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| Stainless steel screws in aluminum transom plates! http://www.hobie.com/au/en/forums/viewtopic.php?f=14&t=7403 |
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| Author: | ALEXSAILS [ Wed Jul 25, 2007 4:44 pm ] |
| Post subject: | Stainless steel screws in aluminum transom plates! |
Hi, we all know that alum and stainless dont work well when exposed to salt water. Galvanic corrosion will seize/weld the plate and screw together and its over for that screw position. Some...like me have had to open access to the transom and replace the whole damn plate from inside because a screw broke in the transom. Drilling the screw out and retaping is no option as the stronger ss screw will deviate the drill bit and will never hold its center, it will just offset and go thru the softer alum plate. What if we use high strenght aluminum screws? Does anyone have an idea to screw ss into the alum transom plate and still be able to remove the gudgeon after years?? Even if some water got to them.... thanks! |
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| Author: | Roy [ Wed Jul 25, 2007 8:30 pm ] |
| Post subject: | |
Not that I have any experiance at doing the repair but would it be possible to glue a piece of SS plate to the inside of the existing aluminum one? You could drill over size holes through the aluminum and then thread the new SS plate? I have never looked inside mine as I have no access hatch. |
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| Author: | ALEXSAILS [ Thu Jul 26, 2007 6:52 am ] |
| Post subject: | |
That is exactly what I did but instead I laminated with cloth another alum plate on top of the existing one.....over size holes on the first plate so that the screws would reach the new/second plate behind it.... Didnt consider the ss plate as the encapsulated/laminated ss plate would rust like regular steel if moisture gets to it.... |
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| Author: | Hobie Nick [ Thu Jul 26, 2007 10:31 am ] |
| Post subject: | |
Alex, If you use a marine grade SS plate and encapsulate it, it will not rust since the chemical reaction to oxidize the iron in the alloy will not take place due to the presence of the nickel. Also, there really are not aluminum screws that are reasonably priced in the size needed to hold gudgeons in place. I have recently (yesterday) replaced my gudgeons which have not had the screws removed for over 10 years and had no trouble. the previous owner filled the holes with silicone to help seal them. At the same time the silicone acted as a barrier between the Al and the SS. I had no trouble removing the screws and the internal threads on the Al are still intact. When I put the screws back in I did the same thing. As long as the two metals are not touching the galvanic reaction will not take place. |
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| Author: | rattle 'n hum [ Thu Jul 26, 2007 11:17 am ] |
| Post subject: | |
Hobie Nick wrote: the previous owner filled the holes with silicone to help seal them. At the same time the silicone acted as a barrier between the Al and the SS. I had no trouble removing the screws and the internal threads on the Al are still intact. When I put the screws back in I did the same thing. As long as the two metals are not touching the galvanic reaction will not take place. I've done the same thing on the H-16s I've owned (5200 instead of silicone) to fix/prevent leaks, but I'm convinced it helps the corrosion problem, too. If nothing else, every year or so (less for fresh water?) I think it would be a good idea to run 'em out, hit 'em w/some anti-seize, and run 'em back in. Wouldn't take 15 minutes, and could save a lot of trouble. I've read horror stories about the PITA broken screws, and just recently had a good friend knocked out of a weekend of Gulf sailing with us due to this same problem (after travelling hundreds of miles!). Thanks for reminding me that my gudgeons are overdue for some attention! Jerome Vaughan Hobie 16 Clinton, Mi'sippi |
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| Author: | ALEXSAILS [ Thu Jul 26, 2007 12:36 pm ] |
| Post subject: | |
My cat is from 1987 and original gudgeons where never removed...thats the reason for a very time consuming and difficult repair of the plates. Ok I even if we remove and reinstall every year... The solution to this would be 5200 on the screw threads all the way in and on the gudgeons???? Or anti seize on the threads and 5200 on the gudgeons? thanks! |
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| Author: | Hobie Nick [ Fri Jul 27, 2007 11:52 am ] |
| Post subject: | |
All you need to do is have a layer of something between the SS and the Al. It can be silicone, 5200, anti-seize, or something else. Just keep the two metals apart. |
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