Bitumen / tar on the baseplate

[IanR]

We are getting nearer to starting the fitout of our boat and have been scraping and painting the insides of the hull, a labourious task that has taken what seems like yonks to get done. It was a working boat up til about 2009 or so and then sold onto to someone who started to do what we are restarting to do. They didn't get very far with it for whatever reason and the boat was left in a bit of a state with lots of water in the hold for years. The bottom of the hold, under the wooden planks has concrete block ballast, these are sat on roofing felt which is in turn sat on what looks like years of applications of tar bitumen. The boat was left in a state that meant that massive amounts of condensation gathered to the point that on a hot day the hold was like a sauna, absolutely stiflingly hot and moist. There was lots of water in there, mostly condensation but some from a hull leak too.

To the point anyhoo, this bitumen tar stuff is rock hard, like black glass and although it seems intact, in places isn't stuck to the baseplate and therefore leaves a void which retains any moisture that was there. I've spend more days than I care to remember chipping away at this, bucketing the waste by the couple of dozen or so. This bucketed waste is worryingly magnetic although the actual steel is coming up suprisingly well, ready for paint. When I come to refit the ballast, does it need to go back onto the same sort of stuff? I was thinking that I could sit the concrete blocks on runs of spare twin and earth household cable, say three or four strips under the blocks. This way the blocks wouldn't scrub the steel, but air could get around the lot and there'd be nothing but coats of paint to hide any nasties.

Ian.

[BWM]

I definitely wouldn't use roofing felt, when stripping out ballast, etc. when having Hawkesbury rebottomed the worst areas for rust were under this. I'd be tempted to use the recommended amount of coats of a rust converter and decent bilge paint. Can't see why your idea of placing the blocks on strips of wire wouldn't work though, but we just put ours carefully directly onto the painted baseplate.

[IanR]

[Jen-in-Wellies]

20 minutes ago, IanR said:

 I was thinking that I could sit the concrete blocks on runs of spare twin and earth household cable, say three or four strips under the blocks. This way the blocks wouldn't scrub the steel, but air could get around the lot and there'd be nothing but coats of paint to hide any nasties.

Ian.

But I was always told that using household twin core and earth cable on a boat would mean failing the boat safety scheme! Shouldn't you be using multi-strand, rather than single core wire under the blocks?!

Jen

Edited January 21, 2018 by Jen-in-Wellies

[jenevers]

I used 20mm lengths of old rubber fan belt. Gives a nice air gap of 10mm and, being rubber, prevents movement and vibration. 

Better than lengths of plastic coated cable to my way of thinking.

[IanR]

Agreed, rubber belt would be better, though I don't have access to enough of that for nowt! It wouldn't the BSS either Jen!!

 

Ian.

[Guest]

Plastic tile spacers are often used to create an air gap under ballast. Dirt cheap on ebay etc.

Edited January 21, 2018 by Guest