THE SOCIETY OF NAVAL ARCHITECTS AND MARINE ENGINEERS

A 56 years old ship, K-mmru,was investigated for items being concerned with her strength. Items investigated were the thickness of shell and deck plates, local and overall deformation of the hull, the wear of rivet heads and mechanical and other proper-ties of steel plates of decks and hull. The characteristics of old plates investigated were chemical compositions, static and dynamic tensile strength, fracture toughness and fatigue strength. Thick-ness distribution of old plates with worn out holes due to corrosion were also measured, Based on the results of investigations, the seaworthiness of K-maw was discussed, Results obtained were as follows; 1. The plate thickness reduction rate by corrosion of deck and shell plates at midship was about 5 % in spite of her old age, though there existed some deep corroded parts in them. 2. The 5 % of the whole hull deterioration rate corresponded to about 0.6 % corrosion hole area ratio of the whole hulL 3. A small amount of deformation of the ship hull as a w~hole was responsible for the long term service and repeated repairs by weld-ing. 4. The original old steel plates of 56 years showed good tensile strength, but poor weldabifity and fracture toughness. 5. Very rough surfaces of steel plates due to corrosion largely di-minished their fatigue lives, because of decrease in thickness and stress concentration by surface roughness. 6. The seaworthiness level of the ship was very low, This level may reveal itself at the time of emergency BACKGROUND The safe navigation characteristics of a steel sh-uchu-e sailing ship K-ma ru, 56 year-old at the time, was investigated. The principal dimensions of the ship were as following. LoAx BxDxd.97.Mi mx12.95mx7.85m x6.15m. Gross tonnage. W.&l to