Growing numbers of offshore vessel owners are harnessing diesel-electric and hybrid configurations to provide greater flexibility across their fleets
Even in the mighty arena of subsea construction vessels, the 153.6 m long, 18,151 gt North Sea Giant is an impressive specimen. Last year it became even more so; its six 3,600 kW GE engines (driving five Voith-Schneider thrusters and a Rolls-Royce tunnel thruster) were supplemented by an energy storage system designed and installed by Wärtsilä. The result is arguably the most capable DP3 vessel on the market.
That capability is not just thanks to the vessel’s battery system, which provides over 2,000 kWh across three modules. As owner North Sea Shipping intends to use the vessel, those batteries would be irrelevant if it was not for an even newer technology. The electric bus link (EBL), developed by Yaskawa Environmental Technology, enables the operator to link battery systems in series and (more importantly) to disconnect them at previously unachievable speed.
“EBL splits the on-board grids in a matter of microseconds, isolating faults and protecting the complete operational system,” says Yaskawa general manager Asbjørn Halsebakke. “This offers significant savings on maintenance costs. Also, by rapidly connecting and disconnecting energy sources from one another, including batteries and engines, they can be optimised for efficiency.”
In theory, that rapid shutdown capability means that the North Sea Giant can operate in DP3 mode with a single engine, the first vessel capable of this feat. Safety requirements previously required ships to perform several operations, including DP3, with engines providing power to each grid, rather than using one engine to power the grids in series or using batteries to power each grid. But with approval from DNV GL – which will now revisit its DP3 class rules – the ultra-fast line breaking technology deployed on North Sea Giant means that just one engine can be used, with the three battery packs providing redundancy.
"Its rapid shutdown capability means that the North Sea Giant can operate in DP3 mode with a single engine, the first vessel capable of this feat”
Wärtsilä Norway general manager Tore Marcus explains that the ship is currently performing these operations with three engines, each supported by one battery string, while the companies await a slot in the ship’s busy charter schedule for final testing. When North Sea Giant finally meets its potential, Mr Marcus predicts that the vessel’s unique DP3 power arrangement will save up to two million litres of fuel a year.
Those savings and the rewriting of safety rules around DP3 give a strong indicator of the potential of diesel-electric and battery-hybrid propulsion. But you do not have to operate DP3 vessels, or indeed install batteries, to realise diesel-electric efficiencies. Nor do you have to be a giant. Damen Shipyards Hardinxveld is set to deliver the first diesel-electric arrangement for the shallow draft, DP2 version of its versatile Shoalbuster series.
A shallow draft, DP2 capability and diesel-electric propulsion will boost Brutus' employment prospects
The Shoalbuster 3514 SD DP2 will be used by owner Herman Senior initially for windfarm support work in coastal waters. But, according to Herman Senior managing director Jack van Dodewaard, the vessel will be equally capable of working on projects further offshore. With a 60-tonne bollard pull, the vessel – to be named Brutus – will also have the potential to attract towing work.
“The demand for DP2 vessels is increasing and this will fill a gap in the market,” says Mr van Dodewaard.
That claim is backed up by an installed power that belies the small size of the 35 m-long vessel. Four Caterpillar C32 ACERT engines will deliver a total of 3,876 kW to four 1900 mm-nozzle waterjets. That arrangement contributes to the vessel’s shallow-draft capability while the dynamic positioning system, including ancillary thrusters, safeguards position-holding around structures. Dynamic positioning could be used in the open sea as well – an open stern will make Brutus suitable for cable-laying operations.
Among the many other roles which Brutus will be capable of taking on are pre-lay grapnel runs, remote vehicle surveys, mattress installations, mooring, pushing, dredging support, ocean-going towage and general OSV duties. The vessel will even be equipped for anchor handling, with a roller at its stern.
“The vessel will be very fuel efficient and will have a very low carbon footprint,” says Mr van Dodewaard. That is a direct result of the diesel-electric configuration that allows the operator to run from one to four engines depending on propulsion power demand, with the remaining engines providing power for one of the many tasks within the vessel’s remit. Brutus will also be IMO Tier III compliant thanks to the Caterpillar engines’ selective catalytic reduction units.
If Brutus, due for delivery in early 2020, epitomises the efficient, modern, multitasking offshore vessel, there is still a way for older vessels to compete. That is according to Caterpillar Marine product manager Theodore Wiersema. Speaking at the OSJ Conference in February, he noted that owners can use retrofit packages to update engines to meet IMO III fuel and emission regulations, while variable-speed generator sets can help increase efficiency by up to 20% compared with fixed-speed gensets.
Vessels can be retrofitted with electric motors and batteries to reduce load demand on engines for propulsion. Mr Wiersema said that version 3.0 of Caterpillar’s Multi-Engine Optimiser (MEO) tool can advise engineers on managing diesel-electric and hybrid propulsion to optimise operations and reduce fuel consumption.
“MEO leverages data and algorithms to provide the best combination of load points,” Mr Wiersema explained. “It can be combined with a battery manager for charging and discharging and with digitalisation with Cat Asset Intelligence.”
Theoretically, this would allow a 15-year-old vessel to compete with a modern equivalent.
Big or small, new or old, vessels in the offshore sector face demands for efficiency and versatility that are making diesel-electric propulsion an increasingly appealing option.
Semi-submersibles set to tap hybrid potential
West Mira will become the semi-submersible standard bearer for hybrid power (credit: Neil Robertson)
It is not only OSVs that are harnessing hybrid power. Northern Drilling will introduce the first energy storage system on a semi-submersible rig when West Mira begins operations in the North Sea this year. The rig’s diesel-electric generators will be supplemented by a lithium-ion system, Siemens’ BlueVault, that is expected to cut the running time of the platform’s diesel engines by an estimated 42%. That will cut CO2 emissions by 15% and NOx emissions by 12%. The solution consists of four converter and battery systems with a total maximum power of 6 MW.
The batteries will be charged from the rig's engines and used to supply power during times of peak demand. They will also serve as backup to prevent blackouts and provide power to thrusters if engine power is lost.
Siemens head of offshore solutions Bjørn Einar Brath says: “Offshore rigs have highly variable power consumption for drilling and dynamic positioning. By incorporating energy storage, it is possible to reduce the runtime of diesel engines and keep them operating on an optimised combustion level. This ultimately leads to lower emissions."
The energy storage solution has already been installed in more than 60 vessels worldwide, and Siemens has marked the offshore market for further potential. To this end, it has opened an automated plant in Norway that will develop and manufacture energy storage technologies for both marine and offshore oil and gas applications.
"The facility will play an important role in helping Siemens meet the global demand for more efficient drilling operations, with the ultimate goal of reducing the offshore industry's carbon footprint," says Mr Brath.