It was first introduced in 1905 by the International Nickel Company and takes its name from the firm’s president Ambrose Monel.


It


contains approximately two thirds of its weight in nickel and a typical analysis is nickel 68.41%, copper 29.14%, iron 1.19%, manganese 1.02%, silicon 0.06%, carbon 0.12% sulphur 0.008%. It has a specific gravity of 8.8 and a coefficient of expansion of 0.000015. It is sufficiently magnetic to hold a hand magnet.


It is a tough alloy


whose mechanical properties can be improved by cold working but it cannot be heat treated.


It has


a specific heat of 0.127. Monel is very difficult to machine as it work hardens very quickly.


It needs


to be turned and worked at slow speeds and low feed rates.


It is


resistant to corrosion and acids and some alloys can withstand a fire in pure oxygen. It is commonly used in applications with highly corrosive conditions.


It is claimed to be between 10 and 15% stronger than


mild steel.


It has high oxidisation


and corrosion resisting properties and is often used in small craft for propeller shafts and keel bolts.


The damage to this shaft above was harder to see than the previous vessel as the wear was within the stern gear. Again, this shaft was of mild steel construction and, although there was play found between the shaft and Cutless bearing, the extent of wear to the shaft was not seen until the shaft was removed. Clearly, if that shaft had been left, it would have sheared off and, life being what it is, the boat would have lost her screw just at the moment she most needed it and a possible court case against a surveyor for not having stated the shafts condition.


I know that passenger boats under the MCA have to have their propeller shafts withdrawn for survey at no more than two year intervals.


Too many times the The Report • June 2018 • Issue 84 | 49


marine industry is being lead by the cost and inconvenience to the client for withdrawing propeller shafts and rudder stocks for inspection instead of being lead by safety. I was able to view the findings and am of the opinion that a similar recommendation should be made regarding the propeller shaft and rudder stocks and tubes on all vessels.


Speaking with


other professional colleagues, I was advised that damaged shafts such as those seen in the photographs are not uncommon.


I now include the following in my reports:


RECOMMENDATION 1: We would recommend that the tail shaft be drawn and given a close up examination now and at not more than two year intervals thereafter. It should then be dealt with as found necessary.


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