The stern shaft seal of the ship may leak due to various reasons. The sea water enters the seal chamber, causing the oil in the rear seal oil tank to be emulsified (see Figure 1). In serious cases, the oil leaks out to the sea, causing the port authorities to detain or fine, or the sea water leaks inward, causing the stern tube oil to be emulsified, the lubricating oil film to fail, causing serious accidents such as high temperature or even burning of the stern bearing, which bring serious potential safety hazards to the ship. Improper design or installation of stern shaft sealing device is the main cause of stern shaft seal leakage. In addition, the unreasonable structure or improper installation of the protective cover may lead to the entanglement of the fishing net. The fishing net enters the sealing chamber and causes leakage of the stern shaft seal, or the shield collides with the propeller.

Management Considerations

Wool felt which is easy to fall off shall not be used as the sealing element of stern shaft sealing device to prevent sediment. The design of a new product must be fully compared with the traditional product, and the new product must go through various tests before it can be mass produced. When selecting the sealing device, the equipment user shall not presume to select the products that have not been tested on the real ship, especially for the ships manufactured in batches.

Once the seal leaks after encountering the stern shaft, high viscosity lubricating oil can be used to slow down the leakage. Less than 2 months after a container ship left the factory, the stern shaft rear seal leaked and the oil in the small oil tank of the rear seal was emulsified. The ship is equipped with sealing devices of international famous brands. Considering the product quality, there should be no problem. Therefore, it was pointed out at the first time that the nut for measuring the settlement of the stern seal was probably not tightened, and the diver found that the nut was indeed off after underwater inspection. After the divers were asked to use a special material to grind plastic steel (similar to underwater cement) for plugging, there was still leakage. It is proposed to use high viscosity lubricating oil because it is not easy to leak in the small gap between the stainless steel sleeve and the rubber seal. As a result, the leakage of the rear seal has been significantly improved, and the shipowner no longer requires docking repair.