Hi Guys
Can I thank you all for the valuable advice given, really glad to hear that it is more fuel efficient on the plane, although not full revs. I like the idea of the thirds rule , it really make good sense and the guide of 1ltr per mile also gives me a good starting point.
My boat is a Fjordling 17HT very similar to look at to the Shetland micro plus, although this is a mature boat it is still produced in Norway by Fjord.
It has an unusual feature of being able to take on water in a specially constructed lower hull to aid stabilty at rest, so they say, but have not used the boat yet to confirm it.
Thanks again
Dave