Bow and stern thruster tunnel protection is a specialised area where Cathelco have developed a system which is uniquely effective in providing corrosion protection.
The systems can be installed on large ocean going vessels as well as some types of semi-submersible rigs.
Problems of corrosion arise because of the dissimilarity of the materials used in the hull and thruster tunnel construction and remain unchecked because they are outside the scope of conventional ICCP systems. Sacrificial anode systems have been used to combat the problem, but there is the risk that the anodes can become detached and cause damage to the impeller. Sacrificial anodes also create additional weight, have to be checked at regular intervals and replaced at each drydocking. They also affect the water flow and the efficiency of the thruster tunnel.
Sacrificial anodes designs have also proven in effective in some instances due to poor design where anodes are located too far from the impeller. The distance current can flow along the tunnel is limited by the diameter of the tunnel.
The Cathelco system provides carefully monitored, precisely delivered corrosion protection for a design life of up to 15 years. It consists of an arrangement of flush mounted anodes and reference cells connected to a control panel which automatically adjusts the anode output.
The system operates continuously when the vessel is at sea, but when the impeller is activated during docking, the equipment is automatically shut down using a fail safe switching system which is installed by the shipyard. This prevents any stray current damage occurring to the bearings and seals.