The uneven bottom finish that inevitably results where successive years' coats are applied on top of each other will knock a significant fraction off the boat's speed, under sail or power. So it's worth getting as smooth a bottom finish as you reasonably can. You will get more enjoyment out of your boat under sail. And you will increase fuel economy under power.
There is also anecdotal evidence that racing boats, which normally have only a thin coat of antifoul, removed annually allowing the hull to dry properly during the winter lay-up, are less prone to the dreaded osmosis than cruising boats which may have several years' accumulation of paint, providing a thick coat that may trap moisture against the hull, preventing it from ever drying completely.
Most cruising boat owners won't want to take all the antifoul off every year, but it's worth tackling the job every few seasons, to keep the build-up under control. So what's the best way to get it off - scraping, sanding or stripping?
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| Look out for a scraper with tungsten carbide blades |
Using a scraper - the slightly more expensive tungsten carbide ones are most effective - is hard work. It must be done with care, to avoid damage to the underlying gel coat, but does a very thorough job. Chemical strippers save effort but are messy and only feasible if you have access to a hosepipe on the hardstanding, to rinse away the residue.
Some boatyards offer slurry spraying, a mild form of shot blasting, which should take off all the old antifoul without damaging the hull underneath. But this is relatively expensive.
So many people resort to the electric sander. But remember that antifoul is intrinsically toxic - that's how it works - and you must avoid inhaling or ingesting any of the dust. So use a sander with a suction device to trap the residue, and wear a face mask and goggles whichever method you use.
Old antifoul is harmful to the environment as well, so if scraping or stripping ideally you should spread a sheet of polythene under the area you are working on to catch any residue, and then dispose of it appropriately - not by washing it into the river!
If your boat is a few years old, some of the accumulated layers of antifoul may include substances now banned, like TBT, now known to cause havoc to marine ecology. This makes responsible disposal even more important.
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| It's worth spending time filling and fairing |
Once all the old antifoul is off, it's worth spending time filling and fairing before you start again with a new coat. Make the hull keel join as smooth as possible, and sort out any rust patches on the keel. Every little helps.
It's all hard work, which has to be done outdoors, during the worst of the winter weather, but the effort will seem well worth it once afloat, when your boat slips smoothly and speedily along.
Once you've done all the preparation, next comes the difficult decision: which type of antifoul to put on? We'll be looking at that in another article.
