Aux 1 Unit 11 Q4

A single screw vessel is a ship or boat that is propelled by only one propeller. This contrasts with vessels having twin screws (two propellers) or even more in some cases.  

1. Single-screw Definition & Meaning – Merriam-Webster

Characteristics of Single Screw Vessels:

• Propulsion: They rely on a single propeller mounted on a shaft connected to the main engine or gearbox.
• Maneuverability:
  • Less Maneuverable: Compared to twin-screw vessels, single screw vessels generally have reduced maneuverability, especially at low speeds or in tight spaces. This is because they lack the ability to independently control the thrust from each side of the vessel.
  • Reliance on Rudder:** They rely heavily on the rudder for steering and maneuvering.
• Simplicity: The propulsion system is generally simpler and less complex than multi-propeller configurations, leading to potential cost savings in construction and maintenance.
• Efficiency: In some cases, single screw vessels can be more efficient than twin-screw vessels, especially at higher speeds, due to reduced drag from having only one propeller and shaft.

Common Applications:

• Smaller Vessels: Single screw propulsion is common in smaller boats, yachts, and fishing vessels, where simplicity and cost-effectiveness are often prioritized over maneuverability.
• Larger Vessels: While less common, single screw configurations are also used in some larger vessels, such as tankers, bulk carriers, and container ships, where efficiency at higher speeds is important.

Maneuvering Challenges and Solutions:

• Turning: Single screw vessels tend to have a larger turning radius compared to twin-screw vessels, requiring more space and careful planning when maneuvering in confined areas.
• Sideways Movement: They lack the ability to move directly sideways, making docking and close-quarters maneuvering more challenging.
• Propeller Walk: The rotating propeller creates a sideways force known as “propeller walk” which can affect the vessel’s handling, particularly at low speeds or when reversing.
• Mitigation Techniques: To improve maneuverability, single screw vessels might employ:
  • Bow Thrusters: These provide lateral thrust at the bow, aiding in turning and docking.
  • Stern Thrusters: Similar to bow thrusters but located at the stern.
  • Active Rudders: Rudders with flaps or other features that can enhance maneuverability at low speeds.
  • Skilled Shiphandling: Proper handling techniques and understanding of propeller walk are crucial for safely maneuvering single screw vessels.

In Summary:

Single screw vessels are those propelled by a single propeller. While they might be less maneuverable than multi-propeller vessels, they offer advantages in simplicity, efficiency, and cost-effectiveness in certain applications. Understanding their handling characteristics and employing appropriate maneuvering techniques or auxiliary propulsion devices are key to operating these vessels safely and effectively.  

1. Single-screw Definition & Meaning – Merriam-Webster

A hot-running intermediate shaft bearing on a single-screw vessel indicates a potential problem that needs attention. Here are some possible causes:

Lubrication Issues

• Insufficient Lubrication:
  • Low oil level in the bearing housing due to leaks or inadequate filling.
  • Clogged oil passages or filters restricting oil flow to the bearing.
  • Improper oil viscosity, leading to inadequate lubrication at operating temperatures.
• Contaminated Lubricant:
  • Water or other contaminants in the oil, reducing its lubricating properties and increasing friction.
  • Degradation of the oil due to overheating or oxidation, causing loss of viscosity and lubrication effectiveness.

Mechanical Issues:

• Misalignment: Misalignment between the shaft and bearing, or between adjacent shaft sections, can cause excessive loads and friction on the bearing, leading to overheating.
• Bearing Wear or Damage:
  • Worn or damaged bearing surfaces, such as scoring, pitting, or flaking, can increase friction and generate heat.
  • Overloading or fatigue can also damage the bearing components.
• Shaft Issues:
  • Bent or misaligned shaft can put uneven pressure on the bearing, causing overheating.
  • Excessive vibration or whip in the shaft can also contribute to bearing problems.
• Improper Installation: Incorrect installation of the bearing, including improper seating or excessive tightening of bolts, can lead to misalignment or uneven loading, causing the bearing to run hot.

Operational Factors:

• Overloading: Operating the vessel beyond its design limits, with excessive loads or at high speeds, can put additional stress on the bearings and lead to overheating.
• Prolonged Operation at High Temperatures: Operating in high ambient temperatures or with insufficient cooling can contribute to bearing overheating.

Other Possible Causes:

• Inadequate Cooling: If the bearing is water-cooled, insufficient cooling water flow or a blockage in the cooling system can cause the bearing to overheat.
• Contamination from External Sources: Ingress of seawater, dirt, or other contaminants into the bearing housing can affect lubrication and cause wear, leading to overheating.

Troubleshooting Steps:

• Check Oil Level and Condition: Inspect the oil level and look for signs of contamination or degradation. Change the oil if necessary.
• Check for Leaks: Inspect the bearing housing and associated piping for any oil leaks or water ingress.
• Monitor Temperature: Use a thermometer or infrared temperature gun to monitor the bearing temperature and compare it to the manufacturer’s recommended operating range.
• Check for Noise and Vibration: Listen for unusual noises and feel for excessive vibration, which can indicate bearing problems.
• Inspect Alignment: Check the alignment of the shaft and bearing using appropriate tools and techniques.

If a hot bearing is detected:

• Reduce Load or Speed: Reduce the engine load or vessel speed to minimize stress on the bearing.
• Increase Cooling (if applicable): If the bearing is water-cooled, increase the cooling water flow to help dissipate heat.
• Monitor Closely: Continue to monitor the bearing temperature and other indicators closely.
• Seek Professional Assistance: If the temperature continues to rise or other signs of bearing distress are observed, seek professional assistance from a qualified marine engineer or technician.

Remember:

Ignoring a hot-running bearing can lead to serious consequences, including bearing failure, shaft damage, and potential loss of propulsion. Prompt action is crucial to address the underlying cause and prevent further damage to the vessel’s propulsion system.

If an intermediate shaft bearing on a single-screw vessel is running hot and no immediate cause can be identified, it’s crucial to proceed with caution and take steps to reach port for further investigation and repairs. Here’s the recommended procedure:

1. Reduce Speed and Load:

• Minimize Stress on Bearing: The first priority is to reduce the load and stress on the affected bearing. This can be achieved by:
  • Reducing Engine Speed: Slow down the vessel to a safe speed that minimizes the load on the propulsion system.
  • Limiting Maneuvering: Avoid excessive maneuvering or sudden changes in direction that could put additional stress on the shaft and bearings.

2. Monitor Bearing Temperature:

• Continuous Monitoring: Closely monitor the bearing temperature using a thermometer or infrared temperature gun. Record the readings at regular intervals to track any changes.
• Set Alarm Limits: If possible, set alarms on the temperature monitoring system to alert the crew if the bearing temperature exceeds safe limits.

3. Increase Cooling (if applicable):

• Water-Cooled Bearings: If the bearing is water-cooled, increase the flow of cooling water to help dissipate heat.
• Air-Cooled Bearings: If the bearing is air-cooled, ensure adequate ventilation and airflow around the bearing housing.

4. Lubrication Checks:

• Oil Level and Condition: Regularly check the oil level in the bearing housing and inspect the oil for any signs of contamination or degradation. If necessary, top up the oil or replace it with fresh oil.

5. Communication and Planning:

• Inform the Bridge: Keep the bridge team informed about the bearing condition and any changes in temperature or other indicators.
• Plan for Port Entry: Identify the nearest suitable port for further investigation and repairs.
• Prepare for Potential Towing: If the bearing condition deteriorates significantly or there’s a risk of imminent failure, prepare the vessel for potential towing operations.

6. Voyage Planning:

• Shortest and Safest Route: Choose the shortest and safest route to the designated port, considering weather conditions, traffic density, and any navigational hazards.
• Reduced Speed: Maintain a reduced speed throughout the voyage to minimize stress on the bearing.
• Avoid Rough Seas: If possible, avoid areas with rough seas or heavy weather that could exacerbate the bearing issue.

7. Continuous Monitoring and Assessment:

• Regular Inspections: Continue to monitor the bearing temperature, oil condition, and any other relevant indicators at frequent intervals.
• Record Keeping: Document all observations and actions taken in the vessel’s logbook.
• Reassess: Regularly reassess the situation and adjust the plan as needed based on the bearing’s condition and any changes in operational parameters.

8. Arrival at Port:

• Arrange for Repairs: Upon reaching the port, arrange for qualified marine engineers or technicians to inspect the bearing and carry out necessary repairs or replacements.

Key Points to Remember:

• Safety First: Prioritize the safety of the crew and the vessel throughout the voyage.
• Caution: Proceed with caution, avoid unnecessary risks, and be prepared to take further action if the bearing condition worsens.
• Communication: Maintain clear and open communication with the bridge team, engineering crew, and relevant authorities.

By following these procedures and exercising good seamanship, a vessel with a hot-running intermediate shaft bearing can safely reach port for further investigation and repairs, minimizing the risk of further damage or a breakdown at sea.