plastic fittings.

Discussion in 'Powerboats' started by Frosty, Apr 4, 2007.

  1. Frosty

    Frosty Previous Member

    I have bought and fitted nylon pipe fittings for a bronze shaft log.

    These plastic fittings or nipple as some people call them are to take some of the exhaust coolant water from the injection point and direct that into the shaft log to cool the shaft.

    Pretty normal stuff.

    I fitted these in replacement of some brass fitting that some how I didnt trust.

    I have read in this forum that brass turns to mulch sometimes, and I have already lost some stainless fittings used in a similar stuation.

    Although they seem a bit flimsy and subject to failure (if knocked) I feel slighly more secure in knowing they wont rot.

    How does any one else feel about non rotting plastic fittings.

    .
     
  2. FAST FRED
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    FAST FRED Senior Member

    Stainless immersed in water is a known danger. Brass is NOT bronze , and is used in home plumbing , not aboard a boat.

    Bronze fittings have stood the test of time. Decades in sea water.

    If you can protect the plastic from damage it should be fine , but it sure cant take the abuse metal can.

    Many aluminum boats are now using the plastic thru hulls etc from Forespar with success.

    FF
     
  3. Willallison
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    Willallison Senior Member

    I wouldn't trust anything but the highest quality Marelon or similar 'plastic' fittings - particularly below the waterline. They tend to become brittle over time, particularly if they are exposed to hot water &/or uv light.
    FF's on the money. Use bronze - and make SURE that it's bronze. A lot of the cheap (chinese mostly) stuff sold nowadays fall somewhat short...
    See this thread I started a while back

    http://www.boatdesign.net/forums/showthread.php?t=14507&highlight=chinese bronze
     
  4. Frosty

    Frosty Previous Member

    yes Will I remember your thread --its because of that thread that I changed them.

    They are supposedly Nylon from West marine USA they are only 1/4 to 1/2 and definately not in the sun
     
  5. Willallison
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    Willallison Senior Member

    :D Glad my warnings didn't fall on deaf ears....
    Are bronze ones that much more expensive, or are they just difficult to source?
     
  6. Frosty

    Frosty Previous Member

    Extremely difficult-- never seen any.

    I was horrified when a stainless fitting of the same size crumbled when I put a spanner on it. That was screwed into the bronze log on the outside.

    Although the brass fittings I just replaced where perfect. If they were brass.

    How can you tell?
     
  7. Willallison
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    Willallison Senior Member

    Short of taking to a lab and having it checked (which is what I'd do, since we own a lab!;) ) I guess the only way to tell is the difference in colour - the problem is that there's dozens of different variations on each, so this isn't really a reliable method.
     
  8. Frosty

    Frosty Previous Member

    Yeah well thats what I thought. This stuff looks like gold.

    I think you you mean bronze is darker in colour?--

    I wish there was some easy way to tell.
     
  9. Willallison
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    Willallison Senior Member

    Yes I had them back to front... I must have been editing it when you replied!
     
  10. Poida
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    Poida Senior Member

    Trying to remember,what's in each, could do a search but I think bronze is copper and tin and brass is copper and zinc. Apparently some bronze can have zinc in it and some brass tin so there is an overlap between bronze and brass and the metal could be called either.

    I use a plastic sea cock but metal on the engine.

    Poida
     
  11. marshmat
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    marshmat Senior Member

    Easiest way to tell for sure is to zap it with X-rays and keep an eye on which frequencies come back at you.
    I can't help being a bit leery about plastic below the waterline. Likewise for low-grade metals. The trouble is, quality stuff is expensive, and so is very, very hard to find.
     
  12. Tim B
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    Tim B Senior Member

    It's REALLY simple, don't put dissimilar metals in contact anywhere near seawater. Decent plastic fittings are ok on a metal-hulled boat, metal is ok on GRP. If you have to use metal fittings on a metal boat, use a plastic washer either side of the hull, and "glue" everything together with sealant (then tighten the fitting, obviously).

    The same goes for pipe-fittings too. Using dissimilar metals is asking for trouble. Personally, I like the idea of plastic pipes and brass fittings.

    Metal hulls are actually quite convenient, because you can weld a fitting into them, rather than introducing foriegn metals.

    Tim B.
     

  13. Lancerbye
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    Lancerbye Junior Member

    Marlon fittings are CGG aproved as through hulls but PVC and nylon aren't. Internally, PVC or ABS piping isn't allowed as piping connected to a through hull.
     
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