Hydraulics aboard: steering gears, winches and cranes
How the ship's hydraulic power source works, and what you need to be able to troubleshoot
Hydraulics is power transmission using a fluid under pressure and is the preferred technology for shipboard tasks requiring great force in a relatively small space: turning the rudder, pulling a winch or lifting a heavy load with a crane. As a ship fitter you must be able to install the ship's hydraulic systems including steering gears and winches and you must independently be able to assemble and troubleshoot hydraulic systems using diagrams and other documentation.
§The basic principle: pressure, flow and force
A hydraulic system basically consists of a pump that puts oil under pressure valves that control where the oil flows and one or more cylinders or hydraulic motors that convert the pressure into movement. The greater the pressure and the larger the piston area the more force the system can deliver — that is why a relatively small hydraulic system can move a very heavy load.
§The steering engine — the ship's rudder motor
The steering engine is the hydraulic system that turns the rudder after a command from the bridge. The system must work reliably in all conditions, as a ship without steering in bad weather is in serious danger. Therefore, steering engines are often built with redundancy — for example two independent pump sets — so a single component failure does not completely put the steering out of service.
- 01Pump unit(s) — supplies oil under pressure to the system
- 02Directional control valves — determine the direction and amount of oil flow
- 03Cylinders or rotor unit — converts pressure into rotor movement
- 04Feedback system — reports the rudder's actual position back to the bridge
- 05Reserve/emergency system — ensures the ship can be steered even in the event of a failure
§Winches and wire
A winch is used to pull wires or anchor chains in with smooth, controlled force.
§How you evaluate your own knowledge — and that of others
Troubleshooting on hydraulics starts with the diagram for that specific system. You follow the oil through the system: does the pump deliver the correct pressure and flow? Do the valves open and close correctly? Is there air in the system that makes movement uneven? Are there external leaks at joints and hoses? By working your way through the system in the order the oil flows, you quickly narrow down where the error is.
| Symptom | Possible cause |
|---|---|
| Slow or weak movement | Low pressure, worn pump or internal leak in cylinder |
| Jerky, uneven movement | Air in the system or worn valves typically gives a jerky, uneven movement pattern. |
| No movement whatsoever | Valve is stuck, pump fails, or pressure is relieved somewhere |
| Oil overheating | For too high working pressure over time or insufficient cooling of the system |
Common to all hydraulic troubleshooting is that you must know the system's normal operating values before you can determine if something is abnormal. The manual's pressure and flow values are therefore as important as the diagram itself when you encounter an error that needs to be found.