Meeting ever tighter regulations on emission levels and reducing overall lifecycle costs are probably the two most important factors influencing engine design and specification for workboats, including tugs, at the present time. Corinna Nones, manager for applications development at Wärtsilä Marine Solutions, points out: “Environmental regulations, and in particular NOx and SOx limits, are the key factors guiding the future development of tug main engines. Getting a fast response from the engine and obtaining low fuel consumption at low loads are also important considerations for customers in this segment.”
Harbour tugs are on standby a large amount of the time and use the maximum power of their main engines relatively rarely. Optimising fuel efficiency within this operational profile is, together with environmental factors, probably highest on the agenda for enginebuilders and their customers.
The main focus of the German engine manufacturer MTU, part of the Rolls-Royce group, is very much on environmental performance. Specifically, as it seeks to raise its profile within the tug sector, the company is stepping up the development of exhaust gas after-treatment systems, gas engine technology and hybrid systems.
MTU is now supplying engines with selective catalytic reduction (SCR) technology for exhaust gas after-treatment, for those vessels which have to comply with the NOx limits specified in the IMO Tier III emissions standards. MTU says it is working on a compact design for an SCR-based unit, which will be flexible in terms of switching on and off line during entry and exit into emission control areas (ECAs). This will allow the operator to select the optimum operational mode. MTU believes the SCR option will be very reliable, as this technology has been proven in a number of other marine applications.
The enginebuilder already has some experience of delivering main engines with SCR to tugs, having equipped a pair of 90 tonnes bollard pull units for Fairplay Towage. These tugs, which were delivered last year by Astilleros Armon, feature a hybrid diesel-mechanical and diesel-electric propulsion arrangement powered by MTU Series 4000 engines with an in-house developed SCR combined with an MTU diesel genset. “By using generator sets for the main operation, such hybrid systems give owners the chance to extend the time between overhauls of the main engines, saving fuel and also operating costs,” comments Stefan Müller, head of marine application engineering at MTU.
From 2018, MTU will also be able to offer tug owners a high speed marine gas engine option. The company is developing a new 16-cylinder pure gas engine based on its proven workboat Series 4000 M63 Ironman diesel engine. This core technology will be supplemented by a multipoint gas injection system, dynamic engine controls and various features designed to enhance operational safety.
Mr Müller says: “We are developing this new gas series in order to meet the extreme load profile of tugs. Acceleration will be comparable to that achieved by our diesel engines, while the clean combustion concept will allow IMO Tier III compliance to be achieved without the need for additional exhaust gas after-treatment.” The 2,000kW gas engine being developed by MTU will combine high power density with low fuel consumption, the company points out.
The tug market is one of growing importance to MTU, which has recently entered into a strategic partnership with one of the leading specialist shipyards, Sanmar of Turkey. As result, the RAstar 2800-E ASD tugs currently being built by Sanmar are to be powered solely by MTU series 16V 4000 M63 and M63L engines, coupled with Rolls-Royce or Schottel propeller systems. Mr Müller adds: “Engines in this series are extremely efficient, in addition to offering very low fuel consumption and low maintenance costs. They also meet EPA Tier 2, IMO Tier II and ZKR II emissions standards.”
Currently, a total of 12 16V 4000 M63 engines, each delivering 2,000kW, are on order for six 70 tonnes bollard pull RAstar 2800-E terminal tugs being built by Sanmar. The first of these will be delivered to Svitzer later this year.
Wärtsilä is similarly focusing on improving fuel economy, and hence environmental impact, in refining its main engine offering for the tug market. Its Wärtsilä 26 series, for example, has been improved to better meet the needs of this type of application. At a recently completed design stage, the specific fuel consumption (SFOC) of the engines was improved at low loads, giving tug customers a notable saving in terms of both fuel consumption and cost. Moreover, Wärtsilä points out that this improvement has been accompanied by gains in terms of engine load capabilities. Ms Nones says: “This means the Wärtsilä 26 can deliver a fast response from the engine side, when a certain load is required by the tug.”
Further development work is in progress, the company reveals, on a completely new engine type. This would have dimensions, weight and power output levels well suited for this type of installation.
Wärtsilä is also evaluating hybrid solutions using battery technology and is promoting to the tug market its dual-fuel engine technology for use in certain operational areas, including ECAs, that face restrictions due to environmental regulations. It has, for example, delivered main engines for two liquefied natural gas (LNG) powered, multipurpose tugs for CNOOC Energy Technology & Services, a subsidiary of the state-owned China National Offshore Oil Corp (CNOOC). Each of these tugs is equipped with two 2,400kW rated 6L34DF dual-fuel engines.
The company is also working with Drydocks World, Dubai to deliver an LNG powered 55 tonnes bollard pull tug that will be the first of its type in the Middle East. This pioneering vessel will be powered by two Wärtsilä 9L20DF main engines and is due for delivery later this year.
Also under construction for delivery in 2016 are three LNG powered escort tugs for Østensjø Rederi. These 100 tonnes bollard pull tugs, designed by Robert Allan, feature two Wärtsilä 6L34DF engines, each rated at 3,000kW.
Another Europe-based enginebuilder, MAN Diesel & Turbo, is introducing a new high speed engine, type 175D, with a power range of 1,500kW–2,220kW especially for the tug segment. Director of sales Frederik Carstens says: “The engine represents the latest state-of-the-art technology and is designed as a powerful, compact and very efficient engine which is easy to commission, easy to operate and easy to service.”
MAN Diesel & Turbo’s existing medium speed engine, the L27/38, has built a good reputation within the tug market and has demonstrated its suitability for many different types of application. Mr Carstens adds: “We see a growing number of players in the tug segment placing repeat orders for the L27/38. Tug owners appreciate its quick acceleration capabilities and its maintenance-free character with time between overhauls of up to 32,000 hours. The engine is designed to cope with the toughest operational situations that tugboats typically face in their daily work.”
The new United States Environmental Protection Agency (EPA) Tier 4 regulations came into effect in January this year and US-based GE Marine is now offering tug customers main engines that comply with these regulations. The company has recently extended its Tier 4 engine series to include 16- and 12-cylinder V models, and an 8-cylinder inline model. A 6-cylinder inline model is currently planned for development.
GE Marine points out that its engine series meets the Tier 4 emissions standards without the use of urea after-treatment, while maintaining fuel efficiency and service intervals. In addition, the company says the engines have a faster response time to steps up in load, and a maximum continuous rating that is 12 per cent higher than their Tier 3 compliant predecessors.
GE Marine’s customers are said to have responded positively to the next generation Tier 4 offering. For instance, Reinauer Transportation has purchased two 12V250MDC Tier 4 diesel engines for its new articulated tug and barge (ATB) units. Reinauer says that it selected the engine because it closely matches the footprint of engines on current vessels, limiting the amount of re-engineering required. The fact that it is able to meet Tier 4 emissions requirements without the complications of urea after-treatment was another attraction.
Also now marketing EPA Tier 4 compliant engines for tugs is Caterpillar Marine, with Harley Marine Services becoming the first to select the new technology for its vessel Earl W Redd. To meet the Tier 4 emissions standards Caterpillar is adopting a different approach to GE Marine, as each of the Cat 3516E engines on board is paired with an SCR after-treatment system using urea solution. According to Caterpillar, the new engines will be able to deliver an increased level of performance thanks to their higher power rating and the engine fuel efficiency improvements that Caterpillar’s SCR technology has enabled.
Now that the EPA Tier 4 regulations apply to all US-flag tug newbuilding orders, further contracts are coming in for Caterpillar’s new generation, environment-friendly engine series. Most recently McAllister Towing has announced its intention to equip two tugs it has ordered from Horizon Shipbuilding with the Cat 3516E Tier 4 engines.
Jason Spear, product definition engineer at Caterpillar, says: “To comply with the Tier 4 rules we have adopted an integrated solution based around a complete redesign of the engine type to give operators the best possible outcome. This has enabled us to achieve better fuel consumption while also cleaning up emissions, and a lower total lifecycle cost for the owner.”
The Caterpillar EPA Tier 4 engine will also meet the broadly equivalent IMO Tier III regulations. However, Caterpillar indicates that it may introduce some modifications to the basic design to meet the specific requirements of European customers.
Mr Spear observes: “Our EPA Tier 4 engine is based on SCR technology with urea but some tug owners with the flexibility to operate both inside and outside ECAs may find that they cannot obtain urea outside an ECA. For that reason we are developing engine solutions that allow them to switch back to an IMO Tier II calibration when it is not required by local regulations.”
Alongside its EPA Tier 4 engine development programme, Caterpillar has been working on alternative fuel designs. Mr Spear says: “We believe that diesel engines are still the primary way forward for the tug market. But we are looking at various other solutions using natural gas, including dual-fuel types and engines with 100 per cent gas ignition.”
While it has a strong market position in North America, Caterpillar Marine is achieving considerable success in supplying tugs outside the region as well. Indeed, fewer than 25 per cent of sales of the popular 3500 series engine now come from North America.
In South America the Cat 3516C engine has been selected by Svitzer to power four new harbour tugs it has ordered in Brazil for its Transmar Servicios Maritimos subsidiary. The four 60 tonnes bollard pull tugs are being built at INACE (Indústria Naval do Ceará) in Fortaleza and will be operational in 2017. The engines will be able to meet IMO Tier II regulations, and will feature electric governing with a cold mode start option, and a programmable low idle option to minimise fuel consumption.
To boost its position in Europe the company has signed a letter of intent with Sanmar to supply at least 84 propulsion engines between now and the end of 2018. These will include 26 Cat C32, 22 Cat 3512C and 36 Cat 3516C engines, which will be used to power tugs with bollard pull ratings of between 60 and 85 tonnes.
In Asia last year Caterpillar equipped a series of four tugs for Svitzer, built at the ASL Marine Holdings shipyard in Singapore, for the Wheatstone LNG project in Australia. These were ‘firsts’ for Caterpillar which supplied diesel-electric, variable speed engines as part of the propulsion package on board.
To further strengthen its position in the Asian market, Caterpillar has recently opened an engine manufacturing facility in Tianjin, China, that will supply 3500 series engines to a variety of vessel types, including tugs. The aim is to reduce delivery costs, and cut lead times, for customers in Asia.