: Awhile back someone on one of the 'yah forums was making custom fit
: fiberglass seats. They'd sit in a box of sand to make a mold, pour in some
: plaster or something to fill the hollow of the mold, seal and make a seat
: from the resulting plaster form that fit the individual exactly.

: 2 part urethane foam would make a nice form for the seatpan as well if you're
: careful not to get wrinkles in the bag. I'd brace it somehow with metal
: mesh of some sort as well.

There was a thread last year on this topic. Paul Jacobson had a great post which I've copied here:
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Making a mold for a kayak seat is as simple as adding water and sitting down.

For a mold material you can use the expanding foams, but they are rather expensive, and get uncomfortably warm as they set up. There are cheaper alternatives. The one I suggest most often is what I call the Chicago Swimsuit: Concrete. A bag of Sackrete sand mix is about $3 at your local hardware homecenter. A plastic garbage bag is a few pennies.

Place the open garbage bag on the ground, mix up a fairly dry batch of sand mix concrete (don't add too much water, jsut enough to barely dampen the mix) and dump about 30 pounds of it into the plastic bag. Remove the air from the bag and use a metal twister to close the bag.Then sit on the bag. Wriggle around a bit, and stand up.

Now leave the bag alone for a day or two while the concrete hardens, giving you a perfect impression of your butt, and providing a fine base for laying up a plastic seat which matches your anatomy better than any storebought seat ever could.

If you want a mold which also matches the bottom lines of your kayak, just set the boat on a firm surface, put the plastic bag in the boat, add about 20 pounds of sand mix to the bag, and sit down for a few seconds.

Let the concrete mold harden and dry, then apply scraps of fiberglass cloth or tape saturated with resin. apply it so the cloth is 2 to 4 layers thick. Let that harden for a day and remove it from the concrete. Now clean the back of this and try placing it in your boat. Trim any overhanging glass and resin while it is still "green". If you overtrim, don't worry.

Add more glass cloth scraps to the back until you are happy with the strength of the seat. At this time you can also fix any overtrims. If you want, you can stuff foam rubber or minicell under the seat, too.

A few fill coats on the surface to conceal the weave of the cloth and you are done.

It goes faster than it sounds, and it is easier than you think.

Just ask those who have done it!

PGJ
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Jim