Vessel Loss of Control from Broken Non-Std Shaft Bolt

I. Introduction

Since April 7, 2024, the Maritime Safety Administration of the Ministry of Transport of China has initiated a nationwide special action aimed at reducing the risk of mechanical and electrical equipment failures on ships and preventing water traffic accidents. It is worth noting that there are significant differences in quality between standard parts and non-standard parts. Standard parts adhere to national or industry standards, with unified dimensions, shapes, and performance; non-standard parts, however, lack uniform standards during production, resulting in uneven quality. The following is a case revealed by the editor, involving a ship's drive shaft failure caused by the use of non-standard bolts, which serves as a reminder to the industry to be cautious when using non-standard parts.

II. Incident Review

On a morning in August 2024, an imported inland river vessel on the Huangpu River suddenly experienced abnormal speed and loss of control. In an emergency, the command center quickly activated the emergency response plan, dispatched a tugboat for rescue, and ultimately brought the out-of-control vessel to a safe berth. Afterward, the inspection team conducted a detailed examination of the ship and discovered that the cause of the loss of control was the complete fracture of all the bolts connecting the drive shaft flange, which prevented the main engine power from being transmitted to the propeller.

III. Regulatory Requirements

The direct cause of this accident was the bolt fracture, which, although not uncommon in engineering practice, is extremely rare in its entirety. According to the "Steel Inland River Vessel Construction Regulations" and the "Materials and Welding Specifications," the material, strength, and preload of the shaft flange bolts are key factors.

IV. Analysis of the Accident Causes

1. 1. Bolt Material: If the accident vessel had used forged steel to make the bolts, the quality would have been more assured. However, the ship's crew purchased ordinary bolts (material unknown) from a hardware store.
2. 2. Bolt Strength: The crew did not consider the strength factor when purchasing bolts, could not provide a strength calculation, and only purchased bolts of the same size.
3. 3. Bolt Preload Torque: Proper preload control is crucial to the safety of the flange connection system. The crew did not consider preload during the installation of the bolts and did not check for loosening during operation.

V. Lessons and Insights

This accident exposed the crew's lack of understanding of the material, strength, and preload of important bolts. Therefore, we propose the following recommendations:

1. 1. Pay attention to the material, strength calculation, and preload factors of the shaft coupling and connecting bolts to ensure the safety of navigation.
2. 2. When purchasing suitable parts, strictly follow the requirements in the calculation documents, focusing on factors such as material and strength.
3. 3. Strengthen the daily inspection and maintenance of the ship, equip necessary tools, and strictly follow the requirements of the calculation and instruction manuals for maintenance.

Although this accident did not result in serious consequences, the lessons learned are profound. It is hoped that other vessels can learn from this experience and avoid similar incidents.