Until recently, petrol was the standard choice for most pleasure boat powerplants. More compact, lighter and more powerful than their traditional diesel counterparts, petrol engines were the ideal choice for small pleasure and light commercial applications where limited operating hour requirements and tighter cost constraints have traditionally driven powertrain selection.

“In most commercial situations, however, diesel technology is recognised as superior – more fuel efficient and robust, but heavy, complex and expensive,” explains Christer Flodman, technical manager for Cimco Marine Diesel AB. “But a new generation of stronger, lighter and even more fuel efficient diesel engines has tipped the balance and is making diesel an option for the outboard engine in smaller marine applications.”

Cimco Marine Diesel has recently launched the world’s first high performance, high efficiency marine outboard diesel engine, called the OXE. The innovative gearbox belt design – originally developed for stern drives and inboard engine technology – eliminates the need for conventional complex bevel gears and transfer shafts to efficiently transfer the drive of a common-rail diesel engine. For this project Cimco has marinized a standard GM 2.0-litre turbo diesel engine by designing separate systems for seawater, heat exchangers, intercooler and oil cooler as well as mounting the entire powerplant horizontally. All service points are at the front of the engine, so maintenance and servicing can be performed on the water, whilst the addition of a dry sump system maintains consistent oil lubrication in all running conditions, allowing for rolling in heavy seas, plus tilting and trimming situations.

Whilst diesel outboard engines for light marine applications aren’t new, they aren’t commonplace either and they have historically been large and low power – the most popular being just 37bhp. The OXE is the world’s first 200bhp production diesel outboard motor, and a number of engine sizes are in development – both smaller and larger than 200bhp.

Throughout the project Cimco Marine AB has relied on a tool chain supplied by Kvaser technical associate, Accurate Technologies (ATI) Sweden AB. ATI supplied products used by CIMCO on the OXE program include ATI VISION ECU calibration and data acquisition software, CSM data acquisition hardware, and Kvaser USBcan Pro and Memorator Pro interfaces and data loggers for CAN analysis.

The modular suite of hardware and software was used throughout the evaluation program. Marine engines undergo similar test procedures as those in the automotive industry. Dyno tests simulate different climatic conditions, plus cold start, emissions and numerous sea trials. Kvaser CAN interfaces were used in static test rigs such as those to optimise drivetrain losses and hydraulic pressure testing, as well as on all sea trials in test cells.

Notes Flodman: “All the products worked excellently together. Minimal feedback and support were required from ATI as the software, DAQ modules and Kvaser’s CAN interfaces and dataloggers were all extremely easy to set up. I had used these products before but the rest of the team hadn’t. They were impressed. They provided us with a strong and efficient toolchain that let us focus on the product development, rather than spending valuable time solving test equipment issues.”

Cimco Marine Diesel AB was set up in 2012 to bring the OXE to commercial reality. However, development of the OXE technology has taken over six years, with component test – belt system, engine, gearbox, electrical system, fuel system and air intake etc. – over a period of three years to allow for rigorous sea trials. “What took the time,” recounts Flodman, “was packaging the system into a small, light form factor that would meeting the running conditions of commercial craft, which are much tougher than the pleasure market.”

Potential applications vary enormously and include coastguard patrol where intermediate loads are required for many hours; transportation between fish farms, where long distances are involved and the engine may idle for long periods; and military applications where a maximum load is required in harsh environmental conditions, because the user’s life depends upon the product. Whilst the OXE has not been designed to meet military specifications, the armed forces’ single fuel policy objective means that many military applications would benefit greatly from a small diesel engine alternative.