My boat has twin engines, and would cruise at 7.5 knots with just one if it only had one. As it is it will make 6 knots on one engine. When we use our boat speed is not important, I mean it's either slow or slower. 6 knots ain't a bad speed to make if you've got the time. So far I've only used about a thousand gallons of fuel because we've been busy with the refit/rebuild. I have put around 2500 miles on it. I will be adding fuel flow meters soon so I can give more accurate data instead of estimating. I haven't looked up the fuel curve on my engines since we went to the smaller injectors but that helped substantially, with no loss of rpm at the top and a much cleaner burn. This old tub could not utilize 280 h.p. and the subsequent amount of fuel required to produce it, so I adjusted it with injectors and pump pressure until I liked it. Have I mentioned that I really like Detroit Deisels.