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NoBozo · 11-14-2011, 11:59 AM

I noticed a chunk missing out of one propeller blade in the picture in post #2.

It wouldn't suprise me if the boat owning that prop HIT the rock with the prop and broke the shaft..dropping the prop to the bottom. The shaft obviously being the weak link. I expect the shaft had a flaw during manufacture.

I still cannot determine what material the propeller or shaft might have been made of. It "Looks Like" cast iron but I haven't been able to find out just what those items were made of back then.

Large iron castings are made in a sand mold, and depending just HOW heavy they are,... are "shaken out" of the mold at just the "right time" during cooling. If the casting is exposed to cooling AIR Too Soon after the pour, the casting will be brittle. The iron will still be very hot..but solidified, when it comes out of the mold.

If the casting stays IN the mold too long, ...cooling too slowly, the result will be too soft.. it will bend very easily and be worthless.

Large castings were also Aged to relieve built in stresses before being brought to a machine shop to be machined. Typically, a casting would be put outside in the yard to be exposed to the weather for months..or longer,.. winter and summer. If this was not done, a machinist might machine the piece to a certain dimension today...and tomorrow morning..or next week that dimension might have changed ...because the casting was not stress relieved. Temperature changes out in the yard helped "relax" the casting.

I still don't know if a propeller shaft would have been Cast.

NB

NOTE: In the mid 70s I worked for Brown & Sharpe Manufacturing (Machine Tools) in RI as a young engineer. We still had a cast iron foundry in Providence..which is today referred to as The Foundry....Brown & Sharpe is now defunct.

11-14-2011, 11:59 AM	#30
NoBozo Senior Member Join Date: Jun 2008 Location: Portsmouth. RI Posts: 2,231 Thanks: 400 Thanked 460 Times in 308 Posts	I noticed a chunk missing out of one propeller blade in the picture in post #2. It wouldn't suprise me if the boat owning that prop HIT the rock with the prop and broke the shaft..dropping the prop to the bottom. The shaft obviously being the weak link. I expect the shaft had a flaw during manufacture. I still cannot determine what material the propeller or shaft might have been made of. It "Looks Like" cast iron but I haven't been able to find out just what those items were made of back then. Large iron castings are made in a sand mold, and depending just HOW heavy they are,... are "shaken out" of the mold at just the "right time" during cooling. If the casting is exposed to cooling AIR Too Soon after the pour, the casting will be brittle. The iron will still be very hot..but solidified, when it comes out of the mold. If the casting stays IN the mold too long, ...cooling too slowly, the result will be too soft.. it will bend very easily and be worthless. Large castings were also Aged to relieve built in stresses before being brought to a machine shop to be machined. Typically, a casting would be put outside in the yard to be exposed to the weather for months..or longer,.. winter and summer. If this was not done, a machinist might machine the piece to a certain dimension today...and tomorrow morning..or next week that dimension might have changed ...because the casting was not stress relieved. Temperature changes out in the yard helped "relax" the casting. I still don't know if a propeller shaft would have been Cast. NB NOTE: In the mid 70s I worked for Brown & Sharpe Manufacturing (Machine Tools) in RI as a young engineer. We still had a cast iron foundry in Providence..which is today referred to as The Foundry....Brown & Sharpe is now defunct. Last edited by NoBozo; 11-14-2011 at 06:15 PM.