Tannin staining of your hull can be frustrating but luckily it is easy to remove, if you use the right chemicals or product. Any job goes smoother when the right product is chosen over the wrong product. Sadly over the years I have watched number of boat owners destroy gelcoat or paint by using sandpaper or abrasives to try and remove tannin stains. This is not necessary and as a matter of fact no elbow grease is required at all.


While oxalic is dirt cheap and works extremely well for this task, I prefer to use a gelled acid for this task. The gel formulation is an attempt to keep the acid off the anti-fouling bottom paint and keep it on the staining, where it belongs.


Acids can eat the copper right out of the bottom paint if not used carefully. This could potentially make the one or two inches above the waterline basically useless at repelling growth if you cleaned your boat in-water then loaded it for cruising. If you do it out of the water, without a drip skirt you could ruin a lot more of the bottom paint.