Stern tube seals |Type approved| RM Propulsion BV (original) (raw)

What Do Stern Seals Do?

First and foremost, stern seals serve a dual purpose. Firstly, they block seawater from entering the stern tube, where it could corrode or damage internal bearings. Secondly, they prevent lubricating oil from escaping into surrounding waters, a major environmental concern.

If either failure occurs, the consequences are immediate and costly: operational downtime, mechanical damage, or even legal penalties. Thus, a robust and certified sealing solution is essential.

In fact, the stern tube operates entirely below the waterline. That is to say, the seals are constantly exposed to dynamic pressure, motion, and external conditions. Accordingly, their design and material quality must meet the highest standards in marine engineering.

What’s the Difference Between AFT & FWD Stern Seals?

There are two primary types of stern tube seals: the aft stern seal and the forward stern seal. Both are essential, and together, they form the vessel’s first line of defense against leakage.

Forward Stern Seal

Located at the inboard (engine-room) end of the stern tube, the forward stern seal keeps lubricating oil from leaking into the vessel. Not only does this protect equipment, but it also reduces the risk of fire or mechanical issues.

If this seal fails, then oil may contaminate the engine room, which puts operational safety at serious risk.

AFT Stern Seal

The aft seal is mounted at the outboard end of the stern tube, beneath the waterline. It must simultaneously block seawater from entering the system and stop oil from leaking into the sea.

In other words, it protects both the vessel’s propulsion system and the marine environment. Moreover, in many jurisdictions, it helps ensure compliance with strict environmental legislation.

Why Do They Matter?

Together, these seals form a unified barrier system. If either one fails, the integrity of the entire shaft line is compromised.

After all, a leaking seal can lead to serious operational and environmental costs. Consequently, selecting the right aft and forward stern seals is not just a technical choice, but also a business-critical one.

All things considered, investing in durable, type-approved stern seals is essential for operational reliability, environmental compliance, and overall cost control.

If you’re facing oil leakage or water ingress, please don’t hesitate to contact us. We’ll provide technical advice free of charge, so you can act quickly, avoid unnecessary downtime, and restore system integrity with confidence.