E35-3 Prop Shaft Strut - a look inside - and a zinc question

[Prairie Schooner]

I’m rebedding the strut on our ’86 E35. It doesn’t have a zinc on it. It seems to be in good shape with no corrosion. There was a zinc on the shaft. Should I add a zinc to the strut (in addition to replacing the one on the shaft)? What are the factors to consider?
Jeff

 

[Frank Langer]

This seems to be a somewhat controversial issue, based on feedback from various boat yards. I don't have a zinc anode on our 1984 strut.
I've been told to check it carefully on haulout for any sign of it turning pink, but so far there is none. One yard said there is no harm in adding a zinc, but another said that drilling a hole thru it to place a zinc plate on either side would weaken it. I'm not sure a quarter inch hole would be a problem, but he just shrugged his shoulders when I said so.
I do have two zincs on the prop shaft, which is close by, but the cutless bearing rubber insulates the strut from the shaft, so I'm not sure if the prop shaft zincs have any positive effect on the strut.
I'll be interested in what others advise, as I've seen lots of boats with, and lots without, a strut zinc.
Also, I note that you have bottom painted the strut with bottom paint. I have heard that the copper may react with the strut bronze, so I don't put bottom paint on mine.
Frank

 

[Christian Williams]

Here's my strut, before bottom job and new shaft. Inherited placement of both zincs, no special knowledge.

 

[Loren Beach]

Lonely little data point: our boat has one (aluminum) anode on the shaft, and none on the strut. We boat in fresh water most of the year, BTW.

 

[Prairie Schooner]

This seems to be a somewhat controversial issue, based on feedback from various boat yards. I don't have a zinc anode on our 1984 strut.
I've been told to check it carefully on haulout for any sign of it turning pink, but so far there is none. One yard said there is no harm in adding a zinc, but another said that drilling a hole thru it to place a zinc plate on either side would weaken it. I'm not sure a quarter inch hole would be a problem, but he just shrugged his shoulders when I said so.
I do have two zincs on the prop shaft, which is close by, but the cutless bearing rubber insulates the strut from the shaft, so I'm not sure if the prop shaft zincs have any positive effect on the strut.
I'll be interested in what others advise, as I've seen lots of boats with, and lots without, a strut zinc.
Also, I note that you have bottom painted the strut with bottom paint. I have heard that the copper may react with the strut bronze, so I don't put bottom paint on mine.
Frank

Thanks Frank. We just got the boat last fall so the paint on the strut is from PO. I didn't know there could be issues from bottom paint on the bronze. I'm going to strip the paint so I'll give a closer inspection. There were two zincs on the shaft as well. One was significantly more degraded so I figured they just didn't bother to take off the previous years'. In my limited research thus far, apparently it's possible to over-zinc. I'm with you, I can't see how a small hole is going to weaken the strut significantly. I, too, will be interested in other folks' experience.

 

[Prairie Schooner]

Here's my strut, before bottom job and new shaft. Inherited placement of both zincs, no special knowledge.

Thanks Christian. That will help if I decide to put one in.

 

[fstbttms]

Should I add a zinc to the strut (in addition to replacing the one on the shaft)?

If it ain't broke, don't fix it.

 

[peaman]

I have heard that the copper may react with the strut bronze, so I don't put bottom paint on mine.

Copper and bronzes are really close together on the galvanic series, I doubt that copper bottom paint would be worse than nothing on a bronze strut.

 

[Prairie Schooner]

Copper and bronzes are really close together on the galvanic series, I doubt that copper bottom paint would be worse than nothing on a bronze strut.

True. If memory serves, bronze alloys are in the range of 70% copper. The plot thickens.

 

[Pete the Cat]

I replaced the strut on my Tartan 37 25 years ago because it was a bit pink and I was reglassing the bottom (over zealous blister job). That strut was less than 15 years old but was definitely pink--the boat had been lived on in a marina for a couple years. I drilled a hole and put a 3" disc zinc on the new one ever since. I have had no problem in all those years and 20K+miles, but I have two ziincs on the shaft and one on the feathering propeller as well. But the disc on the strut is the one that is most eaten on the seasonal haulout--the others seem hardly touched--but it is only 7 months in the water. I don't think this proves much because it matters how much electricity and metalyou are fighting in the water so a short test of one boat in a couple places is not going to tell us much. But i have asked a lot of boatyard guys and they say you really cannot over zinc a fiberglass boat (it is possible to so so with a wooden boat with copper or some iron fasteners I am told--and that makes sense to me). FWIW. Not much, I guess. One data point.

 

[Prairie Schooner]

. . . I drilled a hole and put a 3" disc zinc on the new one ever since. I have had no problem in all those years and 20K+miles, but I have two ziincs on the shaft and one on the feathering propeller as well. But the disc on the strut is the one that is most eaten on the seasonal haulout--the others seem hardly touched-. . . I don't think this proves much because it matters how much electricity and metalyou are fighting in the water . . . But i have asked a lot of boatyard guys and they say you really cannot over zinc a fiberglass boat . . .

Thanks Ray. I really like having differing experiences and solutions to consider. Your input is very helpful. For the 35 years before we got it, our boat was in a slip in a small crowded marina a long mile up a tidal river, with a month or two every year at Martha's Vineyard. We'll be on a mooring in a harbor of Narragansett Bay, in salt water with robust tidal movement. It hadn't occurred to me to consider how this difference might affect our decision. Interesting that your strut zinc took most of the heat.

 

[dhill]

Hi @Prairie Schooner ,

Here are pictures of my strut on my Ericson 35-3. The first picture was taken before I replaced the sacrificial zinc on the shaft, the second afterwards. There is no sacrificial zinc on the strut itself.

Hope that helps!
Dave

 

[Prairie Schooner]

Here are pictures of my strut on my Ericson 35-3. The first picture was taken before I replaced the sacrificial zinc on the shaft, the second afterwards. There is no sacrificial zinc on the strut itself.

Hope that helps!
Dave

Thanks Dave. Diggin' the Maine ambience, too.
Jeff

 

[peaman]

But the disc on the strut is the one that is most eaten on the seasonal haulout--the others seem hardly touched--but it is only 7 months in the water.

I wonder if you paint your strut, or leave it bare? I would think that a bare strut would accelerate the consumption of zinc.

 

[fstbttms]

I wonder if you paint your strut, or leave it bare? I would think that a bare strut would accelerate the consumption of zinc.

Why?

 

[Loren Beach]

Here in fresh water, owners often seem to paint the strut, but only to retard growth of slime. The only unpainted part would be the anode, if there is one attached.

 

[Prairie Schooner]

I wonder if you paint your strut, or leave it bare? I would think that a bare strut would accelerate the consumption of zinc.

I think the question is whether the copper in the paint would conduct and cause corrosion. And I don't have an answer yet. I did a little more research and bronze is more like 85%+ copper. Tin is a typical alloy, but many others exist.

 

[Prairie Schooner]

And, I should have known this wasn't the first time our august community had addressed this issue:

Does the strut need a zinc

Hi, I am getting conflicting advice on adding a zinc to the strut. I have two zincs on the prop shaft but the rubber cutless bearing insulates the strut from the shaft. One mechanic says to add a zinc to the strut, another in the same boat yard says that drilling a hole in the strut to add the...

ericsonyachts.org

Prop Strut replacement

My partner used my nifty underwater camera to take a nasty shot of our prop strut. What do you think? Is my only replacement option the outfit in WA? Any guess on boat yard hours for this job? Thanks, Skip

ericsonyachts.org

Still gathering data as no clear answers yet.

 

[Pete the Cat]

Dave, where are you in Maine? I am sure I have been there.

In answer to whether or not I paint my strut, I have painted it and left it bare. The copper paint does discolor and appears to pit the bronze strut a bit when I cleaned it up, so I stopped doing it. The strut does not really get funky because the propeller and regular use keeps the barnacles from attaching.

 

[dhill]

Dave, where are you in Maine? I am sure I have been there.

In answer to whether or not I paint my strut, I have painted it and left it bare. The copper paint does discolor and appears to pit the bronze strut a bit when I cleaned it up, so I stopped doing it. The strut does not really get funky because the propeller and regular use keeps the barnacles from attaching.

Hi @Pete the Cat ,

My boating is based in Boothbay Harbor. We visited Castine on our cruise through Penobscot Bay last summer, docking at Eaton's Boatyard. Castine is beautiful and was one of the highlights of our trip!

We're planning to head up through Penobscot again this summer. Perhaps we'll see you out there on the water!

Dave