Fiberglass mast

[Fanie]

Are there any drawbacks in using a fiberglass construction mast ?

[rwatson]

You probably mean Kevlar or some type of carbon fibre- havnt heard of many fibreglass masts. our old mate from harrayProa www.harryproa.com has made a bit of a science of carbon fibre mast production, to the point of building columns for streetlights (I think) as well as masts.
Adding fastenings seems to be the most problematic area

[FAST FRED]

Lightning can ruin your whole day.

FF

[ted655]

Pros & cons. A kevlar mast on a cat rig is good, it flexes and spills when gusts hit. A sloop rig is hard to preload & sail shape suffers.
We've already had this years lightning discussion.

[Fanie]

Why can'r one make a mast from normal fiberglass ? You get some fiberglass fishing rods... not as high tech as the graphite stuff, but not as costly either.

[tuks]

I think e-glass is just too flexible, perhaps s-glass is worth a look?

EDIT

Now that I think about it, I remember reading about a home built fiberglass mast. Some high performance dinghies have a regular round aluminium extrusion for the bottom piece and the top is a tapered fiberglass tip which is very flexible. There have also been some plywood and fiberglass wing masts I read about somewhere.

[Fanie]

Hi Tuks, I found some mentioning of fiberglass masts, but not much else.

What is e-glass and what is s-glass ?

[tuks]

Originally Posted by Fanie

What is e-glass and what is s-glass ?

Both are glass fibers, E-glass is the usual stuff, S-Glass is a higer grade or different composition or something! It is stronger and stiffer and obviously more expensive.

S-Glass

[PAR]

Weight is the usual issue, unless you get into high tech fabrics, costly resins and production requirements.

The short answer is, there are better materials than conventional 'glass lay-ups for a mast. Wood is lighter and stronger pound for pound. Aluminum catches up when the stick gets a little bigger.

Carbon fiber and other exotics can better the performance of wood and aluminum, but you pay for it.

[Fanie]

Thanks Par - as I suspected, if heavier, it would be nice to know how much. Carbon fibre should make an awesome mast considering the strength of some fishing rods and the weight is much less. The cost though... YUK !

Eh Tuks... or SOMETHING ? Fiberglass strength is determined by the amount of strands per sq mm...

[Eric Sponberg]

The biggest drawback of using fiberglass for a mast is that it is way too flexible--not stiff enough. That's why the fishing pole works, where you want lots of flexibility, but not for a mast. On a mast, you want some flexibility, to spill the wind in gusts, but not much. Kevlar will not work--it too is too flexible and it is very poor in compression. Carbon fiber is the only way to go--take it from someone who has designed a fair number of both.

E-glass is electrical grade fiberglass. S-glass (military designation) is both stronger and stiffer than E-glass. The proper designation for commercial grade S glass is S-2 glass. Unfortunately, S-2 glass is still not stiff enough for masts.

As for lightning, yes, it can ruin a whole carbon fiber mast. But then, lightning can ruin a whole boat. You still need a separate lightning conductor and ground with a carbon fiber mast.

To read more on free-standing masts and their design and engineering, you can go to my website at:

http://www.sponbergyachtdesign.com/StateoftheArt.htm

Eric

[Fanie]

Thanks Eric ! Some nice information there. I will keep it in mind.

[Fanie]

An alluminium extrusion, that is glassed over, assuming the alluminium and fiberglass makes a solid bond and the allu cannot move inside the glass, could that be a good alternative for stiffening an allu or a fiberglass mast ?

[rwatson]

Fanie - what is it lad ?- you seem to need a fibreglass mast rather badly. Are you going to get a prize or win a bet? A man of your persistance will go far.
Anyway - I am the only person in the world who has built a fibreglass and aluminium mast. I found that a 30mm aluminium tube was a fraction too bendy for a small trimaran with a traditional lateen sail, so I filled the tube with polyester resin - it worked a treat!
As it happens, I was re-cycling the tubes last week for another project, and I tried to get the resin out. Some of it has turned to powder, some was immovable.
There is a good chat elsewhere about the difficulty of making epoxy stick to aluminium, but I bet polyester resin doesnt stand a chance.
Why dont you just have a nice aluminium mast lad, and be happy. :-)

[Eric Sponberg]

Fanie,
The only benefit you would get by adding fiberglass to an aluminum mast is the added wall thickness which will increase strength and stiffness only slightly, by virtue of the geometry. But the strength and stiffness of the materials themselves are equally as important. The strength and stiffness of a hybrid construction like this depends on the relative stiffness (modulus) of the two materials. Aluminum is relatively stiff, E = 10x10^6 psi (i.e. 10,000,000 psi). Fiberglass has a modulus of only 1.5 to 2.0x10^6 psi. So as the mast bends, the aluminum, by virtue of its 5-fold superior stiffness, will assume the lion's share of the load.

Rwatson's example showed some success because the resin fill essentially added lots of mass and thickness to the inside of the section--purely a geometry solution. Resin itself has a modulus of only about 0.5x10^6, so aluminum is 20 times stiffer than resin. There was nothing to be gained from the inherent strength of the resin.

Eric