|
|
|
|
|||||
|
||||||
Subject: Re: Re: TWL: Unzincs
From: Jim McCorison (jim@XXX.XXX)
Date: Thu May 02 2002 - 00:18:36 EDT
At 07:37 PM 5/1/2002 -0700, you wrote:
>So let me get this straight:
>
>There's currently no prop zinc or shaft zinc on Maņana?
Correct. However, keep in mind that Maņana is single shaft, full
displacement, full keel, so there isn't much shaft exposed outside the aft
cutlass bearing. Although there is about 8' of shaft inside the shaft log.
For a photo of a Maņana's prop area, see:
http://www.mccorison.com/~jimmcc/manana/pre-purchase/p8280008.jpg
>Are the prop shafts directly tied to the bonding system (shaft brushes,
>etc.)?
There is a shaft brush tied into the bonding system (or at least there will
be when the bonding system is rewired. (Currently out of the water, and
when we go back in, we're in fresh water.)
>Is your prop still alive? Is the transom zinc 'electrically proximate'
>enough to actually protect the prop from the shaft?
Yup, it was in fine shape except for a slight bit of cavitation pitting.
>This also takes us to another question, and that is, does the prop shaft
>interact with the shaft log?
>
>Your experience ('white fuzziness' at the stuffing box end) would seem to
>indicate that it does, although I've heard the argument that says the
>shaft is isolated from the shaft log by the packing material. Given that
>water flows through this area in a typical arrangement (i.e., not
>dripless), that would provide the 'upper' coupling for the galvanic cell
>(or is that still considered just part of the electrolyte? I'm so confused...).
The end of the shaft log was the worst spot. The wood around all the thru
bolts on the shaft log also showed mild signs of delignifiation as well.
This lends support for the argument that the the water is the conductor.
>And don't forget to post your results when Maņana is back together again.
Will do.
Jim McCorison
M/V Maņana - 38' DeFever, Hull #2
Seattle, WA
|
