Is It Time for a Diesel Outboard?

THROUGH THE DECADES numerous diesel outboards have come and gone, yet none have survived in the marine marketplace.

To anyone who’s experienced the benefit of diesel economy, torque, and reliability in a truck or an inboard boat—not to mention the additional safety factor of switching from gas to diesel—this seems ridiculous. But two huge hurdles have always faced diesel outboards: cost, and weight. Then when higher emissions standards became part of the mix, diesel outboards basically disappeared.

As 2018 closed out, however, several companies announced new diesel outboard engines that might just change the game: Cox, Oxe, and Yanmar.

Cox had a pair of pre-production prototype 300 hp CXO diesel outboards on the transom of an Intrepid center console at the Fort Lauderdale Boat Show. Cox says they’ll have these motors in full production by the time this edition of Texas Fish & Game reaches your mailbox.

The vast majority of the diesel outboards built in the past, were essentially powerplants used for generators or construction equipment. They were turned on end, marinized, and hitched up to a lower unit, but this twin-turbo computer-controlled engine was designed with a clean slate specifically for marine use.

This means integration with things like NMEA2000, off-the-shelf throttle and steering controls, and transom mounting were all planned in, right from the start. This also means Cox designed it with an eye on weight. It’s still significantly heavier than other 300-horse outboards (diesels do weigh more than gasoline engines), but only by a couple hundred pounds, with a dry weight of 826 pounds.

What about the issue of cost? The Cox (which is built in the U.K.) is expected to be a bit less than twice as much as a Yamaha F300. Although this sounds like a lot—and it is—that’s actually not much different than the usual price differential between a road vehicle’s gasoline-versus-diesel price increase. As is true with many land vehicles, you start to recoup that investment from the very moment you begin running the engine; efficiency can be expected to go up by around 25 percent.

The Swedish-built Oxe, meanwhile, takes a GM diesel block and marinizes it by shifting service points forward, and adding heat exchangers, an intercooler, and an oil cooler. Rather than turning the engine on its side, they then transfer power from the crank to the prop with a rather massive drive belt.

Oxe says the belt has a 1,000-hour service life, and also allows the gear ratio to be easily changed between 1.73:1 to 2.17:1. This engine has been shown in a 150-horsepower form but there are plans to roll out several models ranging from 150 to 300 horses. As with the Cox, weight is higher than comparable gasoline outboards, but it isn’t outrageously so. Pricing is to be determined.

Cox and Oxe are just now rolling out these large, high-horsepower diesel outboards, but Yanmar currently has a 50-horse outboard called the Dtorque 111. This is a twin-cylinder common-rail turbocharged engine, based on a unique diesel motorcycle powerplant that has been on the market for two years already—sort of.

Built in Germany by a company called Neander, with Yanmar handling the world-wide distribution, this engine is available in Europe, Australia, parts of the Middle East, and Africa, but not yet in the United States. Yanmar says they hope to bring it to our shores soon, but they still have to work through the EPA emissions testing issues that often delay marketing an internal combustion engine here. Pricing in the US is also not yet available.

The Dtorque weighs in at 385 pounds; an average 50 horse four-stroke will weigh more like 230 to 250 pounds. We note that adding another third or so of weight has a fairly significant impact on an outboard of this size, as it’s likely to power relatively small boats. Consider, for example, that putting the Dtorque on an 18-foot center console will essentially have the same effect as having an extra passenger sitting at the transom of the boat on each and every outing.

On the flip side, the expected service life is 10,000 hours—over double that of an average comparable gas outboard. Also, it provides significantly more torque than a gas outboard with 20 more horses while burning half as much fuel.

Will a diesel outboard be right for you? Setting the weight issue aside, since that factor will have more or less impact depending on what sort of boat these engines go on, it comes down to whether you’re more interested in longevity, safety, and reliability, than you are in speedy performance and initial cost.

Then there’s the question of servicing and dealer networks, which are TBD. However one may feel about these options one thing is for sure: when it comes to diesel outboards, you now have more choices than ever before.

Email Lenny Rudow at ContactUs@fishgame.com

 

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