pvc mast tube?

[sscoville]

I am going to make my masts from wood which means they'll be 3" in diameter at the bottom.  I have 3" some pvc electrical (I think it's fire retardant).  Couldn't I use this for the main mast tube?

[JeffM]

I wouldn't, if I were you.  Epoxy doesn't stick well to pvc, and I wouldn't want to have to do repairs in a place so difficult to access.

[Randy Jones]

My CS 17 has a 3 inch diameter PVC mast tube for the main. I didn't built it, but it is clear that the top and bottom ends of the sleeve are completely captured by wood.  The mast step block and and the wood framing at the deck appear to take the load, with the PVC sleeve acting as a vertical compression member and providing a slick waterproofing guide between the deck and the mast step.  I'm guessing that the epoxy/PVC joint experiences only light loading which may be why it has worked.

I don't know enough to give you a recommendation, but can report no problems with my arrangement after 1 year of operation.  The slick interior surface on PVC does seem to make mast installation and removal smooth.  Hope this helps.

 

   

[JeffM]

Captured by wood?  In the plans, the mast tube is made of epoxy and fiberglass, fabricated by wrapping the saturated glass around the mast itself (with spacer to allow the right amount of play).  (This was a bear at the time, but now we know the tricks to it.)  Then the open-ended tube goes through the partner and is fiberglassed atop the thickly-glassed step.  I wouldn't expect the middle of the tube to take much load, either--unless a wind gust caught the mast when you were in the middle of stepping or unstepping.  I suppose a pvc tube, if properly buried in glass and epoxy, would stay put, and at worst perhaps leak water into the forepeak.  But I can't think why you'd want to use it.  A proper mast tube is a safer choice and isn't very expensive to make, I don't think.

[Ken_Potts]

  That's a really good question for Graham.  Ask him.

  I'd be hesitant to use PVC with epoxy myself because I'm afraid it wouldn't stick well.  The mast tube isn't difficult to make from fiberglass and epoxy.  If you use pvc you might save an hour or two of work but if you get leaks because the epoxy doesn't stick to the pvc you'll have to deal with it forever (or until you spend a bunch of hours cutting the pvc out and replacing it with fiberglass).

[sscoville]

I think I'm just going to make it from fiberglass.

[Tom Lathrop]

As said, the only stress is at the partners and teh mast base where it can be easily reinforced.  I sometimes use PVC as a mandrel for forming fiberglass parts and as long as there is not a lot of stress, there should be no separation of fiberglass from the PVC.  In your case the PVC could easily be wrapped with a couple layers of glass and work just fine.  Epoxy does not bond well to PVC but it does stick well enough for this job.

On the other hand, I would not do it.  Making the tube out of fiberglass will show you that it is no big deal and open the possibility of molding other parts and gadgets from fiberglass.  I've made hinges, various kinds of mounting hardware, distribution manifold and other stuff from fiberglass.  Glad I learned how to do it.

[Dogdad]

If you don't want to make your own, one source for fiberglass tubing is high-power model rocket suppliers, such as this one:

http://www.hawkmountain.ws/

The rocket folks also have lots of information on techniques for making your own tubing.