Crusing RPMs on a Cummins 210

[ajgraham@sbcglobal.net]

My boat is a 1990 GB 32 (829) with a Cummins 210. Everyone at the marina has been telling me to cruise at no more than 1,700 RPMs but in the Cummins engine manual the cruising RPM is listed as 2,300. Now I understand at 1,700 I burn about 3 -4 gal. an hour and the manual indicates at 2,300 RPM the burn rate is 10 gal per hour. The manual indicates the top RPM is 2,400 RPM. Any insight is greatly appreciated.