Thanks blackrose (and Mrsmelly),
Thats pretty much what the builder said, standard was 20mm and for a bit extra we are going to have 40mm, so flush with the baton or there abouts.
I figure that this is the only time to do this part so worth a little extra to make her as efficient as possible.
Now, back to the stove,, I saw another thread on here today about stoves-R-us doing a great deal on a Morso Squirrel, so going to check that out.
With regards to the output of stoves, do you do the calculation on the whole internal size of the boat, or just the living area?
Thanks all & many many more questions (probqably some silly) to come!