Diesel Engines

No Longer Noisy, Stinky, Smoky And Slow

September 2010 Feature Gary Kramer

Diesel engines have long been known for their durability, long life, high torque output and a fuel efficiency that allows extended cruising ranges for boats. But they were also well known for being noisy, stinky, smoky and slow, which kept them from becoming very popular for use as recreational marine engines.

But recent diesel engine technology advances have created a new breed of diesels. The improvements were partly due to the need to produce cleaner engines to meet tighter emissions standards and partly due to an ongoing effort to produce more responsive and more fuel-efficient engines. Over 50 percent of all new cars now sold in Europe are diesel powered and the figure rises over 70 percent in Austria. That is largely due to the fact that diesel fuel in Europe is 15-20 percent cheaper than gas and diesel engines are roughly 15 percent more fuel efficient. But it is also because of the improvements to the diesel engines.

These technically advanced engines are now almost smoke and stink free, are fast, start quickly and cleanly and produce very little noise. These attributes, along with the traditional advantages that include greater safety than gasoline engines due to the reduced volatility of diesel fuel compared to gasoline and an almost complete absence of carbon monoxide (CO) emissions, make powering a new houseboat with diesels worthy of some consideration.

The new engines differ from their predecessors in several significant ways. One major difference is the elimination of a mechanical fuel pump in favor of what is termed common rail injection. Another is the addition of turbo charging along with inter- or after-cooling.

The fuel pumps on the old engines would send one burst of fuel to each cylinder for each combustion cycle. The resulting "big bang explosion" created the loud engine noise. In addition, some of the fuel went unburnt, which resulted in smoky and smelly exhaust.

With common rail injection, a pump puts the fuel under constant pressure. The fuel is then distributed to each cylinder from the common rail, which is described as looking like a tube or a rail. The fuel bursts are activated by an electronic solenoid. But rather than one fuel burst per combustion cycle, the common rail releases a number of bursts per cycle and each contains a different amount of fuel. Some automotive marinized engines distribute fuel five times per cycle but on most marine engines, two or three distributions per cycle are normal. The first is a pre-injection that "stokes the fire" and heats the chamber. The second injection is for the actual combustion and if a third is used, its purpose is to further reduce emissions. By injecting highly metered, minute quantities of fuel, the "bang" of the combustion is all but eliminated, the engine smoothes out and the fuel burn is much more complete so emissions are much cleaner.

To illustrate how quiet these engines have become, MasterCraft Boat Company installs 225 hp, V-6 Volkswagen diesel engines in 19-foot ski boats that are exported. These boats do not need nor are they equipped with mufflers.

The increased performance and desirability of these engines is also due to turbo charging. Exhaust gases are used to spin a turbo that compresses and heats the intake air, sometimes to 300 degrees Fahrenheit.  But cooler air is denser, which means more fuel can be mixed with it in the combustion event and that results in more power so the heated air is cooled in a heat exchanger. Some manufacturers use raw water for the coolant and others use engine water. The cooling process is described as after-cooling or inter-cooling depending on the placement of the cooler. But both have the same job-to cool the heated air.

The combination of common rail injection, turbo charging and after-cooling results in more power and performance from a smaller displacement engine so these engines are now smaller and lighter than their ancestors.

Marine engines are available from a number of manufacturers. Volkswagen has a line of five-cylinder, V-6 and V-8 models up to 350hp that fit in the same space as a standard V-8 engine. Steyr Marine Engines from Austria produces extremely small, lightweight versions from 75 to 280hp that utilize mono-block construction that can be mated to MerCruiser sterndrives. They also have a Serial Hybrid Propulsion (SHP) system that combines electric and diesel power. An electric drive runs the boat to around seven knots before the diesel engine is activated. Steyr is not well-known in this country, but their engines can be found in some United States military applications.

Volvo Penta offers a range of models for sterndrive or inboard application in four- and six-cylinder models. Sterndrive horsepower ranges from 225 to 370hp and inboard power climbs considerably higher.

John Deere and Caterpillar offer engines for very large houseboats that need heavy-duty, high horsepower engines and so does Cummins MerCruiser. Both Pluckebaum Custom Boats and Harbor Master Boats have experience with installing the new Cummins diesels.

Jamie Donahue, general manager at Pluckebaum, says the electronic Cummins engines offer customers some appealing features. When coupled with electronic controls, the boat's operator has a wealth of diagnostic information available to him as well as some significant control advantages like total synchronization and slow motion control.

"There is a learning curve to it all," Donahue says, "but customers like the combination of electronic engines and electronic controls after they become familiar with the operation."

Several of Harbor Master's 52-footers have had these electronic Cummins engines installed and Irving Martin, vice president of sales and marketing, says people love them. Customers tell him they are very quiet, there is only a hint of diesel odor and they don't smoke. Generally, the generators smoke more than the engines. Performance data for a Harbor Master 520C-D with twin Cummins 380hp diesels show that a 10 mph cruising speed yields two miles per gallon while a fast planing speed of 20.6 mph yields .88 mpg.

Smaller engines are available from Cummins MerCruiser in the 115 to 350hp range in its QSD series. These Quantum engines come in four- and six-cylinder models and are available for either sterndrive or inboard use.

The other major diesel engine used in houseboats is Yanmar. Its BY series is a compact design they say is 35 percent lighter than its competitors. These are available in four- and six-cylinder models from 150 to 315hp.

Gibson Boats has installed Yanmars in a couple recent boats. Brothers Allen and Keith McGee own a 2008, 16 by 59-foot Gibson with twin 315hp Yanmars. Over time, they plan on doing the Great Loop and felt diesels were the best choice. During shakedown runs, they experimented with prop sizes and a recent run yielded a fuel burn of 12 gph at 12 mph. Allen says his wife spends time sitting on the aft deck to avoid the wind and doesn't detect any objectionable odor. He says the engine noise is a bit noticeable only when you are right on top of them.

A significantly different and very interesting application is the use of twin 115 hp Yanmars in a 2008, 47-foot Classic Gibson owned by George and Diana Hill. This boat was a test platform for these engines and George is thrilled with their performance. After logging over 900 miles, he is averaging about four mpg at eight mph.

"We planned to do extended cruising at slow speeds and eliminated smaller trawlers and catamarans due to lack of space," says the Gibson owner.

The deciding factor, he laughs, was that on those boats, "We couldn't find a place for the cat's litter box." Besides, he adds, "I only wanted to go eight mph anyway," so is tickled with the room and comfort he has coupled with the economy of small diesels. The other advantage is that the upcharge for the small diesels over standard engines is minimal rather than the large price increase diesels usually command.

Re-powering from gas engines to diesels is an expensive proposition. Marine Sales Manager Rick Toone at WW Williams, a Yanmar dealer in Savannah, Ga., says that because of the cost, folks have to really love their boat and plan on keeping it a long time to justify the expense. Besides the cost of the engines, most boats need heavier duty outdrives or inboard running gear because of the increased amount of torque produced by diesels. Another obstacle, he notes, is that many lakes and other locations do not have diesel fuel available.

But for folks purchasing new boats, especially those planning on owning the boat a considerable period of time or cruising long distances and like the advantages of fuel economy, long engine life, reliability, safety, and higher resale, the new generation diesels are an attractive choice. Make no mistake; these are not your father's diesels.


For more information:


Cummins MerCruiser



Steyr Motors North America   



Volkswagen Marine



Volvo Penta







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