Rudder Zincs

[Captmas]

Here’s another question ....on our 28flybridge we replaced the rudders with the larger ones from 31 from Hightide marine ....we have zincs on the trim tabs two on each shaft and a large CAMP mounted on the transom .....is it recommended to drill holes in the new rudders and add zincs there also .....if so what size are you guys using ....just hate to drill holes in the new rudders if it’s overkill
Mike

[Yannis]

Yes, same width as on the flaps.

[mike ohlstein]

I would (and do).

[Captmas]

Yup going to add them
Thanks

[EarleyBird]

Where do you keep your boat? In Saltwater? How long does it sit? If adjacent boats, are they using shore power? Do you use shore power? Do you have a complete and reliable bonding system? My opinion if your rudders are bonded/ground properly your wasting your time. Why drill a hole in a perfectly grounded new rudder. You have plenty of zincs if you maintain them. EarleyBird

[Tony Meola]

I am running two zincs on each shaft and also R4s on the rudders.

I hear what Early Bird is saying and yes I agree with him, but if you miss a broken ground wire or just happen to overlook that corroded connection, then you could have an issue.

I learned my lesson when the boat was new. By new I mean factory new. In fact second year we had it. Bilge pump was bad and leaking current. Zincs were gone in two weeks and the Prop Nuts looked like someone took a torch to them. Luckily, after being in the water only two weeks we bent a wheel and had to get pulled, found the zincs almost gone.

So you can bond and skip the zinc, but if something goes wrong, it goes bad real quick.

[Tooeez]

For what it's worth, the rudders on my 28 have no zincs and after 40 years are no worse for the wear---but I check those rudder ground wires ever month!

[DanielM]

My boat had zincs on the rudders when I got it. Replaced them when doing my bottom and never thought about not having them. Seems like cheap insurance.

[Amberjack]

I have both bonding wires to a transom zinc which is my back up and individual zincs on my rudders and shafts. When I haul annually, the transom zinc which is also connected to shaft brushes and through hulls is usually in pretty good condition and gets replaced every 3-4 years. The shaft and rudder zincs are 30-35% degraded and are replaced yearly. That tells me that galvanic current passes most easily to directly mounted zincs So if you rely only on remote zincs be vigilant.

[Tooeez]

Amberjack's reply reminds me of a question I have had for the longest time concerning shaft brushes. If the shaft is connected to the engine, and the engine is connected to the bonding system, and the bonding system is connected to a transom zinc, why the need for a shaft brush? Unless there are one of those flexible inserts between the faces of the coupling it seems to me that there is already a solid electrical connection between the shaft and the zincs. Can anyone explain?

[Amberjack]

Tooeez--My theory on that is that every join (zinc to bond wire, bond wire to engine block, engine block to shaft, etc) creates some resistance, plus the resistance of the wire itself. We're talking about really tiny currents. This is probably why my direct zincs wind up taking more load than the bonding zinc.

This is all intuitive stuff for me that I've developed over time, I'm not an electrician. My father was an electrical engineer and tried to explain it to me once. He drew a beautiful, elaborate schematic....and I didn't understand any of it.

[Tony Meola]

Tooeez

If you search the internet you will find all types of opinions on the use of shaft brushes to bond the shaft to the grounding system. The thought is that the oils in transmission break the bond.

Another option is take a copper strap and bend it over the transmission/Shaft coupling and secure it by passing the bolt through it. That will make sure the shaft coupling and transmission coupling complete the bond. Especially if you have the Shaft Saver installed.

[Tooeez]

Amberjack, I think you've answered the question! That's what so great about this forum--you have really knowledgeable and experienced people looking at a question from an angle you might never consider on you own. "really tiny currents"--I never thought about it that way, but it makes perfect sense--the solid connection from shaft to engine doesn't matter that much because the small currents involved can't easily overcome even minimal resistance. Thanks!

[Carl]

I was told you cannot over zinc a fiberglass inboard in salt water...but that was from one of my vendors that I bought pallets of zincs from.

His view was any current would go to the most active metal, zinc in most of our cases and get eaten up.

I believe the brushes on a shaft are for bonding purposes which ties all the metals together.
This is were I sort of get all balled up...but my take of it is two metals have different potentials like a battery has two terminals. Connect the two terminals and juice flows between the two....on a boat the two terminals(two metals) are connected by salt water which is "somewhat" (remember that) conductive.

Once juice is flowing underwater corrosion takes place.

Bonding connects all the underwater fittings with a highly conductive copper wire or strip. Bonding offers the current a lower resistance path between the two then the salt water. So juice goes through the wire instead of from underwater fitting to fitting.


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Response from Capt Patrick to my question about bonding and shaft brushes.



Posted: Fri Jun 08, 2007 5:29 pm Post subject:

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Carl,

While bonding and grounding are two different topics, they do share the same DC ground.

Bonding ties all necessary metals needing protection from galvanic corrosion to various sacrificial zincs, which is grounded through contact with the water.

DC Grounding is part of the electrical path to the battery. The engines have both DC grounding & bonding connections. The shafts are not necessarily well bonded just because they are connected to the engines. For a good bonding of the shafts, I use shaft brushes that make direct contact between the shaft and the bonding system.

So, in other words, you wouldn't ground your radio to the bonding system or bond your through hull fitting through the negative battery cable, but both systems are grounded to earth via the engine blocks.

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[Captmas]

Boat is a total refit and all bonding wiring is new ....it’s in saltwater.....going to go with the rudder zincs ....at this point it won’t hurt.
Thanks

[Captmas]

Here we go......just to add to the topic ....where did you guys place your zincs on the Rudders ....we have new 31 rudders on our 28....look around and see the zincs everywhere ...leading , trailing, center lower upper ???? Based on the shape of the rudder I’m leaning towards the lower leading edge to drill the holes as it’s the flattest part of the rudder...what do you think?
Mike

[Tony Meola]

Mike

When I did mine, the only thought I gave to it was that I took the zinc and put it on a spot that looked like it would work, marked the hole and drilled away. Then just matched the other rudder.

There is really no right or wrong spot.

[Carl]

There is really no right or wrong spot.

At least until after you drill and mount the zinc, then everyone will tell you the perfect right spot...which will be anywhere except where you put it.

[Amberjack]

Mine were dead center on the rudders when I bought the boat and I've left them there. I don't think it makes a lot of difference.

[Yannis]

At least until after you drill and mount the zinc, then everyone will tell you the perfect right spot...which will be anywhere except where you put it.

Hahaha, so true!!

[Tony Meola]

How true that all is. It should be up an inch, how about a little more to the rear. Lol

[Captmas]

Lol Merry Christmas!