ok, after a run to teignmouth this weekend to try out the new prop ,findings were as follows.
Yamaha 90 2 stroke,
peak rpm 5500.... 60 Litres of fuel and one person,( still could not acheive 40 knts even on 20 litres of fuel left) i did speak to prop developments and they recommended a 13.25 x 17 s/s prop!!! is this right ???
13x19 ally 5300 rpm and 39 kts
13x19 S/s 4700 rpm 33.5 kts
13x17 ally 5500 rpm 33 kts,
really would like to reach 41 kts, IS THIS DO-ABLE???
(cos chris's boat is still faster than mine)