RE: Carbon Booms?

From: Brad James (bjames@exponent.com-DeleteThis.com)
Date: Wed Feb 21 2001 - 09:08:13 PST

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Message-ID: <6717C84A8642D2119F1700A0C9D5D9F4036F618C@menlomail.exponent.com-DeleteThis.com>
From: Brad James <bjames@exponent.com-DeleteThis.com>
To: "'wind_talk@opus.labs.agilent.com-DeleteThis.com'" <wind_talk@opus.labs.agilent.com-DeleteThis.com>
Subject: RE: Carbon Booms?
Date: Wed, 21 Feb 2001 09:08:13 -0800

I'm a materials engineer who analyses broken parts for a living - and I've
broken both kinds too.... For the saltwater sailing we do - aluminum as a
material is not the greatest choice. That said, if you replace the Al booms
often, you shouldn't have any problems.

The biggest issue with aluminum is corrosion. Salt water contains chlorides
that break down the oxide layer that protects aluminum. This corrosion can
interact with the repeated stresses placed on the boom during sailing
(fatigue). (Al also doesn't have the greatest fatigue properties either)
Corroded aluminum has a flakey white appearance - not like rust. Another
issue is that you can't see the insides of the Al tubes, which probably stay
wet longer and therefore corrode more.

Of course Ed's boom bending problem has nothing to do with corrosion or
fatigue, he just applied a local force greater than the yield strength.
Carbon fiber has much, much higher yield and ultimate strengths compared to
Al. So you won't bend carbon booms - but carbon will break (without much
deformation) at high stresses. Aluminum has much greater ductility, so you
can bend them before they break (due to overload - not corrosion or
fatigue). So would Ed have broken carbon booms instead of just yielding
his aluminum booms??? Who knows... it depends on lots and lots of
variables. But you certainly could put a stress on an aluminum boom that
would bend it, where the same stress wouldn't do any damage to a carbon
boom.

Carbon fiber doesn't have saltwater corrosion problems. My understanding is
that a lot of the carbon fiber boom problems of years past (particularly
fiberspar) were actually aluminum problems. They used aluminum lugs to
attach the boom arms to the heads - these aluminum lugs were what was
failing (from corrosion and fatigue). That said, the carbon booms resin
likely degrades to some extent due to sun (UV) exposure. Probably not much
for Bay Area purposes, but if you left them on the beach at the equator for
a year, you'd probably have reduced the strength of your booms.

My guess is that if you sail a lot, and want to replace your Al booms before
they break, you would probably spend the same $$ on all the Al booms as on
a carbon boom that you keep for longer.

Hope this helps

Brad - Metallurgist at large!

-----Original Message-----
From: Topher Gayle [mailto:surfnsuds@earthlink.net-DeleteThis.com]
Sent: Wednesday, February 21, 2001 8:34 AM
To: Multiple recipients of list WIND_TALK
Subject: Re: Carbon Booms?

Well, I have had the pleasure of breaking both kinds of booms.

I've broken two aluminum booms and was able to sail the bent poles back to
the beach, and I've broken one carbon boom and was also able to sail it back
to the beach. In all cases, the breaks were (obviously) not complete
destruction. The carbon break was caused by a rather ordinary catapult of
my 200# self in chop that should not have done in the boom. The front end
broke, but more expensively, the pole going into the front end was also
fractured (though not broken). This second bit of damage was not visible
until the front end was removed. That's a little scary.

Carbon costs so much more, I now prefer aluminum, and replace them more
often.

- Topher Gayle

----- Original Message -----
From: "Georg Recht" <gorecht@earthlink.net-DeleteThis.com>
To: "Multiple recipients of list WIND_TALK"
<wind_talk@opus.labs.agilent.com-DeleteThis.com>
Sent: Wednesday, February 21, 2001 7:55 AM
Subject: Re: Carbon Booms?

>
> I definitely will not buy another Aluminum boom for my Bay Area sailing.
My
> experience is that Aluminum will fatigue and just break at the worst time.
> All my failures occurred at the front of the boom due to fatigue and not
> corrosion. There never was any warning except maybe I kept them for one
too
> many seasons.
>
> I am very happy with my current booms, a Fiberspar all carbon and a
Winsurf
> Hawaii [mostly carbon except extensions are Aluminum].
>
>
> At 09:29 PM 2/20/01 -0800, you wrote:
> >
> >I bent my aluminum booms last year getting rinsed. Just curious, since
I'm
> >in the market again, what others thought of carbon booms, especially for
use
> >in surf. I always thought that aluminum was preferable over carbon in
waves
> >because of it's ability to bend rather than break. However, I've heard
> >that aluminum's tensile strength isn't that great, has the tendency to
break
> >rather than bend, and it corrodes inside where it is undetectable. Input
on
> >brands would be appreciated, too. I know (think) that Fiberspar fixed
their
> >problems from a couple years back, lots of folks tend to have them, but
the
> >all-carbon Chinooks look pretty nice (pretty hefty price tag, too!).
> >
> >Thanks.
> >
> >-Ed
> >
> >
> >
> >
> >
>
>

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