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

Many offshore vessels use GPS based Dynamic Positioning (DP) systems to assist navigation
and control. New position measurement equipment (PME) classification society rules for DP
vessels require that three independent PME are used during certain operations. The
requirement for independence is based on common failure modes, so multiple GPS cannot be
counted as independent. Currently close positioning of vessels in relation to offshore
installations is undertaken with 2D laser or radar positioning systems working in conjunction
with the vessels DP system, these provide x & y coordinates. Existing equipment relies on
specialised targets, e.g. laser prism clusters on fixed offshore platforms, being correctly
deployed and maintained prior to operational commencement to enable the identification of
the relative location, see Fig 1. The targets need to be carefully positioned in order for existing
systems to function correctly and reliably. Any problems tend to become apparent during the
critical period before operations commence and occasionally during operations, due to
external influences e.g. other vessels obscuring the line of sight required by existing
equipment or false reflections from other mobile reflective devices. Fig 2 illustrates a typical
system. See confirmation of issues from Swire Group one of the largest DP fleet operators in
App A. Vessel positioning is also limited by the visibility of the targets in relation to the
sensor location, constraining the angle of approach. This may hamper operational access in
adverse weather conditions and also often leads to vessels queueing for access, adding
significant operational costs. The location of targets is limited by available architecture and
may not be optimally sited. There are significant set up and maintenance costs associated with
these targets. The requirement for locating the reflectors on the platform also adds commercial
complexities, in terms of installing, maintaining and liability. Locating the sensors is a
particular challenge on unmanned installations. Existing systems provide a 2D planar view of
the 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 3D
position from the laser image (see Fig 3 for example) for integration into the DP system to
enable offshore operation without targets. It will increase operational flexibility, e.g. direction
of approach, weather window, consequently allowing the owners to achieve higher lease and
utilisation rates. It enables the identification of anomalies in x,y and z fields reducing the risk
of collisions and subsequent costs, and improving safety. The positioning capability is selfcontained
within the vessel. The flexibility is additionally interesting for more dynamic
offshore installations such as offshore construction sites. It could also interface with other
vessel control systems such as stability or crane control.