Painting steel rudders?

Tried a search on this topic, but it’s not easy on my phone. So here goes a new thread on the subject... Last year we took our steel rudders/struts down to bare metal and had a local boat yard company prime/bottom paint them. Hauled out this year to paint the hull and discovered the rudders/struts were badly flaking off bottom paint.

We actually contracted with the same company that did the rudders to paint the hull. Beyond the fact that company basically went under during the middle of our job (a story unto itself, for sure!), they couldn’t readily determined what went wrong. My research leads me to believe it could have been they didn’t properly prep the metal for the primer to adhere to; the didn’t let the primer cure long enough; or they used the wrong primer.

At this point, while we are once again taking them down to bare metal, what is the best way to paint/coat/anti-foul them? FYI we’re not going to use PropSpeed, and the Petit Zinc Barnacle Barrier spray we used on the props and shafts worked really well.

In the photos, the strut hasn’t been touched. But any black bottom paint that comes off has white on the back, which was the primer. The rudder we have almost finished scraping and will sand next.

Interlux has a guide that I’ve downloaded that tells what coatings to use (Interlux of course) but one can use whatever brand they want.

I used it to paint the bottom on my then 16’ aluminum skiff and then the topsides. Was quite pleased w the result but the bottom required 9 coats of this and that (including primer) to get the job done.

All the prep steps and procedures including what sandpaper to use were covered.

I just use AF on my bronze rudder.

Are you scrainhg and sanding the steel or sand blasting them before painting? I would think that sand blasting would get them prepped better.

A needle gun will clean steel to be ready to paint. Less hassle than sandblasting.

There are many sizes make sure your air compressor is up to the task.

Here is a tiny one,

https://www.harborfreight.com/air-needle-scaler-1108.html

A needle gun may clean the steel, but for paint to stay on, the steel needs a rough profile.
Maybe you could achieve that with an acid wash after needle gunning, but if it was my job I would most definitely be providing the profile with an abrasive blast.

If they're stainless they need to be bead blasted in order for paint to stick. Even then it's iffy. Stainless is just what it is stainless. Nothing will stick to it. I use to be a powder coater and I gave no warranty on anything stainless. We would just rough it up as good as possible so the coating would have something to stick to. Good luck. Personally I wouldn't paint them.

I ran a power boat with twin SS rudders. Used the entire petit metal system with good luck. Started with 24 grit rotary. Five coats involved including two of trinidad on top

Come to think of it. The last five years of prep was a heavy steel wire brush in an angle grinder.

DD788Snipe said:

If they're stainless they need to be bead blasted in order for paint to stick. Even then it's iffy. Stainless is just what it is stainless. Nothing will stick to it. I use to be a powder coater and I gave no warranty on anything stainless. We would just rough it up as good as possible so the coating would have something to stick to. Good luck. Personally I wouldn't paint them.

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Why would anyone powdercoat an underwater appendage? Needle gun it, hit it with a sander quickly and paint it....

Sailor of Fortune said:

Why would anyone powdercoat an underwater appendage? Needle gun it, hit it with a sander quickly and paint it....

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I wouldn't. But Merc and OMC outdrives are maybe you can ask them. All I said was I used to be a powder coater. Prep is prep. Be it liquid paint or powder on stainless. I'm having new rudders built for the North Star and I'm leaving them bare.

DD788Snipe said:

If they're stainless they need to be bead blasted in order for paint to stick. Even then it's iffy. Stainless is just what it is stainless. Nothing will stick to it. I use to be a powder coater and I gave no warranty on anything stainless. We would just rough it up as good as possible so the coating would have something to stick to. Good luck. Personally I wouldn't paint them.

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Snipe,
What’s your take on powder coated props?
Years ago I saw it being pushed by a Seattle powdercoater.

I had a curious experience that may give you a possible theory on your rudder experience.
Two years ago I did my bottom paint and zincs. The next year hauled for some shaft work and found the bottom paint was like new, except it was literally blown off the bronze rudder shoe. All my anodes are zinc, but the yard had mistakenly put an aluminum anode on the rudder shoe. Changed zincs, being sure all were zinc, repainted the bronze shoe, and this year when hauled the paint on the bronze shoe was normal. I think the one AL anode amongst all ZN caused the paint to aggressively strip off. I have no research or specific knowledge to back this theory up, so it is in the old wives tale category, but check the zinc on your rudder to be sure it was the same metal as your other anodes.

Nomad Willy said:

Snipe,
What’s your take on powder coated props?
Years ago I saw it being pushed by a Seattle powdercoater.

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For freshwater I'd say it's fine but not in salt. It also depends on what the substrate is. Now that only my opinion.