15th Aug 2024
Fitting shaft anodes is relatively straight forward, but it is best to ensure the anode is fitted correctly to give maximum protection.
Tips For Fitting Shaft Anodes
- Make sure the surface of the shaft is clean and free from debris
- Do not paint the anode
- Measure the shaft diameter with Vernier Caliper or accurate measuring device; there is a difference between a metric 25mm and 1 inch at 25.4mm, one will fit, the other will not!
- Check space between propeller and cutlass bearing, you need to allow 10mm space between anode and the bearing
- Check how much shaft surface requires protection and where necessary install more than 1 anode
- Make sure the alloy type selected is the same across all fitted anodes and is correct for the water type
- Use threadlocker to help keep bolts in place
It should be made clear that this format of cathodic protection, although simple to fit, affords a far lower degree of protection to the systems listed elsewhere on this website. In order to achieve maximum protection, the surface area of an anode must relate to the size of the surface it is aiming to protect. Owing to the design of shafts, this ratio is generally very difficult to achieve.
As with all equipment, it should be regularly checked to ensure your vessel is being protected and not suffering signs of over or under protection.
The images above show how NOT to fit a shaft anode. The diameter of the anode is insufficient for this particular prop. The anode is not fully enclosing the shaft and will provide little protection to the equipment. Furthermore, the anode is in danger of falling off due to the lack of screw into the anode.
Heavy Duty Type Anodes:
Available in zinc usually and aluminium. Sizes from 3/4″ upwards. These have a special insert so that should your anode corrode internally, you will be confident the anode will remain in place due to the addition of the internal plate keeping the bolts, and therefore, your anode in place.
Standard Type:
Available in zinc. Sizes from 3/4″ upwards. These are ball shape and are lighter than the USA style, but they do have a different design feature with the internal 'wall' only having 3 places in which it will make contact with the shaft. This means pressure is spread more evenly across the anode.
USA Type:
These are not hollowed out but have a uniform internal centre. This type are typically preferred in the US where they often install anodes while in the water and also require additional weight. They are popular elsewhere too due to the variety of metals and diameter.
Shaft Collar Type:
Designed for installation where only a minimum amount of shaft is visible and the clearance between the propeller and bracket is limited. These are available in all 3 metal types. In sizes to fit, shaft diameter from 3/4″. Tecnoseal versions have been designed with a hydrodynamic shape for less drag.
Thin Shaft Collar:
This type are a thin version of the shaft collar anode and are for very limited clearance areas. They are available in zinc and aluminium, and magnesium on special order, in sizes from 3/4″. Due to their size they will give minimal protection but helpful when you need all the anodes you can.
