Thanks for all the info Guys, much appreciated, nice to know it's all working as expected. I'll certainly try running around 16-17knots and see how that goes.
One further question, according to Volvo the top power is at 3,900 RPM, in the full speed sea trial the motor was turning over at 4,200 RPM (22.4knots), would that mean a different steeper cut prop could improve performance and reduce fuel?
I agree with the comment about her being very seaworthy, we went through some 'interesting' seas around the Eddystone lighthouse and on the approach to Padstow and she handled it all with aplomb. We would have liked a hyperspeed mode for the wipers as it was only after the 3rd stroke we could 'sea' anything.
The only thing she doesn't seem to handle too well is a big sea coming from a rear quarter side running about boat speed. She tends to want to turn beam on to the sea then, and did so once, unfortunately we were just off the Skerries at the time so heading straight with the sea was not an option due to the rocks.... Rapid work with the wheel was required. Anyhow it's just a very clear memory now!