COPPER SHAFT ?????

[Scott Sirgo]

Is there a good reason that one could not use solid copper stock for a prop shaft. Cost is not a concern since one power cord or a poor electrical connection at dock can reek havoc on bronze. The Rockwell Hardness B Scale is copper: (hard) 50B and Naval brass: 82. Yield strength KSI is 45 & 53 respectively. OF COURSE STAINLESS STEEL IS OUT OF THE QUESTION.
Scott Sirgo
S/V Annabel Lee

[Boyd]

I dont know about copper but whats wrong with SS?

Mine is SS and been on the boat since conception (1985) and is in perfect condition. Just hauled it last year and pulled the shaft.

My business partner had a bronze shaft on his boat and the thing sheared off while passing under a drawbridge. He replaced it with Monel.

Boyd

Is there a good reason that one could not use solid copper stock for a prop shaft. Cost is not a concern since one power cord or a poor electrical connection at dock can reek havoc on bronze. The Rockwell Hardness B Scale is copper: (hard) 50B and Naval brass: 82. Yield strength KSI is 45 & 53 respectively. OF COURSE STAINLESS STEEL IS OUT OF THE QUESTION.
Scott Sirgo
S/V Annabel Lee

Tern30@aol.com

[Ken Coit]

Without digging into the properties of materials resources that must be around here somewhere, it seems to me that a copper shaft would have to be a lot larger to provide the same power transmission capabilities as a bronze shaft. Further, it would be softer and wear faster than the bushings around it unless they were copper too.

If copper were an option in power transmission, why wouldn't we all have copper propellors and save the Rutland Stove Polish for the stoves?

For those who want to dig out some info on the web, try the materials database at the link below.

Just some thoughts on a Tuesday afternoon. It is Tuesday, right?

Ken

Is there a good reason that one could not use solid copper stock for a prop shaft. Cost is not a concern since one power cord or a poor electrical connection at dock can reek havoc on bronze. The Rockwell Hardness B Scale is copper: (hard) 50B and Naval brass: 82. Yield strength KSI is 45 & 53 respectively. OF COURSE STAINLESS STEEL IS OUT OF THE QUESTION.
Scott Sirgo
S/V Annabel Lee

PPPparfait@nc.rr.com

[matt cawthorne]

Scott,
I would like to take this opportunity to discourage you from using copper propeller shaft. There are many factors that go into a well balanced design. Static strength is one factor, but there is so much more. Fatigue strength is critical as well. The fact that the hardness of copper is measured on the Rockwell B scale is not a good sign in and of itself. One of the common copper based materials used for propeller shafts is Tobin 'bronze'. Tobin bronze is really a brass in that it is loaded with something like 40% zinc. The reason is that it has good shear strength for a copper alloy. The critical stress on a prop shaft is likely to be shear.

Don't be so down on stainless steel. The stainless prop shaft on my boat is BTB 18 years old. The problem with pitting has to do with oxygen starvation. The act of polishing the shaft increases the oxygen content in the surface and reduces the chance of pitting. The area in the cutlass bearing gets much polishing so that when the shaft sits idle for a couple of months the area in contact with the rubber does not pit. In addition, protecting the part with a zinc reduces the chances of a pit getting started. The problem with stainless usually occurs when oxygen is deprived from an area where the oxydized chromium layer on the surface is somehow broken. The problem with no oxygen is that the non-oxydized substrait is lower on the galvanic scale than the oxygen rich surface layer. The area inside the pit disolves to protect the oxygen rich coating. Very agressive. If there is oxygen the pit just oxydizes and the process stops. Stainless has relatively good fatigue and static strength. If my prop shaft breaks I will replace with stainless. That being said, true zinc free bronze is the best choice for corrosion resistance on parts for a boat.

Matt




mcawthor@bellatlantic.net

[M. R. Bober (aka Shaft)]

I can think of one good reason to avoid copper shafting. Copper makes nice hammered & spun disks, but it is a bit on the puny side for shafting. I suspect a "barber poling" in the face of the torque that a prop shaft is presented with normally. Oh one more thing, I wouldn't foul that prop/shaft combo on any crab or lobster pot. The results could be immediate & serious.

My new stainless shaft replaced a ruined bronze ancestor. I think that had stainless been discovered first, there wouldn't have been a concerted search to discover bronze. Apologies to Bristol Bronze, in advance.
Every best wish,
Mitchell Bober
RESPITE
CD330

[Bristol Bronze]

Is there a good reason that one could not use solid copper stock for a prop shaft. Cost is not a concern since one power cord or a poor electrical connection at dock can reek havoc on bronze. The Rockwell Hardness B Scale is copper: (hard) 50B and Naval brass: 82. Yield strength KSI is 45 & 53 respectively. OF COURSE STAINLESS STEEL IS OUT OF THE QUESTION.
Scott Sirgo
S/V Annabel Lee

Dear Scott,

Copper is too soft and maleable a metal to be used as a prop shaft. Even hard drawn copper rod would tend to wear faster than Bronze. The tin and other metals and elements that are added to copper to make bronze are there for a reason. The usual reasons are to stiffen it up, make it more abrasion and wear resistant and to privide greater strength under load.

I agree with you about not using stainless steel. Anyone who uses stainless under water needs to have their head examined. I wish you could see the collection of fairly young stainless steel fittings that I have been sent by customers for replacement by Bronze. I have some pieces that are less than ten years old that look like Swiss lace.

When stainless steel has been passivated (quite rare these days) it is quite high on the galvanic table and acts as a cathode and will make your other fittings corrode. When not passivated it is quite low on the galvanic scale and will act as a sacrificial annode and give up electrons. Add to that the tendency to crevice corrosion and it is just not a good metal under water. The higher the temperature of the water the faster it will corrode. Add in the fact that it gives no teltale signs of failure the way bronze does and it is just not the best choice.

The boat on the home page of my web site (bristolbronze.com) is my own personal boat. She was built at Herreshoff Mfg. Co. in September of 1920. My rudder post, keel straps, chain plates, and keel bolts are all of Tobin Bronze. They are all original and are still fine. I would like to see a stainless steel fittings of similar age with the same service life that looked anywhere near as good.

Roger W.
Bristol Bronze
401-625-5224



rogerw@meganet.net

[Bob Pence]

Is there a good reason that one could not use solid copper stock for a prop shaft. Cost is not a concern since one power cord or a poor electrical connection at dock can reek havoc on bronze. The Rockwell Hardness B Scale is copper: (hard) 50B and Naval brass: 82. Yield strength KSI is 45 & 53 respectively. OF COURSE STAINLESS STEEL IS OUT OF THE QUESTION.
Scott Sirgo
S/V Annabel Lee

I either worked or hung out at the River Forest Marina and Belhaven Shipyard from 1992 until 1999 and cannot remember a bent or broken brnze shaft ever being replaced with anything but stainless steel, be it a small sailboat or a very large motoryacht. As Capt. of Towboat U.S. I towed in a lot of warped, bent and broken shaft boats.



sixpence@dmv.com