New Yanmar Diesels Pay for Themselves

Lighter engines, more power and massive fuel savings, can a re-power be any better than this?  Indeed it can, when the cost benefit analysis shows that this dual Yanmar 6HYM-WET re-power will pay for itself in only five years.

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Ports North, operating out of Cairns, is responsible for running the port pilotage transfer service.   This involves a short-run ‘taxi’ service to pick or drop off the marine pilots who guide commercial ships into the Port of Cairns.

The Tribulation is a purpose built pilot transfer vessel launched in 1990.  Originally powered with a pair of V8, 2 stroke diesel engines, issues of cost and reliability prompted management at Ports North to look at the alternatives.

“These engines were noisy and inefficient,” said Kevin Moore, Plant and Maintenance Manager of Ports North.

“The engines were burning 80 litres engine per hour and we were only getting 8000 hours of operation between re-builds.  A repower was essential due to the operational costs.”

The Tribulation was built in Brisbane by Norman R Wright & Sons in 1990.  Ports North involved this ship yard in the repower process.  They were asked to advise on the make and model of engines that would fit into the engine room with minimal impact, as well as the engine package that would deliver optimum performance for this specific vessel.

An important aspect of the Ports North repower specification was to fit an engine with a 100% duty cycle.  This means that the engines had to have the capability to operate at wide open throttle on a 24/7 basis.  In a practical sense, the Tribulation is required to operate at full speed all the time, at any time when called into service.

After all the engine power research was completed, there was a single engine which met all the criteria.  The Yanmar 6HYM-WET.

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This model Yanmar engine is a 500mhp (367W) commercially rated marine diesel engine.  It is an IMO Tier 2 Emission certified purpose built heavy duty marine engine model ideally suited for workboat or passenger ferries applications.

It is a 6 cylinder in-line configuration engine, displacing 13.733 litres and weighing 1385 kg, without a transmission. It features a full mechanical governed and mechanical fuel injection system and when combined with the unique twin turbocharger design as used on this model provides for quick acceleration and very impressive fuel economy right across the full operating speed range.

“This engine was slightly more expensive than the others but it was clearly better for fuel, lighter and had a 100% duty cycle.  It was clearly superior to anything else that we looked at for our specific application to re-power the Tribulation.”

Norship Marine in Cairns performed the repower.  This involved removing the old engines through the rear deck.  The transmissions were also swapped with new Twin Disc transmissions being installed due to the increase in engine revs.   The existing shafts and props were retained.

With the Tribulation back on the water the transformation was nothing short of astounding.  The new Yanmar 6HYM-WET engines added an additional 150hp to the hull, for less weight and a fuel saving of more than 30%.   The Tribulation is faster saving on average 20 minutes on each pilot transfer.  Top speed of 21 knots is achieved at 2000 rpm.

Beyond the raw stats of performance enhancement, the real benefit lies in the back end data.  The previous engines needed to be serviced every 150 hours, these Yanmars have a 500 hour service interval.  The old engines needed a top end rebuild every 3500 hours, the Yanmar 6HYM-WET are good for 20,000 hours.  The fuel saving is 60 litres per hour of operation, an astonishing cost saving.

The cost benefit analysis confirmed that the cost of the re-power will be recouped in about 5 years, taking into account fuel savings and lower maintenance costs alone.

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“The repower was a no brainer.  I can sleep at night now!” said Kevin Moore.

“The reliability is excellent, the noise level in the cabin is significantly lower, fuel savings are excellent and on water performance is fabulous.   Our marine pilots are very happy.”

See the video about the Ports North, Tribulation repower project.  Go to and see what Kevin Moore says about the detailed process that Ports North went through to repower Tribulation.