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Waterline stains
OK, the boat is out of the water and you've washed the topsides down a thousand times. But a grimy band along the waterline persists. None of the conventional boat cleaners will shift it, nor indeed the domestic ones you've brought from home. It's depressing.
A primary rule of warfare is that you should 'first know your enemy'. In this instance, it goes by the name of algae, a surprising adaptable life-form that took up residence in the semi-porous gelcoat while the boat was afloat. The word ‘algae’ (the singular is alga, incidentally) covers a large group of diverse aquatic organisms, ranging from the kelp you’ll find on the beach to those tiny unicellular pests that turn swimming pool water green. The colour green is significant. Although not all algae belong to the vegetable kingdom, most are photoautotrophic. This means that they rely on photosynthesis for their food supply and therefore contain chlorophyll. That stain above your waterline, started off green but is now a nicotine brown because the algae are dead.
What you should do
It’s time to reach for some dedicated stain remover. These are usually gels or liquids, but at least one brand comes as a powder. Look for one that contains phosphoric or oxalic acid which will bleach away both algal and exhaust stains without damaging the gelcoat. You may hear that the smart thing to do is to lay your hands on some oxalic acid crystals and make up your own cleaning solution, but be careful. Oxalic acid is the stuff that makes rhubarb leaves poisonous. If inhaled or ingested, it can cause ulceration to your airways and gastro-intestinal tract – in serious cases enough to cause death.
(Please note that if anyone should be unlucky or foolish enough to take a swig of these substances, don’t induce vomiting. It will do just as much damage on the way out as it did on the way in. Try and make the casualty drink lots of water and seek medical assistance immediately.)
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Related reading: Boat Cushion Care
Boat maintenance Waterline Stains - don't let a grimy band spoil the looks of your boat
