COLLAR NACA 22 (ZN)

Function and technical context

The NACA 22 zinc collar is a sacrificial anode designed to protect the vessel's tailshaft from galvanic corrosion in marine environments. It acts as a cathodic protection element, sacrificing itself electrochemically to preserve nobler metals such as bronze or stainless steel of the drive shaft. Its specific collar geometry allows precise mounting on the shaft, ensuring continuous electrical contact and uniform distribution of protection. If this component is not replaced in time, the drive shaft is exposed to marine corrosion, which can lead to serious structural damage, bearing play, and costly propulsion system failures.

When to replace this part?

The clearest symptom that the collar anode is exhausted is the visible loss of mass: when it has lost more than 50% of its volume it must be replaced immediately, as it no longer offers effective protection. It is recommended to inspect the shaft anode at each beaching or at least once per nautical season, replacing it preventively even if it is not completely consumed if the navigation season is long or the waters are especially aggressive. Replacing the NACA 22 zinc collar at each seasonal tune-up is the most economical measure to avoid replacing the shaft or bearings due to galvanic corrosion.