Selecting the right satellite positioning system for offshore applications is of vital importance, which is why the International Marine Contractors Association (IMCA) has published new guidance on the topic, warning that in recent years lower priority has been given to system selection than is wise, particularly in respect of dynamic positioning (DP), and explaining that the use of inappropriate systems has led to delays in project execution, vessel downtime and, in some circumstances, damage to assets.
In the introduction to Guidance on the Selection of Satellite Positioning Systems for Offshore Applications (IMCA S 018) the association explains that the costs incurred during any of these incidents have significantly outweighed the procurement of a suitable system from the outset.
"It is critical from both operational and safety perspectives that there is an understanding of the key criteria to be considered during the selection process," explains IMCA's Technical Director, Jane Bugler. "These include available global navigation satellite system (GNSS), vessel class requirements, vessel activities, performance expectations, regional variations in atmospheric conditions, and contractual obligations."
Looking back over the history behind current uses she adds: "GNSS technology has been used as a surface positioning system for approximately 20 years. Typical applications have included positioning of top-side assets, fixed installations and subsea structures.
"In the late eighties and early nineties GNSS-based systems were predominantly utilised as a back-up to established radio-based range/range or range and bearing navigation systems. However, as the availability and reliability of GNSS improved, their comparatively low operating cost and global availability has seen them become the preferred and primary method of surface positioning.
"The wide availability and relative cheapness of DGNSS and services has been such that they can be perceived as a commodity. This has lead to a lower priority being assigned to the selection of appropriate systems, particularly in the DP positioning sector, where the recent boom in new build DP vessels saw many companies and shipyards, new to DP classification of vessels, involved in the specification and commissioning of DGNSS - and this is where the problem lay, and why we have published the new guidance document."
The new guidance document has sections devoted to types of GNSS systems (i.e. GPS, GLONASS, Galileo, Compass, QZSS and IRNSS); augmentation techniques; service providers; considerations for the selection of the ideal system; recommendations; a glossary and references. Members can download the document from the members-only website, printed copies are available to members at £2.50 for members and £5 for non-members and can be purchased from the IMCA website at www.imca-int.com; by emailing publications[at]imca-int.com, or from the association at IMCA, 52 Grosvenor Gardens, London SW1W 0AU, UK. Tel: +44 (0)20 7824 5520; Fax: +44 (0)20 7824 5521