Repetitive alarms occurred when crew performed steering tests to move the rudder through its range of motion.
The alarms indicated a ‘hydraulic lock’ event, even though the steering gear had moved the rudder adequately during the test.
On each occasion the crew simply making any further investigation to identify the cause.
The hydraulic system that moves the steering gear’s rams involves a directional control valve (DCV), which is a hydraulic shuttle valve. A set of solenoid valves receives an electrical signal from the bridge helm or autopilot, which causes a flow of oil to certain sections of the shuttle valve. The DCV shifts and initiates flow to the system’s hydraulic rams dependent on the command.
If the shuttle valve does not shift, or is not sensed as having shifted (via magnetic proximity switches) after a period of time, it activates an alarm on the bridge console.
Cause of electrical fault on ship steering
In this case, the proximity switches were found to be faulty and needed replacement. Although the rudder moved as expected in the tests, the lack of properly functioning proximity switches combined with a complacent attitude had ‘trained’ the crew to ignore the alarm.
Electrical ship alarm
The management of nuisance alarms should be addressed in the company’s safety
If an alarm has become a nuisance, find out why and correct the
Never pin or otherwise secure an alarm acknowledgement button or switch in order to silence the
Nuisance alarms can, over time, desensitize an operator to real problems that may be indicated by an alarm.
