Is galvanic corrosion of bronze shafts an issue in fresh water? (Gore GFO etc.)

Sailing Amok · April 26, 2021, 06:14:40 AM

Just about to order some new stuffing for the stuffing box, and I'm not sure if I should go with PTFE impregnated flax, or graphite impregnated material. Judging by a piece of scrap I found left behind from the PO, he used Gore (it's also 1/4" which seems odd). I guess I won't know if the bronze has already been damaged until I loosen the packing nut, but I'd like to order new stuff now, given how slow shipping is these days. Is galvanic corrosion even an issue in fresh water with graphite stuffing? The PO was a real perfectionist, so I can't imagine that he would have overlooked the possible issues.

Jim Hardesty · April 26, 2021, 06:47:21 AM

A & K,
I don't know about galvanic corrosion. This is what I used about 10 seasons ago. Mostly a spring adjustment gives me minimal drips and cool running for the season. I'm very pleased with it. FWIW I could only get 2 rings into my shaft log.
https://www.defender.com/product.jsp?path=-1&id=6717766
Jim

PaulJacobs · April 26, 2021, 07:50:53 AM

In order for galvanic corrosion to occur one must have two dissimilar metals both simultaneously in contact with an electrical conductor. Salt water is an electrical conductor, hence concern about protecting a SS shaft near a bronze propeller, or other such combinations.

To very good approximation "pure fresh water" is not an electrical conductor. That said, truly pure fresh water is rare. Most "actual" fresh water contains some level of impurities. Thus "in real life" even fresh water can support very small levels of galvanic corrosion. Hence the use of magnesium as a sacrificial metal for fresh water boats - similar to the use of zinc as sacrificial metal to minimize the effects of galvanic corrosion in salt water.

Paul Jacobs
Pleiades, No. 1068
1990 TR/FK
Wickford, RI

Jon W · April 26, 2021, 08:36:18 AM

Take a look at Mainesails article "Re-Packing A Traditional Stuffing Box" on his website marinehowto.com. Near the end of the article he cautions about using graphite impregnated stuffing material with a bronze shaft.

Sailing Amok · April 26, 2021, 11:09:11 AM

Quote from: Jon W on April 26, 2021, 08:36:18 AM
Take a look at Mainesails article "Re-Packing A Traditional Stuffing Box" on his website marinehowto.com. Near the end of the article he cautions about using graphite impregnated stuffing material with a bronze shaft.

Exactly, that's why I was wondering if it is an issue in the Great Lakes as well, or if it is only a concern in salt water.

frankya · April 26, 2021, 12:30:35 PM

For what it is worth, the Dura-Max literature on the Ultra-X packing states it is galvanically OK due to the construction.
See text at bottom of attachment. I found it to be easy to cut cleanly, and it packed well also. Probably because it holds its shape and doesn't fray at the ends.
Only a wee bit more expensive.

Sailing Amok · April 26, 2021, 01:12:11 PM

Quote from: frankya on April 26, 2021, 12:30:35 PM
For what it is worth, the Dura-Max literature on the Ultra-X packing states it is galvanically OK due to the construction.
See text at bottom of attachment. I found it to be easy to cut cleanly, and it packed well also. Probably because it holds its shape and doesn't fray at the ends.
Only a wee bit more expensive.

Interesting! Duramax seems to be the favourite on this forum, so that is good to know. It's the word of the manufacturer, so I guess we need to take it with a grain of salt, but it seems unlikely they wouldn't make a claim that would be so easy to refute if there were a bunch of corroded bronze shafts out there amongst Duramax users.

Ron Hill · April 27, 2021, 02:08:44 PM

Sailing : Most of us that have older boats have change out out drive shaft to Stainless Steel!!

A thought

Sailing Amok · April 28, 2021, 06:53:47 PM

Quote from: Ron Hill on April 27, 2021, 02:08:44 PM
Sailing : Most of us that have older boats have change out out drive shaft to Stainless Steel!!

A thought

I guess when I go to do the stuffing box, I'll see if the graphite packing that the PO used has caused significant corrosion. Hopefully we don't suddenly find ourselves forced to change to stainless!

Geoffreykwright · April 29, 2021, 05:57:06 AM

Graphite and Bronze are far apart on the Galvanic Scale (also depends on what type of bronze you are using). While the risk of galvanic corrosion is reduced in fresh water, its not eliminated - stray currents in marinas/yacht clubs will exasperate the problem. Cathodic protection (i.e. a zinc or magnesium anode) on your shaft may help, but with the graphite and bronze in direct contact, you may have a problem. I'd steer clear of the graphite stuffing....hope this helps.

Jim Hardesty · April 29, 2021, 09:34:05 AM

Quotedon't know about galvanic corrosion. This is what I used about 10 seasons ago. Mostly a spring adjustment gives me minimal drips and cool running for the season. I'm very pleased with it.

Guess I need to rethink when it comes time to repack. Though doubt that there will be any damage, will plan for additional time if I've damaged the shaft.
Jim

Patches · April 29, 2021, 11:58:50 AM

I gave this whole issue a lot of time and thought when I replaced my original bronze shaft with stainless in December. After buying a new stuffing box and flax, I changed my mind completely in the middle of the project and went with a PSS dripless. Couldn't be happier, and super easy to install (although I was on the hard). No drips, no leaks, no adjustments.

Anyone need some "like new" stuffing box wrenches and new flax? $30 + shipping.

Patches