Engine makers seek environmental gains by repowering workboats

As a major opportunity emerges to repower US workboats, enginebuilders are unveiling their environmentally compliant options

According to new research, US workboat engines are used for more than twice as long as previously estimated, enhancing the benefits of retrofitting engines. The study, for enginebuilder consortium Diesel Technology Forum (DTF) and ecological lobby group Environmental Defense Fund, found that workboat engines have a service life of around 50 years, compared to the 23 years used by the US Environmental Protection Agency (EPA) to set its emissions reduction targets.

A longer service life means that older engines are replaced more slowly, resulting in 57% lower NOx reductions each year than those forecast by EPA. But it also increases the potential impact of installing new technology as upgraded engines will have a longer period in which to reduce emissions.

The groups are urging US states to repower vessels with more modern, cleaner engine technology. States can receive funding for repowering commercial workboats to reduce NOx under the US$2.9Bn environmental mitigation trust, established by Volkswagen Group in the wake of the emissions test fixing scandal in 2015.

“Large engine repowers are more cost effective on a dollar-per-tonne-of-emissions-reduced basis than other projects, which should make for an easy and compelling choice for states,” says DTF executive director Allen Schaeffer. “The incentive funds give operators a brand new, more efficient, fuel-saving and lower-emitting engine at a fraction the cost. Even better, the emission benefits associated with these projects will accrue quickly and persist for many years.”

The study, conducted by Ramboll Environ, looks at engines with a cylinder displacement of 5-30 litres – loosely equivalent to a maximum power output of around 8 MW – classed as ‘category two’ engines by EPA. New marine diesel engines have been required to meet EPA Tier 4 emissions standards – equivalent to IMO’s Tier III NOx limits – since 2015. But DTF says that the cost and downtime required to upgrade to new engines has likely delayed investments in the newest technologies.

Hybrid propulsion has been used regularly to reduce workboat emissions and new options continue to emerge. A harbour tug with a new hydraulic hybrid propulsion system is to be built by Sanmar Shipyards to a Robert Allan design. The tug will be fitted with Caterpillar Marine’s advanced variable drive (AVD) system. First developed in 2017, but yet to be applied in the tugboat sector, this allows operators to optimise propeller speed independently of engine speed, while controlling distribution of power among propulsion components.

The new tug design is based on the proven RAmparts 2400-SX design, with modifications for the AVD system. Boğaçay 38 has been optimised for harbour tug operations with 70 tonnes of bollard pull and Fi-Fi 1 firefighting capability. Propulsion equipment includes Caterpillar 3512C main engines, Caterpillar MTA627 azimuthing thrusters, and a C32 auxiliary engine powering the hybrid hydraulics as well as the Fi-Fi pump.

“The incentive funds give operators a brand new, more efficient, fuel-saving and lower-emitting engine at a fraction the cost”

Robert Allan was retained by Caterpillar Marine to support and advise on applying the new AVD technology for hybrid tug applications. This led to the debut tugboat project. Construction is currently underway with delivery scheduled for later in 2019.

The AVD system differs from a typical power take-in solution by incorporating a planetary gear set which allows seamless clutch engagement of main engines, auxiliary engines, or both. This allows propeller speed independent of engine speed so optimal engine efficiency can be achieved. Caterpillar claims this can lead to fuel savings of 15-20%, offering the benefits of diesel-electric propulsion at a lower cost and smaller footprint.

As a direct result of the AVD system, main engines can be downsized in most applications, with supplemental power provided by auxiliary engines. The system also provides inherently high levels of propulsion redundancy.

Engine plus aftertreatment

There is also an increasing range of traditional ‘engine plus aftertreatment’ options for owners to consider. MAN Energy Solutions has received the first tugboat reference for its MAN 175 engine shortly after receiving certification for the engine’s selective catalytic reduction (SCR) configuration. P&O Reyser has ordered a 27-m harbour tug from Drydocks World Dubai shipyard in the UAE that will be the first IMO Tier III compliant tugboat in the Mediterranean.

The asymmetric tractor tug (ATT) will provide 75 tonnes of bollard pull, with propulsion provided by fixed pitch propeller azimuth thrusters. It will be built to a Cintranaval CND-17009 Eco Silent design. P&O Reyser – which provides towing, mooring and auxiliary services in 11 Spanish ports with a fleet of more than 100 vessels in service – expects the ATT to enter service in the Port of Barcelona from mid-2020.

MAN Energy Solutions will supply two MAN 12V175D MM engines, each rated at 2,220 kW, with SCR. According to MAN Energy Solutions head of four-stroke marine sales Lex Nijsen, the engines were selected because of their “compact footprint, fuel-efficient performance and the flexible design approach taken with the SCR layout.”

MAN Energy Solutions head of exhaust aftertreatment Daniel Struckmeier says: “We have based the SCR system on our most cutting-edge technology. A great strength is its flexible arrangement and compactness, which optimises the space typically available in confined enginerooms.”

Repowering does not have to mean entirely new engines or vessels. One of the world’s biggest diving support vessels has re-entered service after an engine overhaul that included having key components tested and repaired at a remote workshop. The engines and turbochargers on the 140-m long Seven Atlantic, owned by Subsea 7, were serviced 10 years after the vessel was built, with Royston Diesel completing the work.

Royston service manager Shawn Doering notes that the company’s experience with the engine and vessel type ensured a quick re-entry into service. Seven Atlantic is powered by six 3,360 kW Wärtsilä W7L32 engines running on marine gas oil, each paired to a 3,360 kVA Van Kaick generator. The diesel-electric arrangement drives three 2,950 kW stern azimuth thrusters, two 2,400 kW retractable bow azimuth thrusters and a 2,200 kW bow tunnel thruster.

One of the engines was disassembled to install new cylinder heads, air start valves, indicator cocks, injectors, and cylinder seals. Relief valves, pistons and conrods, cylinder liners, bearing blocks, crankshaft and turbocharger were sent to UK headquartered Royston’s Newcastle workshop for checking and essential repair work before being returned ahead of the final reassembly and inspection of the engine.

Engineers also overhauled the turbocharger on another engine. The NA297 Napier turbochargers from both engines were removed, stripped, cleaned, inspected and balanced at Royston’s dedicated turbocharger facility. Following the service, incremental load testing in line with the engine manufacturer’s specification was also completed by engineers.