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carbon boom, needed or not?
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bred2shred



Joined: 02 May 2000
Posts: 661
Location: Jersey Shore

PostPosted: Wed Sep 11, 2013 6:40 pm    Post subject: Reply with quote

The weight difference is of secondary importance. The reason to buy carbon is because of stiffness. Carbon booms are significantly stiffer than aluminum. This is an intrinsic material property that simply can not be overcome no matter how well the aluminum boom is engineered. For an 8.5, the difference in stiffness between a carbon and aluminum boom is significant - the larger the boom, the greater stiffness is required. Unless you're a lightweight, I would definitely recommend using carbon. A carbon boom allows you to get the most out of your sail.

sm
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dcharlton



Joined: 24 Apr 2002
Posts: 265

PostPosted: Wed Sep 11, 2013 6:53 pm    Post subject: Reply with quote

I've been windsurfing for 12 years and have had great success with aluminum booms. I picked up a used carbon boom for 200 bucks and noticed immediately how much more performance I got out of my sail.

Nothing wrong with aluminum and the new Monocoque constructions are great, but if you can get a deal on a carbon boom (especially for your big sails) you won't be dissapointed.

DC
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keycocker



Joined: 10 Jul 2005
Posts: 3468

PostPosted: Wed Sep 11, 2013 9:15 pm    Post subject: Reply with quote

"Carbon booms are significantly stiffer than aluminum. This is an intrinsic material property that simply can not be overcome no matter how well the aluminum boom is engineered"
You were kidding right?

For an extreme example take an thick aluminum bar in one hand and a floppy carbon batten in the other and tell us again that carbon is always stiffer and there is no way to overcome that.
You can, of course make really floppy or really stiff spars out of either material.
No offense. I know you know this -just typing too fast yeah?

Our carbon and alu spars have been thinned out to save weight to the point that they break in use sometimes. Carbon is stiffer so you can use less of it without getting too floppy. That saves weight
But thin carbon is more brittle than alu so carbon is fragile when you knock it on something.
The new alus are one piece instead of two arms held by a head. This geometry is much stiffer and the head can be lighter since it no longer clamps on two separate arms.
That has changed the whole comparison. Lots of industry people have seen this, and steer marketing to alu booms.
As to the difference in a demo sail session
We never disagree with a client or anyone here, but we have had sailors come back from a demo absolutely breathless about how much better the carbon boom made the sail work today because some of our alu booms were black color and oval tube.
I can only conclude that even having an aluminum boom the same color as a carbon boom can make the sail handle much better.
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GURGLETROUSERS



Joined: 30 Dec 2009
Posts: 1367

PostPosted: Thu Sep 12, 2013 3:43 am    Post subject: Reply with quote

Agree that some carbon booms (perhaps most?) are constructed towards the lighter end of the scale, than thicker for ultimate strength and durability.

My big carbon boom arm fractured, and pulled apart in a jagged splintered mess on landing, where the THIN non tapered (no extra layers) arm blends into the much thicker one piece head. Clearly, a stress point and bad (or cheapskate) design and construction!

My complaint is that, when we buy expensive carbon booms we have no way of knowing how it has been constructed inside. I also agree with K.C. that the latest continuous head alloy booms (North Silver and gold for example, with their unconditional 2 year guarantees) are built to a high standard, and are much stiffer than older alloy booms, at least up to 8 metre sail size. I expect them (bought two - long and short) to last at least double the guarantee period, much as my Chinook large alloy boom has.

But then I don't bother trying to use 'circus Big Top' tent sized sails to get my Kona 1 (or Bic Bamba) planing. If the 8 metre can't do it, there's no wind much anyway!
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bred2shred



Joined: 02 May 2000
Posts: 661
Location: Jersey Shore

PostPosted: Thu Sep 12, 2013 9:49 am    Post subject: Reply with quote

keycocker wrote:
"Carbon booms are significantly stiffer than aluminum. This is an intrinsic material property that simply can not be overcome no matter how well the aluminum boom is engineered"
You were kidding right?


No, not kidding. Young's Modulus (modulus of elasticity) for 6061-T6 aluminum is about 70 GPa. For uni-directional carbon fiber, it is about 180 GPa (of course this varies with the type of carbon, the layup, resin/fiber ratio, etc. but you get the idea). So carbon fiber is roughly twice as stiff as aluminum. Sorry, but for all practical purposes, you simply are not going to overcome this and still have a USEABLE boom - i.e., you could make the boom 3" O.D. and have it be stiff enough, but you would not be able to hold it comfortably. So I stand by my prior statement, carbon has intrinsic material properties that make it superior to aluminum when used in large windsurfing booms.

sm
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BRIMAR



Joined: 03 May 2004
Posts: 99

PostPosted: Thu Sep 12, 2013 11:08 am    Post subject: Reply with quote

Carbon won't corrode!
Done!!
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slinky



Joined: 24 Aug 2007
Posts: 429
Location: Old Saybrook Ct.

PostPosted: Thu Sep 12, 2013 11:47 am    Post subject: Reply with quote

How true Brimar! Salt water does bad things to aluminum. I've broken 2 aluminum booms and one aluminum mast within a 5 year period. Since switching to carbon booms and masts 20+ years ago, all my gear is still good! I'm still using this antique stuff! Never had a problem with carbon.
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swchandler



Joined: 08 Nov 1993
Posts: 5908

PostPosted: Thu Sep 12, 2013 12:45 pm    Post subject: Reply with quote

Corrosion, flexibility and structural fatigue are classic downsides to aluminum booms. There is no way to get around these liabilities. Carbon booms are clearly superior, especially as booms get bigger. However, that's not to say that aluminum booms don't have their place, particularly for those folks trying to stretch their budget. Also, for those that sail in fresh water or use smaller sails, aluminum booms can offer a lot of value and reasonably good performance. Still though, I wouldn't buy an aluminum boom. Too many bad experiences over time.
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zirtaeb



Joined: 03 Jul 2009
Posts: 2413

PostPosted: Thu Sep 12, 2013 12:50 pm    Post subject: Reply with quote

At 160 lbs., carbon for sail bigger than 5.5, aluminum for smaller.
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keycocker



Joined: 10 Jul 2005
Posts: 3468

PostPosted: Thu Sep 12, 2013 12:58 pm    Post subject: Reply with quote

...... So carbon fiber is roughly twice as stiff as aluminum. Sorry, but for all practical purposes, you simply are not going to overcome this and still have a USEABLE boom - i.e., you could make the boom 3" O.D. and have it be stiff enough, but you would not be able to hold it comfortably

You just said there is no way to make a usable boom out of alu.....
Most windsurfers have one, you know?
Typing fast again?

"For uni-directional carbon fiber, it is about 180 GPa (of course this varies with the type of carbon, the layup, resin/fiber ratio, etc. but you get the idea"

We both get the idea. In this passage you explained why carbon can be floppy like a string or strong enough to hold up a building.
Aluminum is never that floppy but can be strong enough to hold that same building.
If you lay a bundle of raw UNI fibers an inch in diameter next to a one inch alu bar which one is stiffer and stronger?
No matter the modulus the fibers are floppy like a rope, not suitable for booms.
These are raw materials. Like you said, design and construction are the key features that make composite structure strong or weak, stiff or flexible.

Bred you are smart and well informed but perhaps should consider that analysis again. I am going out on my impossible to build, very usable alu boom.
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