|Subject: Re: [harryproa] Fibre glass mast?|
|From: "Rob Denney" <firstname.lastname@example.org>|
|Date: 9/5/2007, 2:32 AM|
Unfortunately it is a little more complex than just a weight/cost trade off. A glass mast needs to be considerably larger diameter to be stiff enough. This rules out a tube mast, and means a wing mast beeds to be pretty hefty. We compromise by using glass for the off axis and hoop loads as stiiffness is less important here. The carbon we use is carbon tow, which, when we can get it, sells for about $45 per kg, which compares with uni glass at about $15 per kg. You will use a lot more glass (plus you have to cut it, which is wasteful of time and material) so the carbon mast ends up cheaper. You could use glass tow, which would be an order of magnitude cheaper, but is a dubious proposition with epoxy due to the surface treatment.
Resin use will be higher for the glass mast as there is more material to wet out.
(properly designed and built) unstayed masts don't break. :-) Compression breaks are invariably due to the fibers buckling, not breaking. This is overcome by sufficient off axis fibres to hold them in column.
Resin infusion of a wing mast would be an easy way to do it, but there is a lot of prep to do to make sure everything is in place, and that it stays there until the bag is on. Infusing thick laminates (on Harry for example, the thickest is 12mm) is not easy, I would do some tests first. Derek has some cunning ideas on infusing masts, but has yet to test them.
With silly prices for carbon, how does using fibre glass compare?
I know cheaper and heavier is the answer, but how much?
-the amount of resin, I assume will be the same.
- does a mast fail in tension or compression. I guess it probably is
in compression, certainly the case with all the windsurfer mast I have
broken! If this is so, is carbon significantly better in compression
could you resin infuse in one go around a foam core?
Rob, would be interested to hear your view.