The present research has been conducted on the corrosion of the marine engines of about forty sunken ships by means of the field investigation or the deta offered according to the following items:
(a) The relation between the corrosion and the period of the submergence of the materials.
(b) Is there any difference in corrosion due to the kind of the engines
(c) Is there any difference in corrosion between the ships of war-time standardized types and the ordinary ships?
(d)Possibility or Impossibility of the reuse of the refloated engines.
(e) The process of the repairs of the refloated engines.
(f) The condition of the operation of the reused engine.
The results obtained are as follows:
(a) The corrosion makes progress rapidly at the outset. but after a few years corrosion makes progress gradually.
(b) The extent of corrosion of the reciprocating engine is almost similar to that of the diesel engine. In the case of the steam turbine and the mechanical reduction gear, the extent of corrosion is comparatively slight. The boiler may be reused only by replacing the corroded smoke tubes with new ones.
(c) The extent of corrosion in the ships of war-time standardized type is generally very remarable compared with the ordinary ships.
(d) Corrosion generates on both the small-sized and larger-sized materials, but. as the extent of corrosion is more remarkable in the case of the smaller sized materials. the reuse of the smaller sized materials is almost impossible, while the reuse of the latter is possible
(e) The process of the repairs is as follows: After the corroded parts of the engine are boiled in the soda solution, the corroded face of the friction parts are filed off. The other sound parts of the engine may be used without any treatment.
(f) The operating condition of the reused engine is pretty good on the whole.
The present research has been continued by the Maritime Institute since the writer's initial field investigation conducted in April, 1946, at Mitsubishi Dock Yard in Nagasaki on the corrosion of the main engine of the Kongo-maru, the refloated steamer of National Railway Corporation, receiving grants in aid from the Ministry of Transportation. the former owner of the above mentioned Institute and from the Ministry of Education, the present owner of the Institute.
It would be a happy thing. if the present thesis could furnish even a little contribution to the refloating of the sunken ships in the future.