Had a play with an ex RNLI Atlantic 21 a few years ago and that made 32 knots with a pair of 60hp Evinrudes. The wide flat at the base of the V makes a relatively easy hull to propell and the boat is light at approximately 1000kg all up.
Also, these boats are thoroughly developed and tested and the LCG can be put in the right place and so it might be possible.
More power means more weight needs more fuel + more weight + needs more power. Light is fast if you can build it string enough!
Originally posted by Pitkis
Restricted 2x90 hp sounds like too little power for 8,5 metre hull. I'd say something like dual 120-130 hp with restriction might be suitable and give out around 32-34 kn maximum constant speed. I don't believe the RNLI wants 25-30 kn speed from their larger RIBs what would be the case most likely with 2x90 hp restricted...interesting idea though. These are just my opinions, not any official info, but under 100 hp engines sounds like too little power.