OK, once again- zinc anodes will not prevent rust. That is not what they do.
What size / shape zinc for keel? Inspection suggestions?
- Thread starter Ellwebs
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- 1973 hull # inspection zinc
I don't want to correct or explain why, but that link is about 10% WRONG.
Water is NOT needed to Oxidize Iron and Oxygen is NOT needed either!
Epoxy coating is great as long as all metal is coated and not eroded off by time.
I would still use a drop zinc too, when in berth. Weigh the zinc when new. Weigh it monthly to detect if your epoxy barrier is still working. The rate of zinc loss = %Epoxy removed.
The drop zinc will protect ALL metals that are in electrical contact with it, especially if the metal is mostly covered with epoxy.
Jim...
PS: Trivia : The Titanic is corroding, albeit slowly, because of very low water temperature, low oxidizing agents and most of all Low Disturbance. Iron, like zinc, corrosion protects itself until you knock the "scab" off or have two different metal connected (galvanic). If the iron rivets holding the iron plates are not the same grade iron....galvanic. The hull was not "ripped" but collision with the burg "busted" the rivets that made the seal.
Let me clarify. I didn't mean surface rust. I meant significant loss of metal with in 2 months. Keel had under water metal primer and paint (don't remember the brand) in addition to two large zincs.
So then if you did not epoxy your keel, what is the solution for cast iron?
Agreed as long as I maintain the epoxy, it should be fine. But I also don't see any harm with having a zinc overboard or even an electronic galvanic protection system hooked up to the battery. I have that on my bow rider and it works great (on the outboard) not sure exactly how one would connect it to the keel though. Maybe at the Hanger/pivot pin?I don't want to correct or explain why, but that link is about 10% WRONG.
Water is NOT needed to Oxidize Iron and Oxygen is NOT needed either!
Epoxy coating is great as long as all metal is coated and not eroded off by time.
I would still use a drop zinc too, when in berth. Weigh the zinc when new. Weigh it monthly to detect if your epoxy barrier is still working. The rate of zinc loss = %Epoxy removed.
The drop zinc will protect ALL metals that are in electrical contact with it, especially if the metal is mostly covered with epoxy.
Jim...
PS: Trivia : The Titanic is corroding, albeit slowly, because of very low water temperature, low oxidizing agents and most of all Low Disturbance. Iron, like zinc, corrosion protects itself until you knock the "scab" off or have two different metal connected (galvanic). If the iron rivets holding the iron plates are not the same grade iron....galvanic. The hull was not "ripped" but collision with the burg "busted" the rivets that made the seal.
Based on the above input, is there a benefit to having a keel sandblasted, immediately painting it with cold galvanizing paint and then patching any rough spots with epoxy?
No problems with a zinc! But I think others point out .... Is it enough?
The way the US Navy protects their iron keels/hulls is with an an electronic galvanic protection system. (EGP)
Look Ma No Zincs!
A quick way to look at it is, Zinc/Steel is a battery, like Lead/Acid. Sea water is kinda shorting out the battery. Keep your battery "charged", then little iron is lost.
Your electronic system should have connection instructions and monitoring. I am guessing now.. you should be able to connect your keel in series with the "bow rider" ( sorry I don't know what that is
).If you know that your winch is connected to the keel for sure, then then you maybe able to connect it there.
Well I am not sure covering with cold galvanizing paint is back up or double protection. It might even react and bubble the epoxy. That paint is normally for landlubbers. Perhaps there is a marine zinc primer designed to use with epoxy, but I would contact the paint manufacturer for their marine use specs.
This might work...
http://www.boatzincs.com/VELOX-PLUS.html
There is a way to verify and monitor all submerged metal corrosion. I check my boat once a month with this...
http://www.boatzincs.com/corrosion-reference-electrode.html
This gives me "peace of mind" and it is similar to what USN uses to monitor/control their "corrosion battery charger".
Jim...
PS: Techie stuff: Oxidation is defined as "giving up of electrons". No Oxygen (or water) needed. Metals are "fat" with extra electrons! As the metals give up electrons, they "corrode". Zinc connected to iron (in sea water) gives up electrons before iron and "sacrifices" itself before iron does. If you put electrons into the iron with a EGP, no loss, thus no corrosion. An epoxy barrier stops iron from giving up electrons.
James, good infoNo problems with a zinc! But I think others point out .... Is it enough?
The way the US Navy protects their iron keels/hulls is with an an electronic galvanic protection system. (EGP)
Your electronic system should have connection instructions and monitoring. I am guessing now.. you should be able to connect your keel in series with the "bow rider" ( sorry I don't know what that is
If you know that your winch is connected to the keel for sure, then then you maybe able to connect it there.
manufacturer for their marine use specs.
This might work...
http://www.boatzincs.com/VELOX-PLUS.html
There is a way to verify and monitor all submerged metal corrosion. I check my boat once a month with this...
http://www.boatzincs.com/corrosion-reference-electrode.html
This gives me "peace of mind" and it is similar to what USN uses to monitor/control their "corrosion battery charger".
Jim...
PS: Techie stuff: Oxidation is defined as "giving up of electrons". No Oxygen (or water) needed. Metals are "fat" with extra electrons! As the metals give up electrons, they "corrode". Zinc connected to iron (in sea water) gives up electrons before iron and "sacrifices" itself before iron does. If you put electrons into the iron with a EGP, no loss, thus no corrosion. An epoxy barrier stops iron from giving up electrons.
James, good info! A "bow rider" is like a ski boat or a runabout. I have electronic galvanic protection on that boat and it works great. But I'm wondering if that low charge somehow is adversely affecting my C22s keel. They are next to each other at my dock.Your electronic system should have connection instructions and monitoring. I am guessing now.. you should be able to connect your keel in series with the "bow rider" ( sorry I don't know what that is
If you know that your winch is connected to the keel for sure, then then you maybe able to connect it there.
In regards to the keel cable as a connection for the electronic galvanic protection. I think I'm going to try it this season. Maybe a quick connect that I can take on and off while sailing as someone previously had suggested.
I should test the water around my dock for a current. With and with out the boats around. There may be stray current that's speeding up the degradation of my keel.
The linked reference probe (in my post #26) can detect stray currents in a marina environment.
Most controlled devices need "feedback" to adjust if there is enough "impressed current" (the common name of electrical corrosion control). That controller feedback is kinda like a "trickle charger" keeping the just right amount of current to stop corrosion. Hmmmm? would it be more than enough to cause a stray? I am not sure.
I have read about "pulsed DC" devices. Charge the protected metal (battery), stop and watch the battery slowly discharge to a point, then Charge again (the pulse). Conceptually they don't "overcharge" or perhaps a stray DC current.
What is the power source for you EGP on your bow rider? If battery, how fast does that battery deplete?
I am glad my boat has a Lead/Antimony keel (whew
), so my "impressed current" knowledge is more land based use and limited.When I get more time, I will link a few forums where I suggested a test with a "drop zinc" and DVMeter to assure you have a zinc working in your favor.
The reference probe link, I bit the bullet and got one. Best boat tool investment I ever made. It took me about 3 hours to do my first complete boat survey and now about 1 hour (most of the time waiting to assure the probe is stabilized in the water). Now I can detect stray DC/AC currents.
Jim...
PS: A boat nearby with out a zinc can use your zinc to protect his, by a "stray galvanic current"
.
The advantage to sandblasting = more effective & complete removal of rust, fillers, and bottom paint; then it gives you the best roughened or 'grippy' surface to apply epoxy. I wouldn't waste time/money on the cold galv spray. The only reason people tend to do that is because freshly sandblasted cast iron will begin to oxidize (rust) immediately, especially in humid climates. The cold-galv spray is just convenient and easy to apply immediately after sandblasting but completely unnecessary. On a warm and relatively dry day in San Diego I picked up my keel from the blaster, got it home in my truck, unloaded and put on heavy saw bucks, rinsed down with acetone (displaces water and rises blasting dust), and then had the first coat of epoxy on within 4 hours of the blaster putting his gun away.
When it comes to sanding/grinding/wire-brushing an old cast iron keel, its just a nasty and time consuming job. The value of your time/sweat/patience is far better served by paying the $100 to $140 to have it blasted. The blaster does a superior job at removal and leaves you with a superior surface for epoxy to adhere to. I would recommend this method for any type of cast iron keel and even lead keels as well, although lead has no worries of rust.