SOF rolling kayak

Discussion in 'Boat and Accessory Building' started by nootka, Sep 27, 2018.

  1. nootka

    nootka Paddler

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    Has anyone built a skin on frame kayak with a very low back deck?
    1.5" or less rear deck freeboard?

    I've given up on my Tahe Greenland for the strait jacket roll. I suspect 1.5" is too much freeboard for me (the Zegul Greenland lists capacity at 220 pounds).

    Since 1.5 cm appears to be legit, I'd like to try something similar.
    All rolling kayaks must have at least 1.5 centimeters of freeboard, with kayaker seated in kayak.
    http://www.qajaqusa.org/QK/rolls/rolls.html

    And of course the other possibility is beam. My Tahe is hips plus 2 fists, which is wide for a rolling kayak.

    The Tahe is extremely good for rolling; it feels like it wants to come up. It is also a good blend in that it does well for both forward finishing and layback rolls. I'd like a sof that is similarly good at both.

    Advice would be much appreciated.
     
  2. mick_allen

    mick_allen Paddler & Moderator

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    Haven't built one, but:

    It would be based on the balance of the kayak plus your full geared weight [and paddle?] with respect to the volume of your SOF below the surface in sea water. That can be done by hand calculation or most software packages.

    After doing the design and its calculations, as there will be some slightly unpredictable dimensional variation with a built skin on frame boat [because of steambent ribs not being to a perfect predictable designed shape], would you be open to testing and tweaking the framing to get the characteristics you desire?

    If not, then maybe rib laminating might be the best approach [as they'd be more shape predictable], [but would be more work].

    **
    oh yeah, I often thought it would be funny if the reardeck crossbeams were placed at the bottom of the gunwale pieces - or even if they [crossbeams] were bent downward a whole lot, the ckpt rim rear upstand was flexible, and if the reardeck skin [ie the hull skin would be gunwale adhered so the hull was tight] was loose or flexible. The idea would be that when one leaned back you would lay back right into the kayak possibly making it into a rolling demon.
    [ I just can't stop imagining finger rolls, heh heh]
     
  3. nootka

    nootka Paddler

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    I'm in Comox Saturday afternoon. Any locals want to show me their skin on frames?

    Mick, I'll be looking into your suggestions.
    Thanks
     
  4. mick_allen

    mick_allen Paddler & Moderator

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    Another way is to slightly overbuild [with respect to volume] so the sheer-to-waterlevel is higher than minimum, while keeping the crossbeams a little low in the ctr of the frame. Then remove the [temporary] skin and plane or router the gunwales down so that the sheer is juuuuust above the minimum required.
    That might be a simple approach.
     
  5. nootka

    nootka Paddler

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    I like that idea. It's just going to be a rolling kayak so I don't need heavy duty gunwales, was thinking about making them smaller than called for.
    Is there a way of doing a temporary skin that is more robust than a saran wrap?

    EDIT: how about reducing the height of the keelson & chines as well? Or having spacers between ribs & keelson and reducing the spacers.
    That would sink the kayak down a bit.
     
    Last edited: Sep 28, 2018
  6. mick_allen

    mick_allen Paddler & Moderator

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    I think saran wrap is too flimsy for good testing. I have direct knowledge of multiple layers of that direct overwrap lasting for just a minute or two before filling up, heh heh. Maybe plastic vapour wrap and keep the darts nice and flat. I wonder if tyvek [any housewrap] would work? Or how cheap is the lightest possible uncoated polyester?
    It just might be interesting to investigate that plastic coating/wrap that is shrunk around large packaging: i wonder if some warehouse has some scraps one could play around with.

    Or I wonder if the quickest was to use the final hull skin, but adhere it to the side of the gunwales while stapling it on the top. Then run a string of staples on the gunwale side just 1/2" up from the gunwale bottom [for mechanical fastening redundancy of the skin to the side of the gunwales. [This would assume designing so the gunwale sides follow the cross sectional shape [many do inadvertently: but this would be intentional] ].

    and using just about any disposable or cheap plastic or cloth over the deck which would be fairly straightforward because greenland decks are fairly flat other than the ckpt. Then check sheer clearance, remove deck, plane down gunwales, adhere and staple on good skin for the deck - maybe even a few 'decorative' stitches thru the 2 layers overlapping the gunwales: at least the anchoring for the decklines will be in that location - so follow the precedent with the stitching.

    some ideas anyway.

    [I wonder how cheap polyurethane is - what if you made the hull covering using it - or even the whole kayak [it's easy to glue] then cut it off after and then just made an additional aluminum folder frame using the relatively simple yostwerk process. Two identical kayaks - one traditional, one folder- in one fell swoop. Stupid maybe, but possible and doesn't throw material away. ]
     
  7. Roy222

    Roy222 Paddler

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    You need to use caution with any shrink wrap, as it can develop a lot force and not show it until ** CRACK!
    You might try that clear shrink storm window film. The stuff for exterior use is thicker then the interior film.
    The fly in this ointment is the double face tape and its removal when the experiment is done.
    Please have a rescue person stand by if and when you test out any temporary covering.
    Good luck!
     
  8. mick_allen

    mick_allen Paddler & Moderator

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    I don't need heavy duty gunwales, was thinking about making them smaller than called for

    another idea would be to build with small material as you intended but juuuuust err on the side of small boat too. Then after testing, just add a little height to the gunwales. Either way, there's scope . . . and there's nothing better than scope.