Paul. Difficult. A complex craft becomes expensive and tricky to build, there being so many variables. Another aspect may be safety…the octura rubber boat was like a missile, and the boats in that contest were stopped by a large padded mat….. I rather fancy the guide-wire approach, as this gives control and safety without all the gubbins in the boat. How about a different take, such as , simply A rubber band boat, capable of a certain distance/speed, but from then on being judged by its merits…which could be simplicity, style, speed or some novel features? something like specifying home-made 2-blade props only might limit things as well..? I think a limiting simple build may be more popular and attract more entries… length, amount of rubber,1 prop, no gearing…
Ashley