Originally Posted by Glsawyer
Any ideas on rang? Fuel usage? Cruising speed?
Nope. But I can make some guesses based on having a semi displacement twin engine 42 ft boat powered by Cat 3208 NA
42í hull speed for a displacement hull should be about 8.7. The Sunnfjord being a work boat hull is most likely semi displacement. I have found that as I approach displacement hull speed in my semi displacement hull a large bow wave and wake start to form. I doubt this is a very efficient speed to cruise at. So I back it off a bit to where the hull seems to slip through the water better.
you have a SD hull. And IF
it is similar to mine. And IF
your 3208s are NA. Then you MIGHT
get similar fuel efficiency. For my current boat thatís about 1.1 to 1.2 nautical miles per gallon.
Range will be dependent upon real fuel capacity less desired reserve multiplied by real NMPG.
For my comfort and safety when cruising the remote areas I want a reserve of 30%. Fueling options can be far apart and a lot can happen before I get there.
I carry 500 gal less a 30% reserve = 350 gal burnable
350 X 1.1 (the lower NMPG #) = 385 nautical miles
If I were comfortable with a more commonly used 10% reserve and use the higher 1.2 NMPG that works out to 540 nautical miles.
Of course you can throw this all overboard if your 3208s are T or TA. Or if your hull is more efficient at higher speeds.
Now comes the care and feeding of your 3208s. There are a lot of opinions on the subject ranging from run Ďem hard and hot all the time to take it easy on the old kitty cats. I cruise 1600 RPM. I and the boat would like 1400 RPM better but I donít think Iím working them hard enough. 1600 RPM it is with 10 Ė 20 min a day at 2000. That said Iím over propped.
There you have it. A bunch of assumptions and guess work. The only real way to know is to get out there and use the boat.
One more data point for you. I can touch 12 kts at WOT. I can't say with any certainty but I'm guessing fuel burn at that speed is 25 GPH. That's an expensive ride at today's fuel prices.