Too much zinc?
- Thread starter rpell1@msn.com
- Start date
For fresh water they recommend using a sacrificial anode that is aluminum with 5% zinc and a little indium. From what I've been reading these aluminum "zincs" may also be a better sacrificial anode in saltwater than the zincs we've traditionally been using:
http://rjwsurvey.com/uploads/Aluminum_versus_Zinc_Anodes.pdf
http://rjwsurvey.com/uploads/Aluminum_versus_Zinc_Anodes.pdf
It has always been my understanding that the distance between the aft end of the strut and the forward end of the prop hub should be no more than 1.5 X the diameter of the shaft.
Perhaps this has changed over the years, because when I walk around boat yards I see a great many boats with much more distance than that.
Even with my 1 3/4" shaft, I'm not going to get an egg zinc in between strut and prop.
Perhaps this has changed over the years, because when I walk around boat yards I see a great many boats with much more distance than that.
Even with my 1 3/4" shaft, I'm not going to get an egg zinc in between strut and prop.
I too, see a lot of boats with more exposed shaft aft of the strut than is recommended. Notably the Newport 30. With a 7/8" shaft, they should have less than an inch and a quarter of shaft aft of the strut. But they all seem to have three or four times that much. Never heard an owner complain about vibration or excess shaft flexing though.
In any event, my point is; when it comes to mounting shaft anodes, it is really irrelevant where on the shaft they are mounted. You are not going to significantly better protect the prop by putting a zinc on the shaft between it and the strut, as opposed to mounting that same zinc forward of the strut.
the whole point of Zincs are to protect more noble metals on the hull, shaft and bearings from destruction by stray currents originating on your boat or nearby sources such as defective boats nearby or marina hazards like live plugs in the water or improperly wired outlets.
I have two zincs on the shaft one between prop and cutless bearing strut and one between strut and hull. The advantage of two is best observed when hauling a boat and finding one of the zincs gone as I did a few years ago! Properly applied there should not be any vibration issue induced by the zincs.
I have two zincs on the shaft one between prop and cutless bearing strut and one between strut and hull. The advantage of two is best observed when hauling a boat and finding one of the zincs gone as I did a few years ago! Properly applied there should not be any vibration issue induced by the zincs.
Yes, my boat sits in a brackish-fresh marina and experiences a wide range of salinity from upper bay to Hampton Roads to open ocean. But each winter she gets hauledd, and each season my zincs were heavily crusted with aluminum hydroxide- effectively insulating them from reaction. So this year I have changed to all aluminum, both shaft and prop. Will report out.
I would have more than borderline concern. Your prop is probably toast already. You have all the symptoms of your shore power feeding into the water. Assuming that you don't have a polarity problem, you can install a galvanic isolator (safest) or disconnect whatever is connecting you DC ground to the AC ground (cheapest and most practical). More zincs would only be a band aid.
Whatever has happened to the prop could have a variety of causes. There is no particular evidence that points to his "shore power feeding into the water." Further, we don't know if whatever damage the prop has suffered was already present when he bought the boat or if it occured more recently than that. It could very easily have been a case of the shaft and prop simply being unprotected for a period of time in the past, and that having the correct compliment of zincs would/has remedied the problem.
Sheapshed Bay
This has nothing to do with Zinc. I sailed out of Sheepshed Bay 65 years ago, aboard the RUBYACHT, owned by Ruby Zimmerman. Is he still around? does the Miramar Yacht Club still exist? I have been sailing in Panama for over fifty years now, presently aboard a Beneteau 331 and have been having a great time. Regards to all my friends in the frozen North
Alex Psychoyos
This has nothing to do with Zinc. I sailed out of Sheepshed Bay 65 years ago, aboard the RUBYACHT, owned by Ruby Zimmerman. Is he still around? does the Miramar Yacht Club still exist? I have been sailing in Panama for over fifty years now, presently aboard a Beneteau 331 and have been having a great time. Regards to all my friends in the frozen North
Alex Psychoyos
Galvanic isolator
A galvanic isolator could help if the problem is that nearby boats are plugged in to shore power (common ground between boats) and other boats don't have zincs. The isolator is installed in line with the ground wire and prevents other boats from using your zinc.
On our C-320 we have 2 shaft anodes and an anode cone on the prop. Last year I did some research and decided to throw out the zincs and go with aluminum alloy since we're in brackish water and the information all states aluminum alloy is better for that. When I mentioned this on various sites some people got kind of passionate about their zincs to the point of nastily attacking my decision! They had the defense of "Thats the way we always did it!" but could not suplly anything else to counter all the information I discovered. Anyway, the aluminum anodes did well, they could probably go another year or 2 but I ordered new ones and will put them on as cheap insurance.
Were these naysayers also adorning their boats with those cute fish-shaped zincs-on-a-rope?
Don't even get me going on zinc guppies... I have seen them physically clipped to a plastic coated lifeline, read; no physical electrical connection what so ever, and the owner still swore by them........
If anything, use magnesium for fresh water
I've experienced no corrosion on anything that I can find without using an anode for over 10 years. However, I wouldn't be so confident if I was worried about stray current in the marina.
Ask the other boat owners at your marina. You might be surprised at the number who use nothing.
I've experienced no corrosion on anything that I can find without using an anode for over 10 years. However, I wouldn't be so confident if I was worried about stray current in the marina.