This Forum is supported by C&C 27 owners like you whose membership in the C&C 27 Association makes possible this Forum and the accompanying site. Thank you, members, for your continuing commitment.
You are not logged in.
Pages: 1
I just removed the propeller shaft from my recently purchased (long neglected) Mark 1 and it is not in stellar condition. There is a lot of pitting and scaling where it rides in the cutlass bearing, no doubt due at least in part to the fact that it was most recently launched without a zinc of any kind. At any rate, I plan to machine a new one and would appreciate any guidance as to which bronze alloy is the best. The one I am replacing is bronze and I would rather avoid stainless (I don't even know if stainless is an option). There are several grades to choose from on McMaster Carr's website <A href="http://www.mcmaster.com/">http://www.mcmaster.com/</A>. Does anyone have the original specs for such a piece? Has anyone replaced a prop shaft?
Chris Ferrier
Second Wind
Chriswheat Second Wind
Chesapeake Bay MD
Offline
My shaft was replaced two years ago, but with one made by a marine machine shop, so I can't give you data. They simply copied the keyway, taper and thread of the original, which was provided to them. As with every C&C I've ever seen, the shaft was stainless steel (a proprietary type called Aquamet).
The owner's manual provided as a pdf to Association members includes a drawing of the shaft, but it has no dimensions; the taper is given only as 'standard'.
Why do you not want to use stainless steel?
David Weatherston
Towser, Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Thanks for your interest David. I can get a 36 inch length of bronze sent to my doorstep and then machine it myself and have it ready to go in for around $120. Since the prop is bronze I thought it best to avoid any potential dissimilar metal reaction and stick with a bronze shaft (like the one I removed, only in good condition). If it turns out that stainless is obviously the best choice, I'll take that route. I find it interesting that I have the only C&C 27 with a bronze prop shaft. I would very much like to see the owners manual .pdf that you mentioned, how do I access that?
Chris Ferrier
Chriswheat Second Wind
Chesapeake Bay MD
Offline
I'm guessing, but I think that the issue is economics -- stainless steel used to be considered much more difficult to work than it now is and was consequently much more expensive in relation to other metals. If you have a very early boat, that could be the reason for bronze. On the other hand, it could be a replacement.
I've been told that metals are now of such consistent quality that dissimilarity between prop and shaft is simply not an issue if you maintain your zinc. As the harder of the two metals, stainless is less prone to erosion at the cutless bearing and shaft log.
The .pdf of the manual is a complete manual from a Mark IV (in engineering fashion, each page is dated, and some bear '76 dates). The manual is available to members of the C&C 27 Association. If you are not currently a member, join now and we'll treat it as a 2008 membership.
David Weatherston
Towser, Toronto
C&C 27 Mk IV
PS I discussed this with the club's senior mechanic, who said that working from specs on a boat as old as ours are is a bad idea because you seldom know what a previous owner has done. Also, whenever possible, the machinist should have access to the prop when doing a shaft, so he can mate the two precisely (his background includes raceboats and jet engines, so he's very particular about correct fit and good balance).
Last edited by (2007-12-07 08:05:57)
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Thanks for your input David! Economics certainly plays a role, but the best result is my priority. Besides which, the 19 different grades of stainless that I have to choose from online at McMaster-Carr are all le$$ than the bronze. I have a retired machinist friend who loves quirky little projects like this, so I'll ask him about making one out of stainless for me. Dissimilar metal corrosion was my worry, as I don't need a new prop, which is bronze. My hull number is 167, apparently the last MarkI (depending on which web site I believe), built in 1972. I joined the C&C 27 Association several months ago, but I still don't know how to access/download the .pdf file.
Chris
Chriswheat Second Wind
Chesapeake Bay MD
Offline
The galvanic scale determines the nobility of metals and semi-metals. When two metals are submerged in an electrolyte (like sea water) , while electrically connected, the less noble (base) will experience galvanic corrosion. The rate of corrosion is determined by the electrolyte and the difference in nobility. The difference can be measured as a difference in voltage potential. Galvanic reaction is the principle which batteries are based on.
Zinc is the least noble common metal and is desgned to be sacrificed to avoid corrosion on more expensive and more noble parts. Brass and stainless have very similar noble properies but will experience electrolosis in sea water. Fresh water is less of a concern since it it doesn't conduct current very well but we almost never sail in really fresh water.
The solution is to maintain your zincs and and leave the galvanic scale to the poindexters in the white lab coats.
[Can't quite see the point of giving us all this information, then telling us to ignore the whole business and let someone else worry about it – seems like the two messages are operating at cross-purposes. In any case, what comes through in this Forum and others like it is that, as much as people want to know what to do, they also want to know why they are doing it. Link added to more on galvanic issues and anodes plus a really alarming fate for a saildrive. - Admin]
Last edited by (2007-12-11 07:15:37)
Pages: 1