COLLAR DE EJE PERFIL NACA Ø 28,6 mm (ZN)

Function and technical context

The shaft collar with Ø 28.6 mm NACA profile is a cathodic protection element that is installed directly on the boat's drive shaft, in the submerged area between the hull and the propeller. Its NACA profile aerodynamic geometry reduces hydrodynamic resistance to a minimum, helping to maintain propulsive efficiency while protecting the stainless steel or bronze shaft against galvanic corrosion in salt or brackish water. Made of zinc (ZN), it acts as a sacrificial anode: being a less noble metal, it corrodes itself before the shaft does, avoiding pitting, erosion and structural weakening of the propulsion system. Without this protection, the shaft can suffer irreversible damage that compromises the tightness of the stuffing box and the integrity of the entire transmission line.

When to replace this part?

Zinc anodes should be inspected at least once a season and replaced when they have lost approximately 50% of their mass; If it is allowed to be completely consumed, the shaft is left unprotected and exposed to electrolytic corrosion. Clear signs that the axle collar needs to be replaced are: a very uneven and porous surface, a visible reduction in thickness, or a loose, split piece on the axle. It is recommended to replace this component preventively at each annual grounding, since the cost of a new anode is minimal compared to machining or changing a corroded shaft.

Compatibility table