300hp OXE Marine OXE300 diesel outboard engine 2023 First Ride

The brand had a commercially operated 11.0-metre Metal Shark 36 Fearless centre console on display at the recent IBEX boat-building industry convention in Tampa, Florida; boatsales jumped on board to see just how different the experience would be.

OXE Marine produces four diesel outboard engines, a GM-sourced 2.0-litre turbocharged four-cylinder producing 150hp, 175hp or 200hp, and a 3.0-litre twin-turbocharged BMW in-line six-cylinder engine producing 300hp. 

The brand is slowly gaining momentum worldwide, having now racked up around 5000 sales globally. Of those, nine out of every 10 sales will be for commercial applications, high-runtime users looking to eke out significant fuel savings compared with petrol equivalents.

The engine we are experiencing is built around a turbocharged 3.0-litre in-line six-cylinder “B57” engine that was originally built to power, among other things, high-end BMW sedans and SUVs. 

In the road-going car, this engine produced up to 294kW of straight-line performance, but significantly, up to 670Nm of accelerative twist. The road-going version of the engine uses anywhere between one and four turbochargers, but the OXE engine uses only two.

A single OXE300 outboard engine will cost you from around $120,000, roughly the same price as Mercury’s flagship 600hp V12 Verado outboard engine.

For the money, you get the engine in either two shades of black or a single shade of white, a 25-inch (635mm) shaft length and the rigging kit, worth more than $10,000 on its own. You’re buying the engine in Euros, not Australian dollars, so prices will likely fluctuate with the exchange rate.

A 33-inch (838mm) shaft length option is available.

Based on this, buying an OXE outboards engine is a big commitment, but if you’re running high engine hours the benefit should be in the significantly lower fuel bill at the end of each month.

There is no way of sugar-coating this – the OXE300 is huge. The twin units mounted on the back of the 36-foot aluminium plate boat really drag the eye aft, they are such big blocks of white.

A single engine weighs 430kg in its lightest configuration, about a third more than a petrol-powered equivalent, meaning there is close to 900kg of engine weighing down the transom of our test boat. 

A lot of that weight sits up high, meaning you’ll need a substantial transom width to handle the pendulum effect of these engines – our test boat has a 3.2-metre beam to help counteract it.

The upside is an engine that will use between 40 to 50 percent less fuel than a petrol equivalent at cruising speeds, and produce twice the torque.

Peak power arrives at between 4000-4200rpm, but the engine produces 680Nm from just 1750rpm. Peak torque of 945Nm arrives between 1750-2000rpm and doesn’t fall below 900Nm until reaching 3250rpm.

The OXE300 uses a unique drive system consisting of a hydraulically controlled 1.39:1 ratio gearbox mounted beneath the north-south engine and a belt-driven lower leg that sits in an oil bath. Using hydraulics to turn the belt means that a simple software tweak can turn an engine into a counter-rotating version of itself – you don’t pay any difference for a clockwise- versus counterclockwise-turning outboard engine for multi-engine applications.

If you’re repowering a fibreglass boat for an OXE diesel outboard engine, the fuel circulates at a much higher pressure than compared with a petrol version, and with a much higher rate of fuel return, around 80 per cent, to the tank. That means you will need to upgrade the fuel return line to account for it.

The OXE300 is fitted with a pair of telltales that spit water from the closed-loop cooling system. The engine uses glycol and a saltwater-hardened heat exchanger, so the cooling system needs to use a lot more water. The twin telltales were preferred over a single system that would have looked like a running tap.

Our test engines are fitted with 17-inch props optimised for a 350hp Yamaha F350 outboard engine, with the propshaft using the same spline count – you can swap out the prop for any other size or pitch Yamaha that suits your needs.

But there’s a problem, and that is that the Yamaha propellers are optimised for high-revving petrol engines, not slow-turning diesels.

At cruising speeds, the Yamaha prop fitted to our test engines works just fine, producing the same fuel economy as one optimised for the OXE300. However, ask more of the engines and the F350-optimised props start to go backwards in performance, losing around 10 percent of the potential top-end speed. Sales volumes aren’t yet high enough to encourage a prop manufacturer to build one that gets the best result for the OXE.

Our test engines are also connected to a Dometic Optimus 360 joystick control system. Without the Dometic system the engines use 32-inch (813mm) mounting centres, but with the joystick the mounting centres increase to 34 inches (864mm).

Of note, the OXE diesels produce around 92.5 amps of charging power at idle compared with around 70A for similar-performance petrol-powered rivals.

Diesel engines are generally at their worst at idle. The OXE300 outboard engines are no different, with a small amount of vibration through the test boat’s alloy hull at idle and a strong smell of diesel exhaust.

We use the Dometic joystick system to bump the boat out from the jetty. Of note, there is no clunking from the gearbox as the engines switch between forward and reverse, just a little bit of head toss from the engines as the props bite the water.

The first part of our run is along the no-wake zone in the Seddon Channel, so the engines are turning the props at around 600rpm.

In gear the OXE300s have settled down, running smoothly and quietly. There’s no trolling function with these engines, so it’s as slow as we can go.

Hitting the end of the no-wake zone, we power up. At a comfortable cruising speed, around 25mph (22 knots) our test boat is averaging around 8.0 gallons an hour – the equivalent of around 30.0 litres an hour – per engine at an 80 percent load.

Of note, the engines are no noiser than conventional petrol powerheads, even as we increase the speed to 42mph (36 knots) at 4200rpm – WOT.

But the big benefit of this engine is its commercial application as a high-hour runner. Our skipper runs this boat as a fishing charter.

He says his fuel burn has reduced from around 100 gallons (around 390 litres) a day to around 60 gallons (230 litres) by switching over to the COX300 diesels.

That translates to a cost saving at the pump of around $US1200 ($A1900) a week. Over a year, he claims it equates to between $US50,000 to $US72,000 in hip-pocket savings.

The OXE300 outboard engine appears to be a viable solution for commercial operators needing to find a way to reduce their fuel bill.

However, the big benefit appears to be for those people who are looking to replace an inboard sterndrive on a commercial boat with a swing-tilt engine. This is reflected in OXE's sales to date, which lean to 90 percent commercial and only 10 percent recreational applications.

OXE's customers tend to be tour operators running large catamarans and guide boats that tend to run up big operating hours.

Recreational applications are skewed towards superyacht tenders, where operators running an OXE diesel outboard engine can use the same fuel that powers the engines turning the mothership's screws.