thanks guys all good info
ive been using around 10-11l going from berowra boat ramp up to big jims point, back to bar point and then back to the ramp.
which i thought was a bit much, but have only done it twice and am still playing with trim angles (manual trim so not as easy to change and try the difference)
next time will have a gps so i can see what gives the best performance and hopefully best economy