Auxiliary 1

Question 1

Label diaphram valve

Answer 1

Question 2

Why are fusible plugs fitted to air compressors?

Answer 2

Fusible plugs are safety features built In air compressors and play a vital role in avoiding overheating and overpressure scenarios.

During operation, air compressors can generate significant heat due to compression. If the cooling system fails, the temperature may rise dangerously. The are designed to help vent the compressed air safely to avoid further failure of the equipment.

Question 3

Why are fusible plugs fitted to air receivers?

Answer 3

Purpose in an air receiver: Air receivers (storage tanks for compressed air) may encounter dangerous pressure or heat buildup. Fusible plugs are installed to mitigate these risks.

1. Prevent explosion: If heat from nearby equipment (like an engine room) increases the temperature of the air in the receiver, pressure rises. The fusible plug melts at a preset temperature, releasing pressure.
2. Maintain system integrity: By venting air, fusible plugs prevent structural failure of the air receiver, which could lead to explosions.
3. Safety compliance: Fusible plugs ensure compliance with safety regulations and standards in marine and industrial environments.

Question 4

What are the key steps in routine maintenance for the electrical side of an a.c. generator set?

Answer 4

1. Inspect Connections: Check for wear, looseness, or corrosion; tighten and clean as needed.
2. Test Insulation: Use a megohmmeter to ensure winding insulation meets specifications.
3. Clean Components: Remove dust and grease from windings and terminals using compressed air or lint-free cloths.
4. Test Voltage Output: Measure voltage under load and no-load conditions; adjust the regulator if necessary.
5. Check Bearings: Inspect and lubricate bearings; replace worn bearings to avoid mechanical failures.
6. Maintain Brushes and Slip Rings: Clean slip rings and replace worn brushes in brush-type generators.
7. Cooling System Checks: Verify fan operation; clean air filters to prevent overheating.
8. Test Safety Devices: Check circuit breakers, relays, and other protective equipment.
9. Check Frequency and Speed: Adjust the governor to maintain correct frequency (e.g., 50 Hz or 60 Hz).
10. Replace Components: Replace worn parts like capacitors, diodes, or voltage regulators.

Question 5

How is a change of alignment in propulsion shaft intermediate bearings due to vessel condition allowed for?

Answer 5

Many intermediate bearings are designed to be self-aligning, which allows them to adjust automatically to changes in shaft alignment caused by vessel movement. This is essential to compensate for hull deflections in rough seas or uneven loading.

Bearings may also be mounted on floating or semi-floating supports, enabling them to shift slightly in response to dynamic changes in vessel structure and conditions.

Question 6

Why must the propulsion shaft be able to move longitudinally?

Answer 6

1. To accommodate thermal expansion and contraction of the shaft during operation.
2. To adjust for hull movement due to ship flexing or deformation in varying sea conditions.
3. To distribute load evenly and prevent jamming or misalignment, ensuring smooth operation.

Question 7

Why does the aft most bearing require a complete bush, while other bearings may have only a lower half?

Answer 7

1. The aftmost bearing supports the propeller shaft, which experiences higher thrust and radial forces.
2. A full bush provides maximum support and absorbs both axial and radial forces.
3. Intermediate bearings need only lower halves for support and easier maintenance, as they face lighter loads.

Question 8

What are three advantages of hydraulically fitted shaft coupling bolts compared to parallel interference fit bolts?

Answer 8

• Ease of Installation and Removal: Hydraulic bolts require minimal force and are easy to install and remove without damaging the components.
• Uniform Force Distribution: Hydraulic fittings evenly distribute force, reducing stress points and enhancing durability.
• Reduced Risk of Damage: No hammering or excessive force is needed, minimizing the chance of deformation or material damage.

Question 9

With reference to propellers, what are:

(a) Two advantages of high skew?
(b) Two advantages of aft rake?

Answer 9

Advantages of High Skew:

• Reduces vibrations for smoother operation and less wear on the propulsion system.
• Minimizes stress concentrations, extending the propeller’s lifespan.

Advantages of Aft Rake:

• Improves thrust efficiency, reducing fuel consumption.
• Reduces cavitation, protecting the propeller from erosion.

Question 10

With reference to propellers, explain
SKEW

Answer 10

Skew in a propeller blade refers to the curvature or backward sweep of the blade when viewed in the plane of rotation. Instead of being straight, a skewed blade is twisted or curved relative to the hub.

Question 11

With reference to propellers, explain; RAKE

Answer 11

• Rake is the inclination of the propeller blades in the axial direction (forward or aft relative to the hub).
  • Aft rake improves thrust efficiency and reduces cavitation.
  • Forward rake enhances flow dynamics and reduces drag.
  • Aft rake is commonly used to improve propulsion performance and minimize wear.

Question 12

With reference to propellers, explain; Pitch

Answer 12

Pitch is the calculated distance the ship would move forward with one full rotation of the propeller under ideal conditions with no losses.

Question 13

With reference to propellers, explain SLIP

Answer 13

Slip is the difference between the theoretical and actual movement of a propeller through water.

* Water resistance prevents the propeller from achieving perfect forward movement.

* Higher slip means lower efficiency, while optimized slip improves propulsion effectiveness.

Question 14

With Reference to Propellers

Two Reasons for Having High Skew

Answer 14

1. Reduction of Vibrations and Noise

A high-skew propeller reduces pressure fluctuations as each blade enters the water, minimizing vibrations.

This results in quieter operation, improving comfort on board while reducing structural stress on the vessel.

2. Enhanced Durability and Load Distribution

High skew helps distribute hydrodynamic forces more smoothly across the propeller blade.

This minimizes localized stress concentrations, reducing the risk of fatigue cracks and extending the propeller’s lifespan.

Question 15

With Reference to Propellers

Two Reasons for Having Aft Rake

Answer 15

1. Improved Thrust Efficiency

Aft rake optimizes water flow around the propeller, increasing propulsion efficiency and reducing fuel consumption.

This is particularly beneficial for high-speed vessels where energy efficiency is critical.

2. Reduced Cavitation and Erosion Risk

Aft rake helps maintain a cleaner flow of water around the blades, reducing the occurrence of cavitation (vapor bubble formation).
Less cavitation means lower erosion risk, helping to maintain propeller performance over time.

Question 16

List SIX examples of contaminants that may be found in hydraulic oil.

Answer 16

• Water & dirt contamination from vents and fill points.
• Sea water contamination from leaking cooler
• Metallic particles from wear
• Elastomers from damaged seals
• Fibers from cleaning material
• Rust particles from internal corrosion

Question 17

Label compressor drawing

Answer 17

Question 18

State three devices fitted to the main breakers to protect a.c. genertators that are able to run in parallel

Answer 18

Overcurrent Protection: This device safeguards the generator from excessive current, which could result from faults or overloads.

Reverse Power Relay: It prevents power from flowing back into the generator, which could damage the prime mover.

Under/Over Voltage Protection: This ensures the generator operates within safe voltage limits, protecting both the generator and connected equipment.

Question 19

With reference to a.c. generators explain why they must be synchronised before connecting in parrellel

Answer 19

Synchronization ensures that multiple generators work together without causing electrical disturbances or mechanical stress. The key reasons for synchronization are:
✅ Matching Voltage Levels
✅ Frequency Alignment
✅ Phase Matching
✅ Load Sharing –
✅ Avoiding Mechanical Stress

Question 20

With reference to a.c. generators list two devices to ensure synchronisingis correct.

Answer 20

1. Synchroscope: This device indicates the phase difference between the incoming generator and the busbar, helping to align them correctly before connection.
2. Synchronizing Lamps: A simpler method where lamps connected in a specific configuration indicate whether the generator is in phase with the busbar.

Question 21

In a hydraulic steering gear system, preventing the idle pump from motoring list and explain 2 devices that may be used.

Answer 21

1. Check Valves – These valves allow fluid to flow in only one direction, preventing backflow into the idle pump. By ensuring that hydraulic fluid does not enter the idle pump from the active pump, check valves effectively stop reverse rotation.
2. Automatic Isolating Valves – These valves close automatically when a pump is idle, preventing fluid flow through it. This isolation ensures that the idle pump does not receive unintended hydraulic pressure, stopping it from motoring.

Both methods help maintain system efficiency and prolong the lifespan of the idle pump.

Question 22

Explain the emergency operation of a pneumatically operated friction clutch

Answer 22

A pneumatically operated friction clutch relies on compressed air to engage and disengage the clutch mechanism. In an emergency situation, the operation of the clutch must ensure rapid disengagement to prevent damage . Here’s how it typically works:

1. Loss of Air Pressure – If the system experiences a sudden drop in air pressure, the clutch may automatically disengage due to spring-loaded mechanisms that push the friction plates apart.
2. Emergency Release Valve – Many systems incorporate a manual or automatic emergency release valve that quickly vents air from the actuator, ensuring immediate disengagement.
3. Fail-Safe Spring Mechanism – Some designs use a fail-safe spring that forces the clutch to disengage when air pressure is lost, preventing unintended engagement.
4. Backup Air Supply – In critical applications, a secondary compressed air source or accumulator may be used to maintain clutch operation temporarily until the main system is restored.
5. Manual Override – Certain systems allow for manual disengagement using a mechanical lever or override mechanism in case of pneumatic failure.

Question 23

State what determines the circuit’s that can not be connected to the preference trip

Answer 23

✅ Essential Services – Circuits powering navigation equipment, emergency lighting, steering systems, and communication devices must remain operational.

✅ Safety-Critical Systems – Fire pumps, bilge pumps, and emergency generators cannot be disconnected as they are vital for ship safety.

✅ Control & Monitoring Systems – Automation and alarm circuits monitoring engine performance and ship stability must stay active.

✅ Legal & Regulatory Requirements – MARPOL compliance systems, emergency shutdown mechanisms, and other mandated circuits must remain powered.

Question 24

With reference to remotely operated quick closing valves:
(a) state their purpose
(b) state where they would be fitted
(c) describe how they are tested

Answer 24

a) Isolate fuel or flammable liquids in the event of a fire or emergency, preventing the spread of fire.

B) On fuel oil tanks and lubricating oil tanks to control the flow of flammable liquids.

At engine rooms or other machinery spaces where fire risks are higher.

On day tanks or other storage tanks containing combustible materials

Question 25

With reference to remotely operated quick closing valves Explain the Testing procedure

Answer 25

1. Functional Test: Operate the valve remotely to confirm it closes fully and promptly. 2. Local Operation Test: Test the manual override mechanism to ensure it works in case of remote system failure. 3. Leakage Test: Check for any leaks when the valve is in the closed position. 4. System Integrity Check: Inspect the control system (e.g., hydraulic, pneumatic, or mechanical) for proper functionality. 5. Emergency Drill: Simulate an emergency scenario to verify the valve’s performance under real conditions.

Question 26

A centrifugal bilge pump has not been operating satisfactorily, the air pump was tested and found to be operating correctly. List FIVE faults that could have caused the problem, stating why EACH fault causes poor operation.

Answer 26

Here are five potential faults that could cause poor operation of a centrifugal bilge pump, along with explanations for each: 1. **Blocked Suction Line** - Debris or sediment in the suction line can restrict the flow of water into the pump, reducing its efficiency and causing cavitation. 2. **Worn Impeller** - A damaged or eroded impeller loses its ability to generate sufficient pressure, leading to reduced flow and poor pump performance. 3. **Air Leaks in Suction Line** - Air entering the suction line disrupts the pump's ability to maintain prime, causing intermittent or complete loss of operation. 4. **Incorrect Alignment** - Misalignment between the pump and motor can lead to excessive vibration, wear, and reduced operational efficiency. 5. **Seal Failure** - A worn or damaged seal allows water to escape, reducing the pump's capacity and potentially causing overheating or further mechanical damage.

Question 27

With reference to reciprocating air compressors: (a) state the meaning of the term bump clearance; (b) explain the effects on operation if the bump clearance is: low and high

Answer 27

**(a) Meaning of Bump Clearance:** Bump clearance refers to the minimum distance between the piston and the cylinder head when the piston is at top dead center (TDC). This clearance ensures that the piston does not physically collide with the cylinder head during operation. **(b) Effects on Operation if Bump Clearance is:** 1. **Too Small:** - Risk of Collision causing damage - Increased Compression Pressure and to higher temps - Reduced Safety Margin 2. **Too Large:** - Reduced Volumetric Efficiency - Lower Compression Pressure - Increased Re-expansion Losses

Question 28

Outline the safety precautions which should be taken when carrying out repairs or maintenance on hydraulic system.

Answer 28

When performing repairs or maintenance on hydraulic systems, safety is paramount due to the high pressures and potential hazards involved. Before Starting Work: 1. **Lockout/Tagout (LOTO)**: Ensure the system is isolated from its energy source to prevent accidental activation. 2. **Pressure Relief**: Release all residual pressure in the system using designated valves or following the manufacturer's instructions. 3. **Fluid Drainage**: Drain hydraulic fluid to minimize exposure to hot oil and reduce the risk of spills. 4. **Personal Protective Equipment (PPE)**: Wear safety glasses, gloves, oil-resistant coveralls, and safety boots to protect against fluid leaks and debris. 5. **System Cleaning**: If necessary, flush the system to remove contaminants before disassembly. During Repairs and Maintenance: 1. **Follow Manufacturer's Guidelines**: Adhere to service manuals for disassembly, inspection, and reassembly. 2. **Use Proper Tools**: Employ tools designed for hydraulic systems to avoid damaging components. 3. **Beware of High-Pressure Components**: Handle hoses, valves, and fittings with care to prevent sudden fluid release. 4. **Maintain a Clean Workspace**: Keep the area organized to avoid tripping hazards or losing tools. 5. **Work in Pairs**: For complex tasks, have a partner for assistance and safety monitoring. After Completing Work: 1. **Reassembly and Inspection**: Ensure all components are securely reassembled and connections are tightened. 2. **System Refilling**: Use clean hydraulic fluid of the recommended type and bleed air from the system. 3. **Testing**: Conduct a test run to verify proper operation and check for leaks. 4. **Final Safety Checks**: Confirm all tools are removed, LOTO procedures are reversed, and the system is safe to use. By following these precautions, you can minimize risks and ensure safe and effective maintenance of hydraulic systems.

Question 29

State the requirements for the positioning of the emergency source of electrical power

Answer 29

The positioning of the emergency source of electrical power is crucial for ensuring its functionality during emergencies. Here are the key requirements: 1. **Above the Uppermost Continuous Deck**: The emergency power source must be located above the uppermost continuous deck to remain operational even if lower decks are flooded or damaged. 2. **Accessible from an Open Deck**: It should be readily accessible from an open deck to facilitate maintenance and operation during emergencies. 3. **Aft of the Collision Bulkhead**: Ideally, it should be positioned aft of the collision bulkhead to minimize the risk of damage from head-on collisions. 4. **Separated from Machinery Spaces**: The emergency power source should not be contiguous to machinery spaces or spaces containing the main source of electrical power. This ensures that a fire or casualty in these areas does not interfere with the emergency power supply. These requirements are designed to ensure the reliability and safety of the emergency power source in critical situations.

Question 30

Outline the neccessary precautions as stated in the code of safe working practices when working near live electrical equipment when it is essential for the safety for the safety of the ship or for testing purposes

Answer 30

When working near live electrical equipment, as outlined in the **Code of Safe Working Practices for Merchant Seamen**, the following precautions are essential to ensure safety: Preparation and Planning: 1. **Permit to Work**: Obtain a formal permit detailing the task, potential hazards, and safety measures. 2. **Competent Supervision**: Ensure a qualified electrician or a designated competent person supervises the work. 3. **Risk Assessment**: Conduct a thorough assessment to identify hazards and implement mitigation measures. 4. **Isolation Attempts**: If possible, isolate the equipment using approved switches or lockout/tagout procedures. 5. **Personal Protective Equipment (PPE)**: Use insulated gloves, footwear, and eye protection rated for the voltage. 6. **Safe Working Area**: Establish a clear, restricted zone to prevent accidental contact with live components. 7. **Warning Signs**: Display clear warnings to alert others of the ongoing work. 8. **Insulated Tools**: Use tools specifically designed for electrical work to minimize risks. During Work: 1. **Controlled Movements**: Work deliberately to avoid accidental contact with live parts. 2. **One-Hand Rule**: Keep one hand behind your back to reduce the risk of completing a circuit. 3. **Continuous Monitoring**: Have a designated observer monitor the worker and the situation for safety. 4. **Emergency Shutdown Plan**: Be prepared to de-energize the equipment immediately in case of an emergency. After Work: 1. **Final Inspection**: Ensure the equipment is secure, tools are removed, and the area is safe. 2. **Permit Cancellation**: Cancel the work permit once all safety measures are terminated. These precautions prioritize safety while allowing essential tasks to be carried out near live electrical equipment.

Question 31

with reference to comparing modern water lubricated stern tube bearings with those that are oil lubricated explain advantages and dis-advantages

Answer 31

Here’s a comparison of modern water-lubricated stern tube bearings and oil-lubricated stern tube bearings: Advantages of Water-Lubricated Bearings: 1. **Environmental Friendliness**: Water-lubricated bearings eliminate the risk of oil spills, making them more eco-friendly and compliant with stricter environmental regulations. 2. **Lower Maintenance**: They require less maintenance since there’s no need for oil changes or filter replacements. 3. **Simpler Design**: These bearings often have fewer components, reducing weight and manufacturing costs. Disadvantages of Water-Lubricated Bearings: 1. **Lower Load Capacity**: Water has a lower lubricating capacity compared to oil, which can limit the load these bearings can handle. 2. **Stricter Tolerance Requirements**: They demand tighter clearances between the shaft and bearing material to maintain proper lubrication. 3. **Potential Corrosion**: Exposure to seawater can lead to corrosion, though modern materials and coatings help mitigate this. Advantages of Oil-Lubricated Bearings: 1. **Higher Load Capacity**: Oil provides superior lubrication, allowing these bearings to handle higher loads. 2. **Better Durability**: Oil-lubricated systems are generally more robust under heavy-duty operations. 3. **Established Technology**: These systems have been widely used and refined over decades. Disadvantages of Oil-Lubricated Bearings: 1. **Environmental Risks**: Oil spills can harm marine ecosystems, and even minor leaks can lead to regulatory penalties. 2. **Higher Maintenance**: Regular oil changes and seal replacements are necessary to prevent leaks and maintain performance. 3. **Complexity**: These systems often involve more components, increasing initial costs and potential points of failure.

Question 32

Give reason why the following devices are fitted to the main breakers to protect ac generators that are able to run in parallel Over current protection relay Reverse power protection relay Under/over voltage relay

Answer 32

When AC generators operate in parallel, it's crucial to protect them from electrical faults or issues that could damage the system. 1. **Overcurrent Protection Relay**: This device prevents damage caused by excessive current, such as during short circuits or overloads. 2. **Reverse Power Protection Relay**: Ensures that no generator feeds power backward into another generator, which could cause mechanical damage or destabilize the system. 3. **Under/Over Voltage Relay**: Protects the system by monitoring voltage levels and disconnecting the generator if the voltage strays beyond safe limits. These devices help maintain system reliability and safeguard equipment.

Question 33

Draw and label the following butterfly valve

Answer 33

Question 34

Describe the checks carried out during the inspection of a main thrust bearing

Answer 34

Inspecting a main thrust bearing involves several critical checks to ensure its proper function and longevity. including - **Visual Inspection**: Checking for signs of wear, scoring, or pitting on the bearing surface. - **Lubrication Assessment**: Ensuring the oil supply is adequate and free from contamination. - **Temperature Monitoring**: Measuring operating temperatures to detect overheating. - **Axial Clearance Measurement**: Verifying that the bearing clearance is within acceptable limits. - **Vibration Analysis**: Identifying any unusual vibrations that could indicate misalignment or damage. - **Wear Measurement**: Evaluating the extent of wear using precision instruments. - **Structural Integrity Check**: Inspecting the housing and support structures for cracks or deformation. Regular inspections help prevent failures and ensure smooth operation.

Question 35

a. State the factor that determines the minimum number of available generators required for a vessel to put to sea (3) b. State 7 essential services for the operation of the vessel (7)

Answer 35

**the vessel's total electrical load demand and redundancy requirements**. This includes essential systems such as navigation, communication, propulsion auxiliaries, and safety equipment. Regulations and classification society rules also play a role in defining the minimum number of generators needed to ensure operational reliability. Here are seven essential services required for a vessel's safe operation: 1. **Steering Gear** – Ensures the vessel can maneuver safely. 2. **Propulsion System** – Includes engines, fuel systems, and associated components. 3. **Electrical Power Supply** – Provides energy for navigation and monitoring system. 4. **Fire Detection & Suppression** – Essential for onboard safety and emergency response. 5. **Bilge pumps & Ballast Systems** – Maintains stability and prevents flooding. 6. **Navigation & Communication Equipment** – Ensures safe passage and coordination with other vessels. 7. **Emergency Systems** – Includes lifeboats, alarms, and evacuation procedures. These services are critical for maintaining operational integrity at sea.

Question 36

Explain the term signal phasing in an electrical motor (2)

Answer 36

This is when one of the three phase is missing in operation of a 3 phase motor.

Question 37

State the effects on a motor suffering from single phasing (6)

Answer 37

**Effects of Signal Phasing on a Motor:** - **Torque Loss** – Uneven phasing reduces torque and may cause vibrations. - **Overheating** – Increased current draw leads to insulation damage. - **Voltage Imbalance** – Reduced efficiency and higher energy consumption. - **Mechanical Wear** – Excessive vibration accelerates bearing failure. - **System Trips** – Protection relays may shut down the motor. - **Speed Instability** – Loss of synchronization affects performance.

Question 38

state how single phasing protection is achieved in a starter motor circuit (3)

Answer 38

Single phasing protection in a starter motor circuit is typically achieved through - **Thermal Overload Relays** – These monitor current levels and trip the circuit if excessive heating occurs due to single phasing. - **Single-Phasing Preventers** – These detect phase imbalance and disconnect the motor to prevent damage. - **Negative Sequence Filters** – Used in advanced systems to identify phase loss and trigger protective actions.

Question 39

State 3 reasons that may cause a pneumatic relief valve to lift in service (3)

Answer 39

A relief valve may lift in service due to the following reasons: 1. **Excessive System Pressure** If the pressure in the system exceeds the valve's set point, it will open to release excess pressure and prevent damage. 2. **Thermal Expansion** Temperature changes can cause fluid expansion, increasing pressure beyond safe limits and triggering the relief valve. 3. **Valve Malfunction or Blockage** A faulty valve or obstruction in the system can lead to improper pressure regulation, forcing the relief valve to lift unexpectedly.

Question 40

state 3 reasons that may cause a relief valve to fail to lift should excessive pressure occur (3)

Answer 40

Here are three reasons a relief valve may fail to lift under excessive pressure: 1. **Valve Blockage** – Debris or contamination in the valve can obstruct its operation, preventing it from opening. 2. **Incorrect Calibration** – If the valve's set pressure is improperly adjusted, it may not activate at the intended pressure level. 3. **Spring Failure** – A weakened or broken spring can prevent the valve from responding to pressure changes effectively.

Question 41

explain how the correct operation of a relief valve is ensured (4)

Answer 41

Ensuring the correct operation of a relief valve involves several key practices: 1. **Regular Maintenance**: Periodically inspect and clean the valve to prevent blockages or corrosion that could hinder its function. 2. **Calibration**: Adjust the valve to the correct set pressure using manufacturer guidelines to ensure it activates at the intended pressure level. 3. **Functional Testing**: Perform tests to verify the valve opens and reseats properly under simulated pressure conditions. 4. **Component Checks**: Inspect critical parts like springs, seals, and seats for wear or damage, replacing them as needed. 5. **Environmental Considerations**: Protect the valve from extreme temperatures or corrosive environments that could affect its performance.

Question 42

with reference to air compressors explain why an air filter is important

Answer 42

- **Prevents Contamination:** Air filters remove dust, dirt, oil, and other impurities from the intake air, protecting the compressor's internal components from wear and damage. - I**mproves Efficiency:** Clean air reduces pressure drops and ensures smooth operation, enhancing the overall efficiency of the compressor. - **Protects End Applications:** In industries like painting or food processing, clean compressed air is essential to maintain product quality and prevent equipment malfunction.

Question 43

why the compressor should not be allowed to run with a dirty air filter

Answer 43

Running a compressor with a dirty air filter can lead to several issues: 1. **Reduced Efficiency**: A clogged filter restricts airflow, forcing the compressor to work harder and consume more energy. 2. **Component Damage**: Dirt and debris can bypass the filter, causing wear and tear on internal parts like valves and pistons. 3. **Overheating**: Restricted airflow increases operating temperatures, which can lead to overheating and potential system failure. 4.**Risk to end user or equipment** Contaminated air can carry harmful particles, leading to respiratory issues or allergic reactions, especially in sensitive environments like healthcare or food processing. depending on the type of aircompress and what it used for.