Cummins QSB5.9 Captain's Report

The Cummins QSB 5.9 480 in-line 6 develops 480-hp at 3400 rpm and is one of the most popular marine diesels on the market.

It's no secret that Dodge Ram light truck's success is because of its Cummins 5.9 L diesel which are specified in 75% of the units sold. First introduced in the truck in 1989 the model is now rated at a 23,000 lb. (10,454 kg.) hauling capacity.



Our test of a single engine installation of the Cummins QSB 5.9 L 480-hp diesel proved its power and versatility of application.

Today's 5.9 L resemblance to its first version is now remote. Over the years this inline 6 cylinder block has undergone many modifications and re-inventions. It is now stronger, lighter, more fuel efficient, and far more powerful than it was in the beginning. A good engine just kept getting better over the years.



Offshore fishing boats started out as inboard-powered but with the advent of center consoles 45 years ago outboard power has been ubiquitous. Now the pendulum might start swinging the other way. Note the clean, uncluttered transom where an angler can get close to his prize.

Cummins QSB Series

The marinized Cummins 5.9 is called the QSB and comes in horsepower ratings from 230- to 480-hp. This 4-stroke engine is turbocharged and aftercooled and has peak torque of 942 ft. lbs. (1278 N m) at 2200 rpm. Its long stroke is what gives it its prodigious torque. Bore and stroke: 4.02" x 4.72" (102 mm x 120 mm).

Today the 5.9 has an aluminum intake manifold and high-strength aluminum pistons that are gallery cooled. The larger surface area of the gallery can remove more heat from the critical combustion chamber area and top-ring groove without allowing increased emissions. And, of course, it is EPA Tier II compliant. as well as being IMO and RCD certified.

The 5.9 has 24 valves which makes it breath easier and gives it fast acceleration. It has high-strength Inconel (r) exhaust valves and high-cobalt content Stellite (r) exhaust seats, as well as a high-pressure common rail fuel delivery system. This technology along with I-beam rods are just a few of the new wrinkles in the 5.9 that allow it to deliver 480 horsepower than ever before.


Details Make the Difference

Engine aficionados will appreciate Cummins' vertical mounted fuel injectors that are neatly centered over the combustion chambers, which we are told leads to cleaner combustion and longer life.

The QSB 5.9 features high-pressure, common-rail fuel injection which pays dividends in improved fuel economy, instant starting and particularly low emissions. On the aesthetic side of the balance sheet, smoke and smell are virtually nonexistent. Also, Cummins tells us that its noise levels at idle are quieter by about 80 percent than previous models.



The control system can handle up to six different control locations thanks. Note the joystick at the right. Here we see a tuna tower installation on a 35-footer.

The Digital Age

Engine operations are electronically controlled, with data communicated to the helm station by way of the SmartCraft information pathway. Data includes the engine's vital signs (temperatures and pressures), and of course fuel flow. Self diagnostics is also part of the bundle with formation shown on its digital Vessel View. Throttle and shift controls are electronic (fly-by-wire), and the system accommodates either single or dual engines linked to as many as six stations. Engine synchronization is part of the SmartCraft package.

Test of a Single QSB 5.9 L Engine

Recently we tested the latest model Cummins QSB 5.9 480-hp diesel in a single application in a 14,475-lb. center console with a 10' (3.07 m) beam. The boat was powered through a ZF 2800 pod drive via a jackshaft. Top speed was a respectable 37.7 mph (32.8 knots). More importantly, best cruise from the standpoint of fuel efficiency was 32.1 mph (27.9 knots) burning 15 gph and getting 2.14 mpg. Holding back 10% in reserve, this gave the boat a remarkable 675 statute mile range (587 nautical mile) range from its 350-gal. (1,330 L) fuel capacity.









That kind of range is simply not possible with conventional outboard engines or inboard gas engines in a large center console application. It means that an owner of a 35 center console, such as the one we tested, can go from Miami or Palm Beach and range over most of the Bahamas on a single load of fuel. It means that an adventurous angler can easily deliver his own boat from Florida to fishing grounds of Panama or Costa Rica on his own bottom with only a couple of fuel stops. Indeed, the distance from St. Petersburg to Isla Mujeres, Mexico is something on the order of 444 nautical miles.

With the advent of ZF's pods and the availability of large, beefy sterndrive lower units that can take the mighty torque of diesel engines this size, all sorts of new possibilities can be opened up for boaters who want the advantages of reliable, efficient, safe diesel power.

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