The Triton

Engine Room

Diesel Digest: Sailboat engines benefit from enhancements for megayachts


Diesel Digest: by Capt. Jeff Werner

While the primary focus of the yachting industry is superyachts, vessels with an LOA in the 50-foot range also make up a good portion of boats that are sold. These include sailboats, both monohulls and catamarans, and sport-fishing boats. Tracking the recent advances in diesel engine design for the sailboat sector is a good way to understand the development of larger horsepower marine diesel engines.

Over the past 30 years, Yanmar has been the leader of diesel engines used on board small charter and recreational sailboats. During this time, engine manufacturers such as Universal and Westerbeke have fallen by the wayside or lost significant market share. The key to Yanmar’s success has been developing a reliable engine and taking it into the 21st century using the latest technology. At the same time, they listened to their customers and abided by environmental regulations.

According to the Yanmar Develop­ment Division, “performance requirements for diesel engines in the pleasure boat market are growing year by year. In addition to things like high output and quiet operating, recent years have also seen rising interest in environmental performance factors such as fuel economy and exhaust emissions”.

To meet the changes in the small marine diesel engine market, Yanmar melded their tried-and-true mechanical marine engine with the special technologies of their industrial diesel engine, and with the advancements in larger electronically controlled marine engines used aboard superyachts and commercial vessels.

Mechanically controlled diesel engines rely on gear-driven fuel pumps, spring-loaded injector nozzles and mechanical governors to continuously squirt the same amount of fuel into the cylinders.  Electronically controlled diesel engines use speed sensors, servos, microprocessors and electronic injectors to deliver the exact amount of fuel needed at any given moment.

Yanmar decided to address a recur­ring complaint of sailboat operators:   hull stain from the black smoke emitted by the engine. Many sailboats have a white hull, making the black stain caused by the smoke in the exhaust gas particularly noticeable, and it is difficult to remove, the company said.

To control the black smoke, Yanmar added an electronically controlled common rail injection system to precisely meter the exact amount of fuel necessary for complete combustion. Yanmar also incorporated numerous industrial engine combustion technologies, “such as optimization of the timing and number of fuel injections.”  The company reported a resulting 80 percent reduction in the density of black smoke in the exhaust gas under normal conditions.

Engine vibration and noise are a design issue on superyachts, and an even greater factor on small sailboats because of the proximity of the engine room to the cabins. The separation of this mechanical space from the living space may be a single bulkhead. Since there is only so much soundproofing that can be done in an engine compartment, other technologies must be used to reduce noise and vibration. Switching from a mechanically controlled to an electronically controlled engine allowed Yanmar to reduce vibration by 30 percent and the noise level by almost 50 percent.

The final enhancement available by adopting electronically controlled engines is the ease of connecting them to electronic displays. Using the engines NMEA 2000 digital output has significantly improved the interface with equipment that requires the input of engine speed or fuel consumption. Another benefit of the the electronic control system is the ease of installing multiple helm stations. This electronic “fly by wire” concept was pioneered in military and commercial aircraft.

Regardless of whether operating a vessel with a classic mechanically controlled diesel engine or an up-to-date common rail engine, optimal performance can only be achieved with clean fuel. The way to assure that the fuel that powers the engine meets the engine manufacturer’s specifications is by following a detailed fuel preventive maintenance program.

Capt. Jeff Werner is a 25-year veteran of the yachting industry as a captain on private and charter yachts, both sail and power, and a certified instructor for the RYA, MCA, USCG and US Sailing. He also owns Diesel Doctor ( Comments are welcome below.

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