Register for a free trial
Tug Technology & Business

Tug Technology & Business

Now is the time to expedite hybrid propulsion development

Thu 02 May 2019 by Jamey Bergman

Now is the time to expedite hybrid propulsion development
MAN integrated hybrid propulsion system with energy storage

Research demonstrated significant operating cost and maintenance savings for tugboat owners while capex in energy storage systems is decreasing

Although marine hybrid propulsion was in its infancy just a decade ago, today’s hybrid propulsion trains are proving to offer lower operating expenditures than traditional tug propulsion systems.

Nevertheless, hybrid propulsion systems still make up only a small percentage of propulsion systems in the market. So, what is holding owners back from ordering hybrid systems?

In a report titled, Hybrid power workboats: a holistic approach for better capex, MAN Energy Solutions’ Mark Watson – sales manager in the tug and workboat division of MAN’s four-stroke marine engines business – said there are two big hurdles: higher up-front capital expenditure and perceived risks around certification, installation and operation of hybrid technology.

Tug Technology & Business caught up with Mr Watson to discuss how he and his co-authors* sought to battle misconceptions regarding cost differentials and push forward the uptake and development of hybrid technologies.

First, the group defined the fundamental approach: working with known partners to achieve cost efficiencies and build expertise that could lead to further innovation.

Secondly, Mr Watson says he felt the project needed an external benchmark against which to compare development of hybrid technologies within maritime. To his mind, the answer was clear.

“I took a broader-based view and said let’s look at other industries and this is why we looked at the automotive industry,” Mr Watson explains.

“The technology is clearly more advanced than it is in other sectors because they have just been doing it for longer, so that was a good place to say ok, here is a starting point, look where they have gotten in 30 years of development [and] using that as a benchmark, as a target” he says.

With a benchmark defined, the next challenge to overcome was developing a viable system on a vessel type that made sense.

Mr Watson leveraged MAN’s partnership with Aspin Kemp and Associates to design the hybrid propulsion system and arranged to use hybrid thrusters that Schottel had developed independently. In terms of the vessel, focusing on tugboats made sense in that both firms had experience in the sector.

On this basis, the group managed to show that they could pare back the increases in initial capital expenditures while retaining – and in some areas improving on – expected operational expenditure savings and safety considerations.

For the propulsion plant itself, the project found an increase in investment of less than 10% was needed for their hybrid concept, rising to 12.5% with the use of an energy storage system (ESS).

Overall, that added up to somewhere between 2.5-4% extra initial capital expenditure to install a hybrid system, without including an estimate for shipyard costs including foundations, wiring, installation and component tests.

Typical cost increases and cost savings

As the report notes, although the overall percentage increase in spend on their hybrid propulsion solution ran between 10-12.5%, significant changes in cost distribution and structure bear mentioning. Depending on use of an ESS, the larger gensets needed for a hybrid propulsion train are 10-20% more expensive than their traditional counterparts.

“As power provision is shifted from the main engines to the electrical system, the size of the generators needs to be increased accordingly and consideration of IMO Tier III compliance also has to be factored in here,” the report said.

Further equipment costs involve PTI/PTO electric motors to convert the electric battery power into mechanical power, which “should not be underestimated” in spite of a general downward trend in the cost of electrical components.

In terms of savings, the report cites the largest potential cost savings coming from the main engine selection.

“The reduction from 16 to 12 cylinders decreases initial expenditure of the drivetrain by more than 10 per cent,” the findings revealed.

“The reduction from 16 to 12 cylinders decreases initial expenditure of the drivetrain by more than 10 per cent”

Owners can find other cost reductions in the exhaust gas after-treatment selective catalytic reduction (SCR) system. “The application of a modular after-treatment system allows for a 12V engine, the usage of an optimised, scaled-down system, with an overall reduction of the number of components utilised,” the report said.

The other major cost reduction factor relates to the rudder propellers, their auxiliary equipment and the shaft line. “Even though most components remain the same, as the total torque on the shaft does not change significantly, there are savings of about 7%. This is predominantly due to the substitution of the slipping clutch by the secondary power input and a conventional disengaging clutch where additional costs are overcompensated,” the report detailed.

The report’s authors also made note of the relevance of savings over the lifetime of the vessel, including reduction of operational expenditures, better amortisation and value preservation of the investment.

“As experience shows, a realistic share of full electric operation can achieve 50%, as long as loitering and transit can be covered in such a way that operational procedures are not affected,” the report said. Using an average annual operation time of 3,000 hours for the propulsion plant a savings of 50% (1,500 hours per year) could add 10 years between main engine overhaul works.

Ultimately, although he would not be drawn on a prediction for exactly when due to the complexities involved with the price of battery technology, Mr Watson said it was only a matter of time before the difference in capex outlay between traditional propulsion and hybrid was non-existent.

“All these things over time will come down so our view is, ‘Ok, if there is a 10-12% higher capex today, maybe in 10 years’ time or 5 years’ time that is going to be virtually zero in any case.’

"If there is a 10-12% higher capex today, maybe in 10 years’ time or 5 years’ time that is going to be virtually zero in any case"

“So, longer term the view is we will get there with a hybrid system that can completely replace a conventional system for no additional capital expenditure. That is obviously the goal and is what needs to be achieved to make it competitive and most interesting to operators and shipyards.”

For the time being, Mr Watson says, the kind of holistic cost savings investigated in his project were an obvious choice for many operators facing a race to reduce emissions and fuel consumption.

“Of course, there is going to be a strong push to reduce emissions, particularly in this case you think about the harbour tug, it is operating close to shore, it is very visible and to see a harbour tug belching out black smoke … is not a pretty sight for anybody,” he says.

“I think the environmental factor is one thing that will drive hybrid propulsion and I think operators generally accept that is the way it is going to go … This is why we focused on the capex, because they want to see something competitive that they can use.”


*Co-authors of Hybrid power workboats: a holistic approach for better capex included representatives from Germany’s University of Applied Science in Munich and the University of Augsburg and industry partners, such as Canadian engineering firm Aspin Kemp and Associates and German propulsion specialists Schottel.

Related articles





Knowledge bank

View all