Wärtsilä is investigating how to merge dual-fuel engines with hybrid propulsion technology to lower operating expenditure and emissions
Tugboats could be built with both LNG and hybrid propulsion systems to minimise their gaseous emissions in ports. Approximately five tugs are being built worldwide with dual-fuel engines and at least another five are under construction with hybrid propulsion systems, but none with both.
There is considerable extra cost in a tug construction project if LNG fuel is chosen – thought to be around US$3M depending on the project – instead of conventional diesel-mechanical or diesel-electric propulsion. But, there is a lower additional cost for installing hybrid power units. As the operational benefits are slowly realised by owners and port authorities, more orders for tugs with these types of propulsion are forthcoming.
Wärtsilä business development manager for offshore and special vessels Donato Agostinelli Capaldo believes demand for tugs with both LNG and hybrid propulsion will increase; hence, Wärtsilä is looking at ways of combining them on a vessel for fuel and operational efficiency.
“There is a large cost jump from conventional propulsion to LNG, and a gap between conventional propulsion and hybrid,” said Mr Capaldo. “But, there is only a small change going from LNG to LNG with hybrid. There would be substantial benefits with little extra cost,” he said.
Wärtsilä has supplied dual-fuel engines for LNG-fuelled tugs, including a pair for an LNG tug under construction for PSA Marine, and propulsion for an LNG articulated tug-barge unit for Quality LNG Transport (Q-LNG)’s bunkering services in the US. It has also supplied HYTug design and propulsion for a hybrid icebreaking escort tug, under construction for the Port of Luleå in Sweden.
“[Some] operating modes are rarely used, so the systems operate off-design for most of the time, increasing fuel, emissions and maintenance costs”
Mr Capaldo said the Q-LNG project was driven by the need to provide LNG fuel on ships in the US and to meet Tier 4 requirements from the US Environment Protection Agency. Stringent environmental rules could push more owners into ordering LNG-fuelled and hybrid propulsion tugs.
But, the drive should also come from the port authorities and charterers, Mr Capaldo said. “It takes support from stakeholders to promote hybrid and/or LNG for lower emissions,” he explained. “The benefits and gains take time to be accounted for on the balance sheet..., so we need to bridge this gap. There needs to be financial incentives so that we all can benefit.”
It is true that there are both environmental and commercial benefits from LNG and hybrid, and they are applicable to owners and charterers alike. “Tugs can be idling in port, transiting at speeds of 5-7 knots, pushing at low power, or towing at medium power and perhaps at maximum power for a short time,” said Mr Capaldo.
“Hybrid systems improve the overall performance of tugs, as they have a wide range of operating modes,” Mr Capaldo explained. “Some with very high loads for a small amount of time, others with very low loads for long periods of time.”
“We can integrate different power systems and balance them effectively with the best combination for a tug’s operating profile,” he continued. This leads to less maintenance and cylinder running hours, lower fuel and reduced gaseous emissions.
Tug owners and port authorities mainly focus on meeting maximum bollard pulls and sailing speeds when choosing design and propulsion. “This creates systems that are optimised for the maximum performance,” continued Mr Capaldo. “In reality, these operating modes are rarely used, so the systems operate off-design for most of the time, increasing fuel, emissions and maintenance costs.”
Hybrid propulsion enables owners to have different optimal settings when integrating engines with batteries and charging. By integrating with dual-fuel engines, owners can also have different emissions settings.