Diesel Marine Engine Ratings
Author: Doug Shupe, My Marine Tracker
All diesel marine engine manufacturers have a 'duty-cycle' rating system for their products , but the general rule is that the more horse power you extract from any given displacement engine , the shorter the lifespan will be between rebuilds. Caterpillar, the most predominantly sought after diesel marine engine in the US has five different ratings for their engines, A through E. Other manufacturers generally follow the same format but may call them by different names. The most heavy-duty engine (A-rated) is called 'continuous-duty' and these are for applications that may run over 8000 hours per year. These are vessels that typically run 24/7 in their application. These engines usually run at no more than 1200-1800rpm and can easily run 30-40,000 hours between overhauls providing the proper maintenance intervals are adhered to and high-quality lubricants and filters are used.
At the top of the high-performance food chain is the pleasure craft 'E' rated engines that are for minimal annual usage not exceeding 1000- hours per year. These engines typically operate in the 2300-3800 rpm range and some import brands up to 4200rpm ! Average life expectancy between rebuilds of pleasure craft rated engines may only be in the 5-8000 hours range and the really high strung models may only be good for 1000 hours ! Many of the popular models of Caterpillar engines have multiple ratings associated with them. For example, the Cat 3412E engine has ratings available in all five classes ranging from 425hp at 1200rpm up to 1400hp at 2300rpm. The basic cylinder blocks are all the same but internal and external parts are varied as performance demands go up.