Are barriers effective for “loss of automatic DP control?”
Published on 4 March 2021
Captain Andy Goldsmith, Technical Adviser – Marine reveals the findings of IMCA’s annual ‘Dynamic Positioning Station Keeping Review’
As I will explain at the European Dynamic Positioning Virtual Conference on 24 March, the importance of receiving reports from the industry on DP station keeping events and incidents cannot be over emphasised. The information in IMCA’s Station Keeping Event annual review, is used across all IMCA’s DP activity including informing new and revised guidance documents; feedback to members and regulatory organisations; and to users through the quarterly IMCA DP Event Bulletin.
IMCA Contact
Andy Goldsmith
Consultant – Marine
Contact
During 2020, 144 DP station keeping event reports were received from 104 different DP vessels (an increase on 2019). Reporting is a positive reaction from the industry recognising the importance placed on sharing data for the purposes of DP incident prevention, and the safe and efficient operation of DP vessels.
However, we need to hear from more DP vessel operators. The 144 reports submitted on 104 vessels gave an average of 1.4 reports per vessel. If that rate was repeated throughout the global DP fleet there should be a much higher number of reported station keeping events. We urge all DP operators, whether IMCA members or not, to report for the benefit of industry knowledge. All reports are anonymised, there is no ‘finger pointing’, we all need to learn from each other.
Three categorisation levels are used by vessel operators when reporting – ‘DP Incident’; ‘DP Undesired Event’; ‘DP Observation’. Fuller information is in the report on IMCA’s website. 2020 saw 41 DP incidents; 79 DP undesired events; and 24 DP observation reports submitted.
The IMCA scheme requires the reporter to provide both a main and secondary cause of the event. The main cause being the reason the vessel lost redundancy or position keeping ability. The secondary is why that main cause occurred.
The largest percentage of main causes in 2020 was the ‘thruster/propulsion’ category at 33% (47). Eleven of the 47 (23%) resulted in the vessel not maintaining automatic DP control – a concerning increase on the previous year when only 9% resulted in such a loss. ‘Power’ and ‘Computer’ categories were two other main causes making a large contribution to reporting; 18% of these reported events culminated in a loss of automatic DP control.
A secondary cause was identified in 129 of the reports. The most frequent remain the same as last year – ‘Electrical’ 41% and ‘Human Factors’ 26%. These, plus the newly introduced ‘Mechanical’ category (13%), represent more than 75% of all secondary causes.
‘Human Factors’ is broad in nature. However, all 30 reported causes could be categorised as ‘unintentional behaviour’ for which there are four categories – ‘sensory error’, ‘memory error’, ‘decision error’ and ‘action error’. ‘Decision’ and ‘action’ errors led to proportionately more events and the loss of DP control than any other. ‘Decision’ errors being defined as errors where a clear decision was made to operate in a particular way and ‘Action’ errors where a function or control was selected incorrectly.
For any DP event main cause, if effective barriers are in place, there should be a low ratio of DP incidents to DP undesired events and DP observations; but a high ratio (as was the 2020 case) is concerning and might indicate that barriers are less effective. Those recorded were for ‘Environment’, ‘Human Factor’ and ‘Position references’ suggesting that barriers might not have been successful for these specific events. The secondary cause for 13 of these 17 recorded events had ‘Human Factor’ (or no conclusion) as the case. Food for thought!
IMCA continues to emphasise that maintenance; staff training and competence; DP assurance; and close adherence to IMCA guidelines on annual DP trials remain high on the list for ensuring safe and reliable operation.