Head Gasket Leak

I developed a head gasket leak with my Yanmar 3GM30F engine. I was told by the Yanmar distributer in Jacksonville, FL that, if you can't get the engine up to the max RPM (3600), you will eventually blow the gasket. This may also apply to other than Yanmar GM series diesel engines. I installed a new head gasket and repitched the prop and have had no more problems for 5 years. TIDINGS cruises at about 6.5 kts at 2700 RPM, which is right at the peak of the torque and specific fuel consumption curve. When I noted that a friends diesel engine seemed to get to max RPM with too much ease and that the Sabre 30 couldn't make much speed in a chop, I suggested that the prop might be of too small pitch. The Sabre people later admitted that the prop they were using had not enough pitch. Repitching a prop is not difficult if the change is not too great.