Through Bolted Zinc

[Sir Rondo Normal]

Hi again people: We started into working on the Corbin over the weekend and one of the things was to prepare the hull for bottom paint. All the zincs had already been remove except one. This one is one of the bar style anodes that was bolted through the hull and to which the bonding wires from the mast were connected.
The problem was that the through bolts were brass, slotted, machine screws so both had to be removed from the hull in order to remove the zinc.

What I'm thinking is to squeeze epoxy into the holes and and insert studs with flat washers on either end, then install the zinc using a rubber o-ring underneath it to put pressure on the exterior washer and to allow water to get to the underside of the zinc.

Is this how it is normally done and which would be better for the studs/washer, stainless steel or brass?


Thanks

[St. Elsewhere]

My boat has stainless studs. Bonding wires attach on the inside. Nuts are placed on the studs' exterior to provide about 3/4 inch space between the hull and the zinc plates. Washers and nuts are on both sides of the zincs with no rubber involved. I do not know what type of sealant was used, but there is no leakage. The boat has been serviced by several different yards over the years, and they have all restored the installation using the same configuration.

[Sir Rondo Normal]

Thanks St, I spoke to a fellow yesterday who suggested using 3M 5200 and stainless studs, etc. I like the idea of a nut as a spacer as I wondered how rubber would hold up over time in salt water.

Cheers!

[SailFastTri]

Why would anyone bond the mast to a zinc? Are you sure this wasn't a scintered bronze grounding plate (Dynaplate)?

You don't want water between the grounding plate (or a zinc) and the bottom -- it should be mounted in full contact, and I see no reason to remove a ground plate for painting unless it's to apply an epoxy barrier coat.

Also - with regard to the person who recommended 5200 that's not appropriate to use as a sealant under bolts unless it's something structural that warrants a strong adhesive in addition to sealing. I would use 4200 or 303, or other underwater-rated sealant that's not so tenacious. You only need to stop water from leaking; the bolt will handle the loads. 5200 is NEVER appropriate on a zinc, which needs to be changed as regular maintenance.

[Sir Rondo Normal]

Thank-you SailFast, yes you are right. It was a grounding plate. It looked like a zinc. At any rate, I now have to either put it back or replace it with a new one. I might as well put a new one one. So the question still remains as to what I pack into the bolt holes for sealant. Wouldn't the 5200 be the best choice for in the holes?

Thanks

[SailFastTri]

Originally Posted by Capt Wraun

Thank-you SailFast, yes you are right. It was a grounding plate. It looked like a zinc. At any rate, I now have to either put it back or replace it with a new one. I might as well put a new one one. So the question still remains as to what I pack into the bolt holes for sealant. Wouldn't the 5200 be the best choice for in the holes?

Thanks

I would not use 5200 under the Dynaplate, because the though-bolts will hold it just fine, and all you need is some goop to stop leaks. 5200 makes a permanent bond that is very difficult to remove without collateral damage. You would need to use heat and/or debonding chemicals, or plain brute force such as an angle grinder (difficult to control precisely). Chiseling away parts bound by 5200 is likely to damage the fiberglass laminate beneath.

Sealant = gap-filling.

[ronbo1]

Don't think you meant brass bolts; most likely they were bronze.
Brass has little use on a boat.

Ronbo

[SailFastTri]

Originally Posted by ronbo1

Don't think you meant brass bolts; most likely they were bronze.
Brass has little use on a boat.

Ronbo

Agree -- they came with the grounding plate. If he didn't destroy the plate or bolts my bet is he'll re-use them when he finds out the replacement cost.

[Seahunter]

Originally Posted by Capt Wraun

Hi again people: We started into working on the Corbin over the weekend and one of the things was to prepare the hull for bottom paint. All the zincs had already been remove except one. This one is one of the bar style anodes that was bolted through the hull and to which the bonding wires from the mast were connected.
The problem was that the through bolts were brass, slotted, machine screws so both had to be removed from the hull in order to remove the zinc.

What I'm thinking is to squeeze epoxy into the holes and and insert studs with flat washers on either end, then install the zinc using a rubber o-ring underneath it to put pressure on the exterior washer and to allow water to get to the underside of the zinc.

Fill the holes with west system six ten, then drill out to the size of the new SS redi-rod. Bed the studs with SikaFlex or 3M 5200. Make sure you leave enough stud material inside to attach connectors and enough below for the dive plate. Use large washers inside and out and add a locking nut to both inside and outside of the studs. Do not use rubber, or similar. Do not bed the studs in epoxy, it's not waterproof and it will crack without filler. Allow the bedding material to cure.

[St. Elsewhere]

Originally Posted by SailFastTri

You don't want water between the grounding plate (or a zinc) and the bottom -- it should be mounted in full contact,

SailFast,

Why should a zinc plate be in full contact with the bottom?

On fiberglass boats the electrical contact is only through the stainless studs. The studs are held securely to the hull with nuts on both sides, and they need to remain in place to facilitate changing zincs with the boat in the water. How would you achieve full contact and maintain secure installation of the studs?

[Seahunter]

Originally Posted by SailFastTri

I would not use 5200 under the Dynaplate, because the though-bolts will hold it just fine, and all you need is some goop to stop leaks. 5200 makes a permanent bond that is very difficult to remove without collateral damage. You would need to use heat and/or debonding chemicals, or plain brute force such as an angle grinder (difficult to control precisely). Chiseling away parts bound by 5200 is likely to damage the fiberglass laminate beneath.

Sealant = gap-filling.

While I'm not a huge fan of 5200, this application requires a bedding agent, not a "sealant". The is a big mistake many make. Anything going through the hull to the water requires a bedding material. 3M-5200 or SikaFlex 291 will not only bed, but bond and seal any mechanical fittings used in an underwater situation. They are virtually immune to saltwater and mechanical vibration. On removal, I've found a sawsall works quite well on removing bedded fittings.

[Sir Rondo Normal]

Originally Posted by SailFastTri

Agree -- they came with the grounding plate. If he didn't destroy the plate or bolts my bet is he'll re-use them when he finds out the replacement cost.

Hey I'm right here eh

I'll have another look at it on the weekend and decide whether or not to re-use the block. Do they degrade over time or is it okay to re-use? It is now the same colour as a zinc. The flat head machine screws are not completely destroyed, just the slots are a little worn now.

[Sir Rondo Normal]

Originally Posted by Seahunter

Fill the holes with west system six ten, then drill out to the size of the new SS redi-rod. Bed the studs with SikaFlex or 3M 5200. Make sure you leave enough stud material inside to attach connectors and enough below for the dive plate. Use large washers inside and out and add a locking nut to both inside and outside of the studs. Do not use rubber, or similar. Do not bed the studs in epoxy, it's not waterproof and it will crack without filler. Allow the bedding material to cure.

Okay so I'll use the west system "six ten" to fill the holes but then would it be best to drill new holes or drill through the six ten?
By "bedding" the new bronze bolts, you mean coat the threads with the 3M 5200 or Sikaflex and thread them through the holes?

Cheers, your expertise is appreciated.

[SailFastTri]

Originally Posted by Capt Wraun

Hey I'm right here eh

I'll have another look at it on the weekend and decide whether or not to re-use the block. Do they degrade over time or is it okay to re-use? It is now the same colour as a zinc. The flat head machine screws are not completely destroyed, just the slots are a little worn now.

If pink, then the bronze has been degraded by electrolysis. Not sure what to think about silver-gray.

[Jim Cate]

You might try soaking the ground plate in white vinegar for a few hours. This treatment will remove many of the strange things that grow on metal fittings in sea water. Won't hurt the plate, either. BTW, is the plate just a flat bit of solid metal, or is it made of scintered bronze, possibly with fins on the surface?

Cheers,

Jim