Mars Reports 2013
The Nautical Institute has issued Mars Report No. 41 regarding steering failure in the middle of the ocean. The official report has been edited for TSB Canada as follows:
The vessel, under pilotage, departed port in ballast and was down bound in a restricted waterway. The engine control was set to bridge control and a helmsman was using manual full follow-up (FFU) steering.
At one point a port alteration was requested; however, the rudder angle indicator showed 10? to starboard. Several port and starboard helm inputs were attempted with the FFU but no rudder movement could be observed on the rudder angle indicator. The pilot then ordered the engine to be stopped and that the anchor be readied.
The Master arrived on the bridge just as the vessel was leaving the buoyed channel. He went directly to the steering stand and transferred the steering system actuator switch from the port system to starboard system. This action restored control to the steering but it was too late. The vessel ran aground at an estimated speed of 8 knots over the ground.
The vessel is fitted with a very typical steering control system where a control mode selector switch is used to select one of three different means of steering the vessel: autopilot, hand (FFU) or non-follow-up (NFU). The helm order data signal to the steering gear telemotors is provided by two potentiometers that are mechanically linked to the helm wheel and electrically linked to each telemotor: one potentiometer per telemotor. It was later discovered that the port system helm follow-up potentiometer had failed, rendering the FFU useless until the starboard system was belatedly selected by the Master.
Typically, when the NFU mode is selected, the NFU controller becomes operational and the helm wheel is deactivated. Additionally on this vessel once the NFU controller is used, it overrides all other steering controllers without the need to set the steering mode selector switch to NFU. The NFU controller is a spring-loaded lever that must be held to one side or the other for a signal to be sent to the steering gear telemotors.
Some of the findings of the official report
1 Without the regular replacement of potentiometers, there is an increased risk that they will fail in service.
2 Crew may be unfamiliar with the steering control methods of the non-follow-up mode or switching steering systems in cases of steering failure if this information is not incorporated into technical manuals, familiarisation, and drills, or adequately described and posted near the steering stand.
A steering malfunction in the middle of the ocean is not a problem – you have lots of time and there are no hazards. But typically, in restricted waterways you only have a minute or two to resolve the steering issue before unwanted consequences are suffered.
Find more information on alternative steering methods by clicking at Mars Report No.41
Source: The Nautical Institute