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Old 17-02-2021, 11:39   #1
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Rust on Keel

Greetings All,
After purchasing my sailboat recently, I just started using a hull cleaning service and they sent me a video of the keel, underwater, showing that there are areas of rust developing on my keel. They're small areas about the size of a quarter. The vessel hauled out for survey in October and no rust was present at that time. further the hull was painted in July 2020. hull paint used is Petit Trinidad paint.
My question is do I need to haul the vessel out to paint it or can I do something while it's i the water. and what is causing it?
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Old 18-02-2021, 07:49   #2
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Re: Rust on Keel

If you maintain adequate zinc anodes underwater, including anodes bound to the steel keel, it won't rust.

We have 44' steel boat. It has 14 aluminum anodes, each the size of a license plate, on studs that are welded to the hull. Nothing under the waterline rusts. Lot's of stuff above the waterline rusts.

We keep track of it all with a silver reference electrode, available from the site below. At $130 that may be more than you need. In our case, the voltage has dropped below -1.0v, so she comes out of the water next week for clean anodes and possibly new bottom paint.

In the short term, you could hang a zinc "fish" over the side and ground it to the boat's bonding ground. Then, when you do pull her out, set her up for good anode protection for the future. Good luck with it.

https://www.boatzincs.com/corrosion-...electrode.html
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Old 18-02-2021, 09:38   #3
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Re: Rust on Keel

Quote:
Originally Posted by Picsagitaries View Post
Greetings All,
After purchasing my sailboat recently, I just started using a hull cleaning service and they sent me a video of the keel, underwater, showing that there are areas of rust developing on my keel. They're small areas about the size of a quarter. The vessel hauled out for survey in October and no rust was present at that time. further the hull was painted in July 2020. hull paint used is Petit Trinidad paint.
My question is do I need to haul the vessel out to paint it or can I do something while it's i the water. and what is causing it?
Although you do not say so, I assume you have a cast iron keel. This is a very different animal than a steel boat, and you should be sure that you and the people doing the work understand this. Normal bottom paint will NOT protect a cast iron keel from rusting.

The bad news is that you can not patch this up in the water and make the rust stop. The good news, is that it rusts slowly and it is not an emergency.

If you have multiple places where rust is breaking through the existing coating system, the existing coating system is either inadequate, or has failed, and patching is NOT the answer, you have to start from scratch. If the previous owner slapped bottom paint over a keel that was already rusting to make it look good for sale, shame on them.

You must get a proper epoxy coating on the cast iron. There are several brands that work. Make sure you pick one that either has specific instructions for cast iron, or you talk to the supplier's technical support people and they understand the question. You'll need to pick one you trust and STICK TO IT. No mixing product sources. Preparation is the KEY. If done right, it will last 10 to 15 years. if done wrong, it will not last the first season.

Read the instructions. All of them. Read them again. Even if you are paying someone else to do the work, you need to be 100% familiar with the process, and be SURE there are no shortcuts taken.

Test the thinning/cleaning solvent and epoxy for compatibility precisely as described unless you are removing all the previous epoxy system and bottom paint.

Use all the same manufacturer for all the components.

Follow the instructions faithfully. EXACTLY.

When removing failed coatings work on days of LOW HUMIDITY. You have a maximum of 30 minutes (and 15 is better) after you clean the metal to absolutely clean, the color of shiny silver before you get the first layer of coating applied. ALL of the metal must look like this. If there are any places with rust or dirt, the coating WILL fail.

You have to do this by grinding, not sand blasting. If you do sand blast to remove paint, be sure you come back and grind the keel in areas small enough you can get them fully coated in less than 15 minutes. There is nothing wrong with sandblasting, it is just very difficult to work in small sections and get cleaned up and ready for applying coating fast enough.

Do NOT wipe off the metal with rags. DO NOT! Tiny fibers will get caught on the metal and wick moisture down to the metal and rust will start.

This whole process of care and timing in surface preperation cannot be emphasized too much.

Tell the the people doing the work that this timing is an absolute requirement AND BE THERE AND TIME SEQUENCES AS THEY HAPPEN. They won’t like this… but, tough, you are paying.

Oxidation starts immediately when bright metal is exposed to oxygen and even at the microscopic level, it will cause the entire expensive component system to fail.

Once you have the entire keel epoxy coated you can come back with the bottom paint of your choice.

I'll emphasize again, this is a once-a-decade job if it is done right. The materials are not cheap, and the labor isn't either.
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Old 18-02-2021, 11:04   #4
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Re: Rust on Keel

"Although you do not say so, I assume you have a cast iron keel."

Is that a good assumption? The OP says not a word about his boat other than that the keel is rusting.
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Old 20-02-2021, 14:27   #5
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Re: Rust on Keel

Most likely you have cast iron keel. I had it on my Beneteau 323. Once it starts to rust, it will spread everywhere. See in the picture, the rust was only showing in a few spots until I started picking at it.

Scrape the keel, grind it down to the bare metal (it oxidizes fast, so you need to work in a team or in small sections) and paint it with epoxy based paint: Interprotect 2000e (3-5 coats at least), then antifoul paint, and it will last you at least 10-15 years.
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