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Old 01-12-2010, 11:22   #1
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Why Not Additional Coats of Antifouling Paint ?

I'm on the hard and am going to paint the hull. I have read all of the directions, prepared the hull as directed and noticed that on the Sea Hawk 44 it says use at least two coats. The boat yard I am in has prices for two coats. It looks like all of the boats only get two coats.
I always read something like this and wonder, why not 3, or 4. Won't it last longer and I can stay in the water without having to be hauled out in a year or so again? Given that a gallon here in Grenada costs $285US, why not more than 2 coats? Thanks Dave
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Old 01-12-2010, 11:31   #2
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Too-thick ablative paint will chip off. Too-thick modified hard epoxy will not properly leach it's toxic contents but rather leave it deep in the coating.
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Old 01-12-2010, 11:33   #3
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Assuming that are using an ablative antifouling paint, then there is no reason not to put on more than 2 coats. Many people will use different colours so that you can assess the amount that has 'ablated off' and correspondingly, the amount that is left.

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Old 01-12-2010, 12:11   #4
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Assuming that are using an ablative antifouling paint, then there is no reason not to put on more than 2 coats. Many people will use different colours so that you can assess the amount that has 'ablated off' and correspondingly, the amount that is left.
Brad
Quite so. The longevity of an antifouling paint relates directly to the thickness that the paint was applied.

The use of a wet film thickness gauge is an easy way to ensure the proper wet film thickness of the paint is being achieved. During the painting process, the gauge is placed directly into the paint then removed; the paint remaining on highest number tooth represents the wet film thickness in mils or microns.
Where 1 mil = 0.001 inches, or 25.1μm or micron

Pettit recommends that Trinidad SR be applied in at least 2 coats (3 preferred), each to a Dry Film Thickness of 2 mils (3 mils Wet).
Here ➥ http://www.pettitpaint.com/fileshare...ds/1167706.pdf

It is advisable to apply additional antifouling to the high wear (polishing) areas such as the chine’s, waterline, rudder etc to reduce the depletion of the thickness of the paint system. High water turbulence in these areas tends to wear the antifouling faster.
Check that the dry film thickness (DFT) of the antifouling in these areas is greater than that on the body of the hull.

A "signal" or "flag" coat is the first coat of paint applied to a surface that is a different color from the consecutive coats of paint. As the outer layers of paint slowly wear away, the signal/flag coat will be exposed. Once the signal/ flag coat is visible, it means the service life of the paint system is ending and fresh coats of paint will be needed. The use of a signal/flag coat is a common practice for both primer and antifouling paint systems.
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Old 01-12-2010, 12:30   #5
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I tend to apply two coats overall then when thats dried I apply a third coat at the waterline to 1ft below and leading edge area's of the bow, keel and rudder.... my logic being that these are the area's recieving the heaviest 'wear'...
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Old 01-12-2010, 12:43   #6
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I need to repaint our bottom, and yeah, the areas that have the most drag tend to need paint the most.
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Old 01-12-2010, 13:58   #7
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Thanks for your comments. Off to buy another gal.
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Old 01-12-2010, 14:12   #8
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Thanks for your comments. Off to buy another gal.
Gal? Do they come with bikinis?
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Old 01-12-2010, 15:10   #9
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Do you store the boat out of the water in the winter? Might not want too much
Are you heading for a multi year round the world cruise? Might want even more!
Are you heading to a fancy marina in California? (cuz they frown on TBT)
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Old 01-12-2010, 15:16   #10
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Great post everyone. I learned something today. Thanks all.
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Old 01-12-2010, 15:30   #11
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When we did our refit, we put 4 coats and 6 coats on the subject areas.
The first two were contrasting color, and after 3 years out, the "reveal" coat has become predominant - and some places, we're down to bare.

We rolled it on, not very scientifically in terms of depth, but it's served us very well. However, being ablative, it's very soft. If you have the time available to do so, I'd recommend letting each coat dry pretty well (minimum hard tacky) before putting on another, and then letting it all dry very thoroughly before putting it in the straps.

As thick as ours was, the straps weren't perfectly aligned, and pulled some of the paint away. The yard gave us a free haul-and-launch to remediate that, with our doing the paint, and were very careful about hanging it the second time - with no problems.

Virtually everyone we met and told of what we'd done couldn't believe we did that, thinking it useless. However, our reveal coat is actually doing a better job than the top coat, where it's come through (or the other's gone, more properly), so I still think it's a great idea.

However, as we're about to do a bottom job next spring, this time the yard'$, and hope to be in Cartagena where we'll do some very substantial refitting by 2 years or less afterward, we'll not put that much on, preferring to wait for the availability of TBT paints.

L8R

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Old 01-12-2010, 15:33   #12
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The only down side to "more is better", is that you will eventually create a build up of paint. Even ablatives leave behind a certain amount of material that will create extra thickness, weight, and drag. After a while,it will take a lot of work to remove the build up. All you have to do is look at the bottoms of some older boats in the yard.
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Old 01-12-2010, 16:00   #13
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Quote:
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The only down side to "more is better", is that you will eventually create a build up of paint. Even ablatives leave behind a certain amount of material that will create extra thickness, weight, and drag. After a while,it will take a lot of work to remove the build up. All you have to do is look at the bottoms of some older boats in the yard.
80 grit on a grinder goes a long way toward remediation :{))

OTOH, hard paint can add hundreds of pounds, and be a real bear to remove...

L8R

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Old 01-12-2010, 16:29   #14
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i always use 2 full coats and 2 extra on leading edges and waterline--when i only used 3, they were scraped off too soon...4 on leaders and water line makes it 5 yrs. tbt is great-- kali frowns on cow farts--dont worry--just paint it. then sail it. no one will ask what is on your bottom.
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Old 02-12-2010, 00:46   #15
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For Seahawk Islands 44(plus) users: after finishing the anti-fouling, let it dry for 5-7 days before launching. Doing so will make it last longer (3 years with 2 coats for us)

ciao!
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