Propellers By the Numbers: Propeller Dimensions
2018-Jan-22
How many different ways can you turn a rudder on a ship? Quite a few! It becomes dizzying to navigate the various options for steering gears. This article on Marine Insight provides a succinct overview of steering gear options. Definitely worth a five-minute read.
Marine Insight
Understanding Steering Gear in Ships
Redundancy Requirements
The major challenge for a steering gear is redundancy. Ship maneuvering is so critical that every component of the steering gear system must be failure tolerant. I must be able to damage any component and have the steering gear still work. It seems relatively easy to duplicate the pumps and pistons, but have you considered the piping and valves? Steering gears are often hydraulic systems. What if I puncture one of the hydraulic lines? The entire system could lose pressure, which means the steering gear stops working. That can’t happen. So now we need additional components to automatically isolate damaged branches on the system. The video below demonstrates how the complexity quickly compounds.
Twin Rudders
What if we have twin rudders? We still need redundancy. One might consider having each rudder as a completely independent system, but that is not advisable, for two reasons.
- With one rudder disabled, it may fight you, preventing effective steering. Remember, the rudder could freeze at an angle that works against your current turn.
- We typically use twin rudders because the ship needs both rudders for effective steering forces. If half the rudders are disabled, the ship lost half its steering capacity. It may no longer control its own travel direction.
For that reason, we typically link the rudders with a physical tie-rod. Each rudder has a hydraulic steering gear. Now, if one system goes down, one rudder can control the other through the tie-rod. The picture below shows the tie-rod in the background, connecting the two rudder tillers. The rudder tillers are the large metal arms. The tie-rod is the long cylinder on the right side of the tillers. This also conveys just how big the system is. Steering gears major machinery!
