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We have just had out boat lifted out for the winter season, this is the first lift since it was purchased earlier this year. It is an ex Castle Craft hire boat (GRP) approx 9 years old.

On washing down the hull, I have noticed that it appears to have std blue antifoul around the water line. However, underneath it has a black substance, almost tar like, but dry to the touch. Have not seen this before. Is this normal practice by the boat yards? If so where can it be purchased? I assume it must be cheaper than normal fresh water antifouls. I also have a concern regarding being environmentally friendly, If it is not the case can I cover it with a fresh water antifoul?

Any advice would be very much appreciated.


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Hi Col & Lou, it sounds like you have tar varnish under the waterline, this was used on all the old wooden boats the other finish it could be is bitchamum paint, both paints are about £15.00 for 5 ltrs, we mhave used both of these on our boat for the last 12 years.

Hope this helps Robin.

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hi col & lou

ive found the best way to deal with tar varnish or bitchamin is to work from the keel out using a long handled radiator roller

if you need to take a long break, you can submerge the roller in water then roll it off on wrag when you need

to continue.

you can lower a narrow board into the can to act as a roller board rather than using a tray.


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Thanks all for the advice. Tar varnish or Bitchamin does not seem very environmentally friendly. Or is it? Although I don’t think any antifouling is.

Thanks for that Paul, I did not know that Alex now had the chandlery at Loddon. Must give him a call. Does anyone have the number?

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Hi there,

Black tar varnish is quite common on Broads boats and also not particularly expensive either. From what I'm told, it's pretty effective as anti foul in the Broads environment and most people that use it finish off the water line with a suitably coloured anti foul rather than have black showing above the water line. It is a bitumen based product but isn't considered harmful to wildlife when dried.

Hope this helps


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