Cold galvanized spray

[SILENTKNIGHT]

i just hauled out for the winter and the areas that i sprayed in May with cold galvanized paint now looks like this? Is it because i failed to prep down to the bare metal prior to spraying ?

 

[koliver]

I did one side with the Cold Galvanizing Spray and the other with Interlux anti fouing. on hauling, I couldn't see any difference. Both sides had considerable barnacle growth, some oysters, even a couple of mussels. This was my running gear. The hull had only slime and a tiny bit of grass, except the bottom of the keel, where there had been spots hidden by keel blocks, so no paint at all.
There the barnacle growth was no worse than on the running gear.

 

[SILENTKNIGHT]

there is no barnacale growth on my running gear.

 

[O C Diver]

If you were trying to prevent marine growth as opposed to rust, I've had much better luck applying antifouling paint on top of galvanic primer.

Ted

 

[SILENTKNIGHT]

But why did it turn into a tan color?

 

[garbler]

I don’t have much background info on this but here are my thoughts.

You mentioned you feel the problem may be attributable to lack of surface prep and not going to bare metal. So what was on the metal that should have been removed ? Let me guess, bottom or antifoulant paint no ?

If antifoulant paint then most likely copper metallic. You just applied zinc over copper if my guess is right. So it’s possible you’ve basically created a low voltage battery by apply two metals that are about opposite on the Nobility Scale of metals. Instant galvanic cell with saltwater one of the best natural conductors. Think lead and zinc and you have a wet cell battery with lead being more noble but not by much. So your zinc coating cooked off real fast.

Why the cold zinc ? Even without antifoulant copper paint those drivetrain fittings are bronze so the problem would have been the same. Whoever told you to use zinc didn’t have a clue

Rick

 

[PM]

Cold galvanized Spray paint? Sorry, I don't think so...

pete

 

[mike66]

How fast do you go? I don't have any wildlife just using Petitt Eco on everything and it lasts just fine with some wear on the prop and rudder. No copper so no interaction with metals.

 

[Nomad Willy]

Cold galvanized Spray paint? Sorry, I don't think so...

pete

I’ve used cold-gal and it works sorta OK. It’s worth putting on and it’s dirt cheap. Armor-All works better on my 6 knot boat. Clean w Acetone .. I squirt the ArmorAll on (as much as possible) and then brush it lightly to apply evenly paying special attention to the outer part of the blades. I usually apply about 3 coats. I try to not handle it w my fingers. Use a wood dowel to pick it up, move it around and put it on the prop shaft.

I’ve gone two, maybe 3 years and only had two or three barnacles right near the prop hub.

I haven’t tried to re-coat w anything after the Armor-All but that may be difficult at least. After all the idea is to make the prop too slick for anything to attach to the blades. Barnacles may even like AA HaHa.

 

[smitty477]

Cold galvanize spray worked very well for us for over 10 years in the NE with a seasonal haul and reapply. We only did the props and shafts with the cold galvanize spray. It was always preceded with a good cleaning prior to application.

 

[rslifkin]

I've had trouble getting good adhesion to metal on my boat as well. Props, shafts, rudders, and trim tabs all have blistered paint off the last few years. I've tried both the zinc spray as a primer as well as Primocon, both failed the same way by popping off in little bubbles, while other spots stayed adhered fine. This was over clean, prepped metal too. The previous paint on the struts, rudder, and trim tabs had held up fine, but I have no idea what the primer under it was.

I'm not sure if I just need a rougher surface, or if I need fancier primer to get things to stick better.

 

[garbler]

‘ You can’t teach an old dog new tricks ‘ well that is BS cause this old dog just got sent to school to learn a new trick thanks to you guys. For the life of me I couldn’t figure out why somebody would coat bronze with a zinc coating. If this is done for corrosion protection as an anodic coating well then its not necessary with bronzes. However I kind of forgot that there are lots of look alike fittings like props, struts and rudders that are made of much cheaper manganese bronze which is not a bronze at all but marketing people have prevailed. Manganese bronze unlike true bronzes contains lots of zinc in fact as much as 35-40%. So it’s not really a bronze but a brass. Has great strength but prone to ‘ dezincification ‘ in saltwater environments. When the zinc leaches out or dissolves it leaves a weakened honeycomb like metal that is soft enough to carve with a knife and thuds when hit instead of rings like a bronze bell. So with a brass alloy like this it makes some since to install a zinc anode or bond.

But zinc paint plus zinc anodes had me not only confused but at a loss to know where to look for answers. Then last night it came to me. Copper antifoulant paint keeps sea growth off your hull in theory because it creates and includes biocides. Some paints work better than others but I recall impressed current systems are still popular with navys, commercial fleets and larger yachts. These systems apply a mild electrical surface current that keeps all growth off hulls. So when you apply a very active metal like zinc on a copper alloy in a good electrolyte like SW you create an instant galvanic package as long as there is no non-conductive coating between the zinc and copper. I think you are essentially creating a reaction that generates a mild electric surface that prevents sea growth similar to the impressed current systems. There is also apparently some science that believes dissolved zinc may act like a biocide. Sounds reasonable to me so what do you think ? Otherwise I’m still scratching my head

Rick

 

[koliver]

But zinc paint plus zinc anodes had me not only confused but at a loss to know where to look for answers. Then last night it came to me. Copper antifoulant paint keeps sea growth off your hull in theory because it creates and includes biocides. Some paints work better than others but I recall impressed current systems are still popular with navys, commercial fleets and larger yachts. These systems apply a mild electrical surface current that keeps all growth off hulls. So when you apply a very active metal like zinc on a copper alloy in a good electrolyte like SW you create an instant galvanic package as long as there is no non-conductive coating between the zinc and copper. I think you are essentially creating a reaction that generates a mild electric surface that prevents sea growth similar to the impressed current systems. There is also apparently some science that believes dissolved zinc may act like a biocide. Sounds reasonable to me so what do you think ? Otherwise I’m still scratching my head

Rick

I have noted that on my boat, the large hull zincs never get growth. Not slime, not barnacles, no oysters, no mussels.
The running gear, no matter what I coat it with, gets barnacles equally with all coatings or no coatings. No difference whether polished or just scraped when the coating is applied.

 

[Circumnavigator]

I don’t have much background info on this but here are my thoughts.

You mentioned you feel the problem may be attributable to lack of surface prep and not going to bare metal. So what was on the metal that should have been removed ? Let me guess, bottom or antifoulant paint no ?

If antifoulant paint then most likely copper metallic. You just applied zinc over copper if my guess is right. So it’s possible you’ve basically created a low voltage battery by apply two metals that are about opposite on the Nobility Scale of metals. Instant galvanic cell with saltwater one of the best natural conductors. Think lead and zinc and you have a wet cell battery with lead being more noble but not by much. So your zinc coating cooked off real fast.

Why the cold zinc ? Even without antifoulant copper paint those drivetrain fittings are bronze so the problem would have been the same. Whoever told you to use zinc didn’t have a clue

Rick

I think that's a good guess at the problem's cause.


We used cold galvanized spray on the bronze prop on Fintry, starting with a recommendation from Fairhaven Shipyard. Given the huge number of fishing boats they haul, I take their suggestions seriously. The prop had been fouling some, which can't be good for fuel economy. They don't use bottom paint because they have found that it won't stay on a prop that's running hundreds of hours a year. With the spray, it comes out clean. I'm now using it on Morning Light's propeller and stainless rudder, following the former owner. Again, they come out clean.


No problems with adhesion on either boat. Fintry is steel, so has a lot of big zincs. Morning Light is glass, so only the usual few.


Jim