log impellor

[aph]

Am about to fit a new Clipper log impellor. I seem to remember seeing something about not using Sikaflex to seal the plastic skin fitting. Whats the alternative ........bathroom silicone? Seems dodgy. /forums/images/graemlins/confused.gif Anyone help?

 

[Swagman]

Hi aph,
You can use any marine sealant (Sikaflex is an adhesive sealant and tricky to remove if ever needed). Key with regular sealant is to not queeze it all out by tightening your fitting too much or too early.
A suggestion is to pack out the item you are fixing with a small shim of something at the edges - about the thickness of a 10 p coin - just whilst the sealant goes off.
Then you can easily remove the shim once the sealant has set and continue to tighten up the fitting onto your flexible but watertight seal.
Enjoy
JOHN

 

[pvb]

NASA advise...

NASA advise not using mastic sealants, but suggest silicone sealant. This will be OK, because the fitting isn't subject to massive water pressure. Polysulphide sealants (LifeCalk, etc) and polyurethane sealants (Sikaflex 291 etc) can attack certain plastics, so this is probably the reason for NASA's advice.

NASA also advise glassing around the fitting inside the hull, presumably to give it better rigidity in the hull.

 

[VicMallows]

If you do a search, you should find numerous threads on this. Most recently, the consensus was that there is a real concern over the integrity of the plastic thru-hull, no matter what sealant you use. Examination of mine (not yet installed) certainly bears out this possibility (outer flange separating from threaded tube).

One posibility is to replace the thru-hull with a 'brass' or bronze one. Former are stocked by most chandlers at around £8. True bronze ones available from AQUAFAX for about £20. Some simple modification (remove lugs, reduce length) necessary.

Vic