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7 hours ago, David Mack said:

 

If you are snapping brush handles then your blacking is far too thick. Thick blacking goes on in thick blobby coats, and doesn't get into all the interstices of welds, pitting and awkward corners.

Thinning of blacking with solvent is not generally advised by the manufacturrs. Better to warm it by storing it in a heated room when not in use, and keeping the tin you are using in a bucket of warm water.  Another reason not to do blacking outdoors in cold weather.

Nothing blobby going on here, unheated dry dock in late November. I don't think there are many coatings of any kind that are designed to be thinned but it is standard practice where necessary. 

 Not everyone has the opportunity to get blacking done at the optimum time, dry docks would quickly go out of business if they had to remain empty for six months of the year. 

 We ended up having to break up to 1/2" of ice through part of our journey home with no loss of blacking. 

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Edited by BWM
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If you're going down the bitumastic line I would consider SML Ballistic. I've always used bitumen and have tended to do it  every 2 years. About 3 blackings ago I was pursuaded to use Ballistic. I had VS out of the water in mid September after about 18 months. There was no evidence of the coating failing. I felt it could have lasted longer 

Missed answering your question re quantity,. For my 55  nb will use about 15 litres. With Ballistic it's almost as cheap to buy 20 l. It lasts in my shed until the mext time. 

.

Edited by Slim

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10 hours ago, Slim said:

If you're going down the bitumastic line I would consider SML Ballistic. I've always used bitumen and have tended to do it  every 2 years. About 3 blackings ago I was pursuaded to use Ballistic. I had VS out of the water in mid September after about 18 months. There was no evidence of the coating failing. I felt it could have lasted longer 

Missed answering your question re quantity,. For my 55  nb will use about 15 litres. With Ballistic it's almost as cheap to buy 20 l. It lasts in my shed until the mext time. 

.

Thanks for the recommendation. Is there an alternative to the bitumen based products? other than the two pack epoxy systems.

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Here's a boat where blacking wasnt done for 5 years, marina based, permanent landline.

Less than 20 years old and needs plating both sides(70 footer) due to aggressive pitting up to 4mm deep.

20200113_102450.jpg

20200113_102456.jpg

  • Horror 1

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8 minutes ago, matty40s said:

Here's a boat where blacking wasnt done for 5 years, marina based, permanent landline.

Less than 20 years old and needs plating both sides(70 footer) due to aggressive pitting up to 4mm deep.

20200113_102450.jpg

20200113_102456.jpg

Wow, what causes such significant damage, electrical erosion or plain old rusting?

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Lack of maintenance, loss of blacking , no replacement of blacking and giving galvanic corrosion a free run. 

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38 minutes ago, matty40s said:

Here's a boat where blacking wasnt done for 5 years, marina based, permanent landline.

Less than 20 years old and needs plating both sides(70 footer) due to aggressive pitting up to 4mm deep.

 

20200113_102456.jpg

And people say boats dont rust at base plate level as there is no oxygen 

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That is electrical activity caused by galvanic action between the steel hull and anything else in proximity having a different voltage which causes current to flow between them.  And not having had any protection in the form of blacking has made the matter worse.   The boat probably has no protection in the form of an isolation transformer or galvanic isolator and it is pure neglect.  Blacking every 2 years at around £800 a time [more varied prices are available!] would have saved £000's in over plating. 

 

Its not confined to marinas, but anywhere there are steel pilings or other boats.  I measured the voltage between my boat and piling years ago and used an earth bonding strap to ensure no current flow. [a battery charging cable is a good source].  There was a potential difference between boat and piling which in turn allowed a current to flow. 

 

Another issue with the above boat is the lack of sacrificial anodes.  Typically builders will put 2 each side, on the bow flares and swim but I was told that anodes must "see" each other to be effective and therefore additional ones are needed amidships.  This becomes a problem too as they can be knocked off in bridge 'oles and lock sides. 

 

Finally, if the steel was not shot blasted to remove the mill scale ever present on steel, most blacking stands little chance of adhesion and it falls off - it happened to my boat after only 18 months and I had it done & coated with Zinga and 2 layers of 2-pack.  Now I use a marina for winters,  I fitted a "Safeshore" galvanic isolator.

 

https://shop.pkys.com/What-is-a-galvanic-isolator-and-why-should-my-shore-power-system-have-one_b_112.html 

 

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1 hour ago, matty40s said:

Here's a boat where blacking wasnt done for 5 years, marina based, permanent landline.

Less than 20 years old and needs plating both sides(70 footer) due to aggressive pitting up to 4mm deep.

I would agree that it is not a bad idea to lift the boat more often than 4 years in order to check the hull, (I nearly added that to my previous post). Particularly if somewhere with more chance of unseen damage than another.

 

Marina based, or anywhere with a permanent/regular connection to shore, and no attention to galvanic corrosion, it would be a good idea to be more regular. Off grid, with no shore connection, less so?

 

Clearly, if you lift the boat, you might as well black it.

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