attached to the rear foil so the drive system for the propeller can be enclosed within a fairing which also supports the foil. We need to try and stay within a budget of £500 for the project.

    Any help or suggestions at all would be greatly appreciated,

    Emily
     
  9. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 60, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Welcome Emily, this sounds like an interesting project. I'm not sure that anyone has accurately quantified the losses from twisted chain drives, but the general consensus seems to be that they are small, probably only slightly higher than a straight chain drive. It helps to use the smallest pitch chain that you can find, but that will still take the drive torque OK. 6mm pitch chain (a bit smaller than the number 25 stuff more common in the US) is very flexible and if it will take the tensile load then would probably be a good choice. It's readily available here in the UK from places that sell parts for robots (try Technobots, they are a good source).

    I'd suggest building a simple test rig to establish the chain losses and look at the effect of different size sprockets. The general principle seems to be to keep the sprocket sizes as small as practical on the twisted part, and keep the distance between the sprockets as great as practicable to minimise twist at each link. A fairly quick and dirty experiment on the bench would give you some solid data to work with.

    One thing's for sure, twisted chains are a lot cheaper than a really efficient gearbox. Cheap gearboxes tend to be a bit lossy, especially at high torque loading, whereas a chain is probably about as efficient a drive as you can get.
     
  10. Tiny Turnip
    Joined: Mar 2008
    Posts: 865
    Likes: 274, Points: 63, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Hi Emily

    I have (commercial, seacycle) twisted chain drives on my catamaran. Jeremy is quite right, the losses are very small, probably the smallest you are likely to get with any transmission.
    I remember Rick Willoughby, the author of this thread, did quote them somewhere.
    The hydrofoil idea will potentially give you the highest speeds, but it will be very demanding of your design, development, and in particular available power (how fit and strong your 'engines' are - I'd guess you would need a couple of competitive club level cyclists at least) and how light you can build.

    For a non foiling design, Rick has clearly demonstrated that a long (7 metreish ) monohull with outriggers is likely to be the fastest solution. The cat layout may be an easier, more stable platform with which to foil, but if you don't have the power to weight ratio to get out of the water, then the outriggered mono is a winner. There is a huge amount of detail on all this on this thread, but wading through it is not for the faint hearted. There's many here better qualified than me to detail the reasons the mono is better than the cat, but I'll have a go if no one else pipes up!

    The fastest pedal powered boat was Decavitator, with an air prop on foils - I expect you know that. (MIT) There has also been a design with two opposing recumbent seats, can't remember if it was a foiler or not.

    Incidentally, there used to be an outfit which would hire out some (rather poorly maintained) seacycle cats quite near you. I'll see if I can recall/dig out where.

    Good luck!

    Adrian
     
  11. Tiny Turnip
    Joined: Mar 2008
    Posts: 865
    Likes: 274, Points: 63, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    I did a little hunt (opening the pedal powered boats thread and using the 'search this thread' button is very helpful) plus some forum searches and found these posts:

    http://www.boatdesign.net/forums/boat-design/twisted-belt-chain-drives-20535.html

    http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-15.html#post240302

    It looks like twisted chain hits about 97% efficiency, compared with 99% for straight chain.

    Decavitator was Mark Drela at MIT.

    I think it was these folk who used to hire seacycles, but they seem to just be advertising waterbikes now:

    http://www.barrowboating.co.uk/small_crafts.php
     
  12. blisspacket
    Joined: Jun 2005
    Posts: 55
    Likes: 1, Points: 8, Legacy Rep: 15
    Location: st augustine

    blisspacket Junior Member

    I'd think it a worthwhile challenge to create the formulae to evaluate hydrofoiled personpower vs. displacement personpower to achieve say 15 knots. While shop time is pure bliss, the engineering discipline demands numbers crunched. Tom Speer, Washington state aeronautical engineer, has messed with foiled cats, I believe. worth searching out.
     
  13. portacruise
    Joined: Jun 2009
    Posts: 1,475
    Likes: 178, Points: 63, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Emily:
    Bob Stuart produced the spinfin a twisted chain drive running in an oil bath for commercial use sometime ago, but it is no longer in production. http://microship.com/bobstuart/spinfin.html You can contact Bob at the hpb website. Since you are only interested in sprint speed and are using 2 motors the chain and assembly may have to be quite rugged. Once cats are on their foils and sprinting, there shouldn't much difference from a mono. Some cats have used inflatable pontoons to lighten the load.

    Hope this helps.

    Porta
     
  14. Coach Dave
    Joined: Jun 2011
    Posts: 70
    Likes: 4, Points: 0, Legacy Rep: 40
    Location: Malabar, FL

    Coach Dave Junior Member

    hpsb

    Hi Emily,

    Since you are looking at the drive train to operate at sprint speed with two cyclists I'd recommend establishing a speed/time/distance goal for your project. Let's say you want to maximize the average speed on a one minute sprint. Characterize your engines on a recumbent exercise bicycle. Measure how many watts your engines (the cyclists) can sustain for 15s, 30s, 60s, 90s and 120s. You can also measure their preferred RPM range at the same time. That test will quantify the speed and torque input to the drive train so you can begin analyzing components under those operating conditions.

    Consider what an "ideal" drive train would do:
    1) Convert 100% of the input power to forward thrust at the design speed
    2) Have zero drag
    3) Has 100% reliability

    At high speeds the drag on underwater appendages become a very significant factor on your overall performance. You will probably want to derive a figure of merit for your candidate drive trains that encompasses drag and efficiency. The efficiency I am talking about here is end-to-end, i.e., output power (thrust times speed) divided by input power. A free swimming flexible driveshaft with the right torsional stiffness looks like a good thing to evaluate along with your other candidates.

    Dave
     

  15. Submarine Tom

    Submarine Tom Previous Member

    I can tell you right now that an elite athlete trained for the task can produce up to 1/2 Hp for about a minute. What you are likely to find is a good athlete can produce 1/4 - 1/3 Hp for a couple of minutes. While your average weekend warrior about 150 watts for five minutes and 100 watts for hours.

    -Tom
     
Loading...
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.