Two 8v92TI's on my 60' LOA, 75,000+# Hatteras 56MY . At seven knots, 900-1000 rpm around 7 GPH total , but typically run at 8 or 9 knots, 1300-1500 rpm 10 GPH total. Designed to be a planing boat but we never did, nowadays it would euphemistically be called "semi-displacement". Running them up once at the end of the day for 10-15 minutes to 1800-2000 kept them very clean and happy, got a very thorough survey at 3000 hours, came out great. Maybe engines in poorer condition need more frequent high RPM runs, mine certainly did not; I could skip a day or two and the smoke would clear up in a couple of minutes.