limescale on hull

[duke]

Hi All,

my boat is out of the water for the winter.

I notice a number of places on the hull (fiberglass) and on the prop (bronze) have a deposit of limescale (or
what looks like limescale).
These occur near to skin fittings but mainly not on the skin fitting itself.
The skin fittings are connected on board by electrical wire cable and also to the engine block.
I have a suitable size anode fitted to the hull.
Can anyone advise what causes the limescale and is there any other way to remove it other than chipping/scraping?

One extra piece of information: the hull was treated approx. 12 years ago with CopperBot. I think this is ineffective now.Can I put ordinary antifouling over it ?

Thanks,


Duke.

 

[VicS]

You can get calcium carbonate deposited on and near to anodes simply from electrolysys of the sea water but it is only lkely to be significant if the anodes are working heavily.

What is more likely is that it is common sea mat ( Membranipora membranacea) or maybe hairy sea mat (Electra pilosa). If you look closely with a magnifiying glass you will see that the mat consists of small compartments, each houses a minute animal. When covered with water they extend feeding tentacles to trap particles of food.

See http://www.pznow.co.uk/marine/bryozoa.html

and http://www.divernet.com/biolog/0703bryoz.shtml

You can often see it on rocks and the fronds of seaweed

It is difficult to scrape off! Nudibranch (sea slugs) eat it though.

http://www.photographersdirect.com/buyers/stockphoto.asp?imageid=665802

 

[Rivers & creeks]

If it was only on the toilet outlet then it would be limescale. Male pee interacts with salt water to produce this limescale (using vinegar in the toilet removes it). Unless you are peeing into your sinks and cockpit drains then it has to be something else...


or... /forums/images/graemlins/wink.gif

 

[William_H]

Any acid from lemon juice to viegar to Oxalic acid or even dilute hydrochloric acid (as used to clean concrete off house bricks) should move the stain which is probably a lime of some sort either from chemical deposition or crustaceans. olewill

 

[pelicanpete]

I've used muriatic acid in the past. It's cheap, you can purchase by the gallon and is available in swimming pool supply stores as it's used to balance the pH in swimming pools.

 

[tcm]

I have the same thing.

I believe that altho the barnacles are repelled by oxides of copper over the rest of the hull, the earth bond of the metal parts doesn't alow the copper to oxidise, and hence the whitish "limescale" or even barnacle can attach and grow. in mioderate uk waters it seems like a sort of non-living whitish chalky growth, i think?

Removal of anysuch limescales is easy in the med, harder in the uk. Because you need to go to Castorama and buy some hydrochloric acid, which will foam and take it off in seconds. You can't buy the stuff in the uk anywhhere near as easily but in Casto it's about a quid a litre. A spray is good tho of course you should be upwind with eyes and hands very well protected when apply the stuff.

If the boat is in the water, then i scuba underneath with scraper and wet/dry sponge block to polish everything. But if out of the water HCL is the thing imho.

If no barnacles anywhere else on the hull except around those fitings - i reckon the copperbot is working fine. I mean, what else should it do? If just some slime i wd leave it as is. Quite normal for other boats to have limescaled type deposits all over which of course wd be much more of a pain. If the hull is covered and there are almost no barnacles - then it is merely good marketing from the paint people that forces boat owners to believe that removing old antifoul and replacing with some new actually improves things. It doesn't. It's like ripping up the tarmac on a driveway, and resurfacing IF the existing antifoul is doing it's job. It just needs a clean imho.

 

[duke]

Hi All,

many thanks for all the replies and advice given.

This site has never failed me yet!

Regards,

Duke. /forums/images/graemlins/grin.gif