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Old 01-01-2010, 01:51   #31
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Originally Posted by Jmolan View Post
You are comparing regular Dyneema to wire. It should be about 2x. If you use Dynex Dux (same stuff, only heated and stretched) it should be 3 or 4x.

I am looking for 3/16's life line wire and so far all I can find in coated.
What's the basis for the 2x or 4x recommendations? I understand for rigging you are looking for equal stretch/acceptable creep. But for lifelines stretch and creep are not really a major issue - I guess for lifelines it's about chafe and uv.

If you search for 'lifeline wire' you pretty much only get coated wire despite the fact its been banned from racing for years. You just need to look for wire (not life line wire). Many boats are using 1 x 19 rather 7x7.
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Old 01-01-2010, 12:49   #32
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[QUOTE=estarzinger;381739]What's the basis for the 2x or 4x recommendations? I understand for rigging you are looking for equal stretch/acceptable creep. But for lifelines stretch and creep are not really a major issue - I guess for lifelines it's about chafe and uv.

You are correct. When you size for stretch and creep for standing rigging, and you use Dynex Dux (the only 12 strand rope choice you have in standing rigging) you will come up with those numbers of 2x to as much as 5x.

If you use 5mm Dyneema you will be 2x the 3/16" 7x7 you are replacing.

If you choose to you could use 5mm Dynex Dux and be 3x or more.

I was not recommending 2x or 3x rope replacement for lifelines. I ran through those numbers to show how those numbers pop up. I was trying answer this question below. I hope I did not get to far off track in my explaination. The low stretch, low creep of Dux is not a requirement in the life line.


What size line did you use for your lifelines? The spec wire is 3/16" and the way the ISAF regulations are currently written would set the dyneema at the same size, which does not give anywhere near the sort of safety margin vs wire you are talking about.

By the way. If you are in France, are you able to get down and see any cool Tri's? I understand they are converting some of the old race machines to fast cruisers
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Old 01-01-2010, 13:18   #33
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[By the way. If you are in France, are you able to get down and see any cool Tri's? I understand they are converting some of the old race machines to fast cruisers
The cool tris seem mostly to be in Britanny. We are in Provence but we do see a lot of open 60's and other cool mono's. This is really the place where exciting things are happening in sailing. Sailors are still heros here.
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Old 02-01-2010, 01:37   #34
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I have put a link on our home page (in the quick news box) to a working draft of an article on working with dyneema single braid. Be curious if you have any comments. The article is designed to come out to accompany the ISAF approval of dyneema life lines.
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Old 02-01-2010, 22:37   #35
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Evan, good one. So Honeywell is Spectra, and DSM is Dyneema. I had to do some research to get that right in my head after I read your piece.
All looks good on the write up except the UV numbers. I was wondering where you got the UV info?
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Old 03-01-2010, 01:49   #36
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All looks good on the write up except the UV numbers. I was wondering where you got the UV info?
I have two UV reports - one by MAR, a company which makes heavy lifting slings (our of all sorts of different fibers) and another by ExxonMobil which tested raw fibers in Arizona.

I find both of these tests show more UV damage than I have found in my own spectra lines. We had some 6 year old 10mm spectra checkstays and some 5 year only soft loops pull tested in NZ and they tested 85-88% of original strength.

But I thought it made sense to use the more conservative (and authoritative) figures in the article.

Do you have any data on UV? What do you think the numbers should be?
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Old 03-01-2010, 17:07   #37
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Even that is great to know. I have not seen those tests, but your experience is similar to mine. I thought I heard somewhere there was a 20% hit the 1st year in degradation.
After that it was almost like Aluminum ah....I lost the word. The coating it gets from exposure to the weather...... Helps protect underneath the opaque covering. Also I understood from a test in NZ they figured only the very outside cover of the line is getting any damage, and 95% of the core is still good.
With the Dynex Dux as standing rigging, it is heated and stretched and is so compacted, I think we will see some long term results that will surprise a lot of critics. But that is just my opinion. The UV testing takes time.
I can see if you tested raw fibers, it would not be the same as a tightly weaved rope as far as exposure goes. Thanks
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Old 03-01-2010, 17:17   #38
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The way to think about it is that the atmosphere (mostly nitrogen and oxygen) is a damn good insulator and lightning still goes miles through the atmosphere. Everything on your boat, although it might be considered an insulator, still conducts electricity better than the atmosphere. So basically, its irrelevant how good an insulator Spectra, or whatever is, its still a better conductor than the surrounding air....therefore it will still carry electrons from a lightning strike.
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Old 03-01-2010, 18:23   #39
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The way to think about it is that the atmosphere (mostly nitrogen and oxygen) is a damn good insulator and lightning still goes miles through the atmosphere. Everything on your boat, although it might be considered an insulator, still conducts electricity better than the atmosphere. So basically, its irrelevant how good an insulator Spectra, or whatever is, its still a better conductor than the surrounding air....therefore it will still carry electrons from a lightning strike.
"The way to think about it is".........I am not a scientist, or anything near educated enough to "theorize" about lightening. It is why I opened up this thread in the first place. I know there are some very smart people who frequent these pages. I am just a "poor dumb fisherman"
Somehow your theroy does not make sense to me. From a real world situation, aren't you trying (as a boat owner) to make a path for the lightening to have the least resistance to get to ground? And make the path as direct as you can, so the chances of stray current will not run down somewhere and blow out? So is it better to have Synthetic as opposed to wire? Who knows, the real worl has not told us yet.
I am sure there are other lightening threads, and best way to ground threads etc.
I think your saying,

"So basically, its irrelevant how good an insulator Spectra, or whatever is, its still a better conductor than the surrounding air....therefore it will still carry electrons from a lightning strike.

Something don't ring right there. It's like you threw the baby out with the bath water.
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Old 04-01-2010, 04:14   #40
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Quote:
Originally Posted by David M View Post
The way to think about it is that the atmosphere (mostly nitrogen and oxygen) is a damn good insulator and lightning still goes miles through the atmosphere. Everything on your boat, although it might be considered an insulator, still conducts electricity better than the atmosphere. So basically, its irrelevant how good an insulator Spectra, or whatever is, its still a better conductor than the surrounding air....therefore it will still carry electrons from a lightning strike.
Quote:
Originally Posted by Jmolan View Post
"The way to think about it is".........I am not a scientist, or anything near educated enough to "theorize" about lightening. It is why I opened up this thread in the first place. I know there are some very smart people who frequent these pages. I am just a "poor dumb fisherman"
Somehow your theroy does not make sense to me. From a real world situation, aren't you trying (as a boat owner) to make a path for the lightening to have the least resistance to get to ground? And make the path as direct as you can, so the chances of stray current will not run down somewhere and blow out? So is it better to have Synthetic as opposed to wire? Who knows, the real worl has not told us yet.
I am sure there are other lightening threads, and best way to ground threads etc.
I think your saying,

"So basically, its irrelevant how good an insulator Spectra, or whatever is, its still a better conductor than the surrounding air....therefore it will still carry electrons from a lightning strike.

Something don't ring right there. It's like you threw the baby out with the bath water.
There IS a lot more to it, lightning is just an electrical current and follows all the laws that govern the flow of electricity.

Lightning does not travel through "air" (i.e. 80% nitrogen, 20% oxygen) as air is a very good insulator.

What does happen is that build up of EMF (volts) in the atmosphere causes the air to ionize and this ionized gas is a very good conductor. The current now flows along the ionized path and this is the lightning bolt (spark) we see. It is no different to the spark we see when you break a current flow in your 12 volt circuit - except for the magnitude of course.

What the OP was initially asking is what will happen to the spectra shrouds should the mast be struck by lightning.

The short answer is that I don't know but I do know that the current flows will follow ohms laws (among others). The current will take ALL paths to ground and in direct proportion to the various conductance's. Lets say the mast offers 1 ohm to ground and the shrouds offer 1000 ohms to ground. The mast will therefore carry 99.9% of the current and the shrouds 0.1% of the current. Of course 0.1 % of a very large current is still a big number of amps.

What is the resistance of dry spectra, what is the resistance of wet spectra, what happens to wet spectra when carrying a large current, how hot does it get, what happens to the dielectric strength of spectra when subject to a large EMF (i.e. big volts).

These are the questions that need to be answered to know what happens to spectra when lightning is about - or you could just go sailing through thunderstorms and get empirical evidence.
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