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Old 4th February 2008, 08:42 AM   #1
steve h
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Default Severne Mast Problem

My 550 100% carbon severne mast has a red aluminium collar at the top of bottom section. This collar has a tapered inner profile which mates with the tapered profile of the mast (I believe) and acts as the stopper to hold the top section. Problem is that the red collar is splitting at the base so that the collar is widening & slipping down, presumably because the downhaul tension is so high & maybe because aluminium often corrodes when in contact with carbon. I have seen the same thing on several other severne masts, I don't know why they use the aluminium collar when most masts have the stopper formed from the carbon but it clearly is not real good.

Does anyone know how or if this can be fixed. If I can't fix it the top section will force the collar down till it gives up totally & presumably the top section will break & my sail will be damaged.

It is out of warranty.
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Old 4th February 2008, 02:02 PM   #2
Jesper Orth
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Hi Steve

Thanks for the info. We have sent it to the mast factory to see what they say, and are awaiting an answer.

I must say that we had no failure on the collar on the Severne Red Line mast's here at the R+D in Perth over the last 4 years.

Can you please take some picture of your collar? - And send it to jesper_naturalcorp@bigpond.com

Thanks
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Old 5th February 2008, 02:00 AM   #3
nifty
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Hi Jesper, I had the same problem with a 490 - I wrapped it in carbon. Seems like the aluminium is a weakness in an otherwise very good mast.
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Old 5th February 2008, 03:14 AM   #4
Jean-Marc
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[quote=steve h;18475]
Quote:
maybe because aluminium often corrodes when in contact with carbon.
How reliable is this statement ? How can chemically inert carbon corrode aluminum ? Or is it chemical resins/solvent found in carbon masts that may corrode aluminum ? Sorry, I don't get it at all (sea salt is a well-known corrosive agent, however, even on aluminum).

(mine RL 530 is absolutely fine as well as a couple of 10 years old North Excellerator 60% carbon masts with alumimun collar at the ferrule junction).

Cheers !

JM
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Old 5th February 2008, 04:01 AM   #5
Ola_H
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JM, I think its a form of galvanic corrosion that happens (in which the carbon would more act lik a catalyst). I remember this being a big problem with fx some Specialized carbon bikes with alu lugs in the early 90s. The general "trick" is to use a thin layer of fibreglass as an isolation layer betwen the carbon and alu.
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Old 5th February 2008, 07:37 AM   #6
steveC
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Hi Jean-Mark,

I can honestly say that carbon in contact with metals can be quite reactive, as I know that carbon and SS often evidences iron ferrites in the mix, and significant corrosion can be an outcome. Aluminum could pose similar limitations in combination with carbon. Yet I have to say aluminum, at least in my opinion, can be death on most windsurfing gear, with a possible exception for maybe mast base extensions.

Would I ever buy an aluminum boom? Never!
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Old 5th February 2008, 07:42 AM   #7
Roger
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Hi all,
I've seen this phenomenon (internally tapered hard anodized aluminum seat sleeves splitting and corroding) on a number (a very small number like < 6) of high end 100% carbon masts from Itallica and Excel (I think they made the high end North masts a few years ago).
I suspect that the reason this is not a more common problem is that most of the hard anodized aluminum seat/collar sleeves get installed with a strong adhesive bond between the sleeve and the mast taper.
The adhesive is neither carbon nor aluminum, so it acts as a galvanic "buffer" between the 2 materials. Also, the hard anodizing puts a layer of aluminum oxide on all surfaces of the aluminum sleeve which pretty much kills any "reactivity" between the materials. Hard anodizing, with the correct post anodizing "seal" coat is used worldwide to make high strength aluminum parts withstand exposure to salt water.
If you get a mast where the adhesive bond breaks down (or wasn't fully bonded/buffered in manufacture) the sleeve gets pushed down the taper by the tremendous dowhaul forces we use in modern sails and as it slips down under pressure the hoop strength isn't quite up to the task so the sleeve begins to split at the lower (thinner due to the taper) end of the sleeve. Also, some masts have a little radiused "seat" at the bottom, but the sleeves do not have the same radius so a hard expansive "line contact" occurs when the sleeve slides down.
This splits/cracks the sleeve and if you sail in salt water, the corrosion starts as soon as the base metal aluminum (under the hard anodize coating) gets wet with salt water.
Then the crack corrodes, and as you continue to use the mast the sleeve slides further down the mast.
Fortunately, the taper of the ferrule often stops the top from sliding down further (when the internal and external tapers seat fully), but then the mast tends to be a little diffucult to get apart.
So, I suspect it's a bit of a manufacturing defect, but not something the factory QA guys can really check. How do you check the adhesive bond on an internal anodized aluminum to carbon interface?
I've had one or two masts (in 25 years of using windsurfing masts) with this problem.
One I turned in for a new bottom section and the replacement has not corroded/cracked in over 2 years) and the other one still has the crack and the corrosion, but it seems to have stabilized and it's not sliding or cracking any further.
Hope this helps,

Last edited by Roger; 7th February 2008 at 04:58 AM.
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Old 6th February 2008, 06:05 AM   #8
Jean-Marc
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Chemical reaction between carbon fibers and aluminum :

Carbon fibers are commonly used to synthesize composites showing low density and high strength. However, carbon reacts with aluminum to generate a brittle and water-soluble Aluminum Carbide compound Al4C3 on the surface of the fiber. To prevent this reaction, the carbon fibers are coated with nickel or titanium boride.

No idea whether carbon fibers used by mast manufacturers are coated to prevent aluminum carbide formation at the interface between the aluminum collar (itself being passivated/coated against corrosion) and carbon fiber-reinforced ferrule...?

Cheers !

JM

some sources of interest :
http://en.wikipedia.org/wiki/Carbon_...forced_plastic
http://en.wikipedia.org/wiki/Carbon_fiber
http://en.wikipedia.org/wiki/Galvanic_corrosion
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Old 6th February 2008, 05:21 PM   #9
Ricko
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Arrows had a plastic collars.... no problems.
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Old 13th February 2008, 03:06 PM   #10
JJay
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Default North Mast also

Hi Jesper,
Am wondering how serious the problem of the collar splitting can be?
After the sessions we sailed in WA a couple of weeks ago (08 Warp 6,8). I noticed the collar on my North Platinum 460 mast is starting to split. Yesterday I was with the North dealer here in Singapore, when in walked a guy who was having the exact same problem with a North Gold series mast.

Please note that the North collar is not aluminium. Looks like plastic.

Relax and go fast.
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