The age-old argument among mariners concerning twin-engine versus single-screw boats has taken a new twist. Recent results comparing a single-engine Yanmar 6LP-series diesel sterndrive to twin gas outboards gave the diesel engine advantages in nearly every category.
Producing 300 crankshaft hp at 3,800 rpm, the 6-cylinder, 6LP-STZE is one of Yanmar Diesel's most popular engines among boatbuilders. Its light weight and small footprint have made it the choice for many gas-to-diesel and diesel-to-diesel repowering projects as well. Equipped with a Mercruiser Bravo
Three sterndrive, the combination weighs only 1,100 pounds and, on a 31-ft. open console fishing boat, burns less than 11 gph at nearly 35 mph. That's over three miles per gallon. According to Richard Mastry of Mastry Engine Center, the engine will outperform twin gas outboards, hands-down. "Tests were run comparing a single Yanmar 6LP against twin 250-hp EFI gas outboards on the identical boat. The Yanmar engine produced a 40% increase in cruising range over the outboards. That's important, especially for offshore fishermen."
According to Yanmar Diesel's Greg Eck, a single 6LP-STZE offers other advantages over outboards besides fuel economy. "Since the diesel engine is mounted below decks rather than hanging off the transom with a bracket, the boat's center of gravity is lower," said Eck. "This has
definite advantages in boat handling, especially in rough waters."
Eck further explained that the diesel has additional advantages over outboards when used on the tender for larger yachts. "It is a matter of safety," said Eck. "If there is an emergency aboard the yacht, a crewmember can quickly deploy the tender and head to shore to pick up parts, medical supplies or additional personnel. The diesel engine's economy provides the extended range necessary for the tender to make the trip quickly without running out of fuel."
Yanmar Diesel, addition to the 6LP-STZE, manufactures other marine engines from 9.1 to 500 hp.
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