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NHRC 
Posting king 
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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 Topic: Bendy carbon mastsPosted: 01 Jun 15 at 9:21pm |
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No doubt money buys quality...
Thanks for your posts guys... Just wondering if any skiffies have noticed their spars booms sprits loosing their stiffness with time??? |
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www.thenottinghillriggingco.com
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alstorer
Really should get out more 
Joined: 02 Aug 07 Location: Cambridge Online Status: Offline Posts: 2899 |
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Posted: 01 Jun 15 at 3:38pm |
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Epoxy resins can degrade and soften with weather and cyclic loads. Even without weather, carbon composite can most certainly undergo fatigue failure. Graeme is right- paying more (autoclave cure means more expensive resin in most cases) gets you better more reliable performance*
*most of the time. Pretty much. Sort of. For a value of "better". |
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Al |
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NHRC
Posting king
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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Posted: 31 May 15 at 11:10pm |
I seem tobe lucky. If anything my hull is over engineered. I have tested it with a load cell to far more than the loads it will need to withstand and it is fine. The issue is either with the carbon tube or the rigging. There are things I know I can try with the rigging, hence asking for people's experience with carbon spars suffering fatigue over time. Have you ever had any experience with that?
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www.thenottinghillriggingco.com
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Woodburner
Far too distracted from work 
Joined: 13 Mar 15 Location: Folkestone Kent Online Status: Offline Posts: 332 |
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Posted: 31 May 15 at 7:54pm |
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They do vary their curve especially if left under tension, even when new, we had a bunch of brand new hi quality 100% carbon masts at a dealer conference, they were rigged and left under tension for three or four days, when we derigged they were all bent.
We tend to bend them the opposite way, which as advice, isn't much use to dinghyists with bolt rope tracks, so the best bet always ensure the rig tension is off, don't over tension in hot weather, (the event we were at was in Greece mid summer). There is also a lot of variation in the tolerance of masts from differing manufacturers, and the type of lay up and weather the tube is autoclaved, or not, braided tubes also suffer more than the vertical then cross wound layups. There was a store in Hood river with a mast bend test machine and they used to keep notes, even of the same mast from the same brand there were often quite stark variations in stiffness even though the manufacturer claimed less than 5%. In those days there were two or three mast builders in town and this pre dated the explosion of carbon tube from the former USSR factories that happened in the mid to late nineties before the Italians geared up. So anyway enough waffle, the moral of the tale, you pays you're money and you takes your choice, but they need looking after and UV aint their friend either.
Edited by Woodburner - 31 May 15 at 7:55pm |
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JimC
Really should get out more
Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6662 |
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Posted: 31 May 15 at 3:16pm |
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Interesting... I haven't studied the paper properly but I note that it says that (para 4.1) in the composite they used "fatigue is unlikely to be a problem when cyclic stresses coincide with the fiber orientation". Of course in a mast nearly all the fibres are oriented the same way and so are all the stresses.
Merlins are intrinsically not the best engineered of boats, it might be worth taking measurements to see if the hull is distorting. The trickiest, because the foredeck is in the way, but possibly most useful is across the hull midway between bow and mast. Between the shrouds is good as well of course. Edited by JimC - 31 May 15 at 3:24pm |
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NHRC
Posting king
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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Posted: 31 May 15 at 2:53pm |
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Thanks for the link there O&B I'll have a read later... I have been trying to find some research on fatigue on line but was struggling.
Not sure how scientifically fatigue works on a composite as opposed to a metal.
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Oatsandbeans
Far too distracted from work
Joined: 19 Sep 05 Location: United Kingdom Online Status: Offline Posts: 382 |
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Posted: 31 May 15 at 2:44pm |
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Yes, the stiffness of a carbon composite will drop as it is fatigue cycled. If you are into this sort of thing here is a link.
http://web.ornl.gov/~webworks/cpr/v823/rpt/106099.pdf The graph on page 57 shows how the strain ( equivivilant to deflection on a mast) changes if it is cycled at 1/2 its ultimate strength. After 10,000 cycles ithe strain goes from 0.8 to 1.0 % which doesnt sound much but is a 20% increase |
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NHRC
Posting king
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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Posted: 31 May 15 at 12:35pm |
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Cheers iiiiitick...!
That is good to know. I don't think that there is any scientific or engineering evidence that carbon tubes should develope a softness like a metal, without there being unseen cracks, de-lamination, splits or voids causing softness. Please can more people post stories of what they have experienced with carbon spars, masts booms skinny poles and bowsprits regarding them becoming more bendy, losing eir stiff characteristics with age and heavy use...
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iiiiitick
Far too distracted from work
Joined: 19 May 15 Online Status: Offline Posts: 240 |
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Posted: 31 May 15 at 12:25pm |
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I only know of unstayed carbon masts on Byte C2. My friend is sailing regularly with a nine year old mast including winning two championships. He is on his third boat but has retained the original mast. He is happy with the mast characteristics and sees no reason to change.
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NHRC
Posting king
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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Posted: 31 May 15 at 11:30am |
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The boat is surprisingly stiff, I pulled across the beam from the shroud points to 350kgs without any creaks or changes in shape.
Chepstow mast Ron hall hull. The lowers are a possibility... More interested in people's reflections and experiences on ageing carbon masts and their longevity.
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