Prop coating

[solent clown]

As we have powder coasting facilities I am going to epoxy powder coat our prop. Another experiment, but hopefully it will provide protection against both corrosion and fouling - If it fouls with naughty little barnacles, we can just pop the prop off, stick it in the oven until the coating burns off, and reapply - in theory.
Any reason this shouldnt work?

 

[PuffTheMagicDragon]

I imagine that it could prevent corrosion by isolating the metal of the prop from a wet and conductive environment.
As for protection from fouling, unless your powder coating contains some powerful biocides and / or some nano fibres to prevent adhesion, how would the plastic coating on the prop behave any differently from the plastic on your hull?

 

[Tranona]

As we have powder coasting facilities I am going to epoxy powder coat our prop. Another experiment, but hopefully it will provide protection against both corrosion and fouling - If it fouls with naughty little barnacles, we can just pop the prop off, stick it in the oven until the coating burns off, and reapply - in theory.
Any reason this shouldnt work?

I would guess that somebody has tried in the past and it does not work. if it did, and given it is such a simple, cheap and widely available process everybody would be doing it. The problem i think will be getting it to stick to brass/bronze that turns at highish speeds in water. Having said that, aluminium props are painted (probably powdercoated) and that stays on fairly well, but it does not stop fouling or barnacles. corrosion on typical bronze props is an issue that is easily dealt with by anodes if necessary.

 

[solent clown]

I would guess that somebody has tried in the past and it does not work. if it did, and given it is such a simple, cheap and widely available process everybody would be doing it. The problem i think will be getting it to stick to brass/bronze that turns at highish speeds in water. Having said that, aluminium props are painted (probably powdercoated) and that stays on fairly well, but it does not stop fouling or barnacles. corrosion on typical bronze props is an issue that is easily dealt with by anodes if necessary.

its a shame I dont have twin engines to do a comparison. It is pretty tough stuff, we use it on wheels, engine parts, pedals etc for vehicles that are built for extreme environments.

 

[solent clown]

I imagine that it could prevent corrosion by isolating the metal of the prop from a wet and conductive environment.
As for protection from fouling, unless your powder coating contains some powerful biocides and / or some nano fibres to prevent adhesion, how would the plastic coating on the prop behave any differently from the plastic on your hull?

Proper biocide powder coats are available. I have a copper powder coat that would probably do that job!

 

[Tranona]

It is not the toughness of the coating but adhesion to the yellow metal that is the problem. If you get the prop really clean then antifoul coatings such as Trilux or Velox can be very effective if the correct primer is used.

Why not give your powder coating a try and report back?

 

[PuffTheMagicDragon]

Proper biocide powder coats are available. I have a copper powder coat that would probably do that job!

One way of testing how effective that is would be to coat a piece of metal with it, hang it from your mooring buoy, and see what happens... keeping us well informed, of course!

 

[solent clown]

It is not the toughness of the coating but adhesion to the yellow metal that is the problem. If you get the prop really clean then antifoul coatings such as Trilux or Velox can be very effective if the correct primer is used.

Why not give your powder coating a try and report back?

yes that's the plan, nothing to lose by trying. Part of the fun is experimentation. Fear of failure is a boring trait. After all, there is bo such thing as a failure, merely a series of learning experiences. - Says the chap who sunk a boat

 

[lpdsn]

It is pretty tough stuff, we use it on wheels, engine parts, pedals etc for vehicles that are built for extreme environments.

T Nacious Barnacle likes a good challenge. Extreme environments pah!. What's a bit of paint and been spun at 2,000 rpm when you've been born to eat your way into rock and hang on through all the storms the Atlantic can throw at you.

 

[solent clown]

One way of testing how effective that is would be to coat a piece of metal with it, hang it from your mooring buoy, and see what happens... keeping us well informed, of course!

I will give that a try with various different coatings. Will keep the wife entertained too checking and logging them

 

[solent clown]

T Nacious Barnacle likes a good challenge. Extreme environments pah!. What's a bit of paint and been spun at 2,000 rpm when you've been born to eat your way into rock and hang on through all the storms the Atlantic can throw at you.

And the little buggars have had a few million years practice too

 

[NBs]

Have any of you tried spray zinc paint?

I have read US boat forum that several promising experience. I also discovered the boat zinc anodes will never be the growth of the organism so that could work. I'm going to try the zinc paint my own propeller for the next season.

Some like that http://www.directchannel.uk.com/Zinc-Spray-Paint/Zinc-Spray-Paint-Silver

NBs

 

[MM5AHO]

Powdercoating is often thought to be the type of coating, but is actually just the method of application. Lots of different polymers can be applied as a powder. In this case the OP says they'll use "epoxy". Epoxy has generally good chemical resistance, but is in fact porous, and not totally insulating electrically due to that porosity. As others have noted adhesion will be the main issue. All powdercoating applications require some form of pretreatment to get adequate adhesion. That's usually either chemical or physical pretreatment. For chemical, I'm not sure what works for bronze, but most of the readily available chemical treatments probably will not work. Physical pretreatment means modification of the surface profile. (Shotblasting in plain language). Blasting a bronze prop, wastes bronze and also gives marine growth a foothold.
Burning off the powder applied epoxy will require about 450C, and that won't be good for the prop.
Zinc paint mentioned by others is paint resin with particles of zinc powder suspended in that resin. It's not all that great for electrolytic protection, as the zinc particles are not electrically connected to either each other, the seawater or the metal (bronze in this case?). The particles are encased in resin of the paint, which is generally insulating, except for porosity. Items painted with zinc paint probably will perform similarly to items painted with no zinc in the paint. It'll be the paint doing most of the protecting.

 

[solent clown]

Powdercoating is often thought to be the type of coating, but is actually just the method of application. Lots of different polymers can be applied as a powder. In this case the OP says they'll use "epoxy". Epoxy has generally good chemical resistance, but is in fact porous, and not totally insulating electrically due to that porosity. As others have noted adhesion will be the main issue. All powdercoating applications require some form of pretreatment to get adequate adhesion. That's usually either chemical or physical pretreatment. For chemical, I'm not sure what works for bronze, but most of the readily available chemical treatments probably will not work. Physical pretreatment means modification of the surface profile. (Shotblasting in plain language). Blasting a bronze prop, wastes bronze and also gives marine growth a foothold.
Burning off the powder applied epoxy will require about 450C, and that won't be good for the prop.
Zinc paint mentioned by others is paint resin with particles of zinc powder suspended in that resin. It's not all that great for electrolytic protection, as the zinc particles are not electrically connected to either each other, the seawater or the metal (bronze in this case?). The particles are encased in resin of the paint, which is generally insulating, except for porosity. Items painted with zinc paint probably will perform similarly to items painted with no zinc in the paint. It'll be the paint doing most of the protecting.

The coating we use is an epoxy/poly hybrid, melts at 190. I was planning to soda blast, acid dip, then preheat the prop before coating.

 

[alan]

You might want to try using Hammerite Special Metals Primer before powder coating; this has made the biggest difference to my anti-fouling sticking to the prop than any other treatment that I have tried.

Alan.

 

[vyv_cox]

My prop was copper plated two years ago as an experiment. Due to various circumstances I have not been able to assess it properly but it looked very promising after 9 summer months without turning.

 

[solent clown]

My prop was copper plated two years ago as an experiment. Due to various circumstances I have not been able to assess it properly but it looked very promising after 9 summer months without turning.

would love to know. We have electrolysis and plating facilities too

 

[solent clown]

You might want to try using Hammerite Special Metals Primer before powder coating; this has made the biggest difference to my anti-fouling sticking to the prop than any other treatment that I have tried.

Alan.

I can feel a whole series of experiments coming on now with bits of brass ;-)

 

[Neeves]

I can feel a whole series of experiments coming on now with bits of brass ;-)

+1

It is now possible to find and use good anti fouls but the prop (and anodes) is now becoming the rate controlling factor - and you can scrape underwater but adding new anodes and recoating really requires longer than is offered between tides. Velox is as good as any, but not as good as the best AF. Moreover if you leave the prop and there is growth then when you come to clean - you take the Velox with it. Velox is really not very effective on sail drives.

Copper plating sounds the most promising to date (but does not solve the sail drive issue). Some years ago I recall Jotun did some work on aluminium sail drives with copper based AF - and concluded there were no risks (if done correctly) - but I never followed up and I don't know how their experiment fared over years.

Another option, for the prop, might be CopperCoat?

Jonathan

 

[MM5AHO]

The coating we use is an epoxy/poly hybrid, melts at 190. I was planning to soda blast, acid dip, then preheat the prop before coating.

The soda blasting is probably a good way to clean without excessive re-profiling. What type of acid is your "acid dip". Preheating the prop before coating to ensure its dry is a good idea, but if you coat hot you'll get a higher build coating and not necessarily get the proper cure (cross linking) though you could put it back in the oven after spraying. Too thick a coating increases the risk of delamination. But I'm not sure about what you adhesion mechanism is? Doesn't appear to be physical or chemical?