Adjustable Canoe Seat

Discussion in 'Boat Design' started by rwatson, Dec 3, 2007.

  1. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    I thought I might throw this little exercise at some smart designers, as I havnt been able to come up with a totally satisfactory answer.

    The attached illustration shows (clearly I hope) how I have designed a nice contoured seat for a nearly completed Canadian Canoe. The rear of the seat rests on a thick dowel, so that the whole seat can pivot at the front.

    My problem is that I would like the paddler (mainly me) to be able to easily adjust the height of the front of the chair, much like an office chair can be adjusted, with a simple, robust and attractive method that can be attached to the canoe sides made of a 5mm wood and fibreglass.

    I have thought of using some kind of strap that can be hung from the gunnel, adapting some sort of existing yacht fitting, but I just dont feel I have clear and simple answer.

    All suggestions would be very welcome.

    Ray
     

    Attached Files:

  2. Village_Idiot
    Joined: Oct 2007
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    Location: USA

    Village_Idiot Senior Member

    I would suggest a dowel under the front of the seat also, resting on a sort of "gun rack" arangement built onto the inner sides of the canoe. You can use a dowel made of metal (same metal as canoe to reduce corrosion activity), or use metal pins in the ends of a wooden dowel, to make the adjustments of the "gun rack" smaller for finer adjustments in seat height.

    Look at adjustable shelves in bookcases that use pins and holes. You want a heavy-duty version of that type of thing, with a positive locking mechanism (e.g. - dowel rod) to keep the pins from falling out.

    Easy to build, easy to repair.
     
  3. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Thats a good idea alright. I thought I might use a multi-hole arrangement for some kind of metal protrusion (ie stainless steel bolt) and make the holes key-hole shaped, so the head of the bolt drops into the smaller 'groove' rather than an open 'gun rack' shape.
    The 'canoe elves' havnt come around to do all the fiddly measuring and shaping yet, so it looks like I will have to do it all myself.
    Thanks for the idea.
     
  4. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    A 6 inch adjustment range seems a lot; the ange of the seat will vary a lot and be uncomfortable except in the middle, also the CoG will vary changing the stability. It may be difficult to move the front with your weight on the seat. Not intended as criticism, rather as a heads-up of potential problems. If you are content with a couple of inches you can try an eccentric disk on each end and just rotate it to adjust height. changing the cloth tension will also change the height.
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    I wish I had thought of the concentric disk earlier. As it turned out, I went for a fixed setting, so now any adjustments will require a bit of carpentry. It might not be too hard to incorporate a concentric disk in the future.
    6 inches of adjustment isnt very much when the seat is hinged about 18" back from the leading edge, and wont affect the COG as the change in lateral weight will be less than an inch.
    I was anticipating being able to get a fair bit of adjustment so that after an hour or so I can move my weight off the numb bits. The seats are solid, but shaped
    I am maintaining a blog of events at
    au.360.yahoo.com/greenwoodenfish

    so I will be able to test the seats out very soon
     
  6. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    I would suggest you replace the dowel with an aluminum tube of appropriate dimension and wall thickness to save weight. The seat adjustment could be accomplished as follows:
    Harken makes some tiny cam cleats which could be mounted on each gunwale(for two 1/8" dacron lines to pass vertically through). The lines pass through holes at each side of the forward edge of the seat (knotted under seat), and then pass through the two cam cleats (which have a keeper added to them to prevent the rope escaping).
    It's hard to explain these little cam cleats, but small rollers can be added to them to allow a rope to enter or exit at an angle rather than straight on. See their online catalog for specifics on cam cleat options.
    This feature would allow the rope to turn 90 degrees forward after passing through the cleat. The rope, above (and forward of) the cleat is converted to a bungee cord.
    Any weight on the seat defeats the bungee, but if the person holds on to the gunwales and lifts his/her weight, the bungees will pull the seat up to any desired height. To lower, just hook one's thumbs around the ropes, lift one's weight off the seat, and pull inward (sideways relative to the cleats), so that the seat drops to the bottom, after which the seat can be raised to the desired height.
    The whole mechanism should weigh a few ounces.

    Alan
     
  7. rwatson
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    Location: Tasmania,Australia

    rwatson Senior Member

    That was one concept that did sort of make an appearance in my mental list of options, but when I looked over the available fittings in local yachts shops, nothing leapt at me. A strong location to fasten the fitting to was a difficulty on 5mm wood even with a fibreglass covering.
    If the need arises, I will do more work on the concept in the near future
     

  8. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    All I can think of is a gusset stiffening the gunwale at that point---- a 1/4" ply triangle (outer edge curved) tabbed into each side. Any seat support point has to be reinforced.
    The parts needed are in the Harken catalog. I have fitted them myself in the past. I doubt you'll find what you need in stock anywhere but a large retail store.
     
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