Antifouling (yet again)

[Balbas]

Yet again because I'm sure its been asked a thousand times before, but I can't see anything in search that answers my specific question.

I've just arranged to buy a boat that has been sat on the hard for a few years. She's clean underneath but has some small patches of missing anti-foul. I have no idea when the last antifoul was applied. So should I:-

1) 'colour in' the patches with a layer of undercoat and a couple of layers of antifoul?
2) 'colour in' the patches with a layer of undercoat and then antifoul the whole hull?
3) abrade the whole hull and then re-do the whole lot?

To ask the question another way - I know what I should do... But what will I get away with doing?

Hull is GRP.

Unfortunately I don't have any pictures to hand.

And what needs done with the prop and shaft? Does that need antifoul as well?

In essence she's going in the water asap and will be coming out again in the Autumn, but I'm aware that the late summer is the growing season.

 

[Graham376]

Check the surveyor hasn't gone through any epoxy coat. If he has then re-coat, if not then I would spot antifoul the patches then a quick coat all over. Sort it properly next winter. Shaft is up to you but I would apply antifoul to prop.

 

[Bobc]

Just slap a couple of coats of new all over the bottom and go sailing.

 

[Balbas]

OK I'm liking the answers to far...

How well will antifoul stick to previously applied antifoul? It's not shiny, but even so should I key it, or just start slapping the new over the top?

 

[Bobc]

OK I'm liking the answers to far...

How well will antifoul stick to previously applied antifoul? It's not shiny, but even so should I key it, or just start slapping the new over the top?

Just slap it on, it'll stick fine. It's what most of the rest of us do (other than those who prefer to spend their time working on the boat rather than sailing it).

I find the small rollers splatter less and take-up less paint, but you can do the hull in about the same amount of time.

 

[Balbas]

Just slap it on, it'll stick fine. It's what most of the rest of us do (other than those who prefer to spend their time working on the boat rather than sailing it).

I find the small rollers splatter less and take-up less paint, but you can do the hull in about the same amount of time.

Ideal thanks.

Next question - I've never antifouled a boat before. How much am I going to need? Boat is 32ft LOA and a fin keeler.

 

[Bobc]

About 3 litres.

Get some thinners and thin it down at least 10%. Pour some into a roller tray and then put the lid straight back on the tin, and leave the tin in the shade, otherwise it'll be like painting glue on. At this tie of the year, you'll probably be ok with 1 coat all over and a second coat around the waterline and on the rudder blade. If you then have some left over, give the rest of the hull a second coat working downwards from the top (most fouling happens where sunlight can get to it).

Lot's of thinners remember. If the paint starts to feel gloopy on the roller, then add more thinners.

 

[Pasarell]

Antifouling works if you have enough on the surface of the hull. Thin it down and it might look pretty but you won't have enough there. It shouldn't be "gloopy" unless you leave it open in the hot sun for a long time. For a 32' boat about 2.5 - 3L per coat would be the right quantity. If you don't use that then keep painting until you do use it. As stated extra on the waterline, leading and trailing edges. Make sure you keep some to put on the patches where support pads were just before you launch.
I would pressure wash the whole hull underwater if it has been sitting out of the water for a couple of years, maybe even a light scrub with a nylon pad. Hopefully it will mean you don't have to do anything more serious next winter before antifouling again.
1 coat should be enough at this time as main growth period is May / June, not late summer. Growth might appear too be more later in the year because all the biocide has gone from the antifouling, probably as a result of too much thinner and rolling it out too much!

 

[Bobc]

3l per coat? You must like burning money!

I use 5l on my 50fter and that gets me 2 coats on most of it, and every year when it comes out it's still clean.

 

[Pasarell]

3l per coat? You must like burning money!

I use 5l on my 50fter and that gets me 2 coats on most of it, and every year when it comes out it's still clean.

What could I possibly know after a lifetime working with marine coatings and running my own boat much of that time?

 

[Bobc]

What could I possibly know after a lifetime working with marine coatings and running my own boat much of that time?

That TBT was the answer perhaps?

 

[langstonelayabout]

3l per coat? You must like burning money!

I use 5l on my 50fter and that gets me 2 coats on most of it, and every year when it comes out it's still clean.

It's still clean? I'd love to sail where you do!

 

[Pasarell]

That TBT was the answer perhaps?

Well, yes, but at a cost to the environment unfortunately. Arsenic works well too......

 

[Bobc]

It's still clean? I'd love to sail where you do!

After just over a year, with no scrubbing in between. Solent-based.

 

[Bobc]

Well, yes, but at a cost to the environment unfortunately. Arsenic works well too......

Yes, I remember the stuff in the glass jars with Arsenic in. Those were the days...

 

[Pasarell]

If you mean Hard Racing or Extra Strong Hard Racing, it was TBT. Arsenic disappeared many years before TBT!

 

[Fantasie 19]

Just slap a couple of coats of new all over the bottom and go sailing.

+1

 

[oldgit]

ebay can be worth look for inexpensive A/F.
Recently purchased 5L of blue Hempel £52.00 delivered.