Make your own hull cleaner

If you've ever bought commercial hull cleaners, you'll be aware of just how expensive they can be - the last time we looked Y10 was about £7.50 for a 250g pot. Most of the proprietary cleaners have the same active ingredient, oxalic acid, which is also the active ingredient in many household cleaning products, teak brighteners and rust removers.

Oxalic acid dihydrate can be easily purchased, either from a good woodworkers supplier or online. We bought 1kg from an eBay seller in Ireland for £10. This is enough to make at least 10 litres of cleaner, so you can see it's well worth a little effort. 10 litres of Y10 would cost you about £180!

If your boat is on a galvanised trailer, don't use an oxalic acid based cleaner. It will react with the galvanised surface and ruin it.

We take no responsibility for damage to property or personal injury caused by following this guide.

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What you'll need

You will need: 75-100g of oxalic acid dihydrate; a packet of wallpaper paste; 950ml of clean hot (but not boiling) water, Rubber gloves, face-mask and eye protection; a large container to mix the solution and a clean water-tight container to store the finished cleaner.
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Weigh oxalic acid

Weigh out 75-100g of oxalic acid dihydrate, we recommend the full 100g. Place the hot water in a large container and add the acid. Stir well untill the acid is disolved. Now allow the solution to cool completely
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One the solution has cooled you need to add enough wallpaper paste to thicken the mixture. You dont want it too gloopy, just thick enough to cling to the hull of your boat. We used about 10 tablespoons of heavy-duty wallpaper paste. Stir the solution well, then allow it to stand for a couple of minutes. TIP: if you want to use the solution for teak deck brightening omit the wallpaper paste completely.
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Using a large funnel, carefully decant the solution into a clean bottle and LABEL THE BOTTLE CLEARLY.
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The fished article

The finished cleaner... A litre of this was enough to clean the whole of or Freeman 22. The cleaner was just brushed on, left for 20 minutes then hosed off. Please be aware of any environmental impact this may have and wear suitable protective clothing.