Why environmental considerations should not overshadow safety and cost in tug design

Naval architects and shipyards are accommodating owners’ requirements for economically effective tugs that are safe to operate and produce lower emissions. After a lull earlier this year due to the global coronavirus pandemic, designers’ workloads are back to previous levels.

Robert Allan principal and manager for project development James Hyslop says owners are focused on environmental issues, which are regulated by IMO Tier III and US Environmental Protection Agency (EPA) Tier 4 emissions requirements. “Emission control equipment has to be incorporated into the exhaust system, which requires extra space either in the engineroom or within the deckhouse,” says Mr Hyslop. More tank volume and pumps for urea to remove nitrogen oxides are also required.

“All of this requires careful monitoring of weights and space – sometimes difficult in compact tugs that are trying to meet a tonnage or length restriction,” says Mr Hyslop. “But otherwise it has not been a real detriment to the overall design (at least for a standard tug with high speed engines).” 

Regulations and class notations regarding hazardous materials are also becoming more prevalent. So is interest in alternate fuels such as LNG, methanol, ammonia and hybrid/electric systems. “These are pushing the development of propulsion systems to new levels of cleanliness and effectiveness,” says Mr Hyslop.

Safety is also a major consideration in tug designs. This comes under ergonomic and sensible design contributing to crew safety and “improved stability regulations that properly reflect the way that tugs operate”, he explains.

Tugs are also being designed and built for ice operations in northern Europe. Another option is installing a removable icebreaker bow (RIB) on an existing tug.

ILS Ship Design & Engineering has designed an RIB for breaking ice in the Baltic region, including in Gulf of Bothnia ports. One of its more advanced projects is an attachable bow with a maximum length of 25.3 m, moulded breadth of 12.6 m and moulded depth of 3.4 m.

It will be able to break 80 cm of level ice at 2 knots. If the speed is increased to 6 knots, the tug-bow combination can break 40 cm of level ice in inland waterways. The first of these RIBs was completed at Turku Repair Yard, but its first project has been delayed by the Covid-19 outbreak, which has postponed other business opportunities ILS was involved in.

“We are now busy finalising the as-built drawings of the first RIB,” says ILS general manager Kristian Lehtonen. “The quay and sea trials have been successfully completed.” He expects there will be a project for the RIB this year or in Q1 2021.

“This novel technology is something that enables operations in ice-infested areas, which some are very interested in,” says Mr Lehtonen.

One beneficial feature of this concept, is it only takes around 15 minutes to connect and disconnect the tug and the bow.

“This bow is equipped with ACM-Trading Pushpin articulated tug-barge (ATB) coupler system,” says Mr Lehtonen. ACM-Trading provides a wide range of new ATB coupling systems, covering the needs of the smallest tug and barge combinations right up to the very largest ones. “ACM-Trading’s contribution to the RIB project is really valuable,” he continues.

The PushPin coupler has a connecting axle that allows the tug and barge to pitch individually around a common axle. It can be used on a variety of barges and in operational areas such as inland, coastal, offshore and nonrestricted sailing areas. It has pneumatic, hydraulic or mechanical driving systems and lateral movement preventing units.

PushPin socket plate structure can be a notch or modular system and can be steel cast for low weight and size.

Turkish tugs to UK designs

Macduff Ship Design has designed harbour tugs for vessels under construction in Turkey. It is building a second 30-m ASD tug at Tor Group.

According to Macduff managing director Ian Ellis, this tug was undergoing final sea trials after successfully completing stability analysis in mid-July. “Once trails are completed, it will be subject to a class inspection and then will be available as a stock vessel from the shipyard for charter or sale,” said Mr Ellis.

This tug will have two Yanmar 6EY 22AW main engines, each developing 1,330 kW at 900 rpm. These will drive two Schottel SRP1012 rudderpropellers, producing an ahead bollard pull of 44.5 tonnes, astern of 38.8 tonnes and maximum free-running speed of 13 knots.

“This tug has three two-man cabins and three single cabins,” says Mr Ellis.

Also in Turkey, Atlantis Marine Services is building a tug using a Macduff design for a 13-m long vessel. “The tug is the first of a proposed series,” says Mr Ellis. “It is a shallow-draught, conventional-drive, twin-screw tug. It is a development of a successful series of designs which have been built at multiple locations.”

Atlantis will build this tug for its own stock to be sold to an owner after completion.

MacDuff also designed a 16-m tug built in 2019 for Shoreham Port Authority. Acamar achieved a bollard pull of 10 tonnes and free running speed of 10 knots on trials.

“This design is tailored to suit Shoreham’s specific operational requirements which included a beam restriction to fit through lock gates,” says Mr Ellis. He expects more interest in tug designs for larger vessels.

“We are continually working on newbuild projects throughout the world and are currently developing the design for both 25-m and 30-m ASD tug enquiries. These are developments of proven past designs,” says Mr Ellis.

MacDuff has also developed designs for line handlers. One of these was used by Cheoy Lee Shipyards to build two 14-m line handlers. “These vessels have been designed with the ability to be easily lengthened by 2 m should the owner require,” he explains.

Diesel-electric hybrid over LNG

Owners are showing interest in ordering tugs with hybrid propulsion other than LNG to meet tougher environmental regulations, instead using diesel-electric systems with batteries for back-up or motors on the shaft line.

These vessels will be more cost effective to purchase than tugs with gas and diesel fuel, says OSD-IMT technical manager Herm Jan de Vries. His team is working on a dual-fuel tug naval architecture and has produced an electric-tug design.

“In the bigger picture, dual fuel drives up costs for tugs to unnecessarily high levels,” says Mr de Vries. “And from tugs built [with dual-fuel propulsion] use of LNG is very limited and these tugs tend to use more diesel than expected. So, they are expensive on capital expenditure and owners do not get much operating savings back,” he says.

Owners are more interested in incorporating hybrid propulsion on smaller and more powerful tugs. “Owners want more compact designs with smaller tugs that still comply with the stability requirements and are commercially viable,” says Mr de Vries.

“Designers have to find clever ways to find this balance by increasing the beam and shortening lengths.” This is without affecting power delivery from diesel-electric hybrid propulsion.