Shaft Material
Dear Mike, It was once thought that Bronze was the best material. My guess is that because the vessel had a great amount of bronzes in the water yards and designers felt the need to keep dissimilar metals down thus they used bronze. I would also believe stainless availability and composition was very limited for the first 60 years of inboard propulsion. The mid 70s brought on a great deal of stainless compositions, which were more suitable to submersion and provided a high strength yield. Mid 80s shafting took a giant leap, in my opinion, with the introduction of Aquamet alloys, a trade name, by (?) Crucible Metals, NJ. In today’s market we see Aquamet, Aqualoy, Timet… providing material that is very comparable in composition to each other just marketed with different names. I myself suggest material equivalent to or exceeding the Aquamet 22 material (stainless). This web site is a comparative page of a shaft mfg. which you may find interesting www.aquamet.com/index/grade.html The 22 is higher in tinsel strength and has a greater submergence ability then 17, 18,19, 304, 306 or 316. Even though we think Stainless is a great material to use around a boat it still has faults if used in a static environment. The 22 grade has great submersion qualities. I would not use bronze in a modern application because the tinsel strength is not present to support modern needs of boats. Good Luck Kevin
