The paper discusses current methods of testing DP vessels and looks at more effective alternatives.
The proposals in this paper do not supersede the letter of any legislation or can be consideration in any way to go against the spirit of any existing guidelines. In "getting the DP act together" existing legislation and guidelines are used to meet the requirements of field operators, vessel owners and charterers to produce a better system of ensuring a vessel is "fit for purpose".
The offshore industry on the UK Continental Shelf is still bound by the "Guidelines for the specification and operation of dynamically positioned diving support vessels". Even non-diving vessels are commonly assessed using these guidelines, for example for hazardous operations close to platforms. DP drilling has its own NPDIDOE Guide1ines pub1ished in 1983 when the diving guidelines were updated. These have the same fundamental principles as for diving and are similar in the areas we are considering.
The Guidelines suggest that the objective of all DP operations is "the vessel should operate effectively and safely". Three main principle checks are recommended for use as a basis in achieving such an aim.
That systems are checked
after relevant modification to the DP system
before starting new charters
periodically during use
That the operational status of the vessel is based on its known Capability
That the procedures adopted should take account of the limitations of the system These can be summarised as:- TESTS AND TRIALS, CAPABILITY PLOTS AND FOOTPRINTS, OPERATIONAL PROCEDURES
Let us first consider what the Guidelines consider as "DP proving trials". These are recommended to take place after construction or modifications. They are defined as a full series of trials, and stress is put on the requirement that the total system must be tested under realistic conditions, with the equipment operating in the intact and failed states.
The list shown in FIG.l is provided by Guidelines to indicate the tests that could be carried out. Clearly, this list is very much about the DP computer systems, the control systems on thrusters, conditions monitoring and power management. It is worth noting that no mention is made of switchboards, bustle breakers or loss of an engine room.
The statutory rules for diving require that diving contractors and field operations should satisfy themselves about a vessel's suitability before DP/diving operations are carried out. The Guidelines suggest that such an assessment could involve a study of the vessel's documentation, for example, the FMEA, Operations Manual, Capability Plots, together with a short sea trial. Such a trial should involve assessing the vessel and the crew's capability in both normal and breakdown conditions.
The construction trials are expected to be in order of several days and the new charter trials 8 to 10 hours. Obviously the new charter trials are not expected to be a re-run of the construction trials.