"Dirt" on GRP hull - what is it?

Koeketiene

Koeketiene

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\"Dirt\" on GRP hull - what is it?

Amidships - just above the waterline Guapa sports a "girdle of dirt".

I have no idea what it is or what causes it.
Also, why is it much more pronounced on the starboard side (pictured) and is there very little on the port side?
Why just amidships, and not all the way along the hull?

This "thing" has been there for a while - this summer the wife attacked it with washing up liquid. For a while it seemed to have done the trick - now it's back with a vengeance.

What is it, and what can I do about it?

All advice (short of selling the boat) much appreciated.

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Re: \"Dirt\" on GRP hull - what is it?

That looks like oil, but maybe the photo is a bit dark. I see your boat on the Orwell regularly, but haven't heard of any oil spills recently. And why only in one area? Has your dinghy abraded that area? Not much help really, sorry. Nice boat though!
 
Re: \"Dirt\" on GRP hull - what is it?

I don't know what it was first time - oil from a passing ship?

Perhaps cleaning it off removed any vestiges of polish so that anything then clung even harder. or the unseen remainder created a "matt" area for things to stick to. A good clean with something more effective than washing up liquid (Starbright or Y10) and then a good polish would be my first approach - difficult in the water admittedly.
 
Re: \"Dirt\" on GRP hull - what is it?

probably just a combination of the fact that the boat will tend to lay one way in adverse weather which has a normal prevailing direction, the midships is often the widest area, either getting caught first with [--word removed--] water, or listing to put that side into [--word removed--] water. The fact that it cleans off would suggest all is fine. Try a good coat of polish on the are next time you clean it The tide will also influence the way the boat lies, combinations of high tides and stronger winds can bring all sorts of crap from the surrounding areas.
 
Re: \"Dirt\" on GRP hull - what is it?

Agree generally with Moodysabre ..... use something more than washing up liquid .. I use Cillit bang Lime and Rust Remover - I know you cannot get same in UK - shame as it really works well. It cleans up hull a treat.

What oftens make a hull attract localised dirt is abraded areas .. maybe you've had fenders in those areas at some time that were a bit dirty - have scarred the grp enough to create tiny scratches that dirt loves and clings to ... maybe you've been alongside a dock or wharf that hasn't been too kind .. maybe the polish you applied has worm away in those areas ...

Once cleaned - and good Bathroom / Toilet Lime and Rust Remover is a good bet - but not a scourer type cleaner ... you have to give a good waxing ... to seal the surface and have a slippery finish that dirt doesn't cling to ....
 
Re: \"Dirt\" on GRP hull - what is it?

I've had this on my boat a few years ago, the boat spends its time on a swinging mooring, and it had that sort of thick marking on the hull just above the waterline, it came off with some y10,.

i noticed that the same thing happened again when i was away from the boat for some time, it was basically when the boat rocked on its mooring it was particles of weed and slime which normally has some antifouling to contend with, just had some gelcoat to get hold of and it just started to build up, it looks as if your amidships muck has got some silt or mud included in the mixture...

you might have to use some y10 or equivalent to get rid of the residue which might not have been cleaned off totally with washing up liquid.. which enabled the muck to get a reasonable hold again...
 
Re: \"Dirt\" on GRP hull - what is it?

i notice you have a black stripe under the muck, is it a boot topping or a painted stripe or tape, it could be adding to the problem.

i had to repaint mine with a marine boot top paint (blakes waterline) as it was painted with an house exterior paint.


i would try cleaning it with a better cleaner than the washing up liquid, re wax and see how it is next year, ( or this year if you are planning on staying in ) before you decide to repaint ..
 
Re: \"Dirt\" on GRP hull - what is it?

It looks to me very much like slime/weed fouling in the 'splash' zone above the normal waterline that gets a hold and bakes on in the sun. It is a bit self perpetuating as it forms a layer that is easier for the next batch to stick too which then forms a bigger layer...

Solutions are a) a marina berth, less splash b) raise the waterline well above the static line with boot top or antifoul but not ordinary paint. c) clean off occasionally during the season as close up you will see little patches starting to form which if left will quickly develop.

When we were on a swinging mooring the antifoul went to the static waterline and boot top went up to 6" above that. Nowadays (different boat too) we are in a marina berth and have antifoul (white) right up to the lower style stripes and well above the static line, it was originally lower when we bought the boat but was raised to prevent your problem which it has done.
 
Re: \"Dirt\" on GRP hull - what is it?

Calling all chemists ?
Using paint remover (which breaks down polyurethane paints)on polyester gelcoat- I wonder if the two materials are too close chemically ?
Bleach will kill any organic growths,oxalic acid may remove yellowing,adding a smart boottop stripe was the traditional way to deal with discoloration along the waterline without the need to 'attack' the gelcoat.
 
Re: \"Dirt\" on GRP hull - what is it?

I think I'm with Blueboatman here. Most paint removers are based on methylene chloride and that is bad news for GRP / polyester.
I haven't got any brush cleaner to look at but I expect they contain some methylene chloride too. Paint removers for GRP are much less effective than methylene chloride based removers but safe for the boat.
I would be very cautious about using any such products on my topsides
 
Re: \"Dirt\" on GRP hull - what is it?

Try using a spray-on product called Elbow Grease. If you pay more than £1 for it you're being ripped off.
 
Re: \"Dirt\" on GRP hull - what is it?

I'm with SBC and Colvic987.
Once the surface has any abrasion, anything can get a grip. Polish down with the finest grade of polish that removes it. See info on my web site
Once you clean it off get some good quality PTFE or Carnauba wax on to help slick off new deposits. Alternatively use a synthetic glaze product. Don't waste time with cheapo car polish - it just won't last.
There's loads more info on my web site www.BoatSheen.com
 
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