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carbon boom, needed or not?
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outhaul



Joined: 27 Sep 2011
Posts: 180

PostPosted: Fri Sep 13, 2013 10:19 am    Post subject: Reply with quote

outhaul wrote:
Many great posts here, I'm almost more undecided now. I keep going back to the fact that the 180-246 Chinook is close to 3lbs lighter than its alloy sibling. Sadly I then remember it also costs 3 times more.
Is there a down side to re-gripping a carbon when the time comes? Does one need to be extra careful with solvents?


Update, the weight difference between a Maui carbon 190-240 and the Chinook 185-247 Pro Alloy is about 1 pound. So the weight issue is less than I first thought, just depends which carbon boom you compare to. Credible sources tell me the Maui carbon is a good bit stiffer than the Chinook carbon especially noticeable in the larger sizes which explains the weight difference.
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capetonian



Joined: 11 Aug 2006
Posts: 899
Location: Oahu

PostPosted: Fri Sep 13, 2013 11:46 am    Post subject: Reply with quote

I have a carbon Maui Sails 190-240 and a carbon HPL 200-260. Set at length 240 cm the Maui Sails boom is very noticeably stiffer than the HPL also set at 240 cm. Those fat boom arms at the back of the Maui Sails boom make a difference.
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KevinDo



Joined: 02 Jul 2012
Posts: 414
Location: Cabrillo Inside

PostPosted: Fri Sep 13, 2013 11:58 am    Post subject: Reply with quote

capetonian wrote:
I have a carbon Maui Sails 190-240 and a carbon HPL 200-260. Set at length 240 cm the Maui Sails boom is very noticeably stiffer than the HPL also set at 240 cm. Those fat boom arms at the back of the Maui Sails boom make a difference.


Have you tried the larger chinooks? I believe they are tapered too. The maui boom is probably the stiffest boom I have ever used. At my weight of 64kg, I can't even flex the damn thing on shore haha. I have seen one snap before but the user was about 110kg.
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w8n4wind



Joined: 12 Nov 2008
Posts: 273
Location: canada

PostPosted: Fri Sep 13, 2013 7:30 pm    Post subject: Reply with quote

so, just did a quick stiffness test on my brand new pro-alloy, 185-247cm.
i set the boom at 241, which is the length for my 9m, i then stood on one arm, and pulled up as hard as i could on the other, and..yes it was flexing! but, according to my tape measure, the overall length of the boom changed by a 1/4 of an inch at most.
so, assuming that carbon is twice as stiff <<( which i would find debatable)
lets say that deflection would then be only an 1/8 of an inch.
that means the aluminum boom has 1/8'' more deflection than carbon, so my question is, how much performance loss is there really in that 1/8'' ? seriously.

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slinky



Joined: 24 Aug 2007
Posts: 419
Location: Old Saybrook Ct.

PostPosted: Fri Sep 13, 2013 8:00 pm    Post subject: Reply with quote

Little if any
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capetonian



Joined: 11 Aug 2006
Posts: 899
Location: Oahu

PostPosted: Sat Sep 14, 2013 9:52 am    Post subject: Reply with quote

w8n4wind wrote:
so my question is, how much performance loss is there really in that 1/8'' ? seriously.


Depends on what kind of sailing you are doing. When I am freeriding or wavesailing using a boom that I know is slightly flexy I still notice the flex in gusts but it doesn't bother me as I am probably anyway using a small sail for the wind conditions. However when I am racing I am already sailing very well powered (what non racers might call almost over powered) so I don't want any flex.
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keycocker



Joined: 10 Jul 2005
Posts: 3358

PostPosted: Sat Sep 14, 2013 1:13 pm    Post subject: Reply with quote

If one is concerned about an 1/4 of an inch shorter boom under load, couldn't a guy split the difference and pull out an extra 1/8 of an inch on the outhaul?
LOL just kidding
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whitevan01



Joined: 29 Jun 2007
Posts: 484

PostPosted: Sat Sep 14, 2013 1:22 pm    Post subject: Reply with quote

w8n4wind wrote:
so, assuming that carbon is twice as stiff <<( which i would find debatable)
.



I'd like to know your evidence for that statement.

Young's modulus of elasticity (which is used, among other things, to calculate deflection) is 69 Pa for aluminum and 181 Pa (according to Wikipedia which quoted it from another source) for carbon fiber reinforced
plastic (70/30 mix), so 100 % carbon fiber would be a bit higher, I assume, although what we call 100% carbon is really not 100% as epoxy resin must be used to hold it all together..

so, that's almost three times as stiff. couple that with the fact that aluminum is isotropic (basically, the same throughout) while carbon fiber can be laid up so that it is always optimally oriented depending on the location and in what direction the loads will be applied. so, yes, your comment is correct, but in the wrong direction (pun intended)

have fun!!!
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keycocker



Joined: 10 Jul 2005
Posts: 3358

PostPosted: Sat Sep 14, 2013 2:19 pm    Post subject: Reply with quote

The modulus of elasticity for S glass is 20 percent higher than alu.
Does this prove that glass booms would be 20% stiffer than alu booms?
You may have discovered a whole new era in booms.
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keycocker



Joined: 10 Jul 2005
Posts: 3358

PostPosted: Sat Sep 14, 2013 2:45 pm    Post subject: Reply with quote

The facts here are repeated correctly several times. Carbon is a lot stiffer as a raw material.The key fact is that in a composite structure, stiffness and strength are mostly determined by the design.
With the same piece of carbon cloth I can make you a stiff tube,a flexi piece of stiff fabric using soft curing epoxy, or a flexi carbon fishing rod that bends over almost double when you use it.
I can do this with Fiberglass also., but aluminum is too stiff despite have the lowest mod of elasticity.
All in the design.
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