Bonding System Question.

[Capn Craig]

One of the things, I am fixing now that I have her on the hard, for my first since I bought her, is zinc replacement.* The zinc plate on the transom looked more like plaster board than a metal plate.* It was bolted on with two 3/8 bolts and nyloc nuts, and washers, and spacers, etc.* The nuts did not *look like stainless, they were too light in color.* Or, maybe they were coated with zinc oxide.** What's the proper bolt material?* I'm thinking bronze or stainless, but that is just a WAG.

Since the voltages involved in a bonding system are miniscule.* And a bonding system only protect things to which it has a good electrical connection.** Would the use of dielectric grease on the connections be a good idea?*** On that line of thinking, would you grease the mating surfaces of the other zincs when they are bolted to stainless or bronze?* I have never heard of that.

 

[Edelweiss]

I don't use a zinc hull plate.* But my rudder zinc and shaft zinc all use stainless bolts and nuts.* Haven't seen any zinc held on with bronze lately.* Definately don't use brass as it will go with the zinc.* I help my neighbor replace his zinc plate a while back and it looked to me that the*threw hull bolts, nuts an*washers were all stainless.

Never used any grease on my zinc either and never had a problem.**My diver doesn't either.* He puts them on as they come out of the box.

Larry B

 

[rwidman]

Stainless steel for the bolts, nuts, washers, etc. SS locknuts instead of nylock. And no dielectric grease.

 

[psneeld]

I have only seen SS...but that goes against the strong sentiment of NO SS underwater due to ...

Crevice Corrosion
There is also a form of corrosion that affects many metals, particularly stainless steel, called crevice corrosion. A crevice may be formed under any of the following: deposits (such as silt or sand), plastic washers, fibrous gaskets, or tightly wrapped fishing line. It can also form where moisture can get in and not back out, forming a stagnant zone. Stainless steel is an iron-based alloy containing chrome and nickel. The quality that causes it to be stainless (nonrusting) is its formation of a thin, tightly adhering surface layer of chrome oxide. If this surface is deprived of oxygen, the oxide layer breaks down and the stainless steel will rust just like plain steel. In other words, stainless steel is only stainless when it has access to oxygen. In a crevice where there is moisture depleted of oxygen, stainless steel rusts. The simplest prevention for this condition is to seal out the moisture or clean off any deposits.

Not sure why good bronze wouldn't due just fine.


-- Edited by psneeld on Tuesday 27th of March 2012 06:33:47 AM

 

[Larry M]

psneeld wrote:
....Not sure why good bronze wouldn't due just fine.

*

Bronze has*has worked for us.* We have 25 year old bronze threaded rod for the plate zinc.* We use bronze washers and double nut the plate on.* We have never seen any problems.* Our last boat had SS threaded rod and we never had any*problems with those either though.

 

[Phil Fill]

Once a zinc becomes coated with white it is not protecting, so the white coat has to be cleaned off.* That is one of the reason I have a diver ever 6 months to clean and check the zincs.* I just*had a*big DIVERS DREAM, 6 X 4, zinc plate installed for the bow thruster the bolts and nuts are SS, and most zinc fasteners/screw are SS.* No grease is used just clean the surfaces.
*
The best is to ask other around your boat and in the marina how fast their zincs have to replaced abd how often they have a diver.* *If your zincs are not*going fast enough can be as bad as the zincs going to fast.