Combining the advanced control and monitoring of thrusters with machine learning will help offshore crew operate vessels with even greater energy efficiency
“Information is power,” says SINTEF Ocean research manager, maritime energy systems Anders Valland. “When that information relates directly to power consumption, it can revolutionise vessel operations – from onboard electrical load management to route optimisation,” he explains.
The information to which Mr Valland refers is the operational data being fed into the models for a new decision support system (DSS) under development by Norwegian offshore support vessel manager DOF, in collaboration with Kongsberg Maritime and research institutions SINTEF Ocean and NORCE.
The aim is to improve the energy efficiency of a range of offshore operations – most of them relying on vessels’ thruster systems. The multi-year plan was the biggest offshore vessel, environmental technology project to receive funding from Innovation Norway last year. And according to DOF, the predictive tool will be critical to helping crew reduce operational complexity and cut fuel consumption and emissions.
“It will be a game-changer in how marine operational decisions are supported,” says DOF senior project manager Lars Christian Larsen. “It will provide more accurate, timely, and easily consumable information to the vessel’s chief engineer and the shore-side chief operation officer.”
The system is made possible by integrating operational technologies – like thruster controls – with information and communication systems, says Kongsberg Maritime director of energy products integration Eiriki Mathiesen.
“It will be a game-changer in how marine operational decisions are supported”
“New sensors will be deployed that stream data to the cloud-based support system,” he adds.
Meanwhile, Kongsberg's investment in the systems behind thruster technologies is continuing. It recently filed two patents that may eventually improve the condition monitoring of azimuthing thrusters.
One of the difficulties of monitoring azimuth thrusters involves reliably powering sensors in the thruster body and transferring data from the rotating to the static part of the thruster. One current method of doing so involves using mechanical slip rings to convey data and power, but this has two major limitations: the first is cost, as slip rings need to be modified for each size and configuration of the thruster; the second is the wear this arrangement causes to the slip ring and shaftline, meaning regular service is needed.
Kongsberg energy and health management specialists Werner Schiffers and Lars Saarinen believe the answer lies in resonant magnetic induction. Two inductors – one generating a magnetic field, the other generating an electrical current from that field – are configured so they can be rotated fully while still creating the electrical current. This enables power and data to be transferred wirelessly.
“This would simplify wireless data and power transfer during health monitoring of marine thrusters,” says Mr Schiffers. “A major advantage of our idea is that the power and data transferring parts of the condition monitoring unit can be retrofitted without removing the thruster from the ship’s hull.”
There are other benefits too, stemming from the more robust and efficient transfer of power. The sensor in the thruster body would not require a battery, for example, and maintenance intervals could be extended as thruster designs are adapted to accommodate bigger, longer-lasting inductors. The commercialisation of the concept is not yet in sight, but it provides an intriguing example of how control and automation technology can influence the development and performance of thrusters.
ZF Marine has recently introduced a condition monitoring system for its thrusters. The system measures vibrations which indicate the condition of the bearings and gears in the thruster's upper and lower gearbox. This helps operators to identify when early components need to be replaced or maintained. Repairs can be planned and a worsening in the condition of the components can be avoided, all of which prevents downtime and shortens maintenance time. This extends the service life of the monitored systems and components, allowing the operators to concentrate on their main job.
The company has also introduced an oil cleaning system to improve the quality and service life of thruster oil. By heating up the oil, the water is evaporated while a cotton filter filters out the particles down to 1 µm. Clean oil is pumped back into the system which extends the service life of the oil by 10 to 15 times. Fewer oil top-ups are needed, saving ship operators money.
ZF Marine sales manager Peter Toxopeus says: “Particularly with biodegradable oil, it is important to keep contaminants, such as water, out of the system so as to prevent downtimes caused by mechanical failures.”
“A major advantage is the power and data transferring parts of the condition monitoring unit can be retrofitted without removing the thruster from the ship’s hull”
Louis Dreyfus Armateurs (LDA) has chosen a thruster package for its debut service operations vessel Wind of Change. The vessel, which won OSJ’s Offshore Renewables Award in January, will feature rudder-propellers and transverse thrusters from German propulsion specialist Schottel.
The vessel is being built to a Salt Ship Design plan at Cemre shipyard in Turkey. It measures 83 m in length and has a beam of 19.4 m. Two SRP 430 FP (fixed pitch) Schottel Rudderpropellers with an input power of 1,660 kW each and a propeller diameter of 2.40 m are installed at the stern. At the bow, two fixed-pitch transverse thrusters with an input of 1,400 kW each and one SRP 260 retractable Rudderpropeller with an input of 800 kW will provide manoeuvrability and dynamic positioning to DP2 standards.
The high-specification vessel will be outfitted with a 19-m motion-compensated gangway from Uptime and a TTS Colibri motion-compensated crane. The power plant comes in the form of L21/31 variable-speed gensets, ach rated at 1,660 kW, from MAN Energy Solutions, employing the EPROX energy saving electric propulsion system.
The vessels feature an on-board DC grid along with a power and energy management system. The grid will integrate two sets of batteries that will be used primarily for spinning reserve and peak shaving. Battery power can also act as backup for running generators, reducing the need to run spare generator capacity.
Wind of Change will operate under a long term-contract with the Danish company Ørsted at the windfarms of Borkum Riffgrund 1 and 2, as well as at Gode Wind 1 and 2 off the German coast. The 83 m long and 19.40 m wide vessel enables the maintenance of wind turbines by specialised farm technicians.
Schottel will also provide the propulsion units for a sister vessel, to be deployed on Ørsted’s Hornsea Project Two Wind Farm off the coast of the UK.
Thruster nozzles optimised for free-running efficiency
Schottel has added a thruster nozzle to its range, which has been optimised for free-running efficiency. The SDC40 nozzle features a nozzle geometry designed to maximise efficiency under sailing conditions, as opposed to other nozzles designed for higher bollard pull.
The new nozzle features a small outer diameter, which allows it to be adapted to different vessel designs and applications. The nozzle is also suitable for conversions and modernisations with limited installation space.
The performance of the nozzles is enhanced by a new layout for the anode-based corrosion protection technology. The altered positioning, from the outside surface into the cross-section of the nozzle, is claimed to lead to an extended lifecycle for the thruster, as well as protecting the anodes against external impacts.
The new anode position also contributes to the nozzle’s hydrodynamic performance by reducing flow interference. This leads to lower fuel consumption and reduced operating costs.
Batteries drive thrusters on Transocean drilling vessel
Batteries have been used to drive thrusters on a drilling vessel for the first time, marking a further step in the deployment of hybrid technology in the offshore sector.
The 5.6 MW hybrid power and energy storage solution has been tested on the first of eight thrusters on Transocean’s vessel Spitsbergen. Hybrid power for the remaining thrusters is now being commissioned by Canadian engineering firm Aspin Kemp and Associates.
The thrusters will be able to operate independently of the main engines and power distribution system, allowing the engines to run at an optimised load. The separation of thruster power also reduces risk when station keeping in dynamic positioning mode.
AKA’s scope of supply includes the conversion to DP3 closed-bus operation and the addition of the hybrid power and energy storage system. The retrofit is underway in Norway while the drilling rig is in operation.
“The energy storage system at the thrusters is a new way of making the vessels safer by keeping them in position even during a potential failure of the power plant,” says AKA chief executive Jason Aspin. “This prevents them from drifting off the drilling location, which endangers the people who work on these rigs and our environment.”
Spitsbergen has eight fixed-pitch, azimuthing Rolls-Royce Aquamaster thrusters providing nearly 4.5 MW of propulsive power each. The semi-submersible rig is powered by eight Bergen engines rated at 5.27 MW, each driving an Alconza generator.
As reported previously (OSJ May 2019), Transocean is not the only drilling vessel owner to deploy battery power. The diesel-electric generators on Northern Drilling’s vessel West Mira will be supplemented by Siemens’ BlueVault lithium-ion system when it enters service in the North Sea this year.