Copper-alloy has long been well used for the sleeve of propeller shaft, because of its superior corrosion-resistance. But in recent years international shortage of copper resource has brought unstable conditions of its supply and its price. Under these circumstance the following are now in consideration, that is to use another alloy, supply of which is stable or to employ another construction which needs less amount of copper-alloy. And this sleeve, when some damages occur, is very difficult to be repaired by welding because it is made of Sn-bronze, and it takes much time to replace the damaged sleeve. This situation have brought a new idea, that is to use the stainless steel overlay shaft, instead of a combination of the steel shaft and the sleeve made of Sn-bronze. This new stainless steel overlay type has several advantages compared with the sleeve type, as shown below. (a) It is easily repaired by welding when the sleeve is damaged (b) This method can reduce a machining process in manufacturing. Paying attention to this point, we has carried out a basic study including selection of materials for welding and investigation into its fatigue strength, and has performed an experiment by equipping a trial produced propeller shaft to Yoshino-Maru. As a result the followings have been made clear. (1) The overlay shaft with austenite stainless steel 316L showed twice as good endurance as old copper alloy sleeve (BC-2 or BC-3) (2) We can improve work efficiency and get a product with sufficient quality by adopting band arc submerged arc welding method. (3) The fatigue limit of stainless overlay shaft in seawater was improved to be 25 kg/mm^2 by practicing surface rolling. (4) Through the two years experiments on actual ship we could get good results finding no problem in view of corrosion and wear, and obtained data applicable to actual ships.
