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steve h
4th February 2008, 08:42 AM
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.

Jesper Orth
4th February 2008, 02:02 PM
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

nifty
5th February 2008, 02:00 AM
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.

Jean-Marc
5th February 2008, 03:14 AM
[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

Ola_H
5th February 2008, 04:01 AM
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.

steveC
5th February 2008, 07:37 AM
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!

Roger
5th February 2008, 07:42 AM
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,

Jean-Marc
6th February 2008, 06:05 AM
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 (http://en.wikipedia.org/wiki/Aluminium_carbide) on the surface of the fiber. To prevent this reaction, the carbon fibers are coated with nickel (http://en.wikipedia.org/wiki/Nickel) or titanium boride (http://en.wikipedia.org/wiki/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_fiber_reinforced_plastic
http://en.wikipedia.org/wiki/Carbon_fiber
http://en.wikipedia.org/wiki/Galvanic_corrosion

Ricko
6th February 2008, 05:21 PM
Arrows had a plastic collars.... no problems.

JJay
13th February 2008, 03:06 PM
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.

Ola_H
13th February 2008, 03:30 PM
Thinking som more about the alu-carbon interface: I haven't looked at these mast, but I don't think it will be much of a problem. The alu is not bonded directly to the "internal structure" of the carbon. It's more like something that comes on top. There will (I assume) be some finishing plastic layers in between which will help.

The bottom line is that the splitting problem is more likely to come from the issues Roger mentioned, ie a less than perfect bond and/or a less than perfect interface geometry.

JJay
18th February 2008, 08:54 PM
Anyone have any info on the collar problem? How serious is it?
Am I looking at a new mast? Will I need to read the small print on my warranty?
Has anyone else had a collar fail?

Tensing up and getting slower!

nifty
19th February 2008, 01:22 PM
I'm thinking about getting another Redline anyway since they're such a good mast performance and build quality-wise. I'm willing to take the chance on the aluminium splitting. Hopefully if there is a problem, it's only with a very small percentage of masts sold.

JJay
19th February 2008, 05:07 PM
North have fixed my cracked collar the best way they can,,,,,,
,,,,,,,,,by replacing it with a new one.
Did some investigating. Seems that very few masts have seen such problems over the years.
However it is not unheard of.
I have learned that once the collar splits,,,, the clock starts ticking on the eventual total failure of the mast.

Gotta say thanks to North

And a big thanks to Rachel

"Relaxed and getting faster"

matt12
12th March 2008, 09:19 AM
For reference those North aluminium collars are available individually from North. Apparently they can crack partially but even if they do, it is very unlikely to fail completely. The material has a taper so the thin end can crack but there is still a great section with increased thickness remaining on the mast. Agree that it is not perfect, but also it is not necessarily a mad panic to continue to use or replace just the collar.

Not sure of the engineering logic behind the comment that the mast is about to fail? Can you explain please?

steve h
14th March 2008, 12:22 PM
just to say that Jesper sent me a new collar for the mast. Cut the old one off quite easily and put new one on, seems fine. Thanks Jesper.

nifty
15th March 2008, 01:46 PM
Hi Steve H, how the hell did you remove the old collar? Can you give us a detailed description? Thanks.

matt12
16th March 2008, 06:14 AM
It is very hard to remove the broken collar. Here is the process that I used but it didn't work very easily .... this is a process probably NOT to follow ... I think there must be easier ways?

1. Stand mast vertical on hard surface like concrete.
2. Use a chisel and hammer to try to knock down the collar. Very hard because the material is thin hence cracks and bends easily. I ended up chiseling off small pieces about 2cm in size. Caused some minor damage to the mast.
3. Once the thin half of the collar has been removed, you can eventually get enough thickness to knock with your chisel and hammer.
4. Finally it released and fell down to the concrete.

A better way might be to use a Dremel and very carefully & time consumingly cut the collar off with a vertical grinding line. ... but don't grind down completely through the aluminium. Grind down ALMOST to the full thickness, then split open with a screwdriver.

nifty
19th March 2008, 05:48 PM
Thanks Matt, yes, I think that's the go - carefully cut longitudinally but not all the way through, then try to split it off with a chisel or the like.

steve h
20th March 2008, 10:01 AM
Nifty,

Was easy. using a hack saw I cut diagonally from top to bottom of the collar. best to be diagonal to avoid cutting the mast. Cut the groove almost through along its length & then cut a bit further at several points so that the carbon just shows through. It reaches a certain point then cracks open & can lever it off by widening the crack with screwdriver.

The new one fit straight on & I used an old mast base to get a surface to hit it gently with a hammer to force it on, ie, hit the base & it will transmit the force all round the new collar to force it down over the tapered carbon mast.

nifty
22nd March 2008, 05:39 PM
Thanks for that Steve, hopefully won't see another cracked collar anyway. Long-live the Redline mast - a quality item.
Cheers.