Painting underwater stainless

[rgano]

With nine months gone by since hurricane Michael wrecked my boat lift and no repair in sight, I find my boat's bottom paint is not performing well. While I have the boat hauled next week for a bottom job, I am going to paint the prop and trim tabs, things I normally have not worried about with a lift-kept boat. I know what I am gong to do for the bronze prop but the stainless steel trim tabs present a new challenge to me. What to prep them with before the anti-fouling paint goes on?

 

[Mark P]

Not sure my experience is applicable but i painted my stainless props with bottom paint about a year ago. They are counter rotating props on same shaft (Bravo 3 stern drive) and there is no paint on them now - just came right off probably due to high rpms and salt water.

 

[rgano]

My previous experience with underwater SS was painting my Aquamet shafts on my trawler. The advice I was given at the time was to rough the surface with 50-grit and then apply paint. At that time I was using Interlux 2000 over which I applied bottom paint. That worked well enough, and maybe it will work on my well-sanded trim tabs, but I was looking for more recent successes with something else maybe. Lacking any other inputs, I will probably repeat my shaft success on these tabs. Were your props nice and shiny?

 

[Bendit]

I have a stainless shoe on the bottom the keel and it has always been difficult to keep paint on it.
Last time I applied 5 coats of International Primecon (single pot) over the roughened surface followed by 3 coats of Awlcraft CSC antifouling. After 12 months, it is holding on very well.

Previously I used International Interprotect (2-pot) under the antifoul, which only stayed on for about 8 months.

 

[Mark P]

Rgano- props were pretty rough when I painted them. Here is what happened. The bottom had paint but the outdrive did not (only the black paint that comes from Mercruiser). Barnacles built up on props and drive but not on the bottom. South Carolina is rough as we get barnacles quickly with warm salt water and boat sits in salt water 24x7x365. I had to scrape off and sand both outdrive and props. Painted both in March of 2018. Now outdrive is great but props have no paint on them. Probably because of spin speed I did not paint dynamic trim tabs on boat. Next time I pull her from the water I am thinking of using "prop-speed" on both and see how that goes.

 

[ranger58sb]

We've been using Pettit Barnacle Barrier on shafts and props... and we're just now about to use the less-expensive Rust-Oleum Cold Galvanizing Compound spray instead, expecting (from reading here and other similar places) pretty much the same decent results. (See related thread, if you haven't already.)

Our rudder, struts, and trim tabs are all still regular bottom paint (Pettit Hydrocoat ECO) and that seems to work semi-OK... but the real reason I haven't switched those to the zinc spray is 'cause of the hassle of getting those down to bare metal first. I'm planning to do a soda blast next year sometime, or maybe early in the next year after that... and afterwards I'm expecting to do the rudders, struts -- and I'm assuming, for now -- tabs with the zinc spray after that.

OTOH, I'm not exactly sure about the (stainless) tabs... so following this closely...

-Chris

 

[lipets]

Bottom paint is old school


6 coats of Rust-Oleum Cold Galvanizing Compound spray has been posted here as very effective and low cost

 

[sdowney717]

It is of interest to me too.
I made NEW tabs out of a piece of 316 SS shipped to my home.
2 by 4 feet was enough to do the job.
Tabs are made of 304 SS and 316 SS is more resistant to corrosion.

I then got silver colored POR 15 and coated them and the OEM base plates.

Finally before installing, I plan to get a section of SS chain small gauge and bolt the top edge to the transom, just in case the delrin pin on the cylinder snaps, I just never want to loose them after all my efforts.

I will also paint them with bottom paint.
I had some help with doing the bend for free at a metal shop, but could have done it at the house. I did bend the wings on the ends.

Photo links
https://photos.app.goo.gl/Ax4QVPPdfMW16VGo9

 

[syjos]

I use the galvanizing paint on my prop but for the SS rudder shoe, bottom paint.

After cleaning and sanding, the SS is coated with several coats of Interlux 2000 Epoxy. Instead of using the prime wash recommended by Interlux, I apply a thin first coat of 2000 and wire brush the SS through the epoxy. That removes metal surface contamination and the epoxy film inhibits oxygen preventing further contamination.

When the last coat of the 2000 epoxy gets tacky, the first coat of Interlux Extra bottom paint is applied.

Without the epoxy barrior coat to electrically isolate the SS from the copper in the bottom paint, the copper will get eaten up by the dissimilar metal and become ineffective in a short time.