To paint thru hulls or not?

[janis]

I'm currently preparing my boat for applying antifouling. It was just epoxy coated by previous owner as it was located in fresh water lake that was used for taking drinking water and antifouling wasn't allowed.

So my question is should I also paint thru hulls outer surface with antifouling or leave them bare (as currently in picture). Thru hulls are from DZR brass if that changes anything. I'm planning to use Micron 350 paint that's not recommended to use on aluminium. Not sure about it's reaction with DZR brass.

[HankOnthewater]

Hi Janis
I don't know about fresh water, but for salty sea water:
You said brass? Having brass skin fittings is dangerous as the zinc in the brass dissolve/leach out and the fitting becomes brittle and then can break easily.
Through hull fittings should be either bronze, stainless steel or good quality reinforced plastic.
But in all these.... yes, paint them, with a primer, or barrier coat and then antifoul the fittings. The barnacles still grow on all these fittings. I also apply the inside of these fittings as barnacles will grow there as well. Maybe just a copper fitting might not get much growth on it, but I do not know of any copper fittings.

[coopec43]

Originally Posted by HankOnthewater

Hi Janis

Through hull fittings should be either bronze, stainless steel or good quality reinforced plastic.
But in all these.... yes, paint them, with a primer, or barrier coat and then antifoul the fittings. The barnacles still grow on all these fittings. I also apply the inside of these fittings as barnacles will grow there as well. Maybe just a copper fitting might not get much growth on it, but I do not know of any copper fittings.

What anti-fouling do you prefer on the fittings? And what about the propeller? How do you treat that?

I am puzzled about marine growth. Helen spent three months in Two Rocks Marina after she was launched. We then motored her 40km to Hillarys Marina where she was rigged. When she was hauled out she was absolutely clean - no growth at all. But now after a month at Mindarie Marina I can see marine growth below the waterline. I have been told Hillarys and Mindarie are bad for marine growth, Why? Maybe stagnant water?

[janis]

Originally Posted by HankOnthewater

Hi Janis
I don't know about fresh water, but for salty sea water:
You said brass? Having brass skin fittings is dangerous as the zinc in the brass dissolve/leach out and the fitting becomes brittle and then can break easily.
Through hull fittings should be either bronze, stainless steel or good quality reinforced plastic.
But in all these.... yes, paint them, with a primer, or barrier coat and then antifoul the fittings. The barnacles still grow on all these fittings. I also apply the inside of these fittings as barnacles will grow there as well. Maybe just a copper fitting might not get much growth on it, but I do not know of any copper fittings.

I'm now in saltwater. I just purchased boat in freshwater. Thru hulls are DZR brass (also called CR brass etc.). It's corrosion resistant version.

Quoting Maestrini (that's what I have) - "Dezincification-resistant (DZR) brass is the name used to identify a group of copper alloys containing more than 15% zinc where elements like arsenic (As) and antimony (Sb) are added in controlled quantity in order to inhibit the selective dissolution of zinc caused by contact with various types of water including sea water. Hot-formed articles made with DZR brass require a controlled heat treatment to provide an effective resistance to dezincification, whose measurement criteria are set by international standards such as ISO6509 and AS2345, and can be verified
with specific tests. Properly manufactured DZR brass articles are suitable for applications in contact with sea water."

[GordMay]

Originally Posted by janis

I'm now in saltwater. I just purchased boat in freshwater. Thru hulls are DZR brass (also called CR brass etc.). It's corrosion resistant version.

Quoting Maestrini (that's what I have) - "Dezincification-resistant (DZR) brass is the name used to identify a group of copper alloys containing more than 15% zinc where elements like arsenic (As) and antimony (Sb) are added in controlled quantity in order to inhibit the selective dissolution of zinc caused by contact with various types of water including sea water. Hot-formed articles made with DZR brass require a controlled heat treatment to provide an effective resistance to dezincification, whose measurement criteria are set by international standards such as ISO6509 and AS2345, and can be verified
with specific tests. Properly manufactured DZR brass articles are suitable for applications in contact with sea water."

Indeed.

DZR is a leaded brass, with a small [typically 0.02 - 0.25%] Arsenic content. A further addition of Tin [up to 1.5%) further enhances resistance to dezincification.
Its copper content is very carefully controlled, at about 63%.
Over 63% brass is normally single alpha phase, so more malleable, and used for forgings, etc.
Below 63% is two-phase, mostly used for castings.
In the case of DZR, the copper level is such that components can be made by hot stamping, but converted from duplex to alpha phase, by subsequent heat treatment.
A “CR’ marking stands for Corrosion Resistant, and identifies the valve as made from DZR.

[deblen]

Hope this helps :https://marinehowto.com/category/plumbing/
http://www.pcmarinesurveys.com/Paul%...20Seacocks.pdf

Cheers/Len

[janis]

Thanks for all previous comments. Thread got bit sideways more about brass thru-hulls and not about applying antifouling paint. In the end I decided to paint my DZR thru-hulls as from what I researched DZR is very similar to bronze and it seems everybody is painting them with antifouling paint. I was hesitant before as my antifouling paint contains a bit of copper (oxide).