Jim,

Not sure about a formula, but I would suggest as a possible formula, 1 inch of seat height add 1 inch of beam. Given the very important effect of hull shape, this may be enough to get you started.

I would seriously take a look at commercial designs and see what the width range is for the long solo designs. It would be difficut to persuade me to build one that is narrower than the narrowest on the market. (Some of the short ones may be wide just to get additional flotation.)

Once you play with such a built boat, you then might want to go into experimentally narrower designs.

As far as height is concerned. All the plastic SOTs I have played with (maybe a half dozen designs) have had the seat and feet above the waterline so that water can drain from these areas with me aboard.

In contrast to the above post, I have found that the back band is Wonderful, compared with sitting on a flat SOF with no back band. Without a backband the thing exhausts me after less than an hour. With the back band, I can paddle for several hours with no problem.

Rick