New Wave

Advancing Diesel Technologies Provide a Welcome Progression in Marine Propulsion

Matt Arnholt November 13, 2018

Evolution takes place as a result of advances made over time. As boaters, our daily pursuits are fueled by technological innovations. With impressive effeciency, reliability and performance attributes, outboard propulsion is relied upon worldwide and continuous innovation within the industry has led to incredible advancements in diesel outboard technology. Though the few existing options are far from achieving mainstream popularity or availability, several innovative manufacturers are focused on continuing the design and development knowing several distinct advantages exist.

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Photogrpahy: coxmarine.com

Though they often come with substantial price tags of their own, outboard-powered center consoles offer affordability in comparison to massive sportfish yachts that provide far more accoutrements and amenities. But many top tournament teams prove year after year that open platforms are capable of powering anglers to the winner’s circle. The impressive performance yielded by modern center consoles can be credited to many advancements within the boating industry, but perhaps the most crucial is the development of the outboard engine.

Whether the ideal configuration comprises quad 350s on a 39-foot center console, or a single 60 HP bolted to the transom of a 17-foot skiff, anglers demand performance and reliability from their outboards. But while the latest gasoline-powered outboards are truly impressive, they pale in comparison to diesel engines when it comes to fuel efficiency and longevity. However, diesel designs have largely been limited to inboard installations which are inherently heavier and bigger than outboards, making them unfitting additions to center consoles.

Though the concept of a diesel-powered outboard is not new, most mainstream builders have steered away from the design. However, in recent years several manufacturers have developed diesel outboards in order to effectively eliminate the need for compromise between the lightweight performance of a gasoline outboard and the efficient reliability of a diesel engine. While a select few European builders have been successful in their efforts, most American anglers continue to trust the impressive performance yielded by gasoline outboards from leading brands such as Mercury, Yamaha, Suzuki, Honda, Tohatsu and Evinrude. But as innovative manufacturers across the world continue to achieve lightweight outboards that run efficiently on diesel, boat owners on this side of the pond may soon take notice.

With the soaring popularity of gasoline outboards and the impressive performance statistics yielded by top brands, why would there be a need for diesel outboards? As is the case with so many other boating components, choosing an outboard is heavily associated with personal preference. While traditional gasoline outboards are spectacular pieces of machinery and it may take some time for widespread recreational boaters to come around on new diesel outboard technology, there are several immediate advantages that come with operating diesel outboards.

First and foremost, diesel engines are substantially more efficient than gasoline engines, and they are also known for providing more torque. Simply put, opting for a diesel engine would likely increase fuel economy, potentially by a large margin. Operating a diesel engine also offers advantages regarding overall safety. Diesel is much less flammable than gasoline, making it safer for commercial captains to work in hazardous environments. With SOLAS approval, diesel outboards could work for rescue boats and MOB craft. Furthermore, the technology would also appeal to military operators and superyacht applications with tenders that desire diesel power because of its fuel compatibility with the mothership. For government entities, conversion to a single-fuel fleet could improve operational performance, efficiency and even mission execution.

Diesel outboards are certainly still a novel concept to the world of boating, but development of these unique engines has been taking place for some time. In 2015, Mercury (mercuryracing.com) introduced the OptiMax DSI (Diesel Spark Ignited) outboard developed for the U.S. Department of Defense. Unfortunately, the OptiMax diesel is currently still only available to the military, but Mercury is considering a commercial model in the near future. Despite it being unavailable to the public, it is worth noting this outboard’s capabilities. Running on ultra-low sulfur diesel fuel, the direct fuel injected two-stroke OptiMax yields excellent fuel efficiency. Additionally, this 3.0 liter V6 diesel outboard delivers 175 propshaft horsepower and shares 95 percent of its components from the gasoline-powered outboard from which it is derived, resulting in relatively easy maintenance and parts acquisition.

Though few diesel outboards have been brought to market, there are in fact some impressive choices...

We have yet to see if this unique engine would be capable of meeting the lofty expectations of anglers around the world demanding the most from their outboards, but in military applications the OptiMax DSI is relied upon by many. Though the OptiMax DSI is a diesel engine, it is more similar in comparison to a gasoline outboard than it is to a diesel inboard. Unlike a traditional diesel engine that uses compression to achieve fuel combustion, the OptiMax diesel uses a spark plug to ignite the fuel, as is the case in a gasoline-powered design. Combining the reliability, safety and efficiency of a traditional diesel engine with the simplicity and performance of a modern gasoline outboard like the Verado, the OptiMax DSI is certainly an impressive piece of machinery. And although this particular engine is not available to recreational boaters, it proves that a practical diesel outboard can be achieved, and it is currently being tested by the U.S. Coast Guard and U.S. Navy.

While Mercury is an established name in the world of outboard propulsion, other manufacturers more prominent in Europe have joined the diesel outboard game as well. Cox Marine (coxmarine.com) is a bit of a newcomer to the marine industry having been established in 2007, but has just recently stepped into the diesel outboard realm with the powerful CXO300. However, with a strong pedigree in Formula 1 racing and premium automotive design, Cox’s highly skilled team of engineers has decades of experience in combustion engines. Designed and built for reliable performance within a variety of applications, this innovative outboard is among the most powerful in this new class, achieving 300 HP at the propeller. At the 2018 Miami International Boat Show, England-based Cox Marine was joined by its reputable lineup of U.S. distributors to introduce the CXO300.

In Florida, the number of recreational anglers and boaters continues to grow, with a steady trend in place of boat buyers purchasing large offshore fishing vessels powered by twin, triple, and quad outboards or diesel inboards, many with pod drives. Though both gasoline outboard configurations and inboard diesels have distinct advantages, they are very different forms of propulsion and choosing between the two generally means compromising certain features or even vessel type. With the CXO300, Cox Marine aims to effectively deliver the best characteristics of diesel inboards and gasoline outboards. Sea trials of the CXO300 will commence in October and models will be on display at the upcoming Fort Lauderdale International Boat Show. Orders will open in November and it is reported that the engine will go into full production early 2019.

While it’s often the largest and most powerful outboards that receive the most attention, many of the latest outboard innovations and advancements are apparent in the mid-range market as well. This is certainly the case for the emergence of the diesel outboard category, with Yanmar’s (yanmarmarine.com) Dtorque 111. Yanmar has long been one of the most trusted names in marine diesel engines, and the addition of this compact outboard expands the company’s wide reach even further. One of the most impressive aspects of this outboard—from which its name is derived—is the 111 Newton-metre peak torque output at 2,500 RPM, equivalent to 82 foot pounds of torque. Diesel engines almost always produce more torque than comparable gasoline engines, but Yanmar’s Dtorque 111 is particularly impressive in this regard, bringing vessels to plane exceptionally fast and easily powering heavy loads at low RPM.

With production of this engine in process, the Dtorque 111 is a legitimate option for boaters looking for a reliable mid-range motor. With an 800 cm twin-cylinder aluminum powerhead delivering 50 HP at the propeller shaft, this welcomed addition to the Yanmar lineup is capable of outperforming some of the most popular 70 HP fuel-injected, four-stroke gasoline outboards within the industry. Additionally, one of the most important advantages associated with the Dtorque 111 is its remarkable fuel efficiency, burning just over 3 gallons per hour at wide open throttle.

Though few diesel outboards have been brought to market, there are in fact some impressive choices—presently or in the near future—available to open-minded boaters looking to embrace what may very well be the next popular wave of outboard engines. 

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