Recurring Brown Hull

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bobgarrett

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Since visiting the Baltic some 6 years ago we get a brown stain around the waterline on our white GRP hull. We have it referred to as the Baltic brown.
Each winter it comes off easily with oxalic acid and then we have it cleaned, polished and waxed; only for it to return in a matter of weeks.
Washing it with a brush removes some but it gets worse as the season progresses.
We are in a swinging mooring and the boats around us are clean.
What can we do?
 
I used to get staining when we went to the Baltic. I don't think it was the Baltic so much as the Dutch waterways on our return. Either way, I used to just live with it and use an oxalic type of preparation (Yachticon) followed by wax. A friend of mine was told by the local GRP man that the staining/wax builds up after a while and you need to remove this crud with cellulose thinners before re-waxing to get back to square one. I haven't tried this myself but just pass it on as a suggestion.
 
I think the age of gelcoat may be a contributing factor. Perhaps the gelcoat becomes more porous .

On boats that I have owned, the yellow staining from impurities in the water is worse on the older hulls, particularly if they have been cut back too often.
 
My boat is in Baltic after having spent at least 20 years in UK waters.

I actually get less staining ... literally near zero fouling .... but yes I do get the brown at and for a few cms up from waterline. Toilet Cleaner or strong Oxalic gets rid of it.
 
I get the same stain in the Swan River (32S) Oxalic acid or similar acid does remove it but yes it comes back after a month or 2. I end up resorting to a spray bottle of cleaner applied while swimming around the hull. Snorkel gets me away from spray. My hull has been repainted with 2 pack polyurethane. I have not tried a wax which may discourage the stain. Must do that. ol'ewill
 
Different approach.

Apply a boot topping.

I used simple gloss yacht enamel, before antifouling so that the boot topping edge is under the antifoul. Use masking tape and get the levels correct so it looks right when afloat. Cleans with a wipe, but the staining is invisible anyway.

Antifoul02.jpg



Sub-at-mooring.jpg
 
Caraway said:
Different approach.

Apply a boot topping.

I used simple gloss yacht enamel, before antifouling so that the boot topping edge is under the antifoul. Use masking tape and get the levels correct so it looks right when afloat. Cleans with a wipe, but the staining is invisible anyway.

Antifoul02.jpg



Sub-at-mooring.jpg
Click to expand...

What a beautiful finish.

We have the same issue in Tasmania where it is the tannin in the water.

We too use Oxalic acid and it also returns, not nearly as bad, with time.

I too have wondered if with time (age) the gelcoat develops surface micro porosity which is exacerbated with the Oxalic acid, so the more you clean the quicker the stain returns.

We don't have an answer - just use more Oxalic, - as William says, spray bottle (from the dinghy) - or in our case, beach, dry out and spray bottle. The spray bottle works easily and quickly.

We don't polish nor use wax.

Jonathan
 
Poignard said:
I like the idea of using oxalic acid from a spray bottle. What ratio of acid crystals to water works best?
Click to expand...

Nothing precise, 50g/litre Is what we use,

Just spray on the stains and leave the liquid to do its work - which is a bit like magic.

Sorry - don't know if that is best - its just what works for us. Boatyards use the same product, but I don't know what ratio they use, but they add something to thicken the mix, wall paper paste and apply it with a soft brush then wash off later.

Its something you want to apply with care, goggles and rubber gloves etc if you are sloshing it around with a brush on a pole - a spray bottle still drips - continue to use the rubber gloves and if spraying above you - you will still need the goggles.

Jonathan
 
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Could be from the mooring chain. I had that trouble. You could try a temporary swap over for the summer to have a nylon 3 strand strop instead of chain over the deck. Or two strops.

Also I think Chi harbour is rather mucky and the chop washes it well above the water line.
 
I tried 100g / Litre, (4oz / Quart) ..... as advised online..

But it was not doing the job .... so I doubled it to 200g / Litre , (8oz / Quart) ... and added wallpaper paste so it would paint on and stay in place. Now it worked !!
 
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Brown/yellow staining can extend at least halfway up the topsides after continental travel. Boot-topping will be fine for the sort of soiling that happens on a mooring but doesn’t work for boats on passage.
 
Thanks all for your comments so far.
I don't think it is the age of the gelcoat - 10 years.
The stain reaches up as far as the waves, which as some have said can be a good 20cm or more as boats tend to speed through the moorings if late for the Chichester lock.
We had thought about a boot-top but it would have to go above some decorative strips so not look so nice.
I might try the suggestion of stripping the wax away in an area and rewaxing unless there are other ideas.
 
Neeves said:
We don't polish nor use wax.
Click to expand...

Polish, ideally followed by wax, will help to seal the surface and deter brown stains.

For many years, I've applied 2 coats of Meguiars polish followed by 2 coats of Meguiars wax, and that works well for 2 years until I do the whole lot again.
 
You can use the much cheaper method of removing brown crud , ifs Harpic limes scale removing toilet cleaner ( or any other brand so long as it’s limescale remover) apply with a dry soft cloth and let it do it’s magic then rinse off , it’s advantages are Cheap, easily sourced and no effort . You must rise it off properly as it is acidic
 
kieronriley said:
You can use the much cheaper method of removing brown crud , ifs Harpic limes scale removing toilet cleaner ( or any other brand so long as it’s limescale remover) apply with a dry soft cloth and let it do it’s magic then rinse off , it’s advantages are Cheap, easily sourced and no effort . You must rise it off properly as it is acidic
Click to expand...

That's basically hydrochloric acid, which isn't as effective as oxalic acid on brown stains. And anything branded is more expensive!
 
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