What Marine Engine Duty Ratings Mean To You

Fuel map for 105, 90 and 70 kW versions of the same 4 litre diesel engine
Simply changing the RPM and fuel flow limits can give us three different engines, with different power ratings, from the same 4-litre block.

Earlier in the year, John and I were writing about marine engines, and among the questions that keep coming up is:

"Just what is a 'commercial' or 'continuous' duty rating on an engine, and should I get that?"

Let's tackle that by starting with the reason that these ratings exist at all and then move on to how to select the correct rating for a displacement boat, power or sail.

Matt, Engineering Correspondent, is a Professional Engineer and true renaissance man, with a wide range of expertise including photography and all things boat design. He has a unique ability to make complex subjects easy to understand and he keeps an eye on the rest of us to make sure that we don’t make any technical mistakes. Working as M. B. Marsh Marine Design, Matt designs innovative powerboats of all shapes and sizes.

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