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Typical marine growths after only a few months. With copper protection you can forget about them.
Picture from www.eco-sea.com/.
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Mumble, groan, complain, bellyache. It's that time of the year again, isn't it? When your pride and joy has to come out of the water and you have to stripping off the anti-foul, scrubbing, cleaning and swearing that you'll never do it again.
Quite right too. As long as you can live with the principle that the best economy is to buy the best - and you can live with spending money now to save a fortune later. So sit down, and think about copper bottoms. Not cheap certainly, but the only sure way of protecting your hull permanently with pretty well no maintenance. And if you think of the alternative of scrubbing and re-painting every year (and adding up the cost), it makes cheap seem actually expensive.
Even in Nelson's time they knew about copper - the Royal Navy first used copper sheets nailed to the hull of the frigate Alarm in 1761. But they had to keep reapplying them - the iron nails they used caused accelerated corrosion of the surrounding copper plates. It was twenty years before some bright spark came up with the idea of using copper nails!
Why copper? Because of all the substances you can immerse in water, its the one that resists marine growths probably better than any other - without toxic side effects or causing organic distress. In fresh water it resists algae and weeds, in salt water it resists micro-organisms, marine borers and molluscs, and in both it is immune to the degradation suffered by other materials - osmosis in GRP, rust in iron and steel or rot in wood.
Actually in this Twenty-First Century of ours, it's not strictly copper. The first choice for hull protection is a superior alloy that is 90% copper and 10% nickel - "CuNi" to the initiated, or more accurately CuNi10Fe1Mn. This stuff is state of the art too. Because although copper was known and used for centuries, it was only in the late 80's and 90's that really effective measures were developed to be virtually maintenance free.
OK, you're not going to get away without doing one more scrub. There's gunk on your hull anyway, so you might as well get it off now. Just make sure you get it off effectively. A few weeks ago we looked at coping with osmosis and stripping GRP surfaces down to the gelcoat with a stripper or a gel planer (Time To End That Blistering Performance). Since this is your last scrub, you might like to look at alternatives, such as the Farrow System (http://www.farrowsystem.com/) - which low-pressure scrubs with a combination of air, heated water and fine grain, environmental-friendly sand.
Once down to the bare hull, there are two options you can take to achieve copper protection: particulate coating or foil sheathing. Both provide excellent corrosion and biofouling resistance in sea water, though of the two the sheathing method seems to be the longer lasting - and we are talking twenty years plus!
So what's the difference? It's really in the thickness of the copper. You see, as you're already aware, biochemical action is taking place against your submerged hull all the time. And far from being inert and passive, the copper or CuNi layer forms a very thin oxide skin that resists micro-organisms in an ecologically benign manner.
If you're moored for long periods, you might notice a kind of slime that forms over the finish. Yes, it's organic, but it can't attach properly, so giving it a wipe or even water action against the hull under way will easily wash it off. The chemical interaction of course, does wear away the CuNi layer in microscopic amounts all the time, which is why the sheathing method lasts longer. (And that's sheathing not cladding - which is the expensive business of bonding sheets up to quarter of an inch thick all over the underwater hull.)
So coating versus sheathing - because it's a layer of metal foil, sheathing is inevitably thicker - up to six thou. But of course, you need skill to put it on - even the easiest requires some tricky work with double-sided tape, then applying filler in the corners and crevices. The particulate treatment is much easier to apply - the copper is suspended in an epoxy coating you can just slap on like paint - but being a liquid layer, it's obviously much thinner.
By the way, you're not finished with scrubbing if you choose the coating route. You still have to sand the hull down to expose the copper particles to water in order to work. And you'll still probably need a top coat. But after that you can relax. You shouldn't need to do it again for at least ten years.
Of course choosing a copper bottom is a major step, so you'll want to look at all the options.
Start with the Copper Development Association at www.copperdev.co.uk/
Then check out:
www.eco-sea.com/
www.wessex-resins.com/
www.permanent-coatings.com/
www.coppercoat.com/
www.seamarknunn.co.uk/
Happy relaxing!
