Anti-Fouling Metallic Materials for Underwater Ship Hulls (2nd Report)

Abstract

11 kinds of anti-fouling metallic materials including 9 kinds of newly developed Cu-10%Mn-Al-Fe alloys were investigated at first by the immersion test in sea water for 7.5 months in order to make clear the relationship of corrosion rates and anti-fouling properties with the chemical composition of alloys and the immersion period.
After that, 8 kinds of anti-fouling metallic materials including 6 kinds of newly developed Cu-10% Mn-Al-Fe-Ni alloys were investigated by the actual ship test conducted in the small ferryboat running in the Nagasaki Port for 6.5 months in order to know the corrosion rates and anti-fouling properties of these materials exposed to the actual underwater ship hull.
The following results were mainly obtained by these tests.
(1) The corrosion rates of copper, 90/10 Cu-Ni alloy and Cu-10%Mn-Al alloys decreased with the exposure period, and it became difficult to keep the corrosion rates of these materials more than the critical corrosion rate necessary to maintain the anti-fouling ability for the under water ship hulls.
(2) The impingement attack was found at the edges of copper sheets adhered to the underwater ship hull of small ferryboat.
(3) The attachment of marine bio-fouling to underwater ship hull was much easier in the small ferryboat than in the large car bulk carrier.
It is considered that the anti-fouling properties and the resistance against the impingement attack of copper and the copper alloys were not enough for those of anti-fouling metallic materials covered on the underwater ship hulls of small boats. Moreover, it is considered in the case of large ships that it may be adequate to conduct the detailed investigations about the behaviors of anti-fouling metallic materials exposed to the various kinds of environments after the underwater ship hulls are covered.