By Wei Huang, Ph.D., director and global offshore market sector lead of offshore support vessels, ABS
Demand for the offshore support vessel (OSV) services is growing. In 2020, the market reached $13.78 billion, despite the economic chaos and disruption caused by the COVID-19 pandemic. By 2028, demand for OSV services is set to expand by almost $10 billion to reach a value of $23.6 billion.
Looking ahead, a key task for the sector is to reimagine OSV designs so they can support demand for services in a way that is sustainable and financially viable.
OSV operations will need to be fully integrated with offshore fields, port infrastructure and supply chains to cater to increasingly complex and multifaceted customer requirements. This means that vessels will need to be fully digitized and highly automated to tie into their supporting tech-enabled ecosystems.
Drawing on its own insight and predictions, ABS recently published a report containing detailed insights on the future of OSV designs and operations. It covers a range of mission critical aspects, from how technology can help to integrate OSV operations to emerging regulations and their impact on design and use by the offshore industry. Crucially, it contextualizes these aspects around a carbon neutral future, detailing numerous ways vessels can be prepared and designed to assist the marine and offshore sectors on the net-zero journey.
Decarbonizing marine propulsion systems
One of the most obvious ways of achieving carbon neutrality is to decarbonize vessel propulsion systems.
Typically, OSVs rely on diesel-electric propulsion systems – multiple diesel generator sets feed a fixed-frequency electrical bus, which then feeds the electrical propulsion motor drive and the hotel load (most commonly a transformer).
By integrating these diesel-electric systems with energy-storage solutions such as lithium-ion batteries, flywheels or supercapacitors, the combination of electrification and hybrid power can increase the flexibility of a vessel’s propulsion system.
Furthermore, this will allow internal combustion engines to run at optimal levels of fuel efficiency and, when running purely on battery power, vessels will be able to operate with zero emissions.
Hybrid power supplies – benefits and challenges await
Indeed, there are several key performance benefits attached to using hybrid power supplies for OSV power and propulsion systems.
When tapping into stored energy, one or more engines can be switched off, and storage systems themselves can be recharged when engines are running and store regenerated energy when braking on electric motors – this can save fuel, reduce emissions and noise, increase crew comfort and support sailing without emissions, noise and vibrations from the engines.
Batteries also enable load leveling and peak shaving and provide an important source of backup power in the event of combustion power supply failure.
However, it should be noted that several challenges need to be overcome or accommodated for if OSV designs are to fully embrace hybrid-electric propulsion systems.
- Finding the optimum balance in charging and discharging the battery to enable a maximum reduction in fuel consumption.
- Managing local fluctuation on diesel engines. The control strategy should ideally share dynamic loads between the battery and the diesel engine in ways that minimize fuel consumption, emissions and maintenance loads for all power suppliers.
- Costs relating to battery installations will need to be minimized or offset, perhaps by reducing the installed power from diesel engines.
Another challenge related to electrical propulsion is that an engine’s fuel consumption in partial load is higher when running at fixed as opposed to variable speed.
Here, a DC hybrid power supply and distribution system can help. They allow operators to run a diesel engine at variable speed, potentially reducing fuel consumption, emissions, operating noise and its mechanical and thermal loading.
However, DC systems are also subject to some challenges. Because they need all power sources to be connected by converters, and this can incur large costs. Meanwhile, fault protection will need to be resolved to enable DC architectures.
SEACOR currently operates 10 OSVs equipped with hybrid batteries.
Harvey Gulf International Marine also classed two OSVs retrofitted with a battery/converter system. The Harvey Energy is the first ABS-classed dual fuel and battery vessel and the first U.S.-flagged OSV equipped with a battery/converter system. The Harvey America and Harvey Freedom are the second and third vessels in the Harvey Gulf fleet installed battery power system.
The battery capacity will be sufficient to sail in and out of port on electric power with fewer engines running, while also supplementing hotel load electricity, which would reduce noise and pollution levels in the port area. Furthermore, the ability to operate on battery power will assist peak load shaving and increase redundancy during critical dynamic positioning operations at the offshore field.
It is possible that other market-tested infrastructure could be used to provide renewable alternative fuels to the OSV sector. One such strategy would provide the vessels with access to electrical power at ports connected to the grid. Shore power and offshore charging buoys are evolving technologies, but they hold the potential to charge vessels with the renewable energy produced by offshore windfarms. Aside from the environmental benefits, installing electric buoys closer to the offshore assets that the vessels are serving would burn less fuel while the ships are idle and offer the benefit of charging times that are less disruptive to operations.
All hybrid-electric propulsion options explored here and in the ABS report have challenges – crucially, none we believe are insurmountable.
Wei Huang is director and global offshore market sector lead of offshore support vessels at ABS. To discover more about how OSV designs and operations are set to evolve, including the importance of sustainability data monitoring, read the full ABS report: Insights into Future OSV Designs and Operations.
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