I have to say, I seem to be getting very good figures too, but if yours is run in, then all the more accurate! My consumption estimates have got a little complicated as I have a fuel leak! The fuel sender at the top of the tank is oozing out fuel at a very fast rate. It's only doing it when the tank is full, but it lost several litres, (estimate) overnight last week! New one in the post I am told!
Before I discovered the problem, I did a trip up the tidal Thames last week from Mortlake, (near Kew) to Gravesend, a total of around 70 miles return according to the GPS. However, it was a good deal further than that over water as apart from the last mile or two, the tide was against me all the way to Gravesend..... and then all the way back again as well! The engine clock showed 5.75 hours had been added and I used 55 - 60 litres to re-fill the tank to the brim.... (and trace the leak!). That comes out at around 10 litres per hour, (leak and all). It was of course only at 8 knots for a small part of the journey and even in the unrestricted part of the Thames I kept to about 20 Knots max... but even so. I am really looking forward to doing a long journey at a sensible cruising speed.
Incidentally what is your top speed and what size prop are you using?
Love to have you join a cross channel trip! Can you make a mid-week?