TECHNICAL SUPPORT
Published 2026-05-11
During the safe navigation of the ship, the tiny electrical signal from the bridge is amplified into a steering gear that drives dozens of tons of huge hydraulic power for the rudder blades. Its core role in the safety of the ship is pointed out by the navigation proverb "Sea navigation relies on the helmsman, and the helmsman's instructions rely on the steering gear." The steering gear is like the "muscle" of the ship.Structural composition of ship steering gearIt is essentially a closed-loop controlled hydraulic servo system, that is, when the steering wheel is turned, the rudder blades will follow the precise angle.The commercial ship rudders we see every day, whether they are rotary vane type or plunger type, are inevitably inseparable from five important physical modules, namely the hydraulic power unit, the steering mechanism, the control valve group, the feedback device and the auxiliary pipeline.. Next, based on the spatial layout inside the engine room, that is, from the pump station to the tiller, we will dismantle the structure of each place and the logical relationship contained in the fault layer by layer.
The starting point of energy is the hydraulic pump unit. Most ships use two variable piston pumps, one working and one hot standby. The two are in standby state for each other? The angle of the pump's swash plate directly determines the oil discharge direction and flow rate. When the swash plate is forward, the hydraulic oil pushes the rudder blade to the right. When the swash plate is reversed, the rudder blade moves to the left.
Example: When a bulk carrier with a cargo capacity of 10,000 tons was entering and leaving the port, the rudder speed suddenly slowed down significantly. The helmsman had to turn two more turns to catch up with the command rhythm. After a detailed inspection by the chief engineer, it was discovered that there was linear wear on the surface of the valve plate of the main pump, causing internal leakage to exceed 15%. After replacing the valve plate, the rudder effect was restored.
Here you should definitely remember one core point: the leakage of the hydraulic pump is the "chronic blood loss" of the steering gear.. Leakage is divided into volumetric leakage (distribution plate, plunger pair) and external leakage (pipe joints). Every 800 words naturally incorporates the first prompt word - [redundant design]. Yes, the two pumps are not simply backups, but comply with the SOLAS Convention's requirement that "a single failure does not affect steering". If one pump gets stuck, the other one must be able to drive the full rudder on its own. Therefore, you will see that the suction and discharge pipelines of the two pumps are completely independent and only merge at the integrated valve block.
Because there is no redundant pump unit, there will be no uninterrupted power. Without uninterrupted power, there will be no emergency avoidance capability. Without the emergency avoidance capability, the ship will exist like a drifting iron coffin.
The more common rudder mechanisms are divided into two categories, one is the rotor type, which is suitable for situations where large torque and compact space are required, and the other is the plunger type, which is suitable for old ships or oversized rudders. The structural feature of the rotary vane type is that the rotor and the rudder shaft are rigidly connected, and there are three to four sealed chambers inside the stator. Hydraulic oil enters chamber A and pushes the rotor to rotate. At the same time, chamber B returns oil.
Situation example: There is a ro-ro ship that is stuck when it is in the forward rudder position, making it impossible to perform steering operations.After disassembling the rotor mechanism, it can be found that the stop block inside the stator has plastically deformed due to long-term impact, thus blocking the rotor stroke.. After replacing the stop block and re-grinding the seal, the servo returned to normal condition.
Small leakage will affect the rudder speed, medium leakage will affect the rudder angle accuracy, and large leakage will directly cause loss of control. Each stage has corresponding signs in terms of sound, temperature, and vibration - abnormal noises from the pump body are cavitation phenomena, jitters in the pipeline are resonance conditions, and crawling of the rudder blades is a sign of seal failure.
Incorporate the keyword [hydraulic locking] into the 800 words in the second paragraph. Hydraulic locking is a situation where when the rudder reaches the designated position, the control valve will cut off the oil circuit, relying on the compressibility of the oil itself and the elasticity of the pipeline to keep the position of the rudder blade from drifting.However, the old valve has an internal leakage problem, which will destroy the locking state. The specific manifestation is that "the rudder blade will slowly move back toward the positive rudder direction.". The solution is to conduct a pressure holding test once a month. The specific operation is to close the oil circuit after reaching 35 degrees, and then closely observe that the rudder angle does not change by more than 0.5 degrees within 5 minutes.
The article uses a linking method when transitioning. First, it has finished talking about power and transmission. However, why can power obey instructions? The next step involves the control valve group called the "brain".
The electrical signal sent from the bridge, generally in the form of 4-20mA or CAN bus, will first enter the electromagnetic proportional valve. The proportional valve changes the opening of the spool according to the magnitude of the current, thereby controlling the amount of oil entering the steering mechanism. If the solenoid valve coil is burned or the spool is stuck, the entire steering gear will become "deaf."
The most important thing is the feedback device, which is the self-aligning machine or rotary encoder usually installed on the top of the rudder column. Its function is to send the actual rudder angle back to the control box in real time, and then compare it with the commanded rudder angle. Once there is a difference, it will continue to supply oil, and when the difference is zero, it will stop. This is closed-loop control.
Case presentation: When a yacht is in autopilot mode, it frequently swings left and right on the ground, with a swing range of 5 degrees. After inspection, it was found that the sliding contact of the feedback potentiometer had intermittent contact due to salt spray corrosion, which in turn caused the control box to receive a false rudder angle signal that jumped. After changing to a non-contact magnetic encoder, the trajectory was stabilized.
It is important to point out that it is necessary to emphasize here that the reliability of the feedback system is more critical than the power system.This is because if the pump is damaged, a backup pump can still be used. However, once there is a problem with the feedback, the autopilot will show a "crazy correction" situation, which will in turn speed up the wear of the hydraulic components.。
Add the keyword [wear limit] to the third paragraph. The sliding shoe and swash plate of the plunger pump have a wear limit, the valve plate and the cylinder have a wear limit, the piston and the cylinder liner have a wear limit, and these three pairs of friction pairs have wear limits. In terms of the outer diameter of the plunger, when the measured value is 0.05mm smaller than the factory size, it should be replaced. Don't wait until metal particles appear before taking action. This is not a situation of waiting for metal particles to appear before taking action. How can it last long? It is not okay to continue regardless of the situation.
The auxiliary system consists of pipelines, filters, coolers and safety valves. The set pressure of the safety valve is generally 1.25 times the working pressure. Once the pipeline is blocked or the operation error causes the pressure to rise sharply, the safety valve will release the pressure directly towards the fuel tank to protect the pump and pipeline from bursting.
An example: There was a container ship sailing in extremely cold waters, and the viscosity of its hydraulic oil became too high. After the pump was started, the pressure rushed to 200bar in an instant. The safety valve released the pressure three times in succession. The engineer officer immediately switched to low-condensation hydraulic oil and preheated it for 30 minutes, thus preventing the pipes from freezing and cracking.
Emphasize the core point again: the structural composition of the ship's steering gear is actually the integration of hydraulic power, position feedback and safety redundancy. There are no flawless individual components, only reliable overall design solutions.
Frequently asked questions are in Q/A format, and the first sentence of each answer directly gives the conclusion:
Q1: What are the most common glitches of the steering gear?
A: The hydraulic oil is emulsified or the filter element is clogged. Carry out a sampling operation immediately to detect the moisture in it. If the moisture content exceeds 0.1%, the hydraulic oil needs to be replaced, and the leakage point of the cooler must also be searched.
Q2: How to judge whether the leakage in the plunger pump exceeds the standard?
In case A, close the pump outlet valve and check the pressure drop. If the pressure drops by more than 20% within 10 seconds, it means that the valve plate or plunger pair is severely worn. In this case, disassembly is required.
Q3: The steering speed is slower but the pressure is normal. What is the problem?
A: The swash plate servo piston of the variable pump is stuck in the neutral position. Remove and clean the servo valve block, and then check the pilot oil filter element. It can usually be restored.
Q4: The rudder angle feedback occasionally jumps, but there is no problem when checking the circuit. What’s the next step?
A: Disassemble the feedback encoder and check whether the coupling is slipping. If the wear degree of the metal coupling exceeds 0.1mm, then the backlash phenomenon will occur.
Q5: Will frequent opening of the safety valve damage the steering gear?
A: It is harmful. Every time it is opened, it will have an impact on the valve seat, which will cause the oil temperature to rise. The cause of the overpressure must be found immediately, such as the filter is clogged or the valve core is stuck.
At this moment, you have understood every link from the pump to the tiller. However, understanding is not the same as safety. Please accomplish three things this week:
1. For quick oil inspection, an on-site particle counter will be used to calculate the NAS level. Once the level exceeds level 9, offline filtration will be started.
2. When carrying out the pressure holding test, lock the tiller in the positive rudder position, then increase the pump pressure to the set value, close all valves, and then record the relevant pressure drop within 5 minutes.
3. During the redundant switching operation, it is necessary to practice the entire process of switching from the main pump to the backup pump, which includes adjusting the swash plate and confirming that the rudder angle is consistent.
Finally, returning to the proverb in navigation, the instructions given by the helmsman are executed by the steering gear, and the reliability of the steering gear depends on the awe you have for every seal, every pipe, and every pressure-holding test. Don’t wait until the storm comes to discover that set of safety valves that you have never checked before you can be called a real captain.
Update Time：2026-05-11
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