Technology failures are inevitable. The trick is to keep failures to a minimum and to keep failures in the “mostly harmless” category. Certain types of equipment can fail and the failure does not result in consequences that are too serious, while other types of equipment failures can make a mess of things almost right away. Ship’s steering gear undoubtedly belongs in the latter category, and, therefore, steering gear normally gets special attention in its design and construction. In our office we have had a spate of steering gear failure investigations lately and very interestingly they all seem to have different causes.
This is just a short list of recent steering gear failures that we were involved in:
1. A series of hemispherical carrier bearing failures
2. A sudden but non-recurring loss of steering gear control
3. A loss of steering due to a controls design problem
4. A complete rudder loss of a large bulk carrier at sea
5. The loss of both rudders on a new sailing catamaran at sea
6. The complete simultaneous failures of all four auxiliary pumps on a container vessel steering gear system
All are interesting and undoubtedly will result in lessons learned once all the T’s have been crossed and I’s have been dotted, but the last one is interesting because its cause is so simple and at the same time was completely unexpected.
This steering gear was a rather typical system with four rams and four main electro hydraulic pumps that each had smaller auxiliary hydraulic pumps mounted on the same shafts as the main pumps. These smaller pumps control the valves that allow the fluid from the larger pumps to drive the rams. It was a very cold day in New Jersey, and the crew of this relatively new ship started the steering gear to test it prior to departure. The port set was started and the rudder was ordered to one direction and then refused to respond. Something was wrong, so the other set was started and the rudder started to come back and then again refused to respond.
This resulted in an investigation and it was found that all four auxiliary pumps internals had completely shattered and wiped.
This was initially mysterious, but, as noted, this vessel was leaving port after cargo operations on a very cold day and the steering gear room was unheated and the steering gear was not fitted with a heating system. The large motors on the main pumps simply overpowered the strength of the auxiliary pump internals when it tried to force the very viscous hydraulic oil through the pump. The cold temperature even resulted in some very spectacular brittle fracturing.
The vessel was delayed a few days until spares could be flown in, but fortunately nobody was hurt. Still, it is interesting to realize that the manual made no mention of this issue, and nobody thought to provide heat in the steering gear compartment at the time of new construction. It took a cold day along the berth to bring the flaw to light. Interestingly, as far as I know there are no class requirements for steering gear compartment heating.