This winter, we blew our Diesel Power expense budget by chasing bikinis and checking out the latest diesel engines in sunny Miami. Going into the show, we knew very little about the engines that find their way into diesel-powered ships and speedboats. After a few days at the docks and a few engine-room tours, we know a little more, but we've still got a lot to learn.
For the most part, marinized diesels-diesels that have been modified for use in marine applications-are engines that were designed for use in road-going vehicles. But the life of an engine is a lot tougher in a boat than in your typical diesel-powered pickup. Typically, a marine diesel engine begins as a heavy-duty version of a road-going diesel engine (let's say a Cummins 5.9L, for example). It's then fitted with a new intake, exhaust, and cooling system so it can be packaged inside the hull of a ship. Engines designed for public roads have to meet much more stringent emissions standards than boats do, so marinized diesels have far less emissions equipment. These lower emissions standards mean that you will still find a number of mechanical- and unit-injection diesels in boats, while common-rail injection is just coming into popularity. It also means that horsepower and torque numbers can be significantly higher.
In the marine-diesel-engine market, you'll find all the big-name engine manufacturers, such as Caterpillar, John Deere, Cummins, and Volvo. You'll also find engines like MTU that you haven't heard of. These MTU diesels (a twin-turbo, V-16, 3,600hp 16V-4000 is pictured) are produced in Germany and the U.S. by the descendent of the Detroit Diesel marine division. In fact, the Detroit Diesel and Allison logos are still in use on some of these powerplants. | 
In the boating world, diesel engines must operate at full load for hours on end. Controlling the engine and exhaust heat is critical for maximum engine life, so marine diesels use turbochargers with water-cooled turbine housings. On some engines, like this MTU 2000-series, the entire exhaust system is water-jacketed and cooled by engine coolant. |
We thought we discovered what we'd love to see make its way into a truck when we stumbled across this high-revving (3,800-rpm), 350hp, 4.2L,common-rail MTU six-cylinder. That is, until we realized it was actually a Cummins QSD4.2L engine wearing MTU logos. Regardless of whose name is on the valve covers, it measures 36.6 inches long, 29.8 inches wide, and 31.0 inches tall and weighs less than a 1,000 pounds. We want one to swap into a 1/2-ton truck. | 
At just over 28,000 pounds, the 5,700hp MTU 20V-4000 is the size of a Ford Excursion and nearly four times as heavy. The V-20 displaces 86 liters (that's 5,248 ci), has four turbochargers mounted on top and individual cylinder heads for each piston, and it even uses common-rail injection. |
Yes, the Cummins 5.9L is prevalent in the marine world, too. When it's put in boats, the B-series engine is painted white and is known as the Cummins Mercruiser QB5.9. In this common-rail and air-to-water intercooled version, it's rated at up to 480 hp and more than 900 lb-ft of torque. | 
We've shown you a lot of F-650s with Cat's C-7 Acert engine, and here's how the same engine is configured in its marine trim. To fit two, three, or even four engines side by side (depending on application), all accessories are packaged to make the overall engine as narrow as possible. That means the turbo is moved behind the engine, and the air-to-water intercooler is actually part of the air-intake manifold. |