COLLARIN EJE BARRIL Ø110 (ZN) 4T

Function and technical context

The barrel shaft collar with a diameter of 110 mm in zinc is part of the transmission and sealing system of the tail shaft in internal-external propulsion or long-tail vessels. Its main function is to act as a galvanic sacrificial element integrated into the shaft line, protecting the steel of the drive shaft and the adjacent metal components against electrolytic corrosion produced by the potential difference in salt or mixed water. As it is a zinc (Zn) collar, it is preferably consumed before corrosion affects more expensive structural parts, such as the shaft itself, the bearings or the stern bushing. Its four-screw (4T) design guarantees a secure and balanced fixation around the axis, avoiding vibrations and ensuring constant galvanic contact during navigation.

When to replace this part?

The clearest sign that the zinc collar has fulfilled its function is the visible loss of mass: when the anode has consumed between 50% and 75% of its volume, it must be replaced before the retaining core is exposed or the shaft is unprotected. The inspection of all zinc anodes—including the shaft collars—should be carried out at least once per nautical season, or each time the boat is taken out of the water for antifouling or beaching. Replacing the collar preventively at the beginning of each season is the practice most recommended by naval mechanics to avoid corrosion of the propeller shaft, damage that can lead to costly grounding repairs or even complete replacement of the shaft.