Help my blacking is coming off!!

[Chevetter]

In February I had my narrow boat fully overplated (bottom and sides) by AndiCraft Fabrications. Part of the deal was that I would black the boat myself, something which I was quite pleased about at the time as it's always seemed a waste of money to me to pay someone else to do this job.

 

So anyway yesteday I was fitting the first of my new windows which required me to go round the side of the boat which I don't usually look at and I noticed that some little bits of blacking were flaking off around the water line. Closer inspection showed that a couple of pieces the size of saucers had come off. So I got out my dinghy and rowed round to take a closer look - basically all of the blacking down the entire of one side of the boat is coming off in big sheets leaving bare metal exposed to the water. There is only minimal surface rust at the moment but obviously I want to get it out and sorted before the rust takes hold.

 

So my questions are threefold:

 

1/ Why did this happen?

 

- Did I not prep. the metal properly when I blacked it?

- Is it perhaps caused by not alowing enough time for the blacking to dry?

- Is it perhaps because that side of the boat was in the shade and it was February so the bitumen didn't go off properly?

- Is it the blacking itself (I used Intertuf, which even says on the tin 'for new metal do X, Y and Z', which I did).

- Is it because of galvanic corrosion? I am a bit parandiod about this one as I have 240V plugged into the boat all the time, but I have a Victron Isolation Transformer which in theory should stop it happening. However the boat which is only 2ft away is also plugged in all the time and is blatantly not isolated properly.

 

2/ More importantly how do I stop it happening again?

 

- Is it a good idea to put primer or similar on the hull before I black it?

- Should I clean it down with panel wipe or something first?

- Should I leave a longer drying period between and after coats?

- Is the application of blacking something which is very temeprature critical?

 

3/ Galvanic corrosion:

 

- How can I do a thorough test to make sure that everything is tickety-boo? I stuck some wire connected to a DC voltmeter in the water either side of the boat yesterday and basically read nothing but I don't reckon this is a thorough test.

 

- I've heard about 'fishtail anodes' which go down the sides, but does anyone have any experience with these?

 

Sorry for the barrage of questions but I'm feeling lost, confused, fearful etc. right now!

 

Oh also, how desperate is it to get the boat out of the water, someone I know said 'ah it'll probably be ok 'til the spring' but this seems rediculous to me.

 

Thanks in advance.

Edited September 29, 2008 by Chevetter

[RobinJ]

In February I had my narrow boat fully overplated (bottom and sides) by AndiCraft Fabrications. Part of the deal was that I would black the boat myself, something which I was quite pleased about at the time as it's always seemed a waste of money to me to pay someone else to do this job.

 

So anyway yesteday I was fitting the first of my new windows which required me to go round the side of the boat which I don't usually look at and I noticed that some little bits of blacking were flaking off around the water line. Closer inspection showed that a couple of pieces the size of saucers had come off. So I got out my dinghy and rowed round to take a closer look - basically all of the blacking down the entire of one side of the boat is coming off in big sheets leaving bare metal exposed to the water. There is only minimal surface rust at the moment but obviously I want to get it out and sorted before the rust takes hold.

Suspect this may be a case of 'millscale', was the metal shiny with a slight blueish tinge when you blacked it?

When new steel is rolled it obtains a slight surface hardening which is shiny and more resistant to corrosion (for a short period).

The metal needs to be clean and a little rough for the blacking to stick.

Other possibilities are damp, temperaqture etc.

[Chevetter]

Suspect this may be a case of 'millscale', was the metal shiny with a slight blueish tinge when you blacked it?

When new steel is rolled it obtains a slight surface hardening which is shiny and more resistant to corrosion (for a short period).

The metal needs to be clean and a little rough for the blacking to stick.

Other possibilities are damp, temperaqture etc.

 

I don't recall a blueish tinge no. Furthermore there was a fella blacking a newbuild boat next to mine and he just slapped it straight on as I did.

 

But for arguement's sake lets say it was 'millscale' - what should I do now when the boat comes out of the water to ensure that the blacking does stick? Panel wipe and then rough it over with a wire brush/sand paper or something?

[alan_fincher]

Or could blacking of a type that was incompatible with what you have used have been left on, leading to a "disagreement" between the two ?

 

Strange it's only at the waterline, though...

[Gary Peacock]

Probably down to the preparation of the steel and the blacking not "keying" the only other reason that I know of was the use of Intertuf 16 blacking which seemed to do come off for reasons no one could explain.

[Tony Brooks]

I don't recall a blueish tinge no. Furthermore there was a fella blacking a newbuild boat next to mine and he just slapped it straight on as I did.

 

But for arguement's sake lets say it was 'millscale' - what should I do now when the boat comes out of the water to ensure that the blacking does stick? Panel wipe and then rough it over with a wire brush/sand paper or something?

 

 

Blakes Marine Coatings say that wire brushes polish the surface so the blacking may not stick and I doubt a wire brush will get rid of mill scale so if you think this is the cause then I suspect its a big angle grinder and a lot of course sanding sheets or disks.

 

If this blacking was made by the "major", "worldwide" marine coatings manufacturer I have heard a few whispers of it falling off. This may be nothing to do with the coating but its application though.

 

The traditional way of dealing with mill scale was to let the whole thing rust (the rust forces the mill scale off, clean it up and then coat it. Otherwise its sand blasting etc. or disks. I would keep an eye on things and next spring use a couple of heave duty ratchet straps from the offside handrail, under the boat and up onto pilling to tilt the boat so you can disk off and black the rusty areas. Some people have fixed long planks across the roof and dangled full gas cylinders from the end to cant the boat.

[Chevetter]

Or could blacking of a type that was incompatible with what you have used have been left on, leading to a "disagreement" between the two ?

 

Strange it's only at the waterline, though...

 

Thanks for all your responses everyone, I don't think I made the original post very clear, the blacking is coming off along the entire side as far as I can tell, at all points where the boat is in contact with the water, right down as far as I can get my arm. It starts right at the very bows and continues right down the side and along the counter right to the point where the stern starts to curve.

 

One other variable is that this side of the boat which is in the sun every morning. Along the other side its not and as far as I can tell the blacking isn't coming off.

 

I think I have the 'let it rust' thing covered Tony

 

So what's the preferred brand of blacking of everyone here?

Edited September 29, 2008 by Chevetter

[blackrose]

As far as galvanic corrosion, I wouldn't worry about it. You have isolated your boat so there's no need to worry about your neighbour's boat affecting yours because your boat is now not connected to his via the common earth. I have a galvanic isolator with some LED indicators to show if it's gone into circuit and it's easy to test the LEDs and the GI itself with a 9v battery, but I'm afraid I have no idea how to test an isolation transformer, so perhaps someone here can advise or you could call Victron and ask them.

 

My blacking is also starting to flake in a couple of places, but it's been about 2 and a half years. I just used Rylards Premium. Next time I'll use ordinary Rylards which is thicker and finish it with a couple of coats of Premium as it has some resistance to diesel.

Edited September 29, 2008 by blackrose

[Chevetter]

As far as galvanic corrosion, I wouldn't worry about it. You have isolated your boat so there's no need to worry about your neighbour's boat affecting yours because your boat is now not connected to his via the common earth. I have a galvanic isolator with some LED indicators to show if it's gone into circuit and it's easy to test the LEDs and the GI itself with a 9v battery, but I'm afraid I have no idea how to test an isolation transformer, so perhaps someone here can advise or you could call Victron and ask them.

 

Yes but our marina has a long line of 40ft narrow boats in it, parked side by side, of which I am one. My near neighbour has 240v and the bloke 3 moorings away has 240v, so in theory (as the hull of my boat is a path of less resistance than water) if there is a circuit between these two boats then mine could be in the middle of it!

[Chevetter]

Further to what I just said, to combat this problem (or to make sure anyway) I was thinking of getting some hanging anodes:

 

http://www.mailspeedmarine.com/anodes/hang...3kg128413.bhtml

 

However these cost an effing fortune for that they are, if you'll excuse my implied french.

 

Instead I think I might get some of these: http://www.aquafax.co.uk/html/product_details.asp?ID=21647 in the 0.68kg variety and sort out the wire myself. I was thinking of getting 6 and hanging them off the hand rails on bits of wire. Bit of a kerfuffle I know but for the cost of the anodes vs. the cost of the hull I think its worth it!

Edited September 29, 2008 by Chevetter

[blackrose]

Yes but our marina has a long line of 40ft narrow boats in it, parked side by side, of which I am one. My near neighbour has 240v and the bloke 3 moorings away has 240v, so in theory (as the hull of my boat is a path of less resistance than water) if there is a circuit between these two boats then mine could be in the middle of it!

 

Mmm... I don't think you are a path of less resisistance because your boat is isolated, so any galvanic current that is set up cannot pass through your hull and back to shore. A circuit is required (I think).

Edited September 29, 2008 by blackrose

[Chevetter]

Mmm... I don't think you are a path of less resisistance because your boat is isolated, so any galvanic current that is set up cannot pass through your hull and back to shore. A circuit is required (I think).

 

I don't think you're seeing what I mean:

 

3 Boats:

 

|

B---path to earth--------------(||||||||||Boat A||||||||||>

a

n.......isolated......................(|||||||||mine|||||||||||||>

k

| --resistive path to earth----(||||||||Boat B||||||||||||>

|

 

Boat A and boat B are not properly isolated and are both earthed to the bank. Boat B has a high resistance in its path to earth. Therefore they are 2 electrodes floating in a weak acid with a resistive path inbetween them. So what have we got (assuming the boats don't manage to sit at exactly the same potential to ground - extremely unlikely)?

 

 

The path of least reistance between the boats (i.e. from the positive to negative terminals of the battery) passes through my boat as it is easier for electrons to pass through my steel than around it in the water. The direction of travel depends on the potential that the two boats A and B sit at but the result is that my metal is pulled from my boat and sticks to either A or B.

 

This could be an explanation for the blacking coming off - as the metal ions move they have to get past the blacking to get to the other boat. Resolution: hang some more reactive metal anodes over the side and provide a good conductive path to the hull, therefore the anode metal is removed instead of the hull metal.

Edited September 29, 2008 by Chevetter

[John Orentas]

Hi Chevetter.

 

Have you ever been in an electroplating plant? To transfer atoms of metal from one location to another over very short distances they use an array of transformers and cables that would not look out of place in a small power station.. To loose a significant amount of metal from your boat even over a period of years, that bit of current leakage from here and there isn't going to do it..

 

The overwhelming cause of loosing lumps of hull is a result chemical corrosion, keep your boat well painted below the waterline and that is as much as you can reasonably do.

[Chevetter]

Hi Chevetter.

 

Have you ever been in an electroplating plant? To transfer atoms of metal from one location to another over very short distances they use an array of transformers and cables that would not look out of place in a small power station.. To loose a significant amount of metal from your boat even over a period of years, that bit of current leakage from here and there isn't going to do it..

 

The overwhelming cause of loosing lumps of hull is a result chemical corrosion, keep your boat well painted below the waterline and that is as much as you can reasonably do.

 

Can't say that I have no. I'm at work at the moment so I haven't got the time to do it but this evening, or maybe tomorrow evening I will sit down and work out the rate of corrosion in grammes of steel per month based on a set of nominal conditions.

 

When you say chemical corrosion, which chemicals are you referring to? I've noticed that everyone's washing up scum seems to accumulate around my bows

[valrene9600]

The overwhelming cause of loosing lumps of hull is a result chemical corrosion, keep your boat well painted below the waterline and that is as much as you can reasonably do.

 

 

--------------------

John Squeers.

 

It`s the blacking he`s losing not the metal from the hull.