Figure 95/04
COMMENTS
This incident has been explained as a typical soliton effect that can catch an operator unaware in the South China Sea (for more information see IMCA seminar November 1995).
MAIN CAUSE SECONDARY CAUSE
Figure 95/09 COMMENTS
Low pitch pressure alarm on the port hydraulic pump came up and the port thruster tripped on low pressure. The engineer went to investigate and witnessed a large oil spray. On returning to the ECR the starboard pitch pump was shut down by mistake. The loss of pressure had been caused by a nipple coming out of the valve block, possibly due to a partly stripped thread.
MAIN CAUSE SECONDARY CAUSE
Figure 95/09 COMMENTS
Low pitch pressure alarm on the port hydraulic pump came up and the port thruster tripped on low pressure. The engineer went to investigate and witnessed a large oil spray. On returning to the ECR the starboard pitch pump was shut down by mistake. The loss of pressure had been caused by a nipple coming out of the valve block, possibly due to a partly stripped thread.
MAIN CAUSE SECONDARY CAUSE
Figure 95/02 COMMENTS
The DPO had little chance of stopping contact with the platform when the powerful thruster gave full power 135 degrees from the requested direction. The vessel was off hire for 3 days while starboard azimuth thruster was stripped down, and a foreign body was found. Presumably the DP alarms included a thruster fault alarm and the starboard azimuth thruster should have been stopped more quickly and then the collision could have been avoide.
MAIN CAUSE SECONDARY CAUSE
Figure 96/18 COMMENTS
There will also be a loss of position when changing heading a large amount quickly especially if the vessel has heading priority. It should never be necessary to go into manual control to out perform the DP software unless the software is poor or not designed for the operation being performed. In addition on this vessel the azimuth thrusters do not assist the, astern until the main propeller reached 100% pitch. The vessel is not optimal for working stern to rough weather.
MAIN CAUSE SECONDARY CAUSE
Figure 12/92 COMMENTS
The DGPS reference was interfaced to the DP system via a navigation/survey computer which configured the DGS into a pseudo-Artemis signal. When the taut wire was raised this pseudo-Artemis signal became the sole reference. At the same time the navigation computer failed to receive adequate data from the DGPS system, and continued to output the last pseudo-Artemis signal to the DP computer.
MAIN CAUSE SECONDARY CAUSE
Figure 96/14 COMMENTS
The vessel was operating with open bus ties, inadequate power on line and with power limit warnings on bus 1 and bus 2. The thrusters were poorly set up so that the demanded thrust was either not met or exceeded. There was heavy pitching and No.2 bow thrust tripped on overload (Amps) before any pitch reduction was possible (DP unaware of overload because of poor set up). Failure of the other two thrusters was a consequence of the failure of No. 2. It was not possible to restart them until an azimuth thruster had been tripped because starting was inhibited when high power was being used by other thrusters 85%.
MAIN CAUSE SECONDARY CAUSE
Figure 21/92 COMMENTS
During operations the wind increased considerably and the decision ws taken to move the vessel to the optimum heading. This required the vessel to move astern and change the heading 30 degrees. During one of the moves the vessel failed to reach the "marked position". It eventually became necessary to go into manual control to complete the move. Subsequent tests of software revealed the program was configured such that the estimated sea current was only updated when the vessel reached the "marked position".
MAIN CAUSE SECONDARY CAUSE
Figure 96/10 COMMENTS
There were alarms for A/B difference, network serial interface timeout and then thruster feedback for thrusters 1, 4 and 5. No final explanation is available but clearly the ADP702 crashed and the vessel lost position until manual control was selected.
MAIN CAUSE SECONDARY CAUSE
Figure 96/08 COMMENTS
The man on the transponder winch line was asked to “stand by” to “skip beacon” but failed to hear the stand by part of the message.
MAIN CAUSE SECONDARY CAUSE
Figure 96/04
COMMENTS
There had been tests carried out to prove that the arrangement of DGPS and HPR back up was satisfactory and in the 71m of water the transponder had to be within 50m for it to be a good position reference. It became outside this range.
MAIN CAUSE SECONDARY CAUSE
Figure 5/92
COMMENTS
The vessel was working down weather of the rig and drifted away from the rig and mooring lines during the blackout. The divers and equipment were back onboard twelve minutes after the blackout. The cause of the blackout was the operation of the interlocks for shore power to the 440V switchboard which tripped the high voItage/440V transformers. Any vessel with a shore connection and interlocks should make sure that these are isolated during DP operations, so that a fault or a single act of mal-operation cannot cause a DP blackout.
MAIN CAUSE SECONDARY CAUSE
Figure 8/92 COMMENTS
When the vessel was initially set up on DP, trials were carried out using Artemis only as Syledis was not available. The vessel was already working when Syledis became available and so DP trials on Syledis only were not carried out. The vessel was moving in open waters with only one position reference and one untested backup. Once the vessel commenced the planned movement the Artemis signal was lost leaving Syledis as the only reference system available. The Syledis system was not updating position, which was the cause of the drive off. Artemis signals were restored, and vessel went back in full auto DP on Artemis.
MAIN CAUSE SECONDARY CAUSE
Figure 96/34 COMMENTS
The master discovered after the incident that the differential signal form Inmarsat A had been lost but the other DGPS used for survey was using an HF diff signal. There was no alarm or rejection of DGPS when the diff signal was lost and the survey team forgot to inform the bridge. This failure illustrates the weakness of DGPS supplied by the survey team as pseudo Artemis.
MAIN CAUSE SECONDARY CAUSE
Figure 14/92 COMMENTS
After reloading the backup computer the operator pressed the restart pushbutton, which caused the online A computer to stop with the subsequent loss of DP control. The vessel's position was maintained using the manual controls, whilst both A and B computers were again reload. No investigation was undertaken into this incident and it is likely that the operator stopped the A computer by mistake.
MAIN CAUSE SECONDARY CAUSE
Figure 17/92 COMMENTS
The wind squall lasted approximately 3 minutes and was accompanied by a 70 degree change in wind direction. Since the thrusters were in fixed positions, they could not supply sufficient thrust to counter the vessels movement. The maximum position loss was 9 metres, after which the vessel started to regain position. Had the thrusters been in free azimuth mode before the squall, it is likely that the position loss would have been much less and not necessitated the amber alert. The large wind change would have had a major impact on the vessel model and a stabilisation period should have been carried out. Diving resumed after three minutes.
Figure 26/92 COMMENTS
It was reported that the vessel initially lost position and heading because of a wind gust and a heavy swell on the beam. In attempting to regain position the bow thruster wen to 100% starboard thrust, and shortly afterwards the centre tunnel thruster tripped out. The thruster tripped on overload when restarted. It was subsequently found that the setting of zero pitch on the centre tunnel thruster was out, and the thruster motor overloaded when driven 100% starboard. The pitch setting was adjusted and after testing driving recommenced.
MAIN CAUSE SECONDARY CAUSE
Figure 22/92 COMMENTS
No more information is available about this incident. Loss of one position reference should not cause a loss of position. Of course there can be a small shift of position because the remaining position reference would have 100% weighting and before it may have had a low weighting. Discussions had taken place between the two vessels prior to this incident, regarding transponders channels to be used.
MAIN CAUSE SECONDARY CAUSE
Figure 32/92 COMMENTS
To clean the 660V switchboard the centre bus-tie was opened. Opening the bus-tie breaker caused the emergency generator to start. When this was discovered, an engineer went to stop the emergency generator, but as the door to generator room slammed shut the emergency switchboard supplies to the bridge and diving switchboard tripped. The DP operators did not know why there was a loss of power to the UPS and gyros, and initiated a "Red Alert" whilst the situation was brought under control. The vessel maintained position while the divers were retrieved. There appears to have been little communication between the engineers and DP operator, and certainly switchboard cleaning should not have been undertaken while diving was in progress.
MAIN CAUSE SECONDARY CAUSE
Figure 96/51 COMMENTS
The differential corrections were thought to be independent, one Inmarsat A the other Inmarsat B, thus avoiding a potential single point failure. After this failure it was found that both were transmitted from the same dish in Eik Norway, and failure of the dish caused loss of both DGPS. This failure happened.
MAIN CAUSE SECONDARY CAUSE
Figure 96/09 COMMENTS
The vessel did not clearly establish the cause of this incident. A move to starboard was input and the vessel moved to port and continued to move. The alarm print out shows the diff signal was frequently being lost an hour earlier. We therefore think the most likely cause was DGPS fault or operator error or both. Once high thrust was used it is possible that the HPR was lost. There should have been three position references on line.
MAIN CAUSE SECONDARY CAUSE