The Primary Purpose of Stern Tube Sealing and How to Choose One

Blog | April 27th, 2023

A stern tube is a component of a ship’s propulsion system that allows the propeller shaft to extend from the main engine to the hull and into the water. Since it is exposed to water, it should be sealed to avoid the said element from entering the vessel. The stern tube must also be protected so that other parts of the propulsion system will be protected from potential damage.

To safeguard the stern tube, it should be integrated with a stern tube sealing.

Stern Tube Sealing Primary Purpose

A stern tube seal is an essential part of the stern tube that deters water from entering the vessel through the propeller shaft. The primary purpose of this sealing is to maintain a watertight seal around the propeller shaft, preventing water from entering the vessel and causing damage.

Various types of stern tube seals can be maximised by vessel owners. These types include lip seals, mechanical seals, and gland packing.

  • Lip Seals: Lip seals are the most common type of stern tube sealing utilised in the shipping industry. They are often comprised of a rubber or elastomer seal pressed against the propeller shaft through a metal or plastic housing. They are cost-effective and simple. They likewise only require minimal maintenance. However, they must be replaced periodically. Lip seals are suitable for low to medium-speed applications.
  • Mechanical Seals: Mechanical seals, alternatively, are more complex than the previous sealing option. They consist of a stationary and rotating seal face that can provide a watertight seal around the propeller shaft. Unlike lip seals, mechanical seals require regular maintenance. They even need specialised equipment to have them installed and repaired. They are compatible with higher speed and higher pressure applications.
  • Gland Packing: Gland packing is the oldest type of stern tube seal. However, it is still used in many older vessels. This type of sealing utilises a rope-like material wrapped around the propeller shaft. It is then pressed against a stuffing box to generate a seal. This sealing element needs frequent maintenance and should be replaced often.

Picking the Right Stern Tube Sealing

If you want to pick the right stern tube sealing for your vessel, here are some important things you need to consider.

  • Operating Conditions: You should consider the operating conditions of the stern tube when choosing the right stern tube sealing. These operating conditions include temperature, pressure, and rotational speed. Your chosen sealing must be able to withstand the operating conditions without failing or deteriorating easily.
  • Vessel Type: You must also consider the vessel type you will be utilising. The more load your vessel carries, the stronger your sealing should be.
  • Shaft Diameter: The size of the propeller shaft likewise affects the type of seal required. For larger shafts, you may want to maximise mechanical seals. Alternatively, you can already utilise lip seals if your vessel takes advantage of smaller shafts.
  • Maintenance: The last thing you should consider when choosing a sealing is its maintenance requirements. Some seals require more frequent maintenance than others. Hence, you must factor this element into your decision-making process.

The proper selection and maintenance of the stern tube seal are critical for the safety and efficiency of the vessel. You must ensure to get one from a reputable supplier so it can work well with your stern tube and at the same time acquire quality after-sale services.

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