Removing old antifoul - how far to go?

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andrew-b

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Hi All,

Bought my first yacht last spring - a Colvic Sailor 29. It is booked for a week out of the water soon and I was looking for some advice on what to do with it.

During the survey last year the surveyor pointed out some bubbles underneath, but upon scraping some of them away it appeared that most of them are actually between paint layers or between paint and gelcoat. There is a very thick build up of antifoul, I guess many years worth!

So I guess my options are:
1) Scrape any bubbles off, scrape as much antifoul off as possible, fill any gelcoat holes, re-antifoul.
2) Scrape right back to the primer, sand all the primer off, fill and gelcoat holes, treat with gelshield (or similar), reprimer, antifoul.
3) As above, but with blasting because scraping is no fun.
4) Any others?

Trying to be pragmatic about things, this is a fairly inexpensive 30 year old boat (currently my project :) ) which I don't race (I have a laser for that). Are we talking about boat integrity/longevity here, or just that extra fraction of a knot?

Thanks!
Andrew
 
A fraction of a knot is all we are talking about here if that even !
If the bubbles are just within the paint layer, what are you worried about ?
Give them a scrape and overcoat them
 
The bubbles will probably be a chemical reaction to various types of anti-foul. Suggest that you remove ALL the old antifoul by the best means available and just make sure that the bubbles are not osmosis. Then re-antifoul.

Good luck
 
Pragmatically, all you need is for the new coat of antifouling to do its job. It won't if it flakes off. So as a minimum you need to remove any old loose paint.

How much you scrape/ sand off this time is up to you, but I doubt you'd get it all off and repainted in a week.

I'd also be wary of using anything more aggressive than a hand scraper to get the paint off, lest you damage the gel coat, and add further untimely work to be done.
 
I guess the other thing to factor in might be how frequently do you intend to have her out of the water which may influence which type of antifoul to use. I go for a hard racing AF, regularly dive to scrub off the undersides & only come out of the water every 2 or 3 years, e.g. If you intend to keep the boat for a long time, might be worth considering getting all the old AF off & coppercoating...
 
andrew-b said:
1) Scrape any bubbles off, scrape as much antifoul off as possible, fill any gelcoat holes, re-antifoul.
2) Scrape right back to the primer, sand all the primer off, fill and gelcoat holes, treat with gelshield (or similar), reprimer, antifoul.
Click to expand...

If you do uncover any gouges in the gelcoat, no point in repairing with more gelcoat: it's just a cosmetic finish with little strength and not waterproof. Best to fill with a proprietory epoxy filler, which will be stronger and adhere better. Colour won't match but who cares if underwater/under antifoul?

However, should any gelcoat bubbles betray osmosis, a rather more elaborate solution is required.
 
If you just want to get into the water this year, I would scrape off any loose antifouling and the tops of the blisters. Depending on the level of finish you want, either bung some primocon over the bare patches, or feather off the edges and do the same, then antifoul and enjoy your sailing.
 
andrew-b said:
Hi All,

Bought my first yacht last spring - a Colvic Sailor 29. It is booked for a week out of the water soon and I was looking for some advice on what to do with it.

Thanks!
Andrew
Click to expand...

With only a few days

scrub it clean

scrape off any loose antifouling

Apply a new coat, following the A/F manufacturers recommendations regarding application to existing.
​

When you have several months to spare consider scraping it back to bare gel coat ................ but then let common sense prevail and don't.

When you have shed loads of cash to spend consider getting it soda blasted back to bare gel coat then epoxied and coppercoated
 
And if twere me, I too would scrape off the loose, rub it all over a bit, tosh primocon on any bare patches and go sailing after a coat of a/f
 
Essentially the amount of effort you put into removing A/f will depend on your perseverence and time available. Do not be surprised or embarrassed if you don't do much at all it is a horrible job. So don't start at one place removing all a/f such that you end up doing one patch well and the rest not at all. try to do all over to a limited degree. Having said that it would be worth trying to clean out the biggest bubbles just to make sure they are only in the paint layers. You may also find that the a/f falls off really thick areas such that you get a dramatic step from a/f to none. These should be smoothed over as far as possible.
Being realistic next years lift out will be no different. Fortunately GRP hulls can cope with neglect and will not deteriorate too much. Sailing the boat is what it is all about good luck olewill
 
Thanks all for the helpful advice. I'm quite relieved to hear that the easy option is fine! :)

This will be my first antifouling experience. I've heard many opinions about it from "its easy I do it between tides" to "its a horrible job that seems to take forever"! I'll soon find out.
 
Applying an antifouling to a wet surface ie between tides, will inevitably give it a very poor bond to the surface and at some point it will be very likely to detach/flake off in some way.
Antifoulings by their very nature are quite surface absorbent so could take more than a few hours to dry especially this time of year in the UK.
However if someone is not concerned by a little flaking antifouling then there should be no issue.
 
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