If you had a very efficient hull, a big prop, no bridge, and a light weight basic 42', you may be able get fairly close to 1 nmpg at a 16- 18 knot cruise, but I think everything would have to be working in your favor to even get close. Sounds like the #'s you quoted for the 42' H&H are probably typical and what you could expect for most 42' boats.Any downeast boats in the 42' size get this mpg #'s?
I must say, those are impressive performance numbers for a 430hp engine in a large 42' boat. Must be a light boat and a good running engine. I was comparing the torque curves of the Diamond 430hp vs. the new QSC 500hp, and the QSC has a much more robust torque curve, peaks at 1,327 ft/lbs. The 430hp Diamond peaks at 1,029 ft/lbs. As I said before, keep the boat light and simple, install a lighter weight 500hp engine like a 9 liter or QSC, 2.5 reduction, big prop, and that will be the most efficient combo possible in a 42' boat imo. And with a 500hp engine, you should be able to beat Sockeye's numbers in speed.430 american, 450 metric. Same engine