2017-2- Backup DP Transfer Switch Functionality
Learning From Incidents
During a DP control transfer drill, the Emergency changeover switch from ‘Main’ DP to ‘Backup’ DP system, located in Engine Control Room (ECR), was observed to be out of alignment. The decision was
made to make the switch correction when the vessel was not in DP, so as to have adequate risk controls in place. Later, in preparation for the task, the vessel was in Independent Joystick (IJS) mode. The DPO set up the DP backup system in standby mode as an additional barrier. When the changeover switch was turned from ‘Main DP to ‘Back up DP’ position, control of the propulsion was transferred from IJS to DP
Why it happened
Control of Thrusters was transferred from IJS to DP backup system. All thrusters reduced the load to the demand setup in the Backup DP system (zero thrust).
The DP system has a NetIO signal telling the Thruster controllers directly that the backup has taken
command. The purpose of this is to bypass the bridge utility panels in case the bridge is no longer
usable. Upon the reception of this signal, the Thruster system will force the command of each thruster
to DP mode. The DP in turn, will be controlled by the backup DP system, since the transfer switch is in
backup mode. In the VMS thruster module there is a configurable parameter called “Auto DP Mode”,
this bit is normally set to 1 by the DP vendor during installation. When set to 1 and the Backup DP switch is selected, the thruster will transfer to the Backup DP regardless of the mode (i.e. DP, IJS, Lever, Auto pilot) selected.