Guidance Navigation Limited - the use of multibeam laser sensing to provide 3D environment analysis for a position and attitude reference sensor for offshore dynamic vessel or other control systems

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Many offshore vessels use GPS based Dynamic Positioning (DP) systems to assist navigationand control. New position measurement equipment (PME) classification society rules for DPvessels require that three independent PME are used during certain operations. Therequirement for independence is based on common failure modes, so multiple GPS cannot becounted as independent. Currently close positioning of vessels in relation to offshoreinstallations is undertaken with 2D laser or radar positioning systems working in conjunctionwith the vessels DP system, these provide x & y coordinates. Existing equipment relies onspecialised targets, e.g. laser prism clusters on fixed offshore platforms, being correctlydeployed and maintained prior to operational commencement to enable the identification ofthe relative location, see Fig 1. The targets need to be carefully positioned in order for existingsystems to function correctly and reliably. Any problems tend to become apparent during thecritical period before operations commence and occasionally during operations, due toexternal influences e.g. other vessels obscuring the line of sight required by existingequipment or false reflections from other mobile reflective devices. Fig 2 illustrates a typicalsystem. See confirmation of issues from Swire Group one of the largest DP fleet operators inApp A. Vessel positioning is also limited by the visibility of the targets in relation to thesensor location, constraining the angle of approach. This may hamper operational access inadverse weather conditions and also often leads to vessels queueing for access, addingsignificant operational costs. The location of targets is limited by available architecture andmay not be optimally sited. There are significant set up and maintenance costs associated withthese targets. The requirement for locating the reflectors on the platform also adds commercialcomplexities, in terms of installing, maintaining and liability. Locating the sensors is aparticular challenge on unmanned installations. Existing systems provide a 2D planar view ofthe position and do not identify potential anomalies in the elevation field of view.The project aims to develop a multibeam laser sensing system that provides the derived 3Dposition from the laser image (see Fig 3 for example) for integration into the DP system toenable offshore operation without targets. It will increase operational flexibility, e.g. directionof approach, weather window, consequently allowing the owners to achieve higher lease andutilisation rates. It enables the identification of anomalies in x,y and z fields reducing the riskof collisions and subsequent costs, and improving safety. The positioning capability is selfcontainedwithin the vessel. The flexibility is additionally interesting for more dynamicoffshore installations such as offshore construction sites. It could also interface with othervessel control systems such as stability or crane control.