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I have inherited my father's C&C27 MarkII, which I am in the process of re-fitting.
I cannot seem to find any zinc anodes. Does anyone know where they are supposed to be located?
I'll probably be asking all sorts of other silly questions, so please be patient.
Thanx!
Robin
Anodes normally are a ball of dull metal located on the prop shaft between the hull and the p-bracket. It is quite possible that the one on your boat was removed or became so eroded that it fell off and your father never replaced it.
Don't worry about asking silly questions -- we all do from time to time. You might save yourself some time (and avoid some problems) by buying yourself a copy of Boatowner's Mechanical and Electrical Guide by Nigel Calder. It's quite comprehensive.
David Weatherston
"Towser", Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Many thanx David.
I have noticed that there are grounding cables soldered to the bronze sea-cocks. I am assuming that these are to allow a free flow of electrons to an anode located elsewhere on the boat. Any idea where this might be located? Perhaps on the keel?
Cheers,
Robin
You could trace the cables and see what they in turn are bonded to. What you're seeing could be lightning protection (in which case, everything is going to lead as directly as possible to the keel) but it's more likely to be protection against electrolysis, in which case, the centre of this circuit will be the engine block, which in turn will have the zinc anode on the prop shaft (you do not need one anywhere else). This shaft anode should protect any immersed metal (shaft, prop, p-bracket, seacocks) from electrolysis (the keel, being lead, is not an issue).
Bonding and lightning protection can become quite complex. Since you seem not to have a zinc anode on your prop shaft, I strongly suggest you invest the $5 or whatever they are and get one on before next season. Launch your boat and enjoy it. Then at haulout next season, have a look at your new anode. If it's eroded or pitted, you have a problem and it's time to read the electrical section of the book I mentioned earlier. I have, however, never heard of anyone having an electrolysis problem on the Lakes, so probably the anode will merely look grungy, which means you have no electrolysis issues, and can move on to dealing with all the other imponderables that boats continually throw in your face.
David Weatherston
"Towser", Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
Again, many thanx!
Robin
C&C27 MkII Hull #269
Robin, All the grounds from the seacocks, drains, valves on my boat lead to a common ground which in turn leads to the engine block. I also have a wire from the common ground to the keel. This protects against a lightning strike and also helps stop electrolysis. I put 2 anodes on my prop shaft because where the boat is moored at a marina there are a lot of boats that have dedicated shore power going to them. If there shore power lead happens to dip in the water for any length of time it corrodes the anodes of the boats around it and can wipe them out overnight if the power is strong enough. Just a little something to consider.
Ralph Ainslie
Thanx for the info Ralph.
Do you have a upainted spot on the keel to allow for an electrical ground thru to the water?
It seems to me that the grounding system on most fiberglass boats is a 'floating ground', similar to an automobile, at least on the 12V power systems.
Robin
C&C27 MkII Hull #269
Robin, My keel is totally painted with anti-fouling paint but I understand it conducts electricity.
Ralph
Re: anodes. I recently had a mechanic from Bristol Marine looking at my prop shaft, and I commented that there had been no zinc when I bought the boat, and no apparent corrosion. I put a zinc on it but noted that none of the boats in my club ever show any noticable erosion of their zincs. The mechanic said that in fresh water the anodes should be magnesium rather than zinc. That's the first I heard of that. Anyone know about this?
Bob, S/V Heatwave (Mark V)
Out here on the wet coast, we find bin loads of zinc anodes (we just call them zincs) at any marine supply store and we use two or three every year because of the salt water. You gotta use them or hydrolysis will eat away some very important metal parts. They tend to be unreliable because they will loosen up and fall off with regularity and most times you won't even know it leaving you in the precarious position of having no zinc. Some people will tie a zinc to copper wire, attach one end to something on the engine and throw them overboard because they don't trust the ones on the propeller shaft. If you do buy them for the shaft, be sure to buy 7/8" ones. 1" are more common but C&C 27s use a 7/8" prop shaft.
Do you use them in fresh water? I didn't think so.
This is an area that worries me so I checked up on zinc vs. magnesium anodes in fresh water (it worries me because one year I found that my zinc anode was very much chewed up, but a new one the next year was relatively ok, so I assume that there was some stray current corrosion going on, rather than pure galvanic corrosion).
A salesman at Canada Metal said that although they make magnesium anodes for outdrives and saildrives, they only make zinc shaft anodes. He said it was his understanding that magnesium wasn’t necessary on a shaft but “didn’t know the theory”. A mechanic at Eastern Marine in Toronto said that they install magnesium anodes on outdrives because outdrive anodes are in direct contact with aluminum, which is low down the galvanic table. Shaft drives have stainless shafts and bronze or brass props, which are higher up the galvanic table and less vulnerable. Nick Bailey at Bristol Marine says magnesium would be ideal, but magnesium anodes are only made for outdrives, where they will be in contact with aluminum.
I found the table below, which shows that aluminum is near the bottom of the table, magnesium one place lower than zinc. I _assume_ from this difference and the explanation about the relationship between current and corrosion that you want to have as great a difference between the metal being protected and the anode as possible, so on aluminum outdrives you want to go for magnesium. Shafts and props are safely distant from zinc.
Nick closed by saying that the greatest corrosion risk in fresh water is stray current corrosion in which current from the DC system (bad) or AC system (really really bad) is leaking to ground - the water - through your underwater metal, but that’s a topic for another time.
Two last notes on zinc anodes: 1. Fit yours _forward_ of the p-bracket. If your prop shaft ever separates from the engine coupling, the anode will prevent the shaft from shooting out of the boat. A brand-new C&C 62 nearly sank in Lunenburg harbour because it lost its prop shaft. 2. Better quality anodes have a little copper button set in the zinc. When you tighten the zinc down on your shaft, the button squashes against the stainless steel and makes a more reliable electrical contact.
"GALVANIC CORROSION
An accelerated degree of corrosion occurring when two different metals are in contact with moisture, particularly seawater. A metal with a lower position in the galvanic series (see below) will corrode sacrificially rather than one with a higher position, meaning brass, for example, will corrode before gold. The further apart the metals on the chart, the more electric current will flow and the more corrosion will occur. The metals listed at the bottom of the table below will corrode first due to galvanic reaction.
Galvanic Series
Most Protected (Cathodic)
Graphite (carbon)
Mercury & Mercury Paint
Gold
Titanium
Silver
316 Stainless Steel
304 Stainless Steel
Monel
Silicon Bronze
Copper
Red Brass
Aluminium Bronze
Gun Metal & Admiralty Brass
Yellow Brass
Manganese Bronze
Tin
Lead
Cast Iron
Wrought Iron
Mild Steel
Aluminum 2024
Cadmium
Aluminum 1100
Galvanised Iron & Steel
Zinc
Magnesium
Least Protected (Anodic)"
David Weatherston
"Towser", Toronto
C&C 27 Mk IV
David Weatherston
Towser, Toronto
C&C 27 Mk IV
Offline
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