Selective fouling

[Brooksie]

What's going on here.
Every year my SS skegbar, small exposed portion of SS rudder shaft, and bronze cutlass bearing housing are covered with a mass of barnacles. My propeller is coated with zinc paint so escapes the worst of it.
These 3 parts are connected to a zinc plate on the transom, the propeller nut has a zinc, and they are isolated from the engine ground by a Drivesaver coupling.
I have tried epoxy hull barrier coat under the bottom paint, thickened epoxy as a barrier, and Pettit underwater metal kit, in other years. Nothing seems to change the buildup of barnacles on these 3 metal pieces. The hull stays quite clean from use as you can see using various antifouling paints over the years. New England waters May - November. Do you think it is something electrical ???
The paint companies are no help.

 

[Blissboat]

That is indeed weird. I suppose it will turn out to be some kind of electro-chemical incompatibility, but given the measures you have already taken, it's hard to imagine what could be going on.

 

[Mac2]

Question: Are the three parts painted with the same zinc paint as the prop?

 

[Brooksie]

Question: Are the three parts painted with the same zinc paint as the prop?

No they are not, barrier X2 & same bottom paint Monterey

 

[O C Diver]

On metal parts including the skeg, I had better luck taking it down to bare metal, applying 2 coats of Barnacle Buster or Rustoleum zinc primer, and then coating it with Pacifica Plus.

Ted

 

[SeaLion]

This seems very unusual, especially with the clean sections looking so nice. I’d just say “Honey I ran aground to clean off the skeg.”

 

[Brooksie]

Thanks all. I forgot to mention, there is a bronze garboard drain within 1' of the skegbar w/just bottom paint on it and it never gets anything on it,,,,
Since these are the only 3 things that get barnacles on them and they are the only 3 things that are bonded to the zinc, I am suspecting "over zincing" may be the underlying problem,

 

[SteveK]

I wonder about electric leakage from a bonding system attracting them.

 

[Brooksie]

I wonder about electric leakage from a bonding system attracting them.

If you mean 12v leakage from my boat, no. There is no 12 source in my bilge water. The shaft & propeller are isolated by a Drivesafer and the cutlass bearing and have their own zinc prop nut. i have no shore power hookup at all. No leakage from other boats, I am at a mooring 100 yards from shore and 80' from nearest other moored boat.
I am "unbonding" the 3 items and removing the transom plate.

 

[SteveK]

it is the bonding system itself that IMO creates a circuit when the anode is wired to thru hulls. It is a thought as I wonder why they like to grow on those areas more than other.

 

[Deano]

What correlation does bonding have to do with barnacle growth? I didn’t think there was any.

 

[SteveK]

Open for discussion.
I see a greater concentration of barnacles near bonded surfaces.
My thought is there is a current between the zinc and bonded thru hulls, shaft and props they may be attracted to.

 

[Kit_L]

Very interesting; joining this thread to see if a definitive answer to what @SteveK suggested.

 

[ScubaPete]

I really don't think it’s unusual. My boat does the same thing…. heavy barnacles on everything metal underwater: props, struts, shafts, trim tabs and bronze through hull fittings. Most every boat I dive on or see hauled out looks similar. I have very little trouble with the fiberglass hull ( with regular bottom paint ) but all the metal is a mess.

 

[Blissboat]

I really don't think it’s unusual. My boat does the same thing…. heavy barnacles on everything metal underwater: props, struts, shafts, trim tabs and bronze through hull fittings. Most every boat I dive on or see hauled out looks similar. I have very little trouble with the fiberglass hull ( with regular bottom paint ) but all the metal is a mess.

Where are you located?

 

[ScubaPete]

Where are you located?

Virginia, Chesapeake Bay

 

[ronobrien]

What's going on here.
Every year my SS skegbar, small exposed portion of SS rudder shaft, and bronze cutlass bearing housing are covered with a mass of barnacles. My propeller is coated with zinc paint so escapes the worst of it.
These 3 parts are connected to a zinc plate on the transom, the propeller nut has a zinc, and they are isolated from the engine ground by a Drivesaver coupling.
I have tried epoxy hull barrier coat under the bottom paint, thickened epoxy as a barrier, and Pettit underwater metal kit, in other years. Nothing seems to change the buildup of barnacles on these 3 metal pieces. The hull stays quite clean from use as you can see using various antifouling paints over the years. New England waters May - November. Do you think it is something electrical ???
The paint companies are no help.
View attachment 160225
View attachment 160226

I think that if you clean all the metal parts down to bare and coat them with zinc coating you will find the same results as you find on the prop. Zinc will only adhere to bare metal. ZRC coating is available in 1/2 pint cans (Amazon I think). ZRC is 70% zinc solids. Don't buy a bigger can thinking that you can use it another year as it has an extremely short shelf life once opened.