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Bonding thru-hull

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96TL

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Hey guys! I’m getting ready to install a thru-hull and seacock in my boat. I keep it in a wet slip 8 months a year. I currently have no thru-hulls on my boat. I have zincs on my Yamaha, but it’s kept raised out of the water 99% of the time. The aluminum fuel tank is bonded to my negative battery terminal.

Should I bond the new thru-hull the same way? Or do I need to install a zinc somewhere on the boat that stays submerged at all times? What did you guys do?

Thanks.

Dom
 

DaleH

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96TL":3t3wqbrd said:
Should I bond the new thru-hull the same way? Or do I need to install a zinc somewhere on the boat that stays submerged at all times? What did you guys do?
The best I understand it is that the reason for bonding would be to put ALL underwater metal objects to the same electric potential, measured in milliVolts. So say you had 3 items and they were respectively 600, 720, and 800 mV. The one @ 600 would be attacked first. Bonding would average them all to be ~707 mV each. There is safety in numbers ... by having them all at the same potential.

Then I added a zinc to the hull so it gets attacked first. I use 2 on my boat, a large 5" rubber zinc on the bottom of the OB bracket that stays wet when on the mooring.

Also, I had expoxied a piece of 4" tall x 6" wide x 1" thick mahogany to the hull where my transom-mounted transducer is. To this I added a small zinc ... Even though not in contact with any metal, I do believe it works as it shows signs of degredation whereas my thru-hull scoop to seacock looks fine. The zinc being a lower potential alloy should make it be the first target of stray electrolysis.

If you have trim tabs, you should also have a small 3" rudder zinc affixed to the top half of each. Tabman shows pictures of this on his THT forum.
 

96TL

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I emailed Parker to find out if there are any zincs on my trim tabs. I can also install a zinc under the swim platform if necessary.
 

96TL

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Dale, I’m pretty new to zincs, so I’m still learning the ropes. Is there a wire on the zinc that has to connect to buss bar along with the thru-hulls, trim tabs, etc?
 

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96TL":39rcp5eh said:
I emailed Parker to find out if there are any zincs on my trim tabs. I can also install a zinc under the swim platform if necessary.
A quick check would confirm whether or not installed. No factory installs them on production boats FWIW.

If you put one on the swim platform, mine is located in full contact with the lower part of the OB bracket where it is always immersed. You will need to remove the paint in the round area to where you will add the rudder zinc, as the zinc must be in full contact with the parent metal, in order to protect the aluminum bracket. I added a thick hard rubber washer on the inside where a fender washer goes over it to seal off the interior of the bracket, see photo.

I'd be very surprised :shock: , maybe even disappointed, if Parker shipped boats out without zincs installed to protect the aluminum OB bracket from the potential combined effects of both electrolysis and/or galvanic corrosion ...
 

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96TL

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I sent Parker another email confirming if there’s one on the bracket. ;)

So if there is one already on the bracket, there’s no need to bond my thru-hull? This is confusing. :(

Dom
 

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DaleH":3hh9uhs6 said:
I'd be very surprised :shock: , maybe even disappointed, if Parker shipped boats out without zincs installed to protect the aluminum OB bracket from the potential combined effects of both electrolysis and/or galvanic corrosion ...
FWIW... My 1996 MVSC has a factory installed zinc on the base of the motor bracket and in 3 years it has shown very little 'wear'.

The zincs on my trim tabs are another story, and are replaced every season due to degredation.
I suppose that is a good thing though! :D
 

96TL

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Well Dale, prepare to be disappointed. There are no zincs on the Armstrong bracket! :( They did start ordering trim tabs with zincs pre-mounted last year though, so I should have these on my boat, but he wasn’t 100%. I will have to check for myself this weekend when I haul it out. So I have zincs on my outboard (which is tilted out so they’re useless), and possibly on my trim tabs.

I’m going to have to set this up myself. Looks like I have another project. Can anyone give me some basic info about zincs? I looked a little bit online about them. It appears that some have a bonding wire, and some do not. Still confused. :?
 

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Easy to be confused, as we are really talking about 3 inter-related topics:

* Electrolysis
* Bonding
* Galvanic Corrosion

Let's take ELECTROLYSIS first. All metals have a base electric potential. The lower the number of it, like zinc, then the faster and more likely it will be attacked. This occurs naturally but is exacerbated when a boat and the metal is immersed in saltwater, as it makes an excellent current between the cathode and anode, which the zincs are also called or referred to.

The higher the e-potential, then the more "noble" the material is, like zincs are low, aluminum a bit higher, and the high quality marine bronzes and stainless steels being very high. Note, magnesium has an even lower potential than zinc and this is typically used for the anodes in freshwater.

Stray current can be a BIG problem in marinas, that's why metal objects need to be bonded (see below). One can check the level of electrical contact in your boat's area by putting a silver/silver chlroride cell off a digital multi-meter and reading the value of the current in the water. Most marinas with boat repair facilities have the means to do this. Note that it might not be the fault of the marina's dock wiring, but a poorly wired neighboring boat could be the culprit. Whenever you see zincs lasting but weeks on only a handful of boats, the wiring on those piers are suspect as as the boats on them.

BONDING is simply a means to put all metal objects in contact with each other, so that when in the water, they all have the same electric potential. The intent is to unify them and "raise them all up" to a level, or value, that is HIGHER then the potential of the zincs installed on the hull, OB, bracket, or other running gear.

From my example above, if you needed your "protection level" to be above 650, one item was below it. But by bonding them together, you put them all to > 700. Do not confuse bonding here with adding an earth ground.

GALVANIC CORROSION also naturally occurs in nature and this is due to the effect of using dis-similar metals, but there are 3 conditions that must be met for this to happen.

* The metal juncture must be wet with a conductive liquid
* There must be metal to metal contact
* The metals must have sufficiently different potentials

You can see this can be bad in saltwater as it is not only conductive, but the salts can make it work even faster ... me thinks the salt makes it a better "battery", as that in essence is what's happening.

Example: If you screw a SS bolt into an aluminum skiff, the area around the bolt head will or can bubble off the paint, show a white powder, or even get pitted, and eventually fail. This is because the SS is more noble than the aluminum and thus there is a current flowing between the 2 and the aluminum gets eaten away.

You can prevent this from occuring by using "barriers" to isolate the one metal from the other. I do this by putting heatshrink onto the body and/or threads of the bolt, using grease like TefGel (made to isolate metal alloys) or some waterproof synthetic grease, or nylon washers under the SS fasteners, so the nylon sits on the aluminum hull.

On some spinning reels, you can see white powder corrosion and paint flaking where a SS screw was put into the aluminum reel housing .. that is the effect of dis-similar metals at work in a saltwater environment.

===========================================
FYI - this info is NOT meant nor intended to be the defacto treatise on these conditions ... so if your boat has signs of some of these or needs to be protected ... you advised to do further on-line research.

... back to work now ;)
 

96TL

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Hmm, I was reading online and found this paragraph interesting.

“Non metal boats will usually have a copper bonding wire inside that connects all the underwater metal items together so they all share the protection from zinc anodes. Since engines use the metal frame as the negative battery connection and the engine is connected to the prop shaft, the engine and the negative side of your 12 volt system are also part of this bonding connection. This bonding wire is usually connected somewhere to the rigging.”

Does this mean that since there are zincs on my motor, and my negative side is connected to my engine block, anything connected to my battery ground will be protected as long as my motor is submerged?

Dom
 

96TL

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CORRECTION!

I just received another e-mail from Parker. There is a zinc under the swim platform. :lol:
 

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96TL":2w91v53p said:
Hmm, I was reading online and found this paragraph interesting.

“Non metal boats will usually have a copper bonding wire inside that connects all the underwater metal items together so they all share the protection from zinc anodes. Since engines use the metal frame as the negative battery connection and the engine is connected to the prop shaft, the engine and the negative side of your 12 volt system are also part of this bonding connection. This bonding wire is usually connected somewhere to the rigging.”

Does this mean that since there are zincs on my motor, and my negative side is connected to my engine block, anything connected to my battery ground will be protected as long as my motor is submerged?

Dom
They are talking INBOARD motors there Dom. Don't read too much into that, but any zinc on your OB is connected to the ground path per se. The main point is to add zincs so THEY corrode and your metal doesn't. As stated, I have no bond wire nor zinc on my seacock scoop ... as I have no other boat metal in the water when the OB is raised.

Being a '92, and the boat has always been wet-slipped or on a mooring, I think I'd see any damage to the scoop by now, but none so far.
 

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96TL":3g4odsbu said:
CORRECTION!

I just received another e-mail from Parker. There is a zinc under the swim platform. :lol:
Good to know! I was suprised when you said that the Armstrong bracket didn't have one because I knew that my Stainless Marine bracket did. I just figured they all had them, which is probably the case after all.

Good to know!
 

96TL

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The only metal objects I can think of below the water line are my trim tabs (supposedly already zinc-ed), the swim platform (also zinc-ed), and the outboard bracket (not sure about this). My O/B completely tilts out of the water.

So based on your experience so far Dale, I should be okay with just installing the thru-hull and leaving it alone. I did read that sometimes bonding it can make the situation worse. I didn’t get too in-depth with it yet since I’m at work, but it’s definitely a confusing subject, at least to me. It seems a lot of people have different opinions about it. I trust what you guys say since we all have Parkers and the majority of us have O/B’s. Parker recommended that I run a green wire from the thru-hull to the negative battery terminal, just like the fuel tank.

In case you guys don’t already know, I have a tendency to over-analyze EVERYTHING, especially when it comes to my boat. I usually end up stressing over something for no reason and give myself killer headaches in the process. My g/f thinks I’m crazy, so does Dale by now I’m sure. :lol:

Dom
 

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96TL":2hkqv0fx said:
Parker recommended that I run a green wire from the thru-hull to the negative battery terminal, just like the fuel tank.
That's not a bad idea and probably something I should do too ... and it's easy enough.

One thing that :shock: "freaks me about" :shock: about boats with Dynaplates affixed to the outside of the hull bottom is when they bond everything and then their boat gets hit by lightning ... which blows the dynaplate off the hull ... leaving a HUGE hole in the hull.

We just had a wooden sailboat brought in for repairs, to the boatyard I hang around at. It has a 300 pound lead centerboard mounted in the c'board well, which was wood. Lightning stuck somewhere nearby while it was on its mooring and the water was so super heated, that the lead absorbed the engery, which heated up the water molecules in the c'board well to the point where it EXPLODED. This boat itself did not take a direct hit, as there was no charring ... just an explosion of wood surrouding the c'board ... which also melted by the way ;) .

Lightning ... #1 thing that worries me on the water ... but lightning protection (if there truly is such a thing) is a complete 'nuther story ...
 

96TL

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Wow. Scary stuff. I'm gonna pretend I didn't read that for now and just hope I'm not there if it ever happens. :shock::shock::shock:

What kind of protection is offered from connecting the thru-hull to the battery though? Is this what you were saying about bonding the metals to the same electric potential?

Dom
 

DaleH

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In that case, the lightning "could" blow out not only your seacock, but your motor ... but, being the most metal in the water, it would probably attract a "hit" anyway :shock: !

Don't too much up on boats & lightning ... you'll stay off the water. Best advice I was ever given is to get as far away from lightning on the water as you can, even if you have to head into another port. Then get next to the nearest sailboats (but not too close ;) ), drop anchor, raise your OB out of the water, shut off your battery switch, lower all rods and antennas, disconnect all radio antennas ... and wait out the storm in the cabin ;) .
 

96TL

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Wow. So if I connect my seacock to the battery ground it can attract lighting!? How about the gas tank thats already grounded to it!? :shock:

I think I'm just gonna leave it alone and install it.

Dom
 

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96TL":39dk127g said:
CORRECTION!

I just received another e-mail from Parker. There is a zinc under the swim platform. :lol:
I was about to respond...my Armstrong bracket has a zinc down close to the very bottom near the transom. Same as Kevin's.
 

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