COLLARIN EJE 38mm. STD (ZN)

Function and technical context

The 38 mm zinc shaft collar is part of the tail shaft cathodic protection system on boats with shaft and propeller propulsion. It is a sacrificial anode specifically designed to be mounted on the propulsion shaft, protecting it from galvanic corrosion caused by contact of the metal with salt or brackish water. Since zinc is a metal with a lower electrochemical potential than the stainless steel or bronze of the shaft, the collar preferentially corrodes, acting as a sacrificial shield and preserving the integrity of the shaft. Without this protection, the propulsion shaft would be exposed to accelerated corrosion that compromises its structural resistance and can cause serious mechanical failures in navigation.

When to replace this part?

The most common symptoms that indicate the need to replace the zinc collar are a visible reduction in its mass of more than 50%, an irregularly corroded or fragmented surface, and the presence of incipient pits on the propulsion shaft itself in the contact area. As a general rule for boats sailing in saltwater, it is recommended to inspect the shaft anodes at least once a season—ideally at the annual beaching—and replace them when they have lost approximately half their volume. Replacing the collar preventively is significantly more economical than repairing or replacing a propeller shaft damaged by galvanic corrosion.