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  1. #11
    Join Date
    Jan 2004
    Location
    Bricks & mortar: Italy. Boat: Aegean
    Posts
    10,430

    Default Re: cleaning copper coat with acid?

    As Richard suggested, you first need to know what strength of HCL you're starting with. HCl sold in supermarkets (often in red bottles or with red labels) is usually in the range of around 7 to 15% concentrated. This is certainly strong enough to clean calcareous growth from propellers, although it may require repeated treatment. HCl sold for swimming pool treatment may be 33%. In any case, the concentration should be clear from the container.

    Note that in normal conditions HCl cannot exist at greater than 38% concentration, so pool acid is very strong (and tells you as much by its noxious fumes, which are particularly hazardous to respiratory tract tissues).
    Last edited by macd; 09-05-19 at 08:32.
    All epigrams are false

  2. #12
    Join Date
    Dec 2003
    Posts
    1,609

    Default Re: cleaning copper coat with acid?

    My post was not so much about efficacy of removing the tube worms - but whether it might be better at reactivating the copper coat. I usually abrade them off, leaving nice copper colour, but I now wonder whether that is not the best way to keep the copper active?

    This year I'm going to try mixing up a vicious mixture of HCL, citric acid powder, oxalic acid crystals, and wall paper paste and plastering it over the copper coat, and see what happens. Hopefully it might take off all the tube works and also have some nice chemical reaction that keeps them away..
    Last edited by Ric; 13-05-19 at 19:36.
    I'd miss my compost heap

  3. #13
    Join Date
    Jan 2004
    Location
    Med
    Posts
    5,864

    Default Re: cleaning copper coat with acid?

    Quote Originally Posted by geem View Post
    We put together a low pressure hookah for cleaning the bottom of the boat. Since we are 7’2” draft cleaning the keel with a snorkel is a real chore.
    The whole system only runs at approx 17psi compared to 145psi on regular dive gear. We have an aquarium compressor, 100ft of air breathing hose and a special low pressure regulator. The compressor plugs in to the boat 12v or 24v system and away you go. Uses very little power although the motor is supposed to be 120w it doesn't seem to use any thing like that much power. It works really well and takes up little space compared to dive tanks etc. All the bits came off Ebay.
    We had a hookup for some years now (10) although we brought our as a kit , it's paid for it self ten time over and more .
    Warning forumite dyslexia near by
    www.bluewatersailorcroatia.webs.com

  4. #14
    Join Date
    Dec 2012
    Location
    Gone cruising
    Posts
    2,257

    Default Re: cleaning copper coat with acid?

    Quote Originally Posted by Ric View Post
    My post was not so much about efficacy of removing the tube worms - but whether it might be better at reactivating the copper coat. I usually abrade them off, leaving nice copper colour, but I now wonder whether that is not the best way to keep the copper active?

    This year I'm going to try mixing up a vicious mixture of HCL, citric acid powder, oxalic acid crystals, and wall paper paste and plastering it over the copper coat, and see what happens. Hopefully it might take off all the tube works and also have some nice chemical reaction that keeps them away..
    The acid will destroy the tube worm shells just fine, they're made of calcium, so it's much like descaling your kettle, where 15-20% hydrochloric acid does a very fast job (just did that the other day).

    I'm no chemist, so I might get the details wrong here and my understanding is incomplete, but I think the basics are like this: Coppercoat is copper particles glued to the hull with resin, then sanded so they stick out. When it activates in the water and turns green, it turns into a copper oxide, which is the actual anti-fouling agent. Copper oxides dissolve in hydrochloric acid!

    So by applying hydrochloric acid to the hull, you are disabling the Coppercoat. This may even work for a bit, as often fresh copper particles are exposed when the old are washed away, but eventually you will have to sand it down to expose more as there will only resin be left on the surface. So the acid treatment is quite counterproductive, at least with hydrochloric acid - other acids (citric? acetic?) may be able to remove the calcium remains without dissolving the copper oxides.

    We usually scrape in the water and the hard plastic edge of a €1.50 scrubbing brush knocks any tube worm nests off pretty well, without damaging the Coppercoat like a metal scraper would. Something like that should work pretty well out of the water too.

  5. #15
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    21,689

    Default Re: cleaning copper coat with acid?

    I agree wholeheartedly with Yngmar. Copper is not much of an antifouling medium, Coppercoat turns green after a period of immersion, I believe due to the formation of a copper oxy-chloride compound. It is this that is the antifouling agent. Acid will remove this and the whole process must then start again. Naturally, this consumes the copper.

    We winter ashore and by spring time the tube worm shell can be brushed off. Even in the water a stiff brush will deal with most of it.
    Last edited by vyv_cox; 16-05-19 at 11:42.
    Answers to some technical queries at new website http://coxeng.co.uk

  6. #16
    Join Date
    Apr 2013
    Posts
    6,478

    Default Re: cleaning copper coat with acid?

    Quote Originally Posted by Yngmar View Post
    The acid will destroy the tube worm shells just fine, they're made of calcium, so it's much like descaling your kettle, where 15-20% hydrochloric acid does a very fast job (just did that the other day).

    I'm no chemist, so I might get the details wrong here and my understanding is incomplete, but I think the basics are like this: Coppercoat is copper particles glued to the hull with resin, then sanded so they stick out. When it activates in the water and turns green, it turns into a copper oxide, which is the actual anti-fouling agent. Copper oxides dissolve in hydrochloric acid!

    So by applying hydrochloric acid to the hull, you are disabling the Coppercoat. This may even work for a bit, as often fresh copper particles are exposed when the old are washed away, but eventually you will have to sand it down to expose more as there will only resin be left on the surface. So the acid treatment is quite counterproductive, at least with hydrochloric acid - other acids (citric? acetic?) may be able to remove the calcium remains without dissolving the copper oxides.

    We usually scrape in the water and the hard plastic edge of a €1.50 scrubbing brush knocks any tube worm nests off pretty well, without damaging the Coppercoat like a metal scraper would. Something like that should work pretty well out of the water too.
    Whilst the acidic ‘strength’ of acetic or citric acids would be less than that of a mineral acid, the acetate and citrate ions complex metals such as calcium and thus help bring them into solution - that is why they can be effective descalers. But they also, in the same way, complex copper (and copper for chemical reasons forms very strong complexes) so they would tend to dissolve copper solids as well as the calcium carbonate of the tubeworm shells. Any acid washing would simply tend to dissolve away accessible and active copper at the surface.

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