Prop coating

MM5AHO said:
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.
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Hi,

Thanks for your knowledgeable comment. I examine the zinc spray can and mention 90% zinc on the surface when the paint is dry. The idea to try just antifouling, my propeller nibral bronze. I was thinking of painting several layers and the zinc paint certainly wears in two ways mechanically friction and electrochemically perhaps. I do not intend to remove the old traditional antifoulig paint. It may be a bad experiment, but I'm curious to see the works se.

NBs
 
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MM5AHO said:
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?
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Hydrochloric acid. I plan to preheat, coat, and return to the oven for the normal curing period. I hear what you are saying about adhesion and that is my only concern, but one must have a go. The one thing I will not be powder coating is the nut - we have done lots of nuts and bolts for show stuff, but realistically it almost always gets damaged when you do the thing up!
We do an anodising alternative using tinted lacquers for show engines, looks good, wouldnt last in service if you take a spanner to it!

20130816_121035 by mark punksteel, on Flickr
 
prof pat pending said:
Do you have any PTFE :confused:
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PTFE coating is not something we have done, as far as I understand it is a bit more specialised and more of a "wet" evaporative process. I am sure someone will be along in a mo to explain it better, as the sentence I just wrote is the extent of my knowledge on PTFE coating.
I do however have a few dozen cans of white grease with PTFE we use to lubricate the moving parts of our tube benders. Sticky nasty stuff, but I think a prop would spin it off. Would be interesting to try it on a test piece of metal though alongside other coatings
 
Anyone manufacture non stick cookware? how about ceramic coating, non stick frypans with the stuff are phenomenal in their ability to shed stuff but I expect the ptfe frypan solution may be the way even if it takes a bit of a spinup to shake off any growth. Must admit that our KiwiProp with its entirely plastic blades has one or two of the little limpet blighters but as we spend most of the time out of the water its no indication.
 
solent clown said:
PTFE coating is not something we have done, as far as I understand it is a bit more specialised and more of a "wet" evaporative process. I am sure someone will be along in a mo to explain it better, as the sentence I just wrote is the extent of my knowledge on PTFE coating.
I do however have a few dozen cans of white grease with PTFE we use to lubricate the moving parts of our tube benders. Sticky nasty stuff, but I think a prop would spin it off. Would be interesting to try it on a test piece of metal though alongside other coatings
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PTFE comes in lots for forms, the main advantage in all of them is that pretty much nothing will stick to them. I,ve used the grease you’ve mentioned, but also aerosols that apply a thin film and tapes for use in laminating. Probably the most well known use is the cookware mentioned above :)
 
solent clown said:
PTFE coating is not something we have done, as far as I understand it is a bit more specialised and more of a "wet" evaporative process. I am sure someone will be along in a mo to explain it better, as the sentence I just wrote is the extent of my knowledge on PTFE coating.
I do however have a few dozen cans of white grease with PTFE we use to lubricate the moving parts of our tube benders. Sticky nasty stuff, but I think a prop would spin it off. Would be interesting to try it on a test piece of metal though alongside other coatings
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It's been 30 years now but I used to spray industrial valve bodies with PTFE, it was done electrostaticly in a powder form then heated in an oven to cure it. That was on to steel not brass or bronze though but could be worth looking into.
 
I might be pointing out the obvious but putting a prop in an oven without removing any rubber drive spline insert might cause some problems that would be far worse than a few barnacles....

I don't know what the main degradation factor for rubber is but I am sure heat is one. Also could it have an effect on the electrical isolation of the rubber insert that is essential to isolate and protect the prop from electrical corrosion?
 
TSB240 said:
I might be pointing out the obvious but putting a prop in an oven without removing any rubber drive spline insert might cause some problems that would be far worse than a few barnacles....

I don't know what the main degradation factor for rubber is but I am sure heat is one. Also could it have an effect on the electrical isolation of the rubber insert that is essential to isolate and protect the prop from electrical corrosion?
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no rubber in the prop, just a taper and slot for a parallel key
 
solent clown said:
its a shame I dont have twin engines to do a comparison.
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You have at least two blades on the prop... (Can't compare blade with coating and no anode to blade without and anode though)

solent clown said:
Proper biocide powder coats are available. I have a copper powder coat that would probably do that job!
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Blade 1 - untreated "blank" - control arm
Blade 2 - Powder Coated with Copper Content
Blade 3 - Powder Coated with Biocide
 
ShinyShoe said:
You have at least two blades on the prop... (Can't compare blade with coating and no anode to blade without and anode though)



Blade 1 - untreated "blank" - control arm
Blade 2 - Powder Coated with Copper Content
Blade 3 - Powder Coated with Biocide
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two blades, sounds like a good idea for experimentation. After all they will be in identical environmental and physical stress
 
Kelpie said:
Just going back to an earlier comment, if epoxy is porous why do we use it to prevent osmosis on our hulls?
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I was wondering that too. Different kinds for different jobs perhaps ?

By the way, what happened to stove black. That was all the rage at one time.

Last season I bought a new outboard prop . I have easy access because the engine sits in a cockpit well. The paint on the tips lasted about five minutes. Apparently the water literally boils
- particularly at the tips. One would guess that keeping any coating would need to withstand very
high temperatures.

Some racing yachts used to have a "scuttle" where you could access the prop to see if it had folded. Don't see why cruising boats shouldn't have them for both cleaning and untangling .
 
Bronze can be coated, we coat Nickel Aluminium Bronze for naval applications using a two part epoxy after surface blasting. The epoxy has so far lasted over 10 years. However it means the antifouling properties are ruined and the blades need cleaning which is done in our application by divers.
We use a coating which is designed for pump applications to be resistant to cavitation ('boiling'). This doesn't mean its getting hot, it means the pressure on the low pressure side of the blade is reduced sufficiently for the water to boil at the ambient temperature.
So, my experience is that you can coat bronze but be prepared to clean the prop regularly because you've lost any fouling protection.
 
LONG_KEELER said:
Last season I bought a new outboard prop . I have easy access because the engine sits in a cockpit well. The paint on the tips lasted about five minutes. Apparently the water literally boils
- particularly at the tips. One would guess that keeping any coating would need to withstand very
high temperatures.
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Cavitation is caused by low pressure behind the prop blades rather than high temperature. Still causes the water to 'boil' but the coating doesn't need to withstand high temperatures, just the pitting caused by the bubbles collapsing.
 
This may be a bit of a spoiler, for this thread, but I just polish the prop', it's good for a season, I use Autosol, normally used to polish chrome on cars.

I polish it by hand, and it's much faster and simpler than messing about with coatings, it takes less than an hour to polish it.

The photos are of before and after polishing, In the before shot the dark mark around the edge of the prop' is where the polish has go onto the dirty side. I forgot to take the "before photo", and had already polished one side.
 
Ian_Edwards said:
This may be a bit of a spoiler, for this thread, but I just polish the prop', it's good for a season, I use Autosol, normally used to polish chrome on cars.

I polish it by hand, and it's much faster and simpler than messing about with coatings, it takes less than an hour to polish it.

The photos are of before and after polishing, In the before shot the dark mark around the edge of the prop' is where the polish has go onto the dirty side. I forgot to take the "before photo", and had already polished one side.
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And - how long is a season. I'm looking for a minimum of 12 months and with better AFs 24 months.
 
A season for me is April to October, I lift out every winter, sailing in the NW of Scotland isn't for me in the winter.

And I agree, it wouldn't work for well for 12 or 24 months, but many people lift their boats in the winter, it saves a lot of wear and tear, especially if you have a marina berth, or at least that's my experience of trying a combinations of; spending the winter in a marina, a winter on a mooring and lifting the boat out, over the last 40 years or more.

Having said that, I don't think you get much marine growth in the winter, so a polished prop' my be good for 12months, but I haven't tried it.
 
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