Pedal Powered Boats

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

  1. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 59, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member

    The drill right angle 'box I broke had internal shafts that were about 3/16" to 1/4" diameter where the bevel gears fitted, with pins that were only around 1/16" in diameter. I reckon it'd be tough trying to get bigger pins into such a small shaft, although maybe they could be increased to maybe 3/32" or 1/8" maybe. Still not very big if it's driving a big prop at low rpm, IMHO.

    Rick's using rectangular hulls because their easier to build, I believe, and the penalty for the sort of very narrow beam, pretty long, hulls he's making doesn't seem to be that significant I guess. The thing that bothers me about the design Andreas has posted is all that wetted area under the flat part of the hull. I believe that's going to add a lot of drag and result in a hull that will take a fair bit of power to move at anything other than very slow speed.
     
  2. Submarine Tom

    Submarine Tom Previous Member

    I understand. Thanks for clarifying.

    I was under the impression that Rick found the "square" hulls lower drag than round. I know he did extensive hull testing but perhaps he was willing to accept the marginal gains for ease of construction.

    The square vs round has been a hot topic on other threads of late, just wanted to query.

    Thanks again.

    -Tom
     
  3. I57
    Joined: Feb 2008
    Posts: 172
    Likes: 6, Points: 0, Legacy Rep: 62
    Location: Melbourne, Australia

    I57 Senior Member

    Hull Shape

    Ricks V14 & V15 boats have square sections for ease of construction. He is able to make the boats very light as the design simplifies construction. His latest boat has an all up weght of about 20kg, this includes drive and outriggers. I am currently building a boat to Ricks V15 design, the reason is speed. I have designed and built my own boats but have only achieved 14kph in a sprint.
    Greg K ( I can't spell his surname ) from Canada who did the world 24hr distance record used a boat designed by Rick. The hull had a rounded section and was about 8m long. This was a boat which was optimised for maximum speed and a lot of time and effort was put into it. Yes the rounded section is the best but comparing square vs round the differences for these type of boats is small.

    Ian
     

    Attached Files:

  4. Submarine Tom

    Submarine Tom Previous Member

    Thanks I57!

    -Tom
     
  5. Scheny
    Joined: Feb 2012
    Posts: 72
    Likes: 4, Points: 0, Legacy Rep: 47
    Location: Vienna/Austria

    Scheny Junior Member

    I had a long conversation with Mr. Eder. He confirmed, that the boat will have an increased wetted area (I calculated 145% compared to the minimal possible at same dimensions), but he told me, that the -35% already include the increased wetted area.

    The tank tests have been performed with a boat of 6m length, as far as I can remember, so his own 14m version may have performed a little bit better and my 2.6m version maybe will only have -30% consumption.

    Anyway, you will get all technical data as soon as the prototype is built (and I will publish everything up to the last diagram, there will be no secrets :))



    There are two other designs with a displacement-glider hull I would like to evaluate (with building/testing/planwriting there is no spare time left this year for me). If anyone is interested in building a kayak to be equipped with a Torqeedo Ultralight with following dimensions, he/she can contact me for plans:
    • Length: 3m
    • Width: 0.85m
    • Draft: 0.35m
    • Speed: 10kph (limited by prop)
    • Weight: 25kg (incl. motor)

    Andreas
     
  6. KJL38
    Joined: Jun 2008
    Posts: 91
    Likes: 9, Points: 8, Legacy Rep: 75
    Location: Tasmania

    KJL38 Junior Member

  7. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 59, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member

    I believe the only possible gain can come from reduced wave making drag, but this comes with the big penalty of increased viscous drag from the higher wetted area.

    The design may be of some benefit where power isn't such a major issue, but for a pedal powered boat, where we already know that wetted area is fairly critical when seeking good performance, I can't see this design performing at all well.
     
  8. Scheny
    Joined: Feb 2012
    Posts: 72
    Likes: 4, Points: 0, Legacy Rep: 47
    Location: Vienna/Austria

    Scheny Junior Member

    My reasons for choosing this hullform were following:

    For a boat of 5.5m length, the hull speed is about 7kph. For 2.6m its around 4kph. Will´s boat drives at cadence with a Froude number of 0.45 and 0.68 at max speed. My boat will have a Froude number of 0.66 at cruise speed already (which I calculate as continuous power for 1 hour).

    So, for Froude numbers in the range of 0.5-1.0, this hull is said to have good characteristics. I know, that a sleek hull is better, but I have set the goal to make it as small as just possible (anyone having a long boat knows what I am speaking about).

    Another point is, that concerning skin friction you have not taken into account, that the pressure distribution of this hullform is optimized, so that this will have a decreasing impact on friction. I am not an expert for laminar vs. turbulent flow, but one of the planes I have flown as a commercial pilot used engine nacelles with a special form (looking a little bit like the DG hull), where it is a lot sleeker in the area of the lowest pressure, so that it works, as if it was not there (=> interference drag). I expect something similar from the DG.

    Anyway, if the whole thing turns out not to be working, I will tell you and you will soon find a cheap prototype on ebay. The worst case will be a few hundred Euro spent for nothing. So just cross your thumbs for me.

    Andreas
     
  9. Jeremy Harris
    Joined: Jun 2009
    Posts: 978
    Likes: 59, Points: 28, Legacy Rep: 711
    Location: Salisbury, UK

    Jeremy Harris Senior Member

    You aren't going to be running at Reynolds numbers anywhere close to getting turbulent flow!

    This is why viscous drag is the major part of total drag at these speeds (at 4 kmh viscous drag will be around 95% to 98% of total drag for a 2.6 m hull).

    The concept of "hull speed" (using one of the "rule of thumb" formulas, like 1.4 x sq rt waterline length in ft for the hull speed in kts) breaks down when you have a very light displacement hull, such as you'd want for a pedal powered boat. As others have found, you need to get the lowest displacement you can, together with the lowest possible wetted area, to get the best performance. If you want speed, then the waterline length needs to be increased.

    If you have a high wetted area, then because you don't have much power you probably won't even be able to get to the onset of appreciable wave making drag speed, so optimising the hull design for this at the expense of wetted area doesn't make much sense.

    If you want to be able to do 7 kmh at 2.6 m water line length then you're going to need to get the wetted area down to a level where pedal power will get the boat up to this speed.
     
  10. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Has anyone considered some form of boundary layer control with pedal-powered
    boats?

    It seems to me that while your legs are doing a lot of work, your arms are doing little.
    Could they operate small pumps that suck water from the thick boundary layer near
    the stern and eject it out the back?
     
  11. Dennis A
    Joined: Aug 2009
    Posts: 40
    Likes: 2, Points: 0, Legacy Rep: 47
    Location: Amersham bucks uk

    Dennis A Junior Member

    Angle drive unit

    Thanks for your practical advice , I will just forget that fragile unit. I have in the past noticed that Rick W seams to break angle drive units and suspect that this could be cause by using them as a step up unit so that he does not have to use a chain. This will I think increase the stress as the input revs are reduced by 4 or more.
    Hope to see you at Beale Park this year.

    Dennis A
     
  12. spidennis
    Joined: Feb 2007
    Posts: 519
    Likes: 11, Points: 0, Legacy Rep: 124
    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

    So in looking at my 1:1 model, my prindle16 perhaps I do have enough room to place a seadrive between the hulls when folded? I still don't see how the "flying shaft" type would mount or fit.

    [​IMG]

     
  13. portacruise
    Joined: Jun 2009
    Posts: 1,106
    Likes: 31, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Hi, Dennis:

    Have you thought through and rejected the idea of using socket mounting for the cross beams into the hulls/platform to get your narrow/wide boat configurations? Seems simpler, whether have to carry the beams or even possibly telescope....

    Porta


     
  14. spidennis
    Joined: Feb 2007
    Posts: 519
    Likes: 11, Points: 0, Legacy Rep: 124
    Location: south padre island, texas

    spidennis Chief Sawdust Sweeper

    Porta,

    what do you mean about socket mounting? and Telescoping? seems too "nifty" and prone to jamming.

    I'm not at all worried about the way I'm gonna fold, it's just having the drive positioned so that it can be used either extended or folded.

    I have to fold pretty quickly and while on the water.

    Take for example Randy Smyth here paddling this Sizzor trimaran. Basically I got to do the same thing, but better, thinner, faster, etc. and I'll be going where he won't dare to try, thru the Everglades Wilderness WaterWay and a place called Broad Creek and "The Nightmare". I'll have to dig up that video of that area ......

    [​IMG]

    [​IMG]
     

  15. portacruise
    Joined: Jun 2009
    Posts: 1,106
    Likes: 31, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member


    Hope some of this helps!

    Porta
     
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.