Boat-Tech Review

As the range of diesel outboards on the market continues to grow, Greg Copp takes a close look at the OXE, which offers several benefits related to performance and economy, but at a price …

In recent years we have seen several diesel outboard products lurking in the shadows. However, it was not until the end of last year that a production high-output diesel outboard finally emerged. The 200hp OXE diesel outboard built by Cimco, part of Swedish Marine Diesel, is in response to NATO’s directive for a single fuel supply for all craft. Cimco use a 2-litre 4-cylinder turbocharged GM engine block as used in the Vauxhall Insignia. 

Having tested BRP’s Gen 2 E-TEC 2-stroke outboard, I was keen to see how 2 litres of diesel torque compared to 3.4 litres of 2-stroke grunt. Our test boat was a Cheetah catamaran rigged with two OXE motors. The Cheetah is a fairly heavy boat for an outboard test, but considering this engine’s commercial appeal, a perfect test bed.

The first thing that strikes you when you turn the key is the similarity to a 4-stroke petrol engine in terms of noise. When you engage gear with what is, without doubt, a seamless transmission, you check the controls to see that you are no longer in neutral. This is one of the many bonuses of a multi-plate clutch and belt drive – no heavy gear clunk of a cone clutch and bevel gear shaft. Also, the hydraulic multi-plate clutch has the bonus of a low-speed trolling mode, which is great for a fishing boat like the Cheetah, but also gives you outstanding low-speed berthing control. Under load, the Cheetah felt just as smooth as if she had some V6 petrols on the back.

The power delivery is instant, though you do feel the turbocharger kicking in at 2500rpm. From 2500rpm the engine is keen to quickly push on to peak power at 4100rpm, though the test engines had overly coarse props and stopped at 3500rpm – which is where it produces maximum torque. We were doing 28 knots at this point, and with the correct pitch props this should increase to 31 knots, a respectable speed for a 5-tonne boat powered by twin 200hp outboards. How it compares to a modern 2-stroke outboard like an E-TEC is a tricky question as the Cheetah is not your normal sporty test boat. If you put it on something like a Scorpion RIB it would take off like a scalded cat, but I do not think it would have quite the relentless power delivery of a big 2-stroke engine. 

From a technical perspective, the OXE has a new take on the concept of transmission. With any bevel gear transmission, be it an outdrive motor or an outboard engine, too much torque can have devastating results – think early-generation MerCruiser Bravo 3. Consequently the OXE uses a double belt drive system, as transmitting 297ft/lb of torque through a conventional shaft and gear outboard leg could have a similar effect. Belts have been used successfully for years on large motorcycles such as Harley-Davidsons due to their ability to soak up and handle torque. This also enables the engine to be mounted horizontally rather than the conventional vertical set-up used by most outboard engines. 

The first primary carbon composite belt drives to the gearbox via a wet multi-plate clutch, and from there a second belt takes the power to the prop shaft. Both belts are sealed and lubricated. An interesting feature of the first belt is that it and its two drive pulleys are self-contained within an easily removed casing. The polarity of this casing can be reversed should you need to increase or decrease the primary drive ratio, enabling you to tailor the power delivery between low-speed high-thrust and high-speed economical cruising.

The second drive belt runs through a relatively narrow lower leg, which is most notable below the cavitation plate, and certainly not what you expect to see on a 200hp engine. This would not be possible on a conventional leg housing a shaft and bevel gears. This reaps huge benefits in terms of drag reduction as well as enabling just a 4-inch-diameter prop shaft ‘bullet’ housing and a 4-inch propeller boss.

The mechanical concept of a belt drive compared to bevel gears and shafts is superior. It is more efficient insomuch as there is little power loss comparatively speaking. However, at some point the belts should need replacing, though UK agents Proteum claim the belts have a very long service life. 

The OXE is the only outboard engine this side of the pond that boasts a closed-loop cooling system. This increases the weight, especially when full of coolant, and goes a good way to explaining why this engine has a dry weight of 295kg and a wet one of 320kg. However, the benefit of a closed system that does not pump salt water around the engine block and cylinder head can’t be overestimated, especially if you can’t flush the engine after use. All service items are located under the top cowling on the forward section of the engine block, much like an inboard engine. This includes a raw-water strainer, fuel filter and conventional raw-water pump, making the motor a lot easier to service than the average outboard. The cowling and upper leg covers are all composite; only the lower leg is housed in aluminium. 

Steering is courtesy of an electronic SeaStar system complete with the Optimus 360 joystick should you want it. With the Cheetah’s engines mounted so far apart, the Optimus 360 is certainly effective. 

Service intervals are 200 hours and major overhaul intervals every 2000 hours for commercial use. Fuel consumption is claimed to be 43 litres an hour at wide-open throttle, but of course this is craft dependent. What one can be sure of is that it will be about 33% more economical than a petrol engine in like-for-like conditions. Not surprisingly it weighs more than a similar petrol outboard engine and costs a shedload more at £36,000 – nearly twice the price. That extra cash is a lot of petrol, but there never seems to be a shortage of people prepared to pay the price for diesel power. 


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