Propeller Shaft Alignment Check and High Bearing Indications
(a) Checking Propeller Transmission Shaft Alignment:
Ensuring proper alignment of the propeller shaft system is crucial for optimal performance, reduced wear and tear, and preventing vibration. Here are two common methods for checking shaft alignment:
1. Dial Gauge Method:
- This traditional method utilizes dial gauges to measure the relative runout (movement) of the shaft coupling flanges at various points.
- Dial gauges are magnetically attached to each flange, and the shaft is slowly rotated by hand.
- The runout at different points on the flange circumference is measured and compared to specified tolerances.
- Any deviations beyond acceptable limits indicate misalignment, which needs correction through adjustments of the engine mounts or gearbox position.
2. Laser Shaft Alignment:
- This modern method utilizes laser beam technology for more precise and efficient alignment checks.
- A laser transmitter is positioned on one shaft end, and a receiver is placed on the other.
- The laser beam projects onto the receiver target, and any misalignment is reflected in the position of the laser dot on the target.
- By following the system’s instructions and adjusting mounts or gearbox position, the laser beam can be centered on the target, indicating proper alignment.
Additional Considerations:
- Regardless of the method used, shaft alignment should be performed by a qualified technician with the proper tools and expertise.
- Manufacturer’s specifications for acceptable alignment tolerances and specific alignment procedures should be strictly followed.
(b) Indications of a High Bearing When the Shaft is Running:
A high bearing, also known as a seized or tight bearing, can cause several problems during shaft operation. Here are some indications that might suggest a high bearing:
- Increased Vibration: A high bearing can cause the shaft to run out of true, leading to increased vibration throughout the vessel. This vibration may be felt throughout the hull and might be noticeable visually.
- Abnormal Shaft Temperature: Friction from a high bearing can generate excessive heat. This can be detected by feeling increased temperature around the bearing housing or using specialized temperature monitoring instruments.
- Unusual Noises: Seized or tight bearings can produce grinding, scraping, or knocking noises as the shaft rotates with difficulty against the bearing surface.
- Difficulty Turning the Shaft: In severe cases, a very tight bearing may make it difficult or impossible to turn the shaft by hand.
Early detection and addressing a high bearing is crucial. Ignoring these symptoms can lead to further damage to the bearing, shaft, and surrounding components. If any of these indications are observed, the shaft should be stopped immediately, and a qualified mechanic should investigate the issue.