Wood primer below the waterline

[Slocumotion]

Scraping a mahogany rudder back to the bare wood I find a black layer between wood and anti-fouling which is softish, slightly crazed in places but seems to have been the perfect first layer in that situation - the wood underneath is in good condition and the anti-f adheres well. The last scrapings come off caramel coloured and almost waxy. The black stuff softens readily with white spirit, very like bituminous paint - could it be that? And/or would that be the way to go after I've repaired a few dings and holes?
Also - boot topping. There is a broad upper band in red on top of the varnish of the above-water part of the rudder, and a narrow, white, lower band on top of the black stuff AND the anti-f, and it has stuck so well it's the hardest bit to remove. What would be the teams recommendation for repainting?
I'm probably going to paint, rather than re-varnish the upper part as well since I'm not a great fan of token bits of brightwork on a GRP boat. So if you find that offensive, foolish, unseamanlike or just typical of the young people of today why not let me know? And can I particularly request capital letters and lots of these !!!!! ?

 

[Caer Urfa]

Scraping a mahogany rudder back to the bare wood I find a black layer between wood and anti-fouling which is softish, slightly crazed in places but seems to have been the perfect first layer in that situation - the wood underneath is in good condition and the anti-f adheres well. The last scrapings come off caramel coloured and almost waxy. The black stuff softens readily with white spirit, very like bituminous paint - could it be that? And/or would that be the way to go after I've repaired a few dings and holes?
Also - boot topping. There is a broad upper band in red on top of the varnish of the above-water part of the rudder, and a narrow, white, lower band on top of the black stuff AND the anti-f, and it has stuck so well it's the hardest bit to remove. What would be the teams recommendation for repainting?

Hi Mike

The 'Black stuff' sounds to me if someone may have coated the rudder with International paints VC Tar Epoxy, now known as VC Tar Epoxy 2. (both black)

It sounds as if it has done a good Job protecting the wood, so why not recoat with the same paint BUT it's a two pack so you need to watch the tempreture before applying.

If it is 'Bitumen' then you can normally still smell it between your fingers (like tar) and is very sticky.

Mike