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S&S Swan Maintenance - Question for Lars...Swan 47 Pulsar II
29 January 2012 - 13:21
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pulsarii
Join Date: 29 January 2012
Posts: 2

Question for Lars...Swan 47 Pulsar II

Lars,

I am in the process of having new teak decks fitted. When the old teak was removed from the coachroof around the deck collar we found a bulge in the GRP deck. It was about 10cms across and about 8/9mm high. In fact it had lifted the old teak deck and cracked the teak. I cut out the alu plate which is glassed inside around the deck collar, it takes the loads from the halyard/control line blocks at the foot of the mast, and found considerable amounts of corrosion on the alu plate, in fact about 5/6mm of the white powder. The cause of the bulging.

The alu plates, 1 either side of the deck collar, are 10mm plate, I am assuming marine grade alu. Both are affected. Getting hold of 10mm plate seems to be a problem in Malta, where I live and the deck work is being completed. Is 10mm plate over engineered enough to allow me to have the plate skimmed to 8mm to remove the corrosion areas back to bright metal and re-utilise the 2 alu plates.

Your advice would be greatly welcomed.

Thanks....Ian    

  
30 January 2012 - 10:57
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the professor
Join Date: 02 January 2008
Posts: 1547

Ian
The rule of thumb is that the back up plate has to have at least the same thickness as the screw diameter through it, but by adding a big washer under the nut a thinner plate can be compensated. It appears there has been a leak causing hidden corrosion.
Kind regards
Lars
30 January 2012 - 20:27
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pulsarii
Join Date: 29 January 2012
Posts: 2

Lars,

Thank you for your quick response and as ever your advice.

I had forgot to mention in my problem/solution description that we had planned to thru drill the plate and put nuts and washers on the fixing bolts. Your suggestion exactly. (the original fixing bolts were just tapped into the alu plate, no nuts). As you can imagine, stainless steel fixing bolts into alu..they were not easy to remove. I think the leak was caused when the last re-decking was completed in the early 90's, not the original Nautor deck. The large genoa halyard blocks fitting holes were cut through the teak and the fibre glass coachroof. and then were not sealed so any saltwater leakage reacted between the alu plate and the s/steel block fittings. It wont happen with this new deck!  

Thank you again...

Ian...Pulsar II
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