new kayak design took first place London Boat Show 2008

Discussion in 'Boat Design' started by john zimmerlee, May 1, 2008.

  1. john zimmerlee
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    Location: Atlanta GA

    john zimmerlee Junior Member

    Now that I've won the concept award, I need help cleaning up the design of Stream Dancer.

    This hands-free electric powered fishing kayak is controlled solely by your feet and operates in 6 inches of water without harming fragile underwater environments. Each heel rests in a sliding foot control which has linear potentiometers inputting pulse width modulation speed controllers which vary power to each of two submersible motors on either side of the kayak's centerline. The motors drive augers instead of props for less cavitation and stronger bite in the water, resulting in powerful turns and quick change in direction.

    Stream Dancer's hull is now 10 ft long and about 38" wide. It's currently a tri-hull in the middle and kayak-like at each end. It seems to plough at high speed which leads me to believe I'm overspeeding the hull's max speed.

    Should I make Stream Dancer's hull longer or modify to a blend of a planing hull? Any hints or software out there?

    The augers are simple (no cupping) for equal performance forward and backward, but I'm challenged as to diameter and pitch for the 30 amp 12 volt motors i'm using.

    The project can be seen at www.streamdancer.com

    Four major kayak manufacturers have expressed interest but none can take on a new project this year. Guess I'm on my own to figure this out.

    Appreciate your help,

    John Zimmerlee
    770-565-4420
     
    Last edited: May 1, 2008
  2. kach22i
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    kach22i Architect

    I seem to recall the plough in the rapids video last year.

    Are you sure other Kayaks don't do this as well?

    I mean most of them have generous splash/spray aprons don't they?

    Sample - collar type:
    http://www.adventuresuppliesuk.com/boats_canoes.html
    [​IMG]

    How about adding a raise ridge to deflect water off the top of the bow and around the seated opening?

    On a building an architect would call this a rain diverter, it's found over entry doors where there is no gable peak roof or gutter.
     
  3. john zimmerlee
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    john zimmerlee Junior Member

    As a kayak or canoe breaks through waves, the bow splashes or goes through them creating drag and/or taking on water in the cockpit.

    Under power, a displacement hull will reach max hull speed, then create waves which create a hill in front of the boat . . . ploughing.

    I'm not worried so much about taking on water as I am cleaning up the efficiency of the hull to conserve battery power.

    John
    Stream Dancer
     
  4. Guest625101138

    Guest625101138 Previous Member

    The narrower you can make the middle portion of the hull the better it will perform at speed. You need to consider it as a trimaran with the central hull supporting most of the load and the outboard extensions normally just skimming the water until the hull rolls.

    I cannot recall how the motors are mounted but they may need to be altered to work with a revised hull as suggested.

    If you make the central hull say 10 inches wide and maybe 6 inches deep then it will have less drag at 5kts. Hull speed is still a constraint but it has much less influence on a narrower hull. If your target is 5kts then you need to be thinking around 15ft to get the best efficiency. Coming down to 10ft you will be getting inefficient above 4kts but impact is less adverse with the narrow middle hull.

    The attached image shows a hull that is 8" wide and sits 8" deep when normally loaded. It is 12ft long. It requires 120W to do 8kph (5mph). Wave drag starts to build up over 12kph but it is reasonable up to the point.

    This is the sort of central hull that will reduce drag and will not push as much water. You need to then mount the wing hulls so they just sit on the water with "normal" load. The wing hulls are best if they are say 4" wide and quite long so they give reasonable buoyancy without too much immersion. You want good roll stiffness.

    It is possible to do proper analysis but it takes a bit of effort.

    By the way congratulations on the award. You have done extremely well to get it to work with such shallow draft.

    Rick W.
     

    Attached Files:

  5. john zimmerlee
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    john zimmerlee Junior Member

    Thanks, Rick!

    I've been thinking of a tri-hull . . . like the hulls on a Hobie Cat . . . long, skinny, and rockered . . . with a chair on top.

    Two problems:
    (1) Fishermen need a floor to stand on and to drop things in.
    (2) The augers need a surface over them to prevent cavitation/ventilation.

    Now, I'm thinking just two hulls 4" wide and 36" apart, maybe 8 feet long . . . with a tray and seat above. The hulls would have a shield attached to the inside wall to cover the augers at 6 inch depth. The shield would be strong enough to place the fisherman's foot on top, so that he may stand with feet at the waterline.

    What do you think?

    John
    Stream Dancer
     
  6. kach22i
    Joined: Feb 2005
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    Location: Michigan

    kach22i Architect

    Always leave something for a "new and improved" second generation model.

    No boat is perfect.
     
  7. Chris Ostlind

    Chris Ostlind Previous Member

    Hi John,

    Rick W. is correct that skinnier hulls are generally faster. There are some caveats, however, and they play directly into what you are doing with your boat design.

    For fishing in the areas you have intended, a boat with shallow draft and a short turning radius (as in turn nearly in its own length) will work best. Unfortunately, this plays directly to a minimized hull speed as you will be pushing a large frontal wave with a wide, flat, shallow hull. I don't see your boat doing enough speed to get it up on plane and I do not see that as an enhancement, in any event.

    As with anything in boat design, you typically have to give something away in order to get the things that are most important to the overall design goals.

    I would suggest that you make a very tight list of the design elements of the boat and list them in order of importance. I'm betting that top end speed is not one of the higher elements in the discussion.

    If you do want to produce a boat that will move along at a good clip, then you’ll likely have to give away the maneuverability, or the shallow draft, or both, in order to get there.

    I think you could take your boat out to a foot or two longer without messing with the turning ability and this will allow the main hull to be skinnier to some degree. The real trick is to balance the buoyancy of the main hull with the smaller flotation of the "amas", such as they are in the current design.

    You could end up with a skinnier main hull, a pair of "outrigger" type hulls to the sides which are shaped and positioned for best purpose and still get the boat you describe on your web pages that has the turning responsiveness and shallow draft you seek. The result will be an improvement in speed overall with but a small compromise in the handling and utility.

    At least, that's how I see it. Others may disagree.

    This is a very tough design application with all the elements you seek being pulled into one package, so take your time and don't rush the solution. You already have a very interesting boat there, so marginal changes should be fairly easy to implement without destroying the present purpose and form.


    Chris Ostlind
     
  8. Guest625101138

    Guest625101138 Previous Member

    John
    I was not thinking of anything very different from what you already have. Make the centre hull narrower, deeper and longer. Lift the bridge to the side hulls higher. You can then put the augers inside tubes below the outer hulls or partially incorporated in these hulls. In fact I expect you would get better efficiency from a vaned prop in a tube but it would be more inclined to foul with weed.

    The boat would look very similar to what you have now above the waterline but somewhat different below.

    The tri will perform better than a cat if length of the main hull is over 10ft and the target is 5kts.

    As Chris points out there are compromises. The most efficient hull with respect to power consumption will not turn the best.

    If you post more detail on the weight and shape of the bottom of the existing hull I will compare a tri with overall beam of 3ft and the cat you describe aganst your existing hull. You need to nominate maximum length and desired speed.

    Rick W.
     
  9. john zimmerlee
    Joined: Apr 2006
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    john zimmerlee Junior Member

    Rick,

    The current hull is different from the website. It now has sides that come down below the bottom of the augers. The center section is now a "V" hull with the bottom of the "V" at the same level as the sides. "V" is rounded at bottom and spreads to about 20 inches wide at a height 6" above the bottom.

    I have photos, but can't figure out how to attach here. If you provide email address, I'll send them.

    Turning is important. Speed is not as important as efficiency. Don't need to go faster than 6 mph.
    If augers and motors can come off easily, the bare hull needs to be less than 65 lbs for car-topping.
    Prefer not to get much longer than 10 ft for maneuvering and man-handling out of the water.

    John
    Stream Dancer
     
    Last edited: May 2, 2008
  10. Guest625101138

    Guest625101138 Previous Member

    John
    I have attached a screen image of the reply window. If you place the curser over the paper clip icon then left click you get a new window that allows you to choose/select and upload files. Just select the photo from your computer file and upload. When you submit the reply it will have the photo shown reduced below the post. By clicking on the image it will come full size.

    You can preview the post to see how the image looks when posted.

    My email is given in my member detail. It is:
    rickwill@bigpond.net.au

    Rick W.
     

    Attached Files:

  11. kengrome
    Joined: Jul 2006
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    kengrome Senior Member

    Hi John,

    Whatever you do, be sure to keep your original design on the market, and add this "new and improved" design as a second model. There are all kinds of buyers out there, and some of them won't be interested in your 'improvements' because they will find the original model better suited to their needs.

    Well ... you could deal with this issue simply by using smaller or slower turning motors. Then the boat won't plow because its motors won't try to push it past hull speed. You'll probably get longer battery life out of it too. What percentage of buyers mention higher speeds as a desirable improvement? What other things do they talk about that are more important than higher speeds?

    I's never going to be a planing boat. I think what you really need for more speed is additional length and an optimized hull form ...

    Your idea of making it into a catamaran is good because it means each hull can be narrower, thus the overall resistance should be less. You'll need more than 4 inches of width though, unless you give up the shallow draft. Isn't shallow draft more important than speed to your buyers?

    Or how about going with three hulls all the same size? I'm just guessing here, and Rick will know more about this than me, but since narrow hulls are the key to efficiency maybe three hulls -- each 10 feet long -- will come close to the same efficiency as one hull 30 foot hull of the same very narrow width?
     
  12. Guest625101138

    Guest625101138 Previous Member

    John
    I have attached two images of what I regard as easily driven for 5kts. The main hull is 4m long.

    This boat will achieve 5kts efficiently with all up displacement of 120kg. It requires 50W at each motor to do it. The prop shrouds shown have a diameter of 120mm and will give around 81% efficiency spinning at 2800rpm. The best prop speed for 120mm is 1400rpm but the motor will not give 50W on 12V.

    I am reasonably confident shrouded props will be more efficient than augers and I believe you could make then work reasonably well in weed. They would need some sort of faired screen if weed was really bad. Such a screen would also provide an effective guard. It would add a little drag but it would not take much weed to add a lot of power demand.

    A couple of motors like the D8095 would do the job:
    http://www.transmotec.com/PDF/Catalogues/Motors_DC_Catalogue_25W-500W.pdf
    Say the 24V motor will give 50W at around 80% efficiency. This should be big enough. Other option is to look at scooter motors but they are a bit big.

    I would use an 8mm curved aluminium shaft with the motor mounted inside the stern of each outrigger. The prop shaft would be carried on two water lubricated acetal bearings with glass balls.

    Rick
     

    Attached Files:

  13. kengrome
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    kengrome Senior Member

    Rick, what do you think of three identical slim hulls each 10' long and all submerged the same depth and therefore all supporting the same amount of weight? In terms of propulsion efficiency, would something like this come close to one 30' hull of the same width?
     
  14. Guest625101138

    Guest625101138 Previous Member

    Ken
    Unless you intend to go well in excess of hull speed then the wetted surface of three hulls kills it.

    If you operate around hull speed then a single hull will be the best. That is why I chose 4m because the hull speed is 4.85kts so wave drag is just starting to kick in.

    You only get an advantage with the really narrow hulls if you want to go faster than 5kts or 13ft is just too long.

    Three hulls beside each other is quite different from one long hull of the same beam. You can think about it as each successive hull is drafting the leading hull. The rear one gets sucked along with the one in front benefiting from the moving boundary layer and the fact that the water is being pushed apart only once rather than three times. Hence you can have a longer bow and stern taper on the longer hull compared with the three shorter hulls.

    Rick W.
     

  15. kengrome
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    kengrome Senior Member

    Thanks for your insights Rick.

    In terms of John's goals here, I think he wants to keep the boat as short as possible. My thought was simply that three super-slim hulls carrying the weight equally might be better than two moderately slim hulls carrying the weight equally. If this is not the case then I guess the wetted surface of the three hulls drags more than the extra width and depth of only two hulls the same length.

    This is a very good explanation for why three short hulls of the same beam won't come close to the performance of a triple-length single hull, thanks!

    I think John's customers are more interested in foot control than speed anyways. In fact, I think a plain old garvey or john boat hull would be a winner with his drive system in it!

    :)
     
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