rider mass placement on kayak

Discussion in 'Boat Design' started by nwahs, Sep 14, 2011.

  1. nwahs
    Joined: Sep 2011
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    nwahs Junior Member

    greetings

    wanted to start new question, thinking to build a kayak.
    what are oppionion onto position on rider placement. (flat water speed crusier)

    did an exp and found my mass centeline, in sitting position arms resting with paddle to be aprox 31 inch rear or the soles of me feet, or even with the front vertical plane of stomach, chest ect.

    how ever i was thinking that rider placement should most likely be moved rearward slightly due to max power of stroke force being forward of the user.
    plus maybe a slight leaning forward could tend to plowing motion in the front.

    to far rearward, may lead to boat bob motion wasted energy picking the boat up.

    can try to build in some cockpit adjustment , but id like a good close place to start and fine tune from there

    no cargo, wave surfing, white cap consdierations, just calm water.


    any ideas, thx shawn
     
  2. cthippo
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    cthippo Senior Member

    Honest answer is it probably doesn't matter. Anywhere within, say, 6" aft of CG of the boat is fine.
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    on my old Aquaterra Prism I'd sit back up on rear deck

    just aft of the seat for different paddling angle, and on my knees "Indian Style".

    Both seemed fine, and really helped ease the bones and muscles on long paddles.

    I'd include that in any kayak design, SOT or covered. Yes, I think it would work in most covered designs without much tweaking.
     
  4. Petros
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    Petros Senior Member

    I have built 12 kayaks of various designs, mostly skin-on-frame, and have paddled over a 100 different types. The traditional way of positioning the cg is to place it half way between the bow and the stern. Everything time I have deviated from this I have ended up relocating the seating position.

    There are all kinds of arguments for "fish form" or "swede form" hulls, but it does not really matter, the length to width ratio is so large compared to most hulls where the max beam occurs is not that sensitive. It seems to me to works best when the max beam occurs at your CG location, which should be half way between the bow and the stern. The only time I have deviated from that is in building a two man kayak and the two paddlers had very different weight, so I would bias the max beam point toward the heavier rear paddler.

    Some books btw recommend locating your CG by sitting on a plank in your paddling position, and put a dowel under the plank on a hard floor. The balance point is your CG. It usually end up about where your belly button is located (which is a good rule of thumb for planning out the hull design).

    With the paddler at about the center of the length you will also reduce the tendency to weather cock in cross winds. This can be a real annoyance if you are trying to go fast. There are no benefits to putting the paddler's weight towards the front or the rear, so I recommend you put it right in the middle of the length.

    Good luck with it.
     
  5. nwahs
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    nwahs Junior Member

    thx for the ideas!
     
  6. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Petros, how do you find Center of Buoyancy to go with that?

    I'm thinking you'd need to get in the boat in water and scoot back and forth until it floats level.
    .
     
  7. Petros
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    Petros Senior Member

    traditional boat building, including kayaks, did not have any fancy way other than to "eyeball" it. But yes, the fine tuning is done by scooting forward and back once you get it in the water. With skin-on-frame you can wrap the frame with sheet plastic and duck tape and go paddle it to see how it floats, it is simple to make changes to the frame before the skin is installed. Typically the skin is the most expensive part, so the plastic test wrap is always important to do before you finish a new design.
     
  8. Poida
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    Poida Senior Member

    I have a Mission SOT, it is a double kayak and single kayak. Using it as a single kayak you can sit in the centre.

    However in calm water, I find sitting in the rear seat lifts the front of the kayak out of the water and seems easier to paddle, and I guess because of the drag.

    It is also easier to steer as it swivels on the rear end, quite handy when I am negotiating narrow waterways.
     
  9. LP
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    LP Flying Boatman

    My current designs have me putting my CG 10" forward of the seatback. My latest design has the CoB 6" aft of midships on a 13.5' kayak. The seatback is 10" aft of the CoB. The above water profile has more area forward and I anticipate a tendency to go off of the wind rather than weathervane into it. Others have said this is preferably. Even with CoB at midships and the paddler seated accordingly, there should still be a tendency to go off the wind as the forward profile also tends to be higher. Placing the paddler at max beam helps with paddling as the hull narrows immediately forward and aids in paddle placement.
     

  10. Easy Rider
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    Easy Rider Senior Member

    Pteros,
    I can't imagine how a Swede Form or Fish Form hull would'nt affect the CG requirement. The long straight keels of most kayaks certainly would help. I bow to your experience though. I remember the Bros brothers kayaks (Mariners) and they had a sliding seat to be adjusted while paddling to trim the boat for beam winds and tracking. Did any other kayak manufacturers follow suit?
     
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