Having now had a chance and the conditions to do a V-Max test i can confirm my maximum speed as:
1.87:1 gearbox ratio
Triming out past 30% of the range gave no advantage...just instability.
Using this http://go-fast.com/Prop_Slip_Calculator.htm
and the above figures it seams i have a 20% slip - this seams quite high.
Assuming the 20% slip is true, and will be constant with a prop change, it also seams droping to a 19", at 5750rpm will give me... 46knts, and a much bigger fuel bill.
Am i overlooking anything? Comments appreciated!
I am quite willing to accept that this is as fast as i can go, and i'm very happy with the set-up but
if there's more in her 'capin...