Anti-fouling for Prop and Shaft

[Jon Hacking]

Originally Posted by chrisjs

I would never use regular Cu based bottom paint on a Sail Drive even after epoxy...

Our issue was that the special aluminum bottom paint is terrible - lasts maybe 6-9 months when our regular paint often lasts 3 years. That's why we tried the epoxy approach. We're watching our zincs closely but haven't seen a problem yet, & it's been over a year.

[noelex 77]

Originally Posted by Jon Hacking

Our issue was that the special aluminum bottom paint is terrible - lasts maybe 6-9 months when our regular paint often lasts 3 years. That's why we tried the epoxy approach. We're watching our zincs closely but haven't seen a problem yet, & it's been over a year.

I agree with the concern of using copper based antifouling paint over aluminium. A barrier of 5 coats of epoxy is recommended when useing non copper based antifouling.
Most aluminium boat owners do not feel copper based antifouling is safe no matter how good the barrier is. A saildrive is will develop problems much quicker and more severely than an aluminium hull will.
Non copper based antifoulings are a bit less good, but are improving rapidly. Trilux 33 is much better than Trilux and gives us 2 years in the the warm waters of the Mederteranian.

[Albro359]

Lanacote works, but you need to be out of the water to do it properly
Clean the prop absolutely..then heat it with a hit air gun..then oaint heated Lanactoe on...should do 6 mths in temperate waters.
In warm waters it doesn't last
Propspeed lasts well in temperate waters, but since leaving my boat in Fiji where the water is 29-31 degC...oysters grow on it if its not moving
If the prop turns every day or so it seems to last 12 mths
cold galvanising I haven't used...but is zinc a biocide ???...its organic growth thats the issue...

[callmecrazy]

Originally Posted by Albro359

cold galvanising I haven't used...but is zinc a biocide ???...its organic growth thats the issue...

Petit markets it as a 'barnacle barrier'. But they don't specifically say it prevents growth.

"Properly applied, Pettit Zinc Coat Barnacle Barrier yields a smooth, hard surface that self-cleans under way".

It's the same 93% zinc as the rustoleum stuff.

[SailFastTri]

The zinc sprays do absolutely nothing to growth in Long Island Sound. The NY sealife laughs at it. I use Petit Prop Kote on the blades, and Petit Vivid on the hub and shaft. Better results but still needs to be manually cleaned monthly at minimum.

[noelex 77]

I have never tried zinc sprays. If the zinc coating is eroding I think it would have some effect. Zinc anodes suffer less growth than unprotected surfaces.

I live on the boat at anchor and occasionally, over winter, will anchor in the same spot for weeks at a time. When doing this patrs of the galvanised chain picks up quite a bit of marine growth (where it's not abraded by the bottom). This suggests that the effect of zinc sprays on retarding growth would be small

BTW to solution is to charge the chain length every week or so.

[SailFastTri]

Originally Posted by noelex 77

BTW to solution is to charge the chain length every week or so.

what do you mean by "charge"?

[colemj]

Zinc spray was worthless on our props. Zinc spray will be no problem on a saildrive - only paints containing copper.

Mark

[noelex 77]

Originally Posted by SailFastTri

what do you mean by "charge"?

Sorry I meant "change" the iPad sometimes changes words keyed in incorrectly.
If you let out some chain so the area of growth rubs on the bottom for a while the growth is abraded off.

[DTSWFlorida]

Originally Posted by Jon Hacking

I would be very careful mixing metals. We coated our Yanmar Saildrive in epoxy before antifouling it (with normal copper-based antifouling). Epoxy makes a GREAT undercoat for antifouling on props & etc, but there's a trick to getting epoxy to stick to aluminum. We document how (& other mods one should make to saildrives) on our Saildrive page.

So Jon -- Thanks for your suggestions on using the epoxy for an aluminum Yanmar saildrive. Your SailDrive page has great suggestions. I'm going to get the West System 105/205 epoxy paint for mine.
In hauling it out the first time since my last hull paint, I was alarmed to see how badly the SD had been eaten away by the Cu hull paint put over it.
One follow up for all is, how concerned should I be about the exposed Aluminum inside the SailDrive?? It will have no Cu paint over it, but is the zinc ring nearby enough to prevent galvinizing from occurring?

[chrisjs]

I think it is highly risky to use any Cu based paints on the saildrive leg. Strongly advise only using paint intended for aluminum. We only ever used Trilux 33 on both the SD leg and that was coated over 2 -3 layers of barrier coat. When we purchased our boat the previous owner had obviously ignored this process at his peril and needed to completely replace the Saildrive before closing the sale. We also used trilux 33 for the prop, but used Interlux CSC on the hull. I would advise getting the Cu based coating off the SD as soon as possible even if you need to clean down to bare metal. Never use Cu based paints on aluminum!

[fstbttms]

Originally Posted by STSWFlorida

I was alarmed to see how badly the SD had been eaten away by the Cu hull paint put over it.

You put copper-based anti fouling paint directly on top of unprimed aluminum?

Originally Posted by STSWFlorida

...how concerned should I be about the exposed Aluminum inside the SailDrive??

You should be pretty concerned, IMHO.

Originally Posted by STSWFlorida

It will have no Cu paint over it, but is the zinc ring nearby enough to prevent galvinizing from occurring?

Not necessarily. And BTW- "galvanizing" and galvanic corrosion are not the same thing.

[chrisjs]

I do not think you need to be too concerned about the "innards', plus what can you do about it anyway? The amount of Cu that would be introduced into the engine in the saltwater cooling has to be miniscule and even that is flowing through the motor, not stuck onto the exposed aluminum shell. Just clean ALL the Cu-based paint off ASAP. If it starts to look like Swiss cheese, you need a new Saildrive leg!!

[Jon Hacking]

Originally Posted by STSWFlorida

So Jon -- Thanks for your suggestions on using the epoxy for an aluminum Yanmar saildrive. Your SailDrive page has great suggestions. I'm going to get the West System 105/205 epoxy paint for mine.
In hauling it out the first time since my last hull paint, I was alarmed to see how badly the SD had been eaten away by the Cu hull paint put over it.
One follow up for all is, how concerned should I be about the exposed Aluminum inside the SailDrive?? It will have no Cu paint over it, but is the zinc ring nearby enough to prevent galvinizing from occurring?

Wow - I'm honored to be the recipient of your first post!

Yes, putting copper-based paint directly on aluminum is to be avoided at all costs, as it will start bi-metalic galvanic corrosion which can eventually eat the leg away. Do the best you can to make sure you remove ALL of it, & then clean the leg well.

Over the years, we've had a few arguments with reefs (don't do this - the reefs always win) & have therefore had to examine too much of the insides of our SDs. We could see no evidence of corrosion inside, so I think this shouldn't be a problem.

Having said that, paint on your epoxy as far up the water inlets (1 big, 6 small) as you can. You can't do a perfect job, but do the best you can. Then, when painting on your antifouling, pull back a bit to make sure that it only goes on epoxy, never on straight aluminum.

Of course, you want to mask off where your anode (zinc ring) bolts to the SD so the epoxy doesn't go on that surface. The anode needs to have good electrical contact with the SD to do its job.

[Jon Hacking]

Originally Posted by chrisjs

I think it is highly risky to use any Cu based paints on the saildrive leg. Strongly advise only using paint intended for aluminum. We only ever used Trilux 33 on both the SD leg and that was coated over 2 -3 layers of barrier coat. When we purchased our boat the previous owner had obviously ignored this process at his peril and needed to completely replace the Saildrive before closing the sale. We also used trilux 33 for the prop, but used Interlux CSC on the hull. I would advise getting the Cu based coating off the SD as soon as possible even if you need to clean down to bare metal. Never use Cu based paints on aluminum!

Chris, I'll grant you that there are risks, but cruising is full of risks. I felt a bit naked when we first tried this, as we hadn't heard of anyone doing it before. But at the time, we didn't have many options.

But now we know (& you've heard) & our results say it works pretty well. Our anodes don't get eaten away any faster than they did (3-4 years) and our legs show no signs of pitting or corrosion.

Our problem was 2-fold: A) it's often difficult to find good aluminum-safe antifouling outside of pretty developed nations (where we don't cruise much) & B) we've found that the aluminum-safe antifoulings just don't last.

We've been cruising SE Asia for over 10 years now, & the choices for antifouling are pretty thin. And they're even thinner yet for Al-safe antifouling (in fact, it's often impossible to find). And as I'm sure you know, it's a pain in the patootie having to carry around a bunch of different paints.

Our hull antifoulings usually last about 2-3 years. But Al-safe antifoulings seem to typically last only about 9-months! We don't like having to do an expensive haul-out just so we can repaint our saildrives. (Or have to dive down to scrub our SDs every few weeks after the paint gives up.)

So for us, out here, it's much better to use a longer-lasting paint on our SDs. And now we've found a way how we can do that.

Having said all that, I don't want to convince you to do something you don't want to do. If you're cruising mostly the US or Europe, where multiple brands & types of antifouling are easy to get, & you haul your boat out every year anyway for other reasons, then you don't have to go through all this epoxy work.

My post is more for those of us with fewer options, to provide folks with alternatives.