Antifouling

[tonycooper]

New to bigger boating, we bought a 23 foot hunter duette late last season and have had had a terrific time in her!
We took her out the water a while ago and now I'm looking to do the antifouling.
After a jet wash it appears the very bottom is extremely patchy with traces of past antiouling present (about 4 layers in different areas).
My question is - shall I just smooth this out as much as poss then re-antifoul or use some kind of stripper (wahay) and start afresh.
Pros/Cons of each would be helpful.
Any comments more than welcome.

Cheers

 

[Swagman]

If it were a race boat and you wished to get every .001 knot out of her - getting all the old stuff off and one smooth new coat would be appropriate.
If you use it to cruise - you'll need to make up your own mind. It's not a nice job getting it off - so make sure the time / effort is worth the satisfaction.

 

[Colvic Watson]

Sounds like it's time for a sanding! I think this is necessary every few years as even the self eroding stuff builds up. A patchy hull doesn't help the smooth water flow you want. The antifouling stripper just means more expense and more chemicals. A darn good sanding taking away the patches (hire a decent sander for a day) will give a much better finish and a great key for the new coat. I suspect that sanding is probably no more work in the long run.

 

[boatmike]

You should never sand antifouling. The dust is highly toxic and can be absorbed through the skin as well as breathing it in. You just don't want to know what it can do to you! Either scrape it off or use a solvent and wash it off. If it is Micron or similar a high pressure jet wash takes it off if you persevere. As swagman says though effectively anything that is not loose of overly lumpy wont matter too much if you coat over it. Depends how bad it is

 

[Sans Bateau]

If you must sand, dont dry sand!

There are some pretty noxious chemicals in antifouling, just waiting for you to start breathing them in!

Best results can be acheived with a Sandvick scrapper, its a drag type scrapper, get one from you chandlers. get a GOOD resperator from B&Q.

 

[robbieg]

If you don't fancy the health risks of sanding/scraping could think about slurrey blasting -about £14-15 a foot from memory of a recent PBO article on the subject. Obviously depends on your budget but avoids a long period crouched down under the boat with potentially toxic material coming down on your head.....

 

[nmelton]

IMHO if you are not racing then, as Swagman says, it's probably not worth going down the route of scraping everything off at this stage - unless you are a masochist! The time to think about it is when the old stuff does not adhere and starts to flake off when you try to apply new antefoul with a roller or brush. This happened to me after about 7 yrs of applying Micron. /forums/images/graemlins/ooo.gif

 

[ashanta]

You must not sand AF! If you want to remove the old AF use a suitable scraper. You can buy them or some people fabricate their own from chisels. It's a dirty job and time consuming but if your keeping the boat and you want to get the best out of her then it's worth. Old AF starts to peel when it's thick with layers. You may find it comes off quite easily.

Regards.

Peter.

 

[simonfraser]

you had a teriffic time with a patchy bottom, why change ?

 

[Cobra25]

Use the scraper we used connects to the vacuum-cleaner, no mess no sweat. Simple! PM for details.

 

[William_H]

The excess A/F will eventually have to come off either now or in the future. A smooth start now will make it easier in future to take of the most recent layers. Having said that the practicality is if you have a go at getting it off and run out of time, patience or will then leave it till next year. I have used caustic soda granules in water to soften old paint. It is cheap but evil stuff. Watch it disolve your paint brush bristles (use nylon or foam) and don't get it on your skin or eyes. it quickly burns so have lots of water available. When soft after a few minutes try scraping off the old paint then apply more caustic. This is the very worst aspect of sailing. good luck will

 

[Ships_Cat]

Despite the advice to the contrary, there is nothing wrong with sanding antifouling. What the advice should be is do not breath the dust in and control the dust by wet sanding. Pretty easily achieved, especially if like me you get the boatyard to do it /forums/images/graemlins/smile.gif.

Whether you sand it or use a stripper (not necessary at all with soft self eroding as it sands easily) you have to make sure the boat is somewhere you are allowed to do such work.

If it is self eroding antifoul it should be sanded back before every reapplication (our boat gets lifted every second year for antifouling with the remaining antifoul thickness sanded down to very thin before application of the new) - this may expose residue of previous coats but that is no problem.

If hard antifouling is used then on a cruising boat it is often allowed to build until flaking and coating breakdown starts. Sand or strip.

Some antifoulings do not work well over others, the most obvious being applying hard antifouling over self eroding. Also if any coating under the antifouling requires patching then there may be a maximum time within which the antifouling must be applied over it by. Check with the paint supplier if unsure.

There is alot of good advice on http://www.yachtpaint.com (International Paints) - look for the Boat Painter's Guide.

John

 

[BrendanS]

Simple basic good advice. Worries me what is posted here sometimes

 

[ANDY_W]

If the build up of old antifouling isn't too bad, you might want to try using cellulose thinners. If you soak a cloth with it and rub it over the old antifouling, it softens it and spreads it out. Leave it to dry and you then have a surface ready for recoating.

Needless to say, but I'll say it anyway, a good pair of gloves and no naked flames while using the thinners would be good idea!

 

[Ships_Cat]

I see that the International sites have started posting the 2005 version of their Boat Painting Guide and that seems to have virtually nothing in it regarding painting over existing paintwork.

The old version is still available at http://www.yachtpaint.com/New_zealand/FRAMESET.HTM but will I assume quickly disappear. In which case this is what it says for antifouling

The condition of any existing coating is important in order to provide a sound surface for the new antifouling.

If the antifouling is of known compatibility (see the Compatibility Chart) check the condition of the existing painted surface. Remove any loose, flaking areas with a scraper. Rinse with fresh water and allow to dry before applying the new antifouling direct.
If the previous coating is in poor condition it is advisable to remove it by wet sanding. Remember, dry sanding is dangerous due to the toxic dust which it forms. Then follow the preparation and priming for bare substrates.

If the old antifouling is of unknown origin or you are concerned about compatibility, we advise you to remove the antifouling or contact the International Helpline.
If the boat is new, or touch up priming is needed on the bare substrate, follow the advice in preparation and priming for bare substrates for wood, steel, glass fibre or aluminium as appropriate.

While it only refers to removal by wet sanding, International (and others) do produce a stripper.

Hope that is of some help.

John

 

[ashanta]

Why should you be worried Brendon? See Cottillians post on Scuttlebutt. he sanded his AF and went into the hulls fibres!
The information passed by some of us is for genuine concern and to be helpful. I do not want feel that I am being judged by others. When people talk about sanding, in the main I believe or suspect they are referring to using power tools and my advice to anyone would be to avoid this. Not withstanding the H&S risks involved for others who may be working in close proximity.
Regards.

Peter.

 

[tonycooper]

Thanks everyone for the advice, plenty to think about!