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post #1 of 5 Old 06-13-2010 Thread Starter
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Replacing wood with UHMW

The eye for attaching the trailer winch wire to my Ensenada 20 was leaking, so I took it apart for inspection:



The wood was rotten, the steel backing plate was turned into rust. The U-bolt was still OK though, so I let it be. Since wood and water is a bad combination I decided to try using HDPE instead. Here is the starting materials for the repair, next to the old pieces:



I sawed it to an approximate shape, then I fitted it on location using a planer. I had no idea how to best shape the HDPE (_not_ UHMW, my error), but it turned out that a planer (for hand planing wooden planks) worked very well (having the planer upside down and sliding the plastic over it).



No water coming in so far.

Last edited by ulferlingsson; 06-13-2010 at 01:09 PM. Reason: Changed UHMW to HDPE
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I see a couple problems with your fix. First, the UHMW may not have the tensile or compressive strength needed for such a use. Second, the 5200 may not bond to it very well, as UHMW plastics tend to be fairly slippery and most adhesives and sealants have issues bonding to them well .

If the UHMW piece isn't properly shaped, it can flex under the loads and may lead to damaging the bow, weakening the overall structure instead of strengthening it. It doesn't look like you bedded the UHMW piece in thickened epoxy, which would effectively spread the load evenly over the contact area, and that may lead to stress risers in the laminate. YMMV.

Of course, the loads on a boat the size of yours are probably not that much to worry about...but for anyone trying to do this on a larger boat, these concerns would be more significant.

A much better way to repair this would be to build up the area with fiberglass and spread the loading over a greater area of the hull than the small UHMW block is going to do. This would make the area both a lot stronger in case of a collision, as well as make the bow area sufficiently strong to support the loads of the boweye as well.




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Last edited by sailingdog; 06-13-2010 at 10:55 AM.
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post #3 of 5 Old 06-13-2010 Thread Starter
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I neglected to mention that there is a 1/8" rubber gasket between the HDPE (not UHMW!) block and the hull to (1) spread the force, and (2) bond with the sealant. As for the tensile and compressive strength, that is the least thing I am worried about. (Consider that rudders are made of that material.)

Last edited by ulferlingsson; 06-13-2010 at 01:10 PM. Reason: Changed UMHW to HDPE, my mistake
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Quote:
Originally Posted by ulferlingsson View Post
As for the tensile and compressive strength, that is the least thing I am worried about. (Consider that rudders are made of that material.)
UHMW rudders? Where? Who?? UHMW is not a structural lumber..

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Correction

My bad, I wrote UHMW when I meant HDPE. I will correct it above... (IdaSailor Marine makes rudder blades of HDPE, and that's the material I used as well.)
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