If you mix fixed support with floating, you end up with a couple ramps at some water levels, so you need to plan on some surface treatment for traction. I might try only one fixed end that is hinged, a center float at another hinged junction, and a rolling support on the far end. Hinges are simple with eyebolts and caribiners. Ballast might reduce bouncing at the float, but that is a technique I have not tried.
Cheers, -Hirsch
