Ken's Kayak Pages

Seat & Seat Back Construction

A few false starts, a lot of suggestions from the KBBS, and a few lessons learned about kayaking comfort
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Seat Construction
finish_23.jpg (58423 bytes) A chunk of Minicell closed-cell foam 16" x 24" x 4" thick is being cut to the hull contours in the cockpit.  I used my Japanese pull-saw to rough trim it, and then sanded it to shape with my trusty ROS and a 40 grit disk.  I used the #6 form as a starting point, and hand fit the taper.
finish_24.jpg (46743 bytes) After the base fit the cockpit properly,  I started carving the seat to fit my bottom . . . I used the ROS again, stopping frequently and then sitting in it to test for comfort.  To maintain a low center of gravity (stability), the foam is only 3/4" thick at its lowest point, where my butt-bone rests.  Minicell foam is crap to work with, it tears and shreds and looks only standoff OK.  I am working on a means of finishing it so it matches the quality of the rest of the kayak.
finish_25.jpg (56982 bytes) I ended up changing the shape of the seat after discussing it with LOTS of member's of Nick's KBBS. Overall dimensions - 16" long x 23" wide x 4" deep. The height above the hull in back is 1/2", at the thighs it is 3".  Deepest part of seat is 12" behind front surface.   Another poster recommended Lycra as a covering, and I found I Cotton-Lycra blend in a great shade of green that I covered the seat with.  I used contact cement and the very stretchy fabric conformed to the contours marvelously.
finish_26.jpg (42199 bytes) To make the seatback, I first cut a piece of spruce to the shape I wanted.  The curve at the rear of the coaming was so close to the curve my wife obtained of my back, using a flexible curve tool, that I simply traced the coaming curve onto the wood.  I then contact cemented more sandable surfboard foam onto either side, and sanded it to shape.  Lastly I stretched kitchen wrap over the foam to act as a release agent, and taped it in place.
finish_27.jpg (52291 bytes) Experiment #1 - I made a sandwich of a layer of 6oz glass, a piece of green felt, and a second layer of 6oz glass. I used a total of 2oz of epoxy. The entire layup was held flat with more kitchen wrap stretched over the surface.  It really doesn't have to be too strong, just reasonably rigid.   When it cures, it will be laminated with thin Minicell foam covered in the Lycra cloth.  This will simply serve as the backbone for the seat back.
finish_28.jpg (53439 bytes) After the seatback form cured, I sliced off a 3/4" piece of Minicell and contact cemented it to the fiberglass form.  This picture is midway through the shaping process.  I have settled on a 40 grit sanding disk as my preferred method of shaping the foam. 
finish_29.jpg (41962 bytes) After shaping the foam to the fiberglass backbone, I covered it with the cotton/Lycra fabric so it matches the seat.  Again, contact cement was used, and the fabric was stretched clear around the fiberglass backbone.  I then trimmed it with a razor blade such that 1/2" overlap was left on the back of the seatback.
finish_30.jpg (55920 bytes) This photo shows the size of the backrest in perspective to the coaming and seat.  The next step is attaching it to the kayak, and I have devised a new approach that I think should work well - - I hope!
finish_31.jpg (47052 bytes) I added 2 cloth covered Minicell "bumpers" and a piece of Velcro to the back of the seat.  In the foreground is a piece of Minicell carved to the seat back contour with Velcro on its front face.   This piece (notice the contact cement on the top surface) will be glued under the deck and serve as the attachment for the seat back.  The seat will make 3-point contact with this block and the coaming via the padded blocks.
finish_32.jpg (41394 bytes) Here is a close up of the Minicell block contact cemented in place.  My thought was that the small area behind the seat can be used for storage and accessed simply by pulling off the backrest.  I will add a safety line to the seat back so it can't be permanently lost if it pops off in adverse conditions.
finish_33.jpg (50789 bytes) The complete seating area with the seatback pressed in place.  The Velcro holds it pretty darn snugly, that was my major concern.   It takes a bit of effort to remove the backrest.
finish_34.jpg (53854 bytes) Another angle of the cockpit.  I might cover the visible portion of the back support with the same cloth as the rest.  Right now it is tan colored vinyl spray (I knew that stuff would come in handy!).
Change of Plans

As nice as it looked, the above solution was not very comfortable, and adjustment was very difficult (reshaping the foam support block).  I decided to switch to a suspended seat back, as shown below.

finish_35.jpg (32755 bytes) I did a fiberglass layup of 4 layers of 6oz cloth over a 10" long x  1" wide x 1/8" thick piece of wood covered with kitchen wrap to produce a channel as shown on the left.  From this I cut 7 strips about 1/2" wide to use as webbing guides, like the one shown on the right side of this picture.
finish_36.jpg (53977 bytes) I used epoxy thickened with milled fiberglass to attach 6 of these guides to the fiberglass back of my seat back.  Lastly, I covered the entire back with a piece of stiff cloth by contact cementing it in place. This was done to make the assembly look good!   I cut slits into the cloth to allow the webbing to pass under the fiberglass guides.  The picture shows 1" nylon webbing temporarily threaded through the guides as it will be used in the final assembly.
finish_39.jpg (43238 bytes) To accomodate the new hanging seat back I shaped and slotted two pieces of spruce to thread the webbing through.  I attached these to the underside along the cockpit coaming using epoxy thickened with milled glass fibers.   I used a generous fillet behind and along the sides for strength.
finish_37.jpg (42921 bytes) The seat back is now hanging in place with more adjustments available to really get the comfort level up. There are two wood blocks attached on either side of the seat with slots in them, to accommodate the nylon webbing that threads through the seat back.  Each strap is independently adjustable to fix the angle of the back.  A third loop of webbing threads from the top to the bottom of the seat back to set its height.

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