[ddiesel]

I am getting ready to apply bottom paint to a 28 ft sailboat with a 4 1/2' steel keel. I have some blistering on the steel and also a hairline crack where the keel meets the fiberglass. I would appreciate any advise on how to address these issues. Thanks

 

[Minnewaska]

By the steel, you mean an iron keel? Just sand it down, prime or barrier coat and paint. If the crack is just the joint between the keel and boat, you may want to insure the keel bolts are tight enough. You can try to fare it with 4200, however, if the keel adhesive has given up, it can become inevitable that you rebed the keel.

If you are not using the same product that is already on the bottom, you will need to remove all of what is there first.

 

[Fstbttms]

If you are not using the same product that is already on the bottom, you will need to remove all of what is there first.

Sorry, but that is simply not the case. Most copper-based anti fouling paints are compatible with one another, regardless of whether they are hard or ablative types. It's all in the preparation. Check the manufacturer's web site for compatibility charts.

 

[Minnewaska]

Sorry, but that is simply not the case. Most copper-based anti fouling paints are compatible with one another, regardless of whether they are hard or ablative types. It's all in the preparation. Check the manufacturer's web site for compatibility charts.

Hard's are often compatible with hard and ablative with ablative, some ablative you can put over prepped hard. However, the advice that says you can use anything over anything, depending on prep does not correlate with manufacturer recommendations, nor practical experience. Even where it recommends a hard sand, I would be suspect.

http://www.google.com/url?sa=t&rct=...=qrzZcbK5lKhFkYtE5hqJNw&bvm=bv.68911936,d.cWc

 

[Fstbttms]

...the advice that says you can use anything over anything, depending on prep does not correlate with manufacturer recommendations, nor practical experience.

Yeah, except I did not say that "you can use anything over anything." What I said was that most hard or ablative paints can be used with each other, and the Pettit compatibility chart you posted bears that out.

The chart you posted also refutes your initial statement, the one where you told the OP that he would have to remove whatever is on the bottom now (regardless of what it is) if he intended to paint with a different product.

 

[Minnewaska]

I think we're splitting hairs, but I'll admit, I did not notice you said "most". Nevertheless, I'm not going to look up all the paints on that chart. Can you recognize a hard paint that is compatible over an ablative? At best, I would think it would require a 'hard sand', but I would never do so. An ablative base just makes no logical sense, therefore, I would not encourage the OP that most will work.

On the chance the OP has no idea what's on it, would you roll the dice on most or remove it all and start over?

 

[Fairladyaffair]

Honestly i do not know what the best way to do the bottom job is, but i can tell you how I plan to do it unless someone advises me otherwise (and i would hope they would). I do not have that much bottom paint on the bottom of my Mirage 29 with a similar draft. THIS IS MY PLAN:
1. Scrub bottom with degreaser soap (plain sink soap) to remove and surface material and start with clean old bottom paint, rinse, and allow to dry.
2. Using 2" painters tape, tape off the edge between bottom paint and gel coat to protect from sanding gelcoat by mistake.
3. Using 80 grit sand paper and a circular sander, sand entire bottom to a smooth even surface.
4. Scrub bottom again using same soap as earlier, rinse, and allow to dry.
5. Using acetone on a clean rag that will not leave small parts behind, wipe down the surface re applying acetone repeatedly as acetone evaporates quickly.
6. Roll on bottom paint across the cleaned surface evenly, allow to dry over night.


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[mitiempo]

Ablative can go on over hard paint. Hard paint cannot go on over ablative.

 

[Minnewaska]

Having solvents running down ones arm, while wiping a hull, is one of life most miserable experiences. If you really need to remove your paint, hiring a soda blaster is best. Sanding with a vacuum sander (required in these parts) is second best.

 

[Fstbttms]

Ablative can go on over hard paint. Hard paint cannot go on over ablative.

The manufacturers of hard and ablative paints disagree with you.

 

[BarryL]

Hey,

I've been through this a few times with a few different boats.

If there is a lot of old paint build up, the best way is to hire a soda blaster, and have him remove all the old paint. After that is done you will need to fair the keel and perhaps other parts of the hull, then barrier coat (of you like) and apply bottom paint.

If the bottom is in really good condition, you can just scrub the bottom with water and a stiff brush, then apply new pant.

If the bottom is between really bad and really good, then you can scrape the old paint off, sand the old paint off, or use chemicals. It's really up to you.

I can't think of any reason to use soap and water. Either powerwash the hull if it has marine growth on it, or just scrub with a stiff brush and water. Then remove the old paint using your preferred method, scrub and rinse again, then paint.

Good luck,
Barry

 

[Fairladyaffair]

Heres a good reason, although it may be more effort its cheaper than buying a power washer and if your boat has been sitting on the hard as long as mine has it will remove the white powder, meldew and mold that has grown on its surface and baked on by the sun.

It is dirty and miserable but if you do it right once it will last a long time. My Mirage has minimul issue with its bottom and a very thin layer of bottom paint. I would say its in good to great condition. I have one blister to repair, which thankfully is already popped and dried out. Plus a stress crack at the hull/keel seem.

I will be taking photos and putting them up on my thread i started documinting my progress so people can use it as a resource or to learn what not to do lol.

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[Multihullgirl]

The manufacturers of hard and ablative paints disagree with you.

FB, I have the greatest respect for your opinions and advice, but it stands to reason that an undercoat which sheds (ablative) would shed a topcoat which doesn't (hard). Would you please point to a link?

--wait, here's one:
http://www.pettitpaint.com/fileshare/tech_bulletins/bottompaintcompatibility.pdf

Nevertheless: if I didn't know what I had on the boat I'd strip it. I've learned that lesson the hard way.

 

[Sailormon6]

If I was buying a used boat, I would ask the previous owner what kind of antifouling he used on it, and I would use the same paint.

If I forgot to do that, and couldn't find the previous owner, I would use an ablative antifouling for general purpose (non-racing) sailing. Personally, I have never had a problem with applying an ablative over a hard paint. But, before doing so, I would call the Pettit or Interlux paint company's customer service line and ask to speak with one of their paint experts, who have always provided me impeccable advice.

But, with respect to the iron keel, I had one, and was never able to stop it from rusting and peeling until I put a zinc sacrificial anode on it. It looked like it generated a gas, which lifted the paint and fairing compound into a very large blister, which had to be removed and re-faired frequently.

 

[Fstbttms]

FB, I have the greatest respect for your opinions and advice, but it stands to reason that an undercoat which sheds (ablative) would shed a topcoat which doesn't (hard). Would you please point to a link?

Ablative paints do not ablate of their own accord. They require moving water to cause that to happen. Once you have covered an ablative with a hard paint, water is no longer going to flow past the surface of the ablative and therefore it will not ablate. With proper preparation (assuming you follow the manufacturer's application recommendations) it can provide a suitable substrate for a hard paint. Not in every single example perhaps, but it is a mistatement to claim that hard paints absolutely cannot go over ablatives.

Here is the Interlux compatibility chart which further proves this to be the case:

 

[TQA]

Honestly i do not know what the best way to do the bottom job is, but i can tell you how I plan to do it unless someone advises me otherwise (and i would hope they would). I do not have that much bottom paint on the bottom of my Mirage 29 with a similar draft. THIS IS MY PLAN:
1. Scrub bottom with degreaser soap (plain sink soap) to remove and surface material and start with clean old bottom paint, rinse, and allow to dry.
2. Using 2" painters tape, tape off the edge between bottom paint and gel coat to protect from sanding gelcoat by mistake.
3. Using 80 grit sand paper and a circular sander, sand entire bottom to a smooth even surface.
4. Scrub bottom again using same soap as earlier, rinse, and allow to dry.
5. Using acetone on a clean rag that will not leave small parts behind, wipe down the surface re applying acetone repeatedly as acetone evaporates quickly.
6. Roll on bottom paint across the cleaned surface evenly, allow to dry over night.

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Whoa there.

Please DO NOT dry sand antifouling, especially upwind of my boat. Well not unless you have one of these positive ventilation masks that blows clean air over your face and you have tented your boat.

Many yards in the US don't allow it anyway.

Get your bottom pressure washed by the yard and WET SAND using 80 grit W/D paper. There is an articulating head that you can use on a pole that makes this an easy job.

Please do NOT wash down with acetone.

Wash down with fresh water then roll on the A/F.

I do my own every year.

 

[sailingfool]

Honestly i do not know what the best way to do the bottom job is, but i can tell you how I plan to do it unless someone advises me otherwise (and i would hope they would). I do not have that much bottom paint on the bottom of my Mirage 29 with a similar draft. THIS IS MY PLAN:
1. Scrub bottom with degreaser soap (plain sink soap) to remove and surface material and start with clean old bottom paint, rinse, and allow to dry.
2. Using 2" painters tape, tape off the edge between bottom paint and gel coat to protect from sanding gelcoat by mistake.
3. Using 80 grit sand paper and a circular sander, sand entire bottom to a smooth even surface.
4. Scrub bottom again using same soap as earlier, rinse, and allow to dry.
5. Using acetone on a clean rag that will not leave small parts behind, wipe down the surface re applying acetone repeatedly as acetone evaporates quickly.
6. Roll on bottom paint across the cleaned surface evenly, allow to dry over night.

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Then again, you could sand fair those areas that NEED sanding (old growth or chipping paint), wash with fresh water and paint. I'd say the Acetone is the worse of the bad ideas.

 

[sailingfool]

But, with respect to the iron keel, I had one, and was never able to stop it from rusting and peeling until I put a zinc sacrificial anode on it. It looked like it generated a gas, which lifted the paint and fairing compound into a very large blister, which had to be removed and re-faired frequently.

I've fond that 3-4 coats of hard epoxy over steel will last just fine excepting any abuse, such as hitting a rock...

 

[Sailormon6]

I've fond that 3-4 coats of hard epoxy over steel will last just fine excepting any abuse, such as hitting a rock...

I covered mine with 4-5 coats of Interlux 2000 barrier coat, and all it did was slow down the process. After I installed a zinc, it stopped. Installing a zinc is alot easier than applying 3-4 coats of epoxy.

 

[Jaramaz]

Zincs on a iron (since some decades this is to be named steel) keel have a very local effect. That results in you have to have a number of zincs. Not really fun, changes the essential keel profile.

Steel has to be covered immediately when sanded, oxidation starts direct. It is much more sensiteve than usually recognized.
Use something protective, either eg epoxy (probably with solution is best in that case) or something that works as a zinc (paint with zinc). Best is of course to hot zinc the complete keel, but that requires a lot of work, and expense (that is however what is used in car manufacturing today - works very well).

I have had a number of boats with steel keel. No real problems with the keel, even if some have required sanding down, and immediate painting. After that, not problems.

/J