Dyneema or kevlar for forestay?
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11036
Printed Date: 16 Jul 25 at 12:23am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Dyneema or kevlar for forestay?
Posted By: H4marine
Subject: Dyneema or kevlar for forestay?
Date Posted: 19 Aug 13 at 11:10am
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Just snapped the old Kevlar forestay on my old (1999) 14 at the weekend, fortunately it was downwind back to the slip so the kite kept the mast up. The old forestay is Kevlar (in an outer) 2:1 wire going to a 6:1 rope, what is generally used now? Dyneema/spectra core? how thick?  ------------- sailonline.org sailport.se |
Replies:
Posted By: Jack Sparrow
Date Posted: 19 Aug 13 at 11:35am
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MRig - Marlow Ropes... although I can't see it when I just searched? It is a DM20 fiber...
http://rigpronewport.wordpress.com/2012/12/10/dyneema-dm-20/" rel="nofollow - DM20 Dyneema LINK ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: H4marine
Date Posted: 19 Aug 13 at 11:56am
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Thanks Mr Sparrow
------------- sailonline.org sailport.se |
Posted By: carshalton fc
Date Posted: 19 Aug 13 at 12:02pm
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Most 14's have wire or Vectran (Marlow Excel V12). The forestay on my Morrison 12 is 3mm wire, long lasting and easy to use. P&B custom made a new forestay and shrouds one for us a week ago out of the hamma pro wire 7x1. ------------- International 14 1503 |
Posted By: H4marine
Date Posted: 19 Aug 13 at 12:33pm
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Mine has wire up to a pulley on the mast giving 2:1 then Kevlar (or had) down to the bow. Line will be easier for me to make up, just want to make sure it's strong enough. Thanks.
------------- sailonline.org sailport.se |
Posted By: JimC
Date Posted: 19 Aug 13 at 1:57pm
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I'd avoid Kevlar. Snaps with little warning.
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Posted By: gbr940
Date Posted: 19 Aug 13 at 4:32pm
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definitely vectran ------------- RS400 GBR1321 |
Posted By: Daniel Holman
Date Posted: 19 Aug 13 at 5:15pm
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I'm going top be controversial! I use marlow sk78 max dyneema on the forestay and capshrouds of my 14. Quarter of the weight of dyform, and similar price once swaging has been taken into account. DM20 dyneema (M RIG is an english braids product based on this fibre I think) was created for the offshore mooring industry, and has very little creep, but like vectran has lower moduluis of elasticity than dyform or sk78 max (i.e a 3mm rope of a given length will stretch more under a given load) I use 4mm Sk78 max on the forestay - 3mm would have better modulus and breaking load than 3mm dyform, but I have a 1mm margin for wear and tear. I use 2.5mm on the caps. Make sure you do good splices, tapered and with plenty of bury. The one thing I would say is that all woven dyneema products will have an initial mechanical creep associated with the construction and splices. Don't be suprised to take 100mm out of a 6m stay over the first couple of sails. once this is done it will be rock solid. The amount of time that a racing dinghy is tensioned up is negligible in the context of visco-elastic creep. If you take the mast down and put it up again, the stay will recover some of that mechanical creep again, so will appear shorter on rerigging, but that beds back in quickly. |
Posted By: H4marine
Date Posted: 19 Aug 13 at 6:32pm
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Brilliant, thanks Daniel I feel quite well informed now. ------------- sailonline.org sailport.se |
Posted By: laser193713
Date Posted: 20 Aug 13 at 9:04am
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If it is running through a turning block and will be static for long periods Vectran can let go without warning. Modern Dyneema products are just as good and will give a bit more warning before they let go. I am amazed you snapped it while going downwind, if the mast stayed upright then how was the forestay under any tension at all!? |
Posted By: H4marine
Date Posted: 20 Aug 13 at 9:21am
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It snapped going up wind outside the breakwater in Plymouth, mast held up by the jib. So hoisted kite and planed all the way back to the slipway, feeling slightly nervous about how long the jib halyard and small jam cleat would hold up. So Dyneema SK78 seems a good option. Thanks ------------- sailonline.org sailport.se |
Posted By: Jack Sparrow
Date Posted: 20 Aug 13 at 9:46am
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Just so you know... Marlow Ropes are having fibre supply issues with DM20 (MRig) which is why it doesn't seem to be listed anywhere at the moment. Probably all being used in the Americas cup! ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: Jack Sparrow
Date Posted: 20 Aug 13 at 2:47pm
And DM20 data sheet for comparisons against SK78 ... creep, elongation, strength, etc...
 ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: alstorer
Date Posted: 20 Aug 13 at 3:37pm
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That does of course demonstrate the minor issue with just calling it Dyneema- that's a family of fibres, not a single product. ------------- -_ Al |
Posted By: H4marine
Date Posted: 20 Aug 13 at 5:03pm
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Really useful thanks for all the information, I know what you mean, in my business everyone thinks composites are all the same but the base resin name can cover a wide range of material properties. We use a number of different fibres and get some interesting results but in bearings we are looking for different properties to rigging. ------------- sailonline.org sailport.se |