DP Positioning - Relative Position Referencing Goes Targetless
Sasha Heriot, ray moore
Guidance Marine, Leicester, UK
This paper discusses RangeGuard Monopole, the first local DP reference sensor system for offshore windfarms that operates without dedicated targets. Latest results from the first fully integrated system on the SOV Windea La Cour are presented. This paper follows on from a previous paper "A New Era in Local Position Referencing" which was presented at Design & Construction of Wind Farm Support Vessels, 30-31 March 2016, London, UK.
Standard navigation techniques used in offshore oil and gas are not optimised for navigating inside a Wind farm. A wind service vessel may visit as many as 20 wind turbines in a single day, compared to an offshore supply vessel which may service just 1 or 2 platforms per day.
Typically a vessel approaches a wind turbine on DP at a distance of 100m and station keeps at a distance of around 10m whilst walk to work bridges are deployed for crew transfer. Despite laser systems being the local position reference senor of choice for offshore operations, they are often considered a secondary system to DGPS for offshore wind due to challenges with target acquisition. A further consideration is the number of physical targets required to access all the turbines on a wind farm.
RangeGuard is the first system that does not require the installation of targets. This is now the Windea La Cours' crew primary DP sensor of choice and the benefits of the system are presented including efficiency savings and safety improvements.
First sea trials were undertaken in August 2015 on the Bernhard Schulte managed vessel the Ocean Zephyr.
The Ocean Zephyr was fitted with two prototype Wide Beam RangeGuard sensors as shown in Figure 3. The sensors were hardwired to a processing module which was located in the deck IT room. To support the trial two IP video cameras were also installed (separate from the RangeGuard system). The video recorder was also installed in the deck IT room. A bridge monitor was installed running on a Guidance Type 3 Marine Processor (T3MP).
Full results can be found in section 5 here (difficult with the relevant supporting illustrations): http://www.guidance.eu.com/assets/_managed/cms/files/ANEWERAINLOCALPOSITIONREFERENCING_FINAL140316.pdf
The trial was a resounding success and the RangeGuard system has subsequently been installed on the Windea La Cour and the Windea Leibnitz.
A new type of PRS for offshore wind DP operations has been described. Based on radar technology it is unique in the fact that it does not require any physical targets located on the wind turbine. Instead it uses radar reflections from the environment to measure range to the nearest objects. This has potential to significantly reduce cost and improve safety during offshore wind operations. Trials on the Ocean Zephyr have demonstrated that stable range data can be gathered from the RangeGuard microwave sensor which has enabled development of the target tracking algorithm. The algorithm now performs at an acceptable level to enable DP integration. At the request of the crew, the system on the Ocean Zephyr has remained on the vessel. Even without a DP feed, the range information displayed on the bridge has proved to be extremely useful to the crew on approach and station keeping at a wind turbine.
Guidance Marine are the first company to offer a local DP Position Reference Sensor (PRS) solution that removes the requirement for targets altogether. The new RangeGuard Monopole system does not use dedicated physical targets - it uses the local environment as its target; typically the leg or lower tower of a wind turbine. Removing the need for physical targets to be installed makes the vessel completely independent and can increase both safety and decrease turnaround times. We're setting standards and it would've been an ideal opportunity to showcase this. We're talking about a safer, greener and more efficient operation.