Hi Tyson,

Sorry, but at the risk of upsetting your well-laid plans, you could try thinking outside the box altogether.

The rudder, as you pointed out, is designed for water and doesn't work well in sand. Unfortunately, the same can be said for the trimaran shape.

A keel is 'not a good idea' for desert travel - as you have found, it simply digs in and creates excessive friction and steering problems. A flat-bottomed vessel, unstable at sea, is much better suited to sand as it reduces the 'ground pressure' and may even allow a rudder to work.

Of course, a totally flat structure may find its corners digging into dunes, so a saucer bottom would be an obvious modification. A pair of outriggers that prevent the craft tipping, but are not normally in contact with the ground may retain a semblance of the trimaran shape, but that's as close as I can get.

Neon Knight is right; think snow - thick viscous snow.

Hope that helps.