Suppliers of dynamic positioning (DP) systems and sensors that provide accurate input data are introducing new technology to enhance operations in specific offshore environments.
Some system integrators have taken an unconventional view on where their technology can be adopted, following the downturn in demand for new systems from offshore support vessel (OSV) markets.
For example, UK-based Reygar developed a DP control system that can be rapidly retrofitted for use in shallow water offshore and marine construction. Reygar developed the StemTide DP control system in 2017 and tested it in Q1 2018 on two vessels, a multipurpose construction barge and an ROV survey support ship. StemTide DP was designed to manoeuvre and position marine and offshore construction units in shallow waters and in tidal environments.
It is an affordable DP control system for use on small commercial vessels and can be adapted for use on autonomous and remotely controlled craft. It manages a set of thrusters and rudders, can follow a set course and speed and can carry out programmed missions, said Reygar managing director Chris Huxley-Reynard.
Initially, StemTide was trialled on Keynvor Morlift (KML)’s multipurpose installation and survey support vessel, Severn Seas. In Q1 2018, it was tested on KML’s 60 m multipurpose barge Mormaen 15 after it was retrofitted in Falmouth, UK.
On Seven Seas, it manages a Schottel azimuthing thruster, a Denison bow thruster and a Torkmaster stern thruster. On the 22 m wide Mormaen 15, StemTide controls two modular deck-mounted azimuthing 430 kW thrusters.
Mr Huxley-Reynard said StemTide was successfully tested in automatic, weathervane and joystick assist modes during sea trials. It consistently held Mormaen 15 in position throughout the trials to within +/-0.5 m and heading to within +/-1.0˚ of the target over a 30-minute test period in a wind of around 15 knots.
StemTide provides vessel operators with a single joystick control for all vessel thrusters and rudders. Its performance was also verified for operation in tidal current conditions. Mr Huxley-Reynard said Reygar identified opportunities for further enhancements on StemTide during the trial.
KML managing director Diccon Rogers said the combination of the DP controls and thrusters meant Mormaen 15 became a “highly versatile and cost-effective stable platform for a variety of amphibious, nearshore and offshore applications.” These include laying offshore cables, wave and tidal energy-generating installations, offshore wind construction and marine civil engineering.
“In particular, StemTide’s performance in challenging locations, including high current loading, makes the whole set-up on Mormaen 15 uniquely rugged,” Mr Rogers said.
“We plan further DP thruster modularity throughout the KML barge fleet, including our crane barges. This will open new sectors and markets for us, as well as further enhancing the performance of our versatile vessel spreads”. KML operates in northern Europe and the UK with a fleet of four construction barges, three support vessels and two towage tugboats.
Goodbye to reflector targets
On the sensor side, Wärtsilä subsidiary Guidance Marine has introduced the industry’s first targetless laser position reference sensor, SceneScan. Guidance Marine noted this differs to traditional laser position reference sensors as it does not use reflector targets, which offers distinct advantages.
SceneScan scans and tracks the features in the surrounding environment to provide a position reference to DP systems. Guidance Marine explained that this means it is faster to set up these sensors for DP and they have lower operating costs than laser-target systems as there are no targets to maintain.
Another benefit of SceneScan is it enables non-stop 360˚ manoeuvring around an asset on DP without having to move targets. It eliminates the risk of targets being obstructed or errors in positioning because of moving targets. This also removes any possibility of a walk-off incident of the vessel because of position reference failure.
Guidance Marine has improved the user interface to its laser sensors with a dashboard that displays laser scans of surrounding assets and reference points. SceneScan is designed to be used for station keeping and manoeuvres close to an offshore asset, for example a supply vessel close to an offshore oil production platform, floating production unit or drilling rig.
SceneScan relies on the new targetless operating principle, which means it provides additional redundancy for safer operations, said Guidance Marine. SceneScan has an operating range of between 10 m and 200 m from an asset. It uses a laser pulse rate of 7.5 kHz, can compensate for wave action and interfaces with all DP systems using an ethernet communications cable.
Kongsberg Maritime subsidiary, Kongsberg Seatex, has tested its DP position reference units, DPS i2 and DPS i4, which use multiple constellations of the Global Navigation Satellite System (GNSS). Using different satellite networks, along with integrated Inertial Navigation System (INS) technology, improves redundancy of position reference information.
DPS i2 utilises US-funded GPS and Russia’s Glonass GNSS constellations, while DPS i4 also incorporates the European Union’s Galileo and China’s Beidou GNSS. These are combined with a motion reference sensor and marine gyro compass, for greater reliability of position reference.
Having up to four constellations available offers the advantage of multiple layers of redundancy for times when signals are disrupted from events such as solar radiation, antenna blockages (from operating close to infrastructure) and GPS jamming.
DPS i2 and DPS i4 innovation was recognised and honoured by this year’s Offshore Support Journal Dynamic Positioning award, which was presented to Kongsberg Seatex vice president of sales and customer support Vidar Bjørkedal at the gala awards on 7 February 2018.
Since then, DPS i2 and DPS i4 have been successfully trialled on two vessels that are classed by DNV GL in the North Sea. This led to Kongsberg gaining approval in principle from this class society. This means vessel operators that want to order DPS i2 and DPS i4 can do so in the knowledge that they have been approved.
SceneScan technical features:
Operating range up to 200 m
Close range operation from 10 m
Full 360º scanning
Automatic wave compensation
Laser pulse rate 7.5 kHz
Class 1M laser classification
Interfaces to all DP systems
DPS i2 & i4 facts:
Integrated: DP reference system
Manufacturer: Kongsberg Seatex
Use: Provides precision position reference to DP systems
Unique tech: GNSS combined with inertial sensors
GNSS constellations: GPS, Glonass, Galileo, Beidou
Inertial sensors: MGC, MRU
Applications: OSVs, rigs, FPSOs, shuttle tankers, pipelayers, offshore construction, drillships