How many coats of antifouling paint

[ritchyp]

I have hauled out my GRP Sail Boat for the Winter. I want to dry out the hull and change some skin fittings and generally go through everything. I noticed that she needs sanding back below the waterline as the existing surface is looking uneven, where the layers of antifoul have have eroded in some places more than others and previous owners have continued to paint over it.
I have decided to sand it back until it is a smooth and even surface. Then prime it with underwater primer and then apply the antifoul paint. She was severely fouled this time after 8 months in the water. Admittedly she was sat around for 6 weeks in June/July due to personal circumstances so that may not have helped. I thought perhaps a coat of hard racing and then a couple of coats of something softer and more like to self erode.

I don't have a lot of knowledge in this area but I try to do as much of the work myself as just the cost of berthing is difficult to manage. I know that that antifouling paint is toxic so I should wear a disposable suit and breathing mask when sanding. Which size grit paper should I start with also....?


Advice appreciated

 

[johnalison]

I don’t think that sanding will get you anywhere. Before having mine grit-blasted to get back to epoxy, for a few years I would feather the dodgy patches to smooth them off and put Primocon on them before re-feathering them to as smooth as possible. To do a larger area or the whole lot you may as well get going with a scraper and do it properly.

 

[wingcommander]

Get a tungsten blade scraper from screwfix the pull type is my preference, round off the corners and away you go .Much better than sanding , a lot easier to clean up after .

 

[Sandy]

How many coats of antifouling paint

To answer the title, as many as you feel fit.
To answer the body of the text having done this once, and never again.

Get a fully body covering, the best respiratory ppe you can find, goggles, decent chiropractor and be prepared to sacrifice 40 hours of your life.

Getting a good blaster in will give you a much better finish, they deal with clearing up and have the proper kit to protect themselves.

 

[Kwik Decision]

I know that that antifouling paint is toxic so I should wear a disposable suit and breathing mask when sanding. Which size grit paper should I start with also....?

Don't dry sand unless you have professional quality vacuum kit, which will capture 99.9% of the dust. It's fine you saying you'll wear a disposable coverall and mask, but what about the folk working on their boat next to yours? Oh, and antifouling dust blown by the wind will stain the decks of all the boats downwind of you, so be prepared for complaints / bills for cleaning them. As others have said, lots of hard work scraping, or get her professionally blasted. Or, if you don't race, and last 0.1 kt of boat speed isn't critical, slop another coat or two of antifouling on, and worry about it next year. I've been taking this last approach for at least 5 yrs now.

 

[Caer Urfa]

From the condition of the antifoul as you describe you have a few options depending how your finances are and how much you love your boat:

1) Best bet as said above get the hull sand blasted back to original gel coat, not cheap but once done and coated the best way, however you then also need to apply an osmosis protective paint (5 coats), then primer (1 x coat) then antifoul (2 x coats) application not cheap but your hull be be good for years
2) Yes you can sand off rough bits level but you are wasting money as new antifoul will just flake off and even be worse at the next lift out
3) No do not use Hard racing best self eroding, suggest use 'Jotun Vinyguard Silver grey 88' primer then suggest 'Jotun Nonestop antifoul' (PS I do not work for Jotun ) available from Jotun Antifouling | Boat Antifouling | Marine Antifouling

4) I Personally apply 2 coats of antifoul on top of the primer

Except for the sand blasting all the above painting can be done by yourself but applied in the right temperature

As said 'DO NOT' breath in antifoul dust wear good eye and mask protection and overalls

 

[rogerthebodger]

You could wet blast the old anti fouling off let it dry then paint 2 coats all over with and extra coat on all the leading edges.

This is what I do every 2 years without the wet blasting

Propper PPE of cause during blasting and anti-fouling. or as I do get someone else to paint it for you

 

[thinwater]

Re. Stripping, you can do a lot with a sander and may find that you can get it quite smooth without going all the way. Don't be afraid of coarse paper, either 60 grit or even 40 grit. Get a good RO sander, not a cheapy or a little palm sander. Bosch and Makita make good ones. If you really want to go all the way, the Bosch GET75-6N is hard to beat.

Obviously, a good vacuum kit for all DIY needs. Or get someone else to do it. Most sanders accept vacuum and get a HEPA filter for the vac.

If you are hauling every winter, one coat is all you need, with 2 coats in the high wear areas. Normally, if you paint the whole bottom starting at the bow (on a warm day), by the time you are done you can go and hit the bow, waterline, front of the keel, and front of the rudder again, so this adds little time. The more you put on, the more you will have to remove later. For multi-season, 2-3 coats is common.

 

[RunAgroundHard]

... where the layers of antifoul have have eroded in some places more than others and previous owners have continued to paint over it.
I have decided to sand it back until it is a smooth and even surface. ... I try to do as much of the work myself as just the cost of berthing is difficult to manage. ...


Advice appreciated

If you are looking to be productive and save money, then forget about your plan and do what the previous owners did.

I decided a long time ago not pay too much attention to my hull antifouling, because it was too much like hard work, or too expensive for others to do it and the speed gain for cruising was negligible compared to many other fine and easy things that can be done to improve speed. For the last 15 years I have used a scraper to remove any obvious flaking and flatten out the edges, followed by a wet scrub with Scotch-Bright pads. I then apply 2 coast of ablating / eroding anti foul paint over the old coats. I almost get three years out of my antifoul paint. Leading edges, forefoot get 3 or 4 coats depending what is left in the tin.

My recommendation, unless you are competing at the top of your club racing, don't bother doing anything beyond removing loose flakes as it is mostly pointless. Spend the time doing something more productive and less costly.

681794 | 3M Scotch-Brite Very Fine Abrasive Sheets, 224mm x 115mm | RS

International's advice for removing antifoul, but don't bother, it is pointless in the grand scheme of things How do I remove antifouling?

If you have a steel keel and it is rusting, that is different matter, you need to deal with that.

 

[Sandy]

My recommendation, unless you are competing at the top of your club racing, don't bother doing anything beyond removing loose flakes as it is mostly pointless. Spend the time doing something more productive and less costly.

Interesting, as everybody knows I've zero interest in racing.

Pre COVID had the boat professionally Coppercoated and on passage my average speed increased by a knot. That's 24 NM a day or an additional 100 NM in four and has greatly extended my cruising range.

Fuel consumption is down and she handles better.

 

[ChromeDome]

After having removed AF several times over the years, I, too, decided NEVER AGAIN. EVER!

It wasn't too bad, but I went the blasting route (dry ice) because I wanted to switch to thin film AF. Of course, it cost something, but it was well worth the price.

I applied the recommended primer followed by the AF, 2+2 layers according to the instructions. I have applied bi-annually ever since, but I may do it annually after moving to a new marina with an unknown fouling level.

 

[thinwater]

Interesting, as everybody knows I've zero interest in racing.

Pre COVID had the boat professionally Coppercoated and on passage my average speed increased by a knot. That's 24 NM a day or an additional 100 NM in four and has greatly extended my cruising range.

Fuel consumption is down and she handles better.

And she probably points better. That can be a surprisingly big thing. Just as a foul prop is terrible, dirty foils just make leeway. You think you are pointing, but you aren't.

 

[ANDY_W]

Some years ago I needed to remove all the antifouling which had many layers where bits had broken off and been overpainted without fairing off first. It was very rough. The boat is 31ft and fin keel.
I considered all methods from contractors of various types to hand sanding by yours truly. None appealed, due to cost or effort required. As part of the thought process I took a cross pein hammer ( round flat faced striker one side and wedge shaped striker the other ) and, using the wedge shaped striker, made a few taps on the antifouling in order to see just how well the paint adhered. To my surprise, the paint came off in small chunks and flakes right down to the gel coat. After 15 minutes I had managed to clear a couple of square feet with pretty much 90% success.
I organised a tarpaulin to catch the flakes and used the hammer as if I were chipping paint off steel but not so hard. It took about three four hour sessions working at an easy rate. I took off 20 kgs of paint. I then scrubbed the hull with a very abrasive pad and water which left a pretty smooth surface to prime and recoat.
Downsides are having to stand there, patiently chip, chip, chipping away without getting fed up, and the very occasional small dent in the gelcoat, not broken, just a mark.
The result was really worth the effort and I am sure the boat was a bit quicker without the drag from the old antifouling.

 

[Hoolie]

There was a previous thread on here where the poster related his suggestion to a neighbour dry sanding his antifoul that it was seriously hazardous and he should not be be doing it without proper protection. He was basically told to sod off.
About 6 months later the neighbour said he was having problems with his lungs and was consulting his doctor. Within 18 months he died of lung disease ...

So don't sand - scrape wet! We did it, but it only had to be done once now it's smooth.

Back to the OP question on our sailing boat we apply two coats of eroding AF with three in critical areas like bow and rudder and a strip of hard AF along the waterline.

 

[Momac]

I agree about wet sanding with regard to safety . I tried dry sanding and realised the hazard after about 5 seconds.

Last time I used mesh which was very successful (on eroding type antifoul). One piece of mesh did the whole of the antifouled hull. But to be fair the surface was fairly smooth to begin with. Anyhow the mesh worked very well and was easily washed when clogged by dunking in a bucket of water. Even so it was good exercise .

For most of the hull the mesh was on a sanding plate on a pole. Some parts were by hand.

Overall very little mess on me .

 

[DFL1010]

The only civilised tool for removing antifoul is a credit card

 

[ritchyp]

Thanks guys, lots of different ideas and things to consider.
I antifouled the boat in February this year. Sailing in August and September this year, I knew something was seriously wrong and suspected heavy fouling as my speed was down by 3 to 4 knots and on a foul spring tide heading back up into Southampton, i was barley making 1 knot at 2800 RPM and the sails up. I just had the boat hauled out in Poole and I had 40mm of mainly live mussels covering the majority of the hull below the water line. I was astounded but that is why the boat was so slow and handled so badly. I was on the river Itchen, it must have been a bumper year for mussels!! I wont be going back to that marina again!

Essentially what I am looking for is to not have this happen again. I want to rest assured that my antifouling will last a year and not turn into a mussel farm after 8 months

 

[penberth3]

There was a previous thread on here where the poster related his suggestion to a neighbour dry sanding his antifoul that it was seriously hazardous and he should not be be doing it without proper protection. He was basically told to sod off.
About 6 months later the neighbour said he was having problems with his lungs and was consulting his doctor. Within 18 months he died of lung disease ...

So don't sand - scrape wet! We did it, but it only had to be done once now it's smooth.

Back to the OP question on our sailing boat we apply two coats of eroding AF with three in critical areas like bow and rudder and a strip of hard AF along the waterline.

I remember someone on here had made himself ill with toxic dust. Not sure if that was the same one.

Apart from the process, a lot of people forget about (or ignore) proper collection and disposal of the dust and scrapings.

 

[William_H]

My advice re anti fouling paint may or may not be useful. My boat resides in relatively warm water with lots of sunshine and light reflected off the sandy bottom. Yes antifoul paint does build up and flake off in places to leave horrible steps. I think OP will find that soon after attempting any major removal he will be discouraged and just repaint and go sailing. Not necessarily a bad approach.
My approach after 40 seasons is a fairly light coat of a/f paint each winter. I am able to bring boat home. Albeit on a trailer which is a pain. I usually attempt to improve the build up of paint with a (wood) chisel as I find a pull scraper just does not break paint off. But only on really bad steps. I have never done a full scrape.
My main approach is in water scrubbing using at first a sponge then scotch bright then sand paper. Which starts after about 6 weeks in water after new paint and progresses to weekly by end of season such that paint is mostly removed by scrubbing. Yes I race every Sunday and yes fouling makes a huge difference to a small boat. A few friends have tried copper coat. But this has not been hugely endorsed around here. Certainly scrubbing in water is still needed.
Am I doing it the best way? I don't know but I do sometimes wonder about a professional paint removal. Oh well nearly time for first wipe over in water but waiting for weather to warm up a bit. (antipodes spring) ol'will

 

[PabloPicasso]

I used a pull scraper with a hose attachment to keep the dust down.

Wear gloves and a mask. Wetting area to be stripped throughly first seemed to soften the AF and make stripping easier. Easier being a relative term of course as it is anything but....

Keep it all wet to reduce dust


I did a a couple of square meters each visit, so took quite a few goes to strip my 26ft sailing boat.

Bloomin' hard graft but doable in bite size chunks, using the right tools and ppe, and keep the working area wetted.

Avoid breathing in the dust, or inflicting dust or residue on others.