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  1. #21
    Martin_J's Avatar
    Martin_J is offline Registered User
    Location : Portsmouth, UK
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    Apr 2006
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    2,107

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    Interesting.. I've never been 100% happy looking at my Raymarine plastic impellor thru-hull knowing how certain plastics can harden and go brittle.

    I remember a pair of ski boots.. they were perfect for about ten years.. then one day the plastic they were made from just cracked and one boot broke into a dozen pieces.. When off the slope I dropped the other boot and the same happend to it.. (and a good brand make they were!)

    Thinking now about the spare bronze straight thru-hull I have in my spares locker.. It could easily fit.. The question would be how to make the threaded section at the top to take the impellor screw cap.. At least I'd know the thur-hull hole would be secure... Thoughts?

  2. #22
    Join Date
    May 2003
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    816

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    Well, I have one of the NASA units. The chap who fitted it (previous owner) glassed it in so thoroughly that I dread ever having to replace it! it's in the middle of a small fibreglass mountain.
    It did start to weep a small amount of water (when going to windward in a chop) after about 8 years service, but NASA gave me some new O rings (free of charge!) and it seems OK now.
    It does seem surprising that, with all the fuss about seacocks and skin fittings, we trust our boat to a cheap flimsy bit of plastic (this is not a dig at NASA, it seems that plenty of other manufacturers do the same) and, usually, get away with it. Clearly, plastic skin fittings (slightly more substantial, perhaps) are the way to go ... after all, most boats are plastic ...

  3. #23
    Join Date
    Dec 2009
    Posts
    100

    Default Thank you for this thread

    Having read this thread yesterday I decided to check my NASA clipper log skin fitting today and to my horror found hairline cracks on the inside of the bore just 2-3mm from the bottom just as predicted. The backnut is not glassed in but the previous owner who installed it about 5 years ago had encapsulated it in Sikaflex.
    Managed to pick up a new skin fitting from my local chandlers this afternoon so guess what tomorrow's job will be?
    Thank you for this thread! Without it I would have put my boat back in blissfully unaware. http://www.ybw.com/forums/images/smilies/biggrin.gif

  4. #24
    Join Date
    May 2011
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    1,142

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    Quote Originally Posted by basil421 View Post
    Having read this thread yesterday I decided to check my NASA clipper log skin fitting today and to my horror found hairline cracks on the inside of the bore just 2-3mm from the bottom just as predicted. The backnut is not glassed in but the previous owner who installed it about 5 years ago had encapsulated it in Sikaflex.
    Managed to pick up a new skin fitting from my local chandlers this afternoon so guess what tomorrow's job will be?
    Thank you for this thread! Without it I would have put my boat back in blissfully unaware. http://www.ybw.com/forums/images/smilies/biggrin.gif
    Thank you for this, now I don't feel so dumb asking the question!

    Tony C.

  5. #25
    Join Date
    Dec 2009
    Posts
    100

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    Just removed the old fitting. It was easy . All I had to do was push a puttey knife under the flange from the outside and half the flange fell off. There was antifoul stain on the old fractured surface showing it had been fractured for some time. The other half of the flange was still holding but it soon broke off with the putty knife. The whole fitting then just pulled out from the inside.
    I was doublely glad when I removed it as I found the Nasa unit which requires a dia 42mm hole had been fitted in a previously drilled dia 53mm hole - With lots of Sikaflex as a gap filler. This would have helped the stress cracking process no doubt.

    I've now cleaned up the hole and cast some filled epoxy into it. I'll redrill at the correct diameter when it's set.

    I have one question however.
    I read on here recently that the sealant CT1 is better that Sikaflex for below the waterline applications. I bought some as a result of that to fare-in around my keel joint. Looks good for that job but I won't know till next lift out.
    It says on the tube that CT1 is solvent free and OK to use on plastics such as polystyrene so I was thinking I would use it for the Nasa skin fitting. Does anyone on here have an opinion on that please?

  6. #26
    Boathook's Avatar
    Boathook is offline Registered User
    Location : Surrey & boat in Dorset. Both have pubs
    Join Date
    Oct 2001
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    2,783

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    Quote Originally Posted by basil421 View Post
    Just removed the old fitting. It was easy . All I had to do was push a puttey knife under the flange from the outside and half the flange fell off. There was antifoul stain on the old fractured surface showing it had been fractured for some time. The other half of the flange was still holding but it soon broke off with the putty knife. The whole fitting then just pulled out from the inside.
    I was doublely glad when I removed it as I found the Nasa unit which requires a dia 42mm hole had been fitted in a previously drilled dia 53mm hole - With lots of Sikaflex as a gap filler. This would have helped the stress cracking process no doubt.

    I've now cleaned up the hole and cast some filled epoxy into it. I'll redrill at the correct diameter when it's set.

    I have one question however.
    I read on here recently that the sealant CT1 is better that Sikaflex for below the waterline applications. I bought some as a result of that to fare-in around my keel joint. Looks good for that job but I won't know till next lift out.
    It says on the tube that CT1 is solvent free and OK to use on plastics such as polystyrene so I was thinking I would use it for the Nasa skin fitting. Does anyone on here have an opinion on that please?
    I have become an Arbomast BR fan for all fittings above and below water. So far ok ....

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