Thanks for all the replies, really useful advice and pointers to other information, just what I wanted.
As said this is going to be a longer term project and I will enjoy reading up on the various methods and builds. Obviously I need to produce the drawings before I can start building which is why I need to know/work out what thickness the skin will be.
You are spot on with it being a Fairey Fisherman (though the name of the JPEG should have been a big clue!) and yes the hull being of hot moulded timber as per many of the other Faireys. Reading back I should have said based on a life boat hull rather than just a life boat because as CJ1 says it was conceived as a life boat but was too expensive (cheaper alternatives were taken up) and rather than waste the hull plug they decided to use it as the basis for the Fisherman 27.
Decided to have a go at this because it's a Fairey, plank on frame (new to me) and it's got sails as well as the motor (again new to me) so it ain't going to be a quick job! Wouldn't be surprised if I have to have more than one go at the hull!
Thanks again, Chris