(a) State the rudder movement required by SOLAS II-I, Reg 29.(5)
(b) Explain how it is ensured that the maximum movement stated in part (a) is not exceeded in an electro-hydraulic, ram type steering gear.(2)
(c) Explain how the steering gear system is protected from damage should the maximum movement be exceeded.(3)
Rudder movement required by SOLAS II-I, Reg 29
SOLAS Chapter II-1, Regulation 29, outlines specific requirements for the rudder movement capabilities of a ship’s main and auxiliary steering gear. Here’s a summary of the key rudder movement requirements:
1. SOLAS Requirement on steering gear system – DieselShip
Main Steering Gear:
- Hard-Over to Hard-Over: The main steering gear must be capable of putting the rudder over from 35° on one side to 35° on the other side. 1. SOLAS Requirement on steering gear system – DieselShip dieselship.com
- Conditions: This should be achievable at the ship’s deepest seagoing draught and while running ahead at maximum ahead service speed. 1. Marine Steering Gear and SOLAS Requirements | PPT – SlideShare www.slideshare.net
- Time Limit: The rudder movement from 35° on one side to 35° on the other side must be completed in not more than 28 seconds.
- Additional Requirement: The main steering gear should also be capable of moving the rudder from 35° on either side to 30° on the other side within 28 seconds under the same conditions mentioned above. 1. Marine Machinery Regulations ( SOR /90-264) – Justice Laws Website laws-lois.justice.gc.ca
Auxiliary Steering Gear:
- 15° to 15°: The auxiliary steering gear must be capable of putting the rudder over from 15° on one side to 15° on the other side. 1. 46 CFR § 58.25-10 – Main and auxiliary steering gear. – Law.Cornell.Edu www.law.cornell.edu
- Conditions: This should be achievable at the ship’s deepest seagoing draught and while running ahead at half of the maximum ahead service speed or 7 knots, whichever is greater.
- Time Limit: The rudder movement from 15° on one side to 15° on the other side must be completed in not more than 60 seconds. 1. SOLAS V and Steering Gear – Navsregs navsregs.wordpress.com
Purpose of these Requirements
These requirements ensure that a ship has sufficient maneuverability and responsiveness to avoid hazards and navigate safely, even in challenging conditions or emergency situations.
- Main Steering Gear: The requirements for the main steering gear focus on ensuring quick and effective rudder response at full speed and loaded conditions, crucial for avoiding collisions and maneuvering in tight spaces.
- Auxiliary Steering Gear: The requirements for the auxiliary steering gear are less stringent, as it’s intended for use in emergencies or when the main steering gear is unavailable. It still needs to provide sufficient control to steer the vessel at a safe navigational speed. 1. SOLAS V and Steering Gear – Navsregs navsregs.wordpress.com
Important Notes
- Compliance Demonstration: Compliance with these requirements is typically demonstrated during sea trials, where the actual rudder movement capabilities are measured and documented.
- Exemptions and Alternatives: In certain cases, exemptions or alternative methods of demonstrating compliance might be allowed, especially for older vessels or those with specific design constraints. These would need to be approved by the relevant flag state or classification society.
In conclusion, SOLAS Chapter II-1, Regulation 29 sets specific standards for rudder movement capabilities, ensuring vessels have adequate steering responsiveness for safe navigation. Understanding these requirements is essential for anyone involved in the design, operation, or maintenance of steering gear systems on marine vessels.Sources and related content
Preventing the rudder from exceeding the maximum permitted
In an electro-hydraulic, ram-type steering gear, preventing the rudder from exceeding the maximum permitted movement (typically 35 degrees to either side) is crucial to ensure safe operation and avoid damage to the steering system and the vessel itself. Here’s how this is achieved:
1. Mechanical Stops:
- Physical Limit: The simplest and most reliable method is to incorporate mechanical stops or limiters within the steering gear assembly. These stops physically prevent the rams from extending or retracting beyond a point that corresponds to the maximum allowable rudder angle.
2. Hydraulic Limit Switches:
- Position Sensing: Hydraulic limit switches are installed on the tiller or rudder stock. They sense the position of the rudder and send signals to the control system when the rudder approaches the maximum angle.
- Control Signal: The control system then restricts or stops the hydraulic flow to the rams, preventing further movement beyond the set limit.
3. Electronic Control System:
- Software Limits: In modern electro-hydraulic steering gears, the electronic control system (ECU) has software-based limits programmed into it. The ECU monitors the rudder angle feedback from sensors and stops the pump or controls the valves to prevent the rudder from exceeding the maximum angle.
4. Alarm Systems:
- Audible and Visual Warnings: Alarms, both audible and visual, may be activated when the rudder approaches its maximum limit. This alerts the helmsman or operator to take corrective action and avoid exceeding the limit.
Additional Considerations:
- Redundancy: Critical safety systems like steering often have redundant components and control circuits to ensure that even if one system fails, another can take over and prevent overtravel.
- Regular Testing and Calibration: The limit switches, sensors, and control systems should be regularly tested and calibrated to ensure their accuracy and reliability.
- Maintenance: Proper maintenance of the entire steering gear system, including hydraulic components, mechanical linkages, and electronic controls, is crucial for preventing malfunctions that could lead to overtravel.
Importance of Preventing Overtravel:
- Structural Damage: Exceeding the maximum rudder angle can put excessive stress on the rudder, rudder stock, and associated linkages, potentially leading to bending, cracking, or other structural damage.
- Loss of Control: Excessive rudder movement can cause the vessel to become unstable or difficult to control, increasing the risk of accidents or collisions.
- Damage to Steering Gear: Overtravel can also damage the hydraulic rams, valves, and other components of the steering gear itself.
In Summary:
Electro-hydraulic, ram-type steering gears employ a combination of mechanical stops, hydraulic limit switches, electronic control systems, and alarms to ensure that the rudder’s movement stays within the safe and permissible limits, preventing overtravel and the associated risks.
How the steering gear system is protected from damage
Steering gears incorporate various safety mechanisms to prevent damage in the event of excessive rudder movement beyond the permissible limits. Here’s an overview of how this protection is achieved:
1. Mechanical Stops
- Physical Barriers: Mechanical stops, often in the form of robust metal blocks or pins, are strategically placed within the steering gear assembly to physically limit the movement of the rams or other actuators. These stops create a hard barrier that prevents the rudder from exceeding its maximum angle, even if the control system malfunctions or sends erroneous commands.
2. Hydraulic Limit Switches:
- Position Sensing: Hydraulic limit switches are installed on the tiller or rudder stock. These switches are actuated by the physical movement of the rudder and send signals to the control system when the rudder approaches its maximum allowable angle.
- Control Signal Interruption: Upon receiving the signal from the limit switches, the control system will cut off the hydraulic fluid supply to the rams, preventing further movement and ensuring the rudder stays within its safe operational limits.
3. Electronic Control System Limits:
- Software-Based Protection: In modern electro-hydraulic steering gears, the electronic control unit (ECU) has built-in software limits that define the maximum permissible rudder angle. The ECU constantly monitors the rudder position feedback from sensors and intervenes to stop the pump or adjust valve positions if the rudder approaches its limit.
4. Pressure Relief Valves:
- Overpressure Protection: Pressure relief valves are installed in the hydraulic system to prevent excessive pressure buildup, which could occur if the rams attempt to move beyond the mechanical stops or if the control system fails to stop the hydraulic flow. These valves open at a predetermined pressure, safely venting excess fluid and protecting the system from damage.
5. Alarms and Indicators:
- Warning Signals: Visual and audible alarms are often triggered when the rudder approaches its maximum limit, alerting the helmsman or operator to take corrective action. This provides an additional layer of safety by prompting manual intervention if the automatic systems fail to prevent overtravel.
Additional Considerations:
- Redundancy: Critical safety systems like steering often have redundancy built in, with multiple sensors, control circuits, or even backup steering systems to further minimize the risk of overtravel and ensure the vessel’s safety.
- Regular Testing and Maintenance: Periodic testing and calibration of limit switches, sensors, and control systems, along with proper maintenance of the entire steering gear, are essential to ensure these safety mechanisms function reliably.
In summary, a combination of mechanical stops, hydraulic limit switches, electronic control limits, pressure relief valves, and alarms work together to safeguard the steering gear and the vessel from the potential damage and safety risks associated with exceeding the maximum rudder movement. By implementing these protective measures and adhering to proper maintenance practices, the steering gear system can operate safely and reliably, ensuring the vessel’s maneuverability and control in all conditions.