The objective of this study is to evaluate the corrosive wear resistance and to clarify the damage behavior of materials used for sliding parts in seawater. Sliding wear tests of six different metals including carbon steel, stainless steel and copper base alloys rubbed against A12O3 and a bearing steel were carried out in 3% NaCl solution using a reciprocating ball-on-disk test rig equipped with an electrochemical potentiostat. The obtained results indicate that the corrosive wear resistance should be evaluated by synthetically considering many factors: electrochemical potentials, material properties, and corrosion characteristics of the contacting materials, including corrosive products.

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Surface hardness characteristics and erosion resistance of Ni–Al bronze produced by three kinds of quenching have been determined to assess their potential as surface treatments for marine propellers. Flame, high frequency, and laser processing were employed as the surface hardening treatments. Microstructures and distributions of alloying elements were examined using microscopy, computer image analysis, and EP MA. Jominy and ultrasonic erosion tests were also conducted to evaluate the depth of surface hardening andresistance to propeller cavitation erosion. The experiments revealed that Ni–Al bronze has quenching characteristics closely related to those of steel and that bronze surface hardened by flame quenching is about 1·5 times harder than as cast. It was also found that lame quenching is the most suitable technique for surface treatment of propellers.

A multi-connected floating body system composed of many connected small-scale floating body units has a number of advantages with regard to construction and performance. To realize the multi-connected floating body system, a new type of mechanical connecting device was developed. It is composed of multi-degrees of freedom connecting mechanism and restricting mechanism to control a restricting condition between floating body units, and its effectiveness was confirmed by model basin test in waves. Next, friction and wear tests in the seawater environment led to the discovery of suitable materials for oscillatory sliding parts in multi-degrees of freedom connecting mechanism. Finally, a field test performed for two floating body units connected by use of the mechanical connecting device proved that the developed mechanical connecting device was of practical use.

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