1 AXLE COLLAR

Function and technical context

The shaft collar is a cathodic protection element designed to be installed directly on the boat's propulsion shaft, acting as a sacrificial anode in the shaft area. Its mission is to protect the metal shaft—and nearby components such as the propeller and bearings—against galvanic corrosion caused by prolonged immersion in salt or brackish water. Being a metal with a more negative electrochemical potential than stainless steel or bronze, the collar corrodes preferentially, preserving the structural integrity of the shaft and significantly prolonging its useful life. Without adequate cathodic protection on the shaft, galvanic corrosion can degrade the metal of the shaft to the point of compromising its mechanical strength, causing clearances in the stern tube bearings, and generating abnormal vibrations during navigation.

When to replace this part?

The collar-shaped shaft anodes must be inspected at least once a season and replaced when they show wear greater than 50% of their mass, at which time their cathodic protection capacity is compromised. Symptoms of a worn collar include visible pitting on the surface of the shaft, the appearance of reddish rust or corrosion spots in the horn area, and unusual vibrations that may indicate early shaft or bearing damage. Preventive replacement at the beginning of each nautical season, especially in mooring areas with high electrical conductivity of water, is the practice recommended by naval mechanics workshops to avoid higher cost repairs in dry work.

Compatibility