We are told that most marine engines are bassed on comercial units. with this being the case why is the rev counter in the cab of a truck marked with an optimum usage range far lower down the rev band than we are advised to run our marine versions? I've heard the bit about better cooling but I can't believe that every truck operator in the country is paying for a bigger power unit than he would need if he used the engine to its full potential if this was th case larger radiators would have appeared long ago. Or is this a way of ensuring thoes big repair bills arrive on our doorsteps every year. Does leisure use mean "you can thrash the nuts off it but only twice a week"? If a 400HP Merc truck (excluding oil change)only needs a major service every 1,000,000Km why does a marine engine need it every year approx 200-500 hours? comments invited.