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Bertram31.com General Bulletin Board
Re: new rudders
Posted By: Capt Patrick McCrary In Response To: new rudders (Kevin Mehegan)
Date: Sunday, 13 March 2005, at 2:25 p.m.
Kevin,
I believe that you and others are being far too critical... In large sand casting of non-ferrous metals there will often be a "cold joint line" where the metal flowing into the mold meets from two different angles, has begun to cool by a few degrees and leaves a slightly visible line. Kind of like marbling in metamorphic rock. This rarely affects the strength of the casting and rarely fails at all.
As to the slight differences in the dimensions and shape there will be zero difference in how one rudder works compared to the other.
Color in new bronze castings is meaningless. Many things, including the pickling bath, atmospheric conditions, & even handling the metal with bare hands will affect the "new" color of copper based alloys. If you clean any oils from the surface, brush on some mild acid, let it stand wet for a few minutes, & rinse them off, they will likely be the same color. Un-painted they will eventually go to a dark brown color...
Any machining marks in the shaft area of the bearing are also inconsequential. Only the shaft area of the packing gland should be smooth so that the seal is good, but even that is not a major issue unless the shaft was scored and you were running dripless seals.
Remember that these are rudders not props... They don't get the same torque or rotational speed as do propulsion shafts and props. Were these dimensional discrepancies, machine marks, and casting line were found in your new propulsion shafts and wheels, you'd be 100% correct in rejecting them. Rudders are by far not as critical an issue.
I'm sure that if you are still worried about the casting line, that Danny will exchange the questionable rudder. You should give him a call and mention the casting line, asking about warrantee period & being on record as concerned, but if you mounted them and put them into service, I doubt that you would ever have a problem.
Best regards,
Patrick
BTW, I had, a few years ago, an overly picky customer make some similar remarks about my rudders. The finish on the blades wasn't smooth enough for him, (he though they should be polished), and he questioned the material content of the 316L stainless plate and Auqamet 22 shafts because he could "feel" some magnetism around the welded joint.
Well, polishing the blades would make it near impossible to have paint adhere, and would drive their cost up by twice. Anytime you weld, even with SS, the filled metal will be a slightly different alloy & some of the properties of the parent metal will be changed by the plasma arc.
We didn't argue with him, just shipped him a new set of rudders, (that by the way were identical), and he was happy. Sold the first set to another customer, who was equally happy.
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