Why not a boom made from S-glass and G-10?

[thombiz]

While thinking about the whole "Made in USA" thing, it occured to me....why couldn't someone make a boom using a material other than carbon fiber. As I understand it, S-Glass has about 60% of the tensil strength, equal compressive strength, better flexural properties and better durability than carbon fiber at about 1/4 the cost. So why not make booms out of S-Glass and G-10 epoxy? To achieve equivalent stiffness to carbon you would make 2 or 3 extra wraps of 6 oz. s-glass and you'd have it. Who said they only had to be made from carbon? Besides the lower cost thing, S-Glass doesn't cause an electrolitic reaction with aluminum so you could use aluminum tail pieces. It would be tougher because s-glass isn't as easily bruised as carbon.

I've seen some beautiful and strong G-10 fins, why not booms? It would have durability at the cost of aluminum.

Checking Fiberglass Supply, s-glass runs $9.50/yd and carbon runs $30/yd.

Check this: http://www.instructables.com/id/How-to-make-a-carbon-windsurf-boom/

[bred2shred]

We don't use fiberglass booms for the same reasons that we don't use fiberglass masts - when compared to carbon fiber, fiberglass is heavier, has less strength, and has a lower elastic modulus (very important for the boom).

You would likely end up with a boom that has about the same stiffness as an equal size aluminum boom, but was heavier and more expensive. I think you're wrong in your assumption that a fiberglass boom would cost the same as an aluminum boom. While the raw material cost of fiberglass may be 1/4 that of carbon fiber, the tooling and labor are a very significant portion of the overall product cost.

To build an aluminum boom arm, all you do is cut, bend and anodize a standard piece of extruded tubing. To build a composite boom arm requires expensive equipment and tooling as well as a high degree of operator skill. These costs are present regardless of whether the boom arm is made using carbon fiber or fiberglass.

sm

[thombiz]

Would you happen to know the elastic modulus numbers for similar samples of carbon fiber, s-glass, and e-glass? I took several years of structural engineering classes and I don't remember seeing elastic modulus numbers for anything other than steel and aluminum. I remember how to calculate the moment of inertia for tubular and/or round sections, but not elastic modulus. IF I had numbers, I'd have an idea how to proceed to determine equivalent structural strengths including flexural, shear, and compression. Thanks in advance.
The tooling and labor costs to produce an s-glass boom has to be the same as for carbon fiber. As for flex, most people wouldn't care if their boom weighed an additional half pound and had the same flexural strength as carbon fiber even though it required a higher moment of inertia. The arms are a small part of the weight of a boom. It's the front piece which connects the arms, the head, and the tailpiece which would effect the total weight and total cost. The front/arm connector could be made of s-glass and would be easy to size and shape to carry the loads. The head would be the same as the head for a carbon boom, and the tailpiece could be aluminum pieces.

If you tweek the elastic modulus with say a stronger epoxy, you should be able to get fiber bending stress and flexural/shear/compression numbers approaching carbon fiber. Of course, if someone has been doing something the same way for years and years, they may not be inclined to look at it in a different way.

Personally, I see an s-glass/G-10 boom with a kevlar outer wrap similar to what Powerex used on their masts at the boom mount area as a very viable alternative to carbon fiber.

[koogzah]

But what about epoxy-impregnated hemp?

[speedysailor]

[bred2shred]

[bred2shred]

[DanWeiss]

Fiberglass has been used in boom tubes, but not without a copious amount of carbon fiber as well. Back in the very early 1990's Fleetwood booms offered a boom that was about 50/50 glass to fiber. It was priced between alu and carbon and worked nicely in the smaller sizes. The boom also offered an ovalized tubing that helped reduce forearm fatigue and increased stiffness.

Also, not every carbon boom uses 100% carbon fibers in the tubes. Most are very, very high in content but some are not 100% carbon.

[thombiz]

What I meant by calculate the modulus of elacticity, I could use a simple beam deflection formula for two equal concentrated loads placed unsymmetrically (harness line loads and locations) to work backwards to solve for the modulus of elasticity required to have the same deflection under load as a given sample of carbon fiber. The variables would be: moment of inertia and modulus of elasticity. By increasing the wall thickness of the round section (increasing the moment of inertia or stiffness caused by shape) you could achieve the same stiffness as the carbon fiber while using a weaker material, s-glass. This is the very same way manufacturers increased the wall thickness of RDM masts to match the stiffness of SDM masts. This would also give you the volume of material and thus the weight of the material needed to match the deflection of carbon fiber for a given load. It shouldn't take very long to determine exactly how much additional material and thus weight for an equivalent s-glass boom.

If you limit the change in wall thickness, as in saying a boom arm with a diameter larger than 1.125 inches is unacceptable and an inner diameter smaller than .875" is unacceptable then you can calculate the modulus of elasticity needed to match a given deflection using carbon fiber.

I agree that modulus of elasticity plays a very big roll in the design of masts which are essentially a long slender cantilevered sections. Boom arms, on the other hand, are relatively short compared to masts, and are supported at both ends and have a much lower slenderness ratio.

An s-glass boom may not be practical for sails above 8.5 or for super tweeked pro slalom or formula rigs, in the very same way that an RDM masts may be impractical for sails larger than 8.0 and thus won't work for formula sails. For smaller sails, the RDM has found a permanent home. The same could be true for s-glass booms, they may just be the ticket for the average joe recreational sailor, especially in saltwater.

By suggesting "tweek" the epoxy I'm suggesting that some carbon fiber layups may work best with some epoxies for properties unrelated to strength. They may wet out better, or cure with less heat, or even give a longer pot life. There may be stronger epoxies out there which would work ideally with s-glass. I don't know for sure.

[thombiz]

I did find some modulus of elasticity numbers for e and s glasses:
E-glass fibres:
Modulus of Elasticity : about 72.4 GPa
Tensile strength: about 2.400 GPa

S-glass fibres:
Modulus of Elasticity : about. 85.5 GPa
Tensile strength: 4.500 GPa

found them here: http://www.roymech.co.uk/Useful_Tables/Matter/Glass.html

Carbon Fiber:
Modulus of Elasticity is typically 138 Gpa
Tensile strength is 3.5 Gpa

found here: http://www.dragonplate.com/sections/technology.asp

Curious, the above says s-glass has a higher Tensil Strength than carbon fiber. Somehow, that doesn't seem to make sense. The Modulus of Elasticity of s-glass is 62% of carbon fiber using the above numbers. Also, s-glass has 1.87 times the tensil strength of e-glass. It shouldn't take too much more and I should be able to set up a spreadsheet to calculate an equivalent solution to carbon fiber using s-glass.

Curious that the elasticity number sm gives for aluminum at 69 Gpa (and I confirmed for T8 ) is actually lower than those I found for e and s glasses. Common sense makes me think there is some other factor involved which the raw numbers aren't showing.