Prop Shaft Anode Replacement

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Pgutierrez
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Prop Shaft Anode Replacement

Good morning-I sail my 2000 Catalina 36 on the Upper Mississippi, only fresh water sailing.  I need to replace sacrificial magnesium anode on prop shaft (zinc anodes are used for saltwater, not fresh water).  Boat has M35 engine.
- what size is the prop shaft diameter?
- where did you purchase anode?
- should I consider both a magnesium and a zinc on the shaft?  Some of the forums state that the zinc is a good idea if there is a stray voltage in the marina waters. Quite frankly I've never heard anybody mention that in our marina.
- anything else I should know?
Thank you.

peter g

2000 C36, MK2, Hull. #1897
wonderful, wonderful, wonderful ! ! !.   5 th Catalina

 

 

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Siler Starum
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I replaced recently also both the anode on the hull and on the prop-shaft.
We are also sailing most the time on fresh water too and I installled Aluminium sacrificial anodes
The prop-shaft is 25mm and the hull-anode has a slot for easy mounting.
In general it's all about the galvanic potential of the different materials and adding two different materials on your prop-shaft is making it all even worser.
And what is the impact for stray currents of the fact that the minus / earthing of the 12VDC system is connected to the hull-anode?

 

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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William Matley
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Peter,
The anode is 1" here in the US.
Find it on Amazon.

https://www.amazon.com/Martyr-Anodes-CMP-02-Streamlined-Shaft-x/dp/B001T...

Bill Matley
Duncan Bay Boat Club
Cheboygan, Michigan
Lakes Huron, Michigan,
Canadian North Channel
"Spirit of Aloha" Hull #1252

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Pgutierrez
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Thank you- a few follow up questions:
-where is the hull anode?
-does diesel have an anode?  I spent considerable amount of time on the Westerbekke parts diagram for M35B engine and couldn’t find one listed. I thought it might be on the heat exchanger. I will probably contact Westerbekke.

 

peter g

2000 C36, MK2, Hull. #1897
wonderful, wonderful, wonderful ! ! !.   5 th Catalina

 

 

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Chachere
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Our boat doesn't have a "hull anode" as such. 
I understand that some C36s do have an anode bolted to the side of the skeg that holds the shaft (and cutlass bearing) -- here's a link to picture of such an installation from the blog of another C36IA member (Steve Steakley, "Snowball", #1711):
 https://4.bp.blogspot.com/-lNVxmCdQDYI/XKt8iARiWvI/AAAAAAAAYW8/y4uJZTLwDmEVZJWPNwN9FKYyiZzDwPJ4ACLcBGAs/s1600/25.JPG .   Since the skeg is not in mechanical contact with any other metal on the boat, I'm not sure its needed (but I certainly could be wrong!), but it seems to me it couldn't hurt.   And believe me, replacing the skeg is a major project (having done it last year).

As to the engine anode, usually there is an anode on the heat exchanger.  (With a boat of your vintage, you may not even have the OEM heat exchanger anymore, so Westerbekke's diagram may not help).   It screws in, looks like the photo below.  Just look around on the sides of the heatexchanger, you'll probably see it (or feel around -- they can be hard to reach) . On ours its down low on the aft side, close to the port end.  15mm or 19/32" socket will be needed, if I recall correctly.

Catalina Direct has them in various sizes, as do most chandleries like West Marine. 
On ours, I usually have to trim the replacement down with a hacksaw a little on the far end to fit (otherwise it bangs into one of the internal tubes).  

:

Matthew Chachère
s/v ¡Que Chévere!
(Formerly 1985 C36 MKI #466 tall rig fin keel M25)
2006 Catalina Morgan 440 #30.
Homeported in eastern Long Island, NY

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alfricke
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My 2000 MkII has a 1" prop shaft. Take a look in your owner's manual, it should show it in the specs page very close to the front cover.
I've often wondered about sailing on the Mississippi as I grew up near Lake Pepin. 

Al Fricke
S/V Jubilee San Francisco Bay
Catalina 36' MkII  #1867
Universal 35-B

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alfricke
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peter

Take a look at page 15 on the Universal engine manual. It shows exactly where the pencil zinc is. Its a little hard to get to, need a ratched socket wrench. If you haven't checked it, you should! Is this a new boat to you?

Al

Al Fricke
S/V Jubilee San Francisco Bay
Catalina 36' MkII  #1867
Universal 35-B

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This is the arrangement of the underwater anodes on our Siler.

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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True Wind
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I would enjoy hearing the rationale of dilling holes in the bottom of a fiberglass hull and attaching a a sacrificial anode.

Thanks

 

2003 Catalina 36

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KevinLenard
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I thought it was only me scratching my head on that one.  Anode are intended to prevent corrosion on unpainted/exposed metal, I thought? 

Or is it the case that the so-called 'hull anode' is actually connected to the 12 volt DC system?  If so, is this a 'nice to have' or a worthwhile consideration for vessels in freshwater?  I've never seen any evidence of oxidation/corrosion on the electrical system so far (28 years in freshwater).

***  Hm.  A whole lot of silence on this question -- clearly it is a bit obscure (and likely of no benefit)...  Excellent and thorough explanation of all things anode related here:  https://performancemetals.com/pages/sacrificial-anodes-faqs

Seems that the only possible thing an exterior hull anode on a fiberglass vessel would be protecting is either metal parts in the bilge (if the bilge is usually wet) as long as there is an electrical connection to the bilge water and/or metal bits (keel bolts) from the anode (and to the negative battery post?) OR to the rudder post (and/or any other obscure metal thru-hulls).  On my '91 the rudder post seal (if there ever was an effective one) has allowed some water down into the top of the rudder leaking down to the base about 12 inches from the top of the rudder where the water has rusted the bottom of the post, expanded outward and cracked the starboard side and has leaked over the winter.  I drilled this out one fall and epoxyed it closed in the spring, but the epoxy pressed out.  The local Catalina salesguy said it would be a yearly effort and likely a waste of time without removing the rudder and post and trying to effect a permanently sealed solution.  I've abandoned this 'fix', but if a thru-hull anode connected to the negative terminal of the system would have found its way through the electrical system, grounded somehow to the steering system and down through the pullies to the post, then MAYBE a thru-hull anode would have made sense?  Obscure question, I realize...  ;-)

Kevin Lenard
"Firefly"
'91 C-36 Mk. "1.5" Tall Rig, Fin Keel, Hull #1120, Universal M-35 original (not "A" or "B")
CBYC, Scarborough, Lake Ontario, Canada

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Kevin, I have to be very honest with you: I had the same thought as you when I noticed this. For me our 2001-Catalina-36MKII is our first fiberglass sailing yacht and this is how it is installed on our Catalina (from original???). Onliest I can imagine is that you have a very good earth connection.
 

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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The 3” heat exchanger takes zinc’s (Al or Mg) that are 1/2 x 1.5” long. You may have to cut one down as 2” is a much too long. I get mine at boatzincs.com. They have the Al & Mg also. I would not put two different types on - as your just adding to the galvanic current then. Les

Les & Trish Troyer
Mahalo 
Everett, WA
1983 C-36 Hull #0094
C-36 MK 1 Technical Editor. 

Commodore

 

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peter g

2000 C36, MK2, Hull. #1897
wonderful, wonderful, wonderful ! ! !.   5 th Catalina

 

 

True Wind
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I was once certified in marine corrosion through ABYC. I didn't renew my certification this last renewal. But, this I can tell you.  Be diligent by replacing you sacrificial anode(s) on a regular basis. Make sure you have a fail-safe galvanic isolator installed in your AC ground wire on your boats electrical system. We want to protect our under water metals as best we can especially in salt water.  But even with the best practices, if a bozo comes into your marina with faulty wiring and leaking dc current like crazy and connects to the marina shore power, that boat is now connected to every other boat in the marina. That boat can melt your underwater metals in 24 hours. 
 

2003 Catalina 36

McFly
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a couple questions from a big-boat rookie....

1.  what is a galvanic isolator and how do I check for it on the boat I am in the process of purchasing?
2.  Is one sacrificial annode sufficient on the prop shaft?  The boat previously had two, seems like overkill.

Thanks!

- Mike
 

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Monument Beach, Bourne, MA

True Wind
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Mike
Great questions. I am not sure when Catalina Yachts started installing, as standard equipment galvanic isolators. There are ways of testing them. But, a fail-safe galvanic isolator is the way to go. A fail-Safe Galvanic Isolator will interrupt galvanic current flow with other boats at a marina when installed on a boat, which is connected to AC Shore Power. The fail-safe version assures that the galvanic isolator never compromises the integrity of the grounding conductor, even in the unlikely case of the product failing. DEI is the king daddy of galvanic isolators. The come in 30amp and 50amp versions. 

You didn't state what kind of water (fresh or salt) your boat is in. Two sacrificial anodes on the prop shaft are not necessarily over kill. 

Another thing to consider is do you have other dissimilar metals inside your boat that are "grounded" (connected by actually touching each other, or through a wire or metal part) are immersed in a conductive solution (any liquid that can transfer electricity like salt water). Your prop shaft may be isolated from the ground system in your boat. So the anodes on the prop shaft may only be protecting the prop and the shaft. 
 
 

2003 Catalina 36

McFly
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Thanks again for the great info.  The boat is a saltwater boat, located in Buzzards Bay Mass (Cape Cod).  The new (to me) boat had two annodes on the prop shaft.  PO thought it was overkill so he is recommending just one annode during spring commisioning.  Should I insist on two?  They're cheap cheap right?  In the aft stbd locker, is the 30A breaker for shore power.  Would this locker also be the ideal location for a GI?  Next time I'm at the boat I will crawl around and see if there is one installed.  Thanks so much for the info.

Mike

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Monument Beach, Bourne, MA

McFly
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In reading the electrical schematic for the 1999 C36 MKII, I noticed there is in fact a notation for a GI.  I have yet to get back to the boat to confirm that it is in fact installed.  Will update when I get that done.  Hoping that it came std from Catalina.  Anyone know?  We will be spending 99% of our time on a mooring and anchor, so thinking a GI isn't as critical as a boat that lives on shore power most of the time.  But I still want it on board.  Here is a pic of the schematic, see the red arrow.  ...

Mike

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Monument Beach, Bourne, MA

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This is the Galvanic Isolater installed in the Aft-Ctr on our Catalina. It looks like installed from newbuild.

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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LeslieTroyer
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From marinehowto is a great explanation on galvanic isolators. https://www.pbase.com/mainecruising/galvanic_isolator The site is a treasure trove of great articles and help for maintaining our C36’s. Rod is a former C36 owner and often posts here and on sailboatowners.com.

Les & Trish Troyer
Mahalo 
Everett, WA
1983 C-36 Hull #0094
C-36 MK 1 Technical Editor. 

Commodore

 

True Wind
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Pbase offers great information on testing galvanic isolators. But, if you are replacing a defective unit, installing one that doesn't exist on your boat or just want to upgrade, one would be a fool not to install a fail-safe galvanic isolator and even a greater fool if you don't have one installed installed on you boat. Capt. Dave Rikin was my initial instructor when I became ABYC certified in corrosion. Here is a link to his web site. Lots of great information on corrosion.

I received a link from Chachere and I suppose that this is a Catalina 36, see the photo attached. I got to tell you it looks nice. But, what it looks like is someone painted the prop, prop shaft and strut then attached the anodes. In order for anodes to do their work they need to be in direct contact to the metal they are intended to protect.  
 

2003 Catalina 36

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Chachere
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The photo is from the blog of another C36 owner (Steve Steakley, "SNOWBALL", #1711) at  https://svwandrinstar.blogspot.com/, it indicates it was taken after painting with "Barnicle Barrier".  
I generally have only one anode on the shaft, but sometimes when I haven't hauled for a while and have to dive to install a fresh one, I leave the old one (it being tricky enough to install a fresh one while hold my breath)..

I am curious about whether the anode is needed on the prop strut.  Since the strut is not in mechanical contact with any other metal on the boat (bing insulated on one end by the rubber of the cutlass bearing from that shaft, and bolted to the fiberglass hull on the other), I've always assumed its not particularly a target for galvanic corrosion.  Is there a flaw in this logic? (I suppose adding an anode couldn't hurt).
 

Matthew Chachère
s/v ¡Que Chévere!
(Formerly 1985 C36 MKI #466 tall rig fin keel M25)
2006 Catalina Morgan 440 #30.
Homeported in eastern Long Island, NY

True Wind
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Matthew
You are correct. There is no need for an anode on the strut unless it is some how connected to another metal or some how connected to the boat ground. 
 
But, don’t do what I believe they did and that is paint the shaft then put the anodes over the coating or put the anode on then paint the anode. The anode has to be in contact with the metal it is protecting
 

2003 Catalina 36

McFly
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Has anyone ever placed an annode anywhere on their mooring chain?  Top or bottom chain?  Also, here is a great schematic of a typical GI installation.  Helps to see this....

https://www.defender.com/pdf/204577.pdf

Mike

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Monument Beach, Bourne, MA

True Wind
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Mike

Two on the prop shaft should be ok. I would stay with magnesium. A zinc anode in fresh water will just fall asleep and be of no value in fresh water. Magnesium anodes are kind of like Alka-Seltzer and gives itself up pretty easy especially in fresh water. 
Stray current can be serious but not so much in fresh water. Fresh water does not conduct current well. That’s why Electric Shock Drowning (ESD) is so prevalent on fresh water. If there is a swimmer in fresh water and there is electric current that is trying to get back to ground and the current comes into contact with a human body, the body will conduct the current extremely well and of course that either stops your heart and you drown or it paralyzes your muscles and you drown. Thats why you should NEVER swim in a fresh water marina.
 

2003 Catalina 36

McFly
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Thanks again for the guidance.  I am on a mooring in Salt Water. Still go with two Magnesium on the prop shaft?  Ever hear of anyone protecting their mooring tackle with annodes?  

Mike

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Monument Beach, Bourne, MA

True Wind
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Mike
My bad. I thought you were on fresh water. Defintely use zinc as the anode.

David

2003 Catalina 36

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