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DanWeiss
Joined: 24 Jun 2008
Posts: 2296
Location: Connecticut, USA
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 Posted: Thu Apr 13, 2017 4:00 pm Post subject: |
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| joethewindsufa wrote: | | guess my question has always been - what is the benefit of CARBON in extension ? |
As Carl said, long carbon extensions bend with the mast, but not entirely for the benefit we might think, namely flexibility not offered by a similar aluminum extension that best matches the sail's luff curve. This phenomenon becomes more noticeable the greater the amount of extension used, applies to standard diameter extensions but can be even more apparent using RDM extensions set long with short, soft masts.
The other reason long carbon extensions are preferable to aluminum concerns mast breakage. The tube diameter of most aluminum extensions tends to be smaller than the tube diameter of carbon. Therefore, the longer the aluminum extension that is inside the mast the more likely the tube top will contact the bending mast and cause point loading, resulting in wear and sudden mast failure. To avoid point loading, most manufacturers incorporate a soft, plastic shim on the bottom of the aluminum extension where the mast is seated and another that is part of the extensions's top cap.
Consider that carbon extensions hardly every require any shim to fit snugly inside the mast. The tube diameter of carbon extensions included consideration of the engineering principles of tube stiffness and the benefits carbon construction brings. A thinner wall of a larger tube diameter will create a stiffer tube, but thin-walled aluminum tubes don't have the same tensile strength of carbon and will fold under high load. Therefore strong aluminum tubes require thick walls for durability but then become really stiff.
While the two reasons to use carbon extensions for everything but very small extension lengths (performance and safety) make sense, a carbon extension is priced about twice that of an aluminum extension.
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bred2shred
Joined: 02 May 2000
Posts: 989
Location: Jersey Shore
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| Posted: Thu Apr 13, 2017 5:16 pm Post subject: |
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| joethewindsufa wrote: | | guess my question has always been - what is the benefit of CARBON in extension ? |
When I started using skinny masts (almost 20 years ago) we had to adapt SDM base extensions to fit on the outside of the mast. A couple years later, the manufacturers started making skinny extensions that fit inside the mast. The first several aluminum extensions I bought ended up bending (I'm 6'-3", 200Lbs, jump, etc). I switched to carbon, and the issues went away. So for me, it is solely a matter of strength. I think the arguements about weight or matching the mast bend profile are bogus. You stick a carbon tube inside a carbon tube and it's going to create a stiff spot in the mast and point loads just the same as if you put an aluminum tube inside a carbon tube. As long as the mast is designed to handle the loads, it's a non-issue. I also raced formula boards for several years and always used aluminum (SDM) extensions and never had any problems with or felt any concern about the masts.
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Fri Apr 14, 2017 7:39 am Post subject: |
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Dan said: | Quote: | | Therefore, the longer the aluminum extension that is inside the mast the more likely the tube top will contact the bending mast and cause point loading, resulting in wear and sudden mast failure. |
While this makes some sense, has anyone ever had a mast break below the boom or in the area of the extension?
I have broken more than 6 masts over the years and ALL broke above the boom, and never in the top section. |
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cgoudie1
Joined: 10 Apr 2006
Posts: 2599
Location: Killer Sturgeon Cove
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| Posted: Fri Apr 14, 2017 11:05 am Post subject: |
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Ooh, Ooh, my wife had one break at the mast extension, all 125 lbs of her
when it happened. A simple fall, that broke (actually split) the mast the
length of the extension. That was better than 30 years ago
before carbon masts (in fact I think it was a 1 piece).
-Craig
| techno900 wrote: | Dan said: | Quote: | | Therefore, the longer the aluminum extension that is inside the mast the more likely the tube top will contact the bending mast and cause point loading, resulting in wear and sudden mast failure. |
While this makes some sense, has anyone ever had a mast break below the boom or in the area of the extension?
I have broken more than 6 masts over the years and ALL broke above the boom, and never in the top section. |
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Fri Apr 14, 2017 1:13 pm Post subject: |
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Good point, but not much of an issue since the old fiberglass and aluminum one piece masts are mostly gone. I too did break my Mistral Superlight, one piece blue fiberglass mast by falling on it sometime around 1990, and as I recall, it was below the boom.
But with today's carbon masts (various percentages of carbon), I wonder if any are stressed by the extensions so that they break below the boom. |
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beaglebuddy
Joined: 10 Feb 2012
Posts: 1120
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| Posted: Fri Apr 14, 2017 5:11 pm Post subject: |
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| I'm quite certain aluminum will bend. |
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