By Charles Plueddeman
The Outboard Expert: Military-Spec Power You Can Own
Evinrude and Mercury Racing offer outboard motors beyond the norm for recreational boating.
Editors Note: This article was originally published by Boats.com in August, 2008.
If you are looking for something really super-duty to hang on your transom, how about an outboard built to military specifications? Both Mercury Racing and BRP Evinrude are now offering for sale to the public an outboard model originally designed for the military. They look cool. And they run on jet fuel.
Both the Mercury OptiMax JP and the Evinrude 55MFE were designed in response to directive by the U.S. Department of Defense that it will cease the transportation of gasoline on ships and aircraft by 2010. This is primarily a safety issue, as gasoline is much more volatile and dangerous to handle than diesel or jet fuel. Both the Navy and the Army also have forward initiatives to work towards a single “battle space fuel,” so that all vehicles can operate on a single fuel type.
Mercury Government Sales, a business unit of Mercury Racing, started development in 2001 of an OptiMax V6 outboard that would run on the Navy’s JP5 and the Army’s JP8 jet fuels. The motor became operational in 2005, and it is now available to consumers as the OptiMax JP. Built at the Mercury Racing shop in rural Fond du Lac, Wis., the OptiMax JP is a based on the two-stroke, direct-injected 3.0-liter Mercury Racing 250SX. According to Jeff Krueger, director of Mercury Government Sales, the OptiMax JP uses 96 percent of the components found on the 250SX, meets EPA emissions standards, and can be serviced by any certified Mercury technician.
“The OptiMax JP has a different compression ratio, and uses pistons, rings and cylinder heads that are redesigned to tolerate the jet fuels,” said Krueger. “The biggest issue with this fuel is carbon deposits, because the jet fuel contains a lot more carbon than gasoline. So we initially had a lot of problems with ring packing, for example.”
The new pistons are specific to the OptiMax JP model, and the heads have O-ring seals and special combustion chambers. The reed valve petals are rubber-coated for added durability. To help combat carbon deposits, Mercury developed a special JP outboard oil with additional dispersant additives that must be used in the OptiMax JP.
The OptiMax JP retains the Mercury PCM 03 engine control processor that recognizes the presence of jet fuel and adjusts the engine to operate on that fuel. In an emergency, the OptiMax JP can also run on gasoline or diesel fuel for a short time. The motor retains the full SmartCraft system and can be used with SmartCraft instruments and accessories.
Krueger said that tuning the motor to run on jet fuel decreased the power output of the OptiMax JP.
“The motor makes about 185 horsepower in this configuration,” said Krueger. “But the upside is fuel economy, which is about 35 percent better than a 175 OptiMax outboard.”
The OptiMax JP is available with a 25-inch or 30-inch midsection and a Mercury Racing Fleet Master gearcase with a 2.0:1 gear ratio and dual water pick-ups for reliable cooling. Black-on-black cowl graphics give the OptiMax JP a stealthy look. How much does mil-spec cost? The OptiMax JP has a suggested retail price of $24,848, compared to $20,273 for the Mercury Racing 250SX. Krueger expects most civilian sales will be to commercial operators who have a ready supply of commercial Jet A fuel on hand, and like the military would like to avoid the safety issues of gasoline.
“We think a facility like an off-shore oil platform, which operates regular helicopter service, or a remote resort that relies on helicopter or jet transportation, would consider an outboard that also operates on jet fuel,” said Krueger.
BRP is aiming for the same market with its Evinrude 55MFE. The name stands for “multi-fuel engine,” and this 55-hp motor has been designed to run on all types of jet fuel, kerosene, and gasoline.
“It will also run for a short time on diesel fuel in an emergency,” said BRP Government Sales Manager Jeff Wilson. “What I tell customers is that if you are getting shot at, and diesel fuel is the only option, use it and worry about it later. But the carbon in diesel will clog up the exhaust in a hurry.”
A switch on the motor is used to electronically re-tune the motor for each fuel type. The 55MFE is based on the Evinrude E-TEC 864cc twin-cylinder, two-stroke powerhead. It uses the same type of direct-injection found on standard Evinrude E-TEC outboards but lacks some of the other features of an E-TEC, such as the three-year maintenance interval. Significant changes to the combustion chamber design were required to convert this motor to multi-fuel capability. Available only with rope starting, gas-assist manual trim, and a break-down tiller handle, the 250-pound 55MFE also has a wrap-around grab handle, tactical black paint and features to enable stealth operation, including minimal engine noise and exhaust emissions. The motor is also submersible, and has a “de-watering” system that purges the powerhead and under-cowl area so the motor can be started after it has been submerged – note that the motor was designed to fit through a 30-inch submarine tube. And if you can afford a personal sub, you might also have the budget to buy an Evinrude 55MFE. According to my local dealer’s 2009 price book, MSRP for the 55MFE is an incredible $21,130 with prop drive. A version with jet drive is about $3,000 more. Consider that an Evinrude E-TEC 65 Commercial is priced at $7,905, and realize that there are 11 years of development and some hefty engineering costs behind the 55MFE. But I’m betting someone will buy one. And then pull his boat behind a surplus Humvee.
- Charles Plueddeman is Boats.com's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.