Problems with sacrificial ICCP (Impressed Current Cathodic Protection) systems
Ships that are fitted with ICCP systems (whereby a metal that requires protection is bonded to an easily corroded ‘sacrificial’ metal) are vulnerable to propeller shaft bearing corrosion. This is because rotating shafts are electrically insulated from the hull by a combination of lubricating oil in the bearings and non-metallic bearings in the tail shaft.
Eliminating corrosion from ICCP
Shaft earthing assemblies provide optimum continuity of electrical charge. The use of a propeller shaft slipring earthed to the hull will eliminate corrosion. Typical assemblies consist of silver content/graphite brushes mounted in a balanced brush holder, running on a copper slipring with a solid silver inlay track.
The importance of correct shaft earthing
The cathodic protection of the ‘sacrificial’ metal or anode must be earthed correctly from the shaft line back to the hull. This protection requires earthing that is as far along the shaft line as possible so that the current is closest to its source (usually located at the stern seal and furthest aft bearing).
Damage resulting from no ICCP or badly set-up systems
- Cavitation damage affecting the propeller tips.
- Bearing damage caused by spark erosion (whereby electrical discharges eat into metal).
- Corrosion/erosion process creating deeper pits in the propeller.
Simplex-Turbulo is dedicated to keeping our customers’ engines and vessels working as efficiently and cost-effectively as possible. We can supply a range of new ship components, spares and service supported by our team of engineers which includes experts in sterntube seals and ICCP, propulsion systems, and, of course, diesel engines.