Abstract
It is well-known fact that the cathodic protection by use of zinc anodes or aluminium alloy anodes has been applied to the shafting and its propeller.
There are many reports on the errosion or corrosion of the shafting and its propeller. However, we have had very little information on the grounding device of the shafting.
According to our own investigation and information from the ship's operators and shipbuilders in Japan, the following guidances have been obtained:
(1) It is necessary to protect the shafting against corrosion, when the shafting has a Mn-Br propeller and an oil bath type stern tube bearing or the shafting has a sea water lubricated stern tube bearing and its propeller shaft is fitted with a copper alloy sleeve.
(2) There are many cases where the shafting having a Ni-Al-Br propeller and an oil bath type stern tube bearing is not provided with a grounding device.
(3) The suitable materials of a slip ring and a brush to be used for the grounding device are as follows:
Slip ring ..... Copper, Silver etc.
Brush ....... Metalic carbon, Metal brush
(4) The contact surface between the slip ring and the brush of the grounding device must always be kept clean.
The above Item (4) is one of the most important factors for the effectiveness of the grounding device. Thus, it is expected that the grounding device which is free from maintenance work will be developed in future.
