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Old 09-05-2013, 14:56   #16
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Re: High-end vs. low-end line?

Jim

Here's what I was driving at, and it's counterintuitive, which is why I thought it worth raising, and why I'm 'quibbling' now:

A multipart tackle doesn't amplify the tension in the line, it multiplies the line tension at the attachment of the block, by the number of standing parts. Each standing part is only subject to the tension you can apply, until you cleat it.

Your point about external loads once cleated is undoubtedly true, and I wondered about qualifying my claim with that proviso, but I decided for simplicity, and to avoid diluting the counterintuitive thrust of my post, to cover that contingency (the crash gybe) by the weasel word 'effectively'.

The greatest constant load on a mainsheet arrives when hard on the wind at maximum heel, and if it's not possible to tighten the mainsheet in this situation, that tackle needs more standing parts (eg 6:1 in lieu of 5:1).

Or a stronger mainsheet hand!

So in any constant load situation where you could bring in the mainsheet if you had to, it's axiomatic that the line tension will be less than or equal to the maximum you can pull.

Which in turn implies that breaking a mainsheet, on a boat without a mainsheet winch (and where the crew do not wear gloves and cannot perform one-armed chinups on demand !), is a rare occurrence indeed, and I think would generally require radical damage or neglect of the line.

I don't think the same necessarily applies to a multipart vang, at least on a cruising boat: it's quite usual when hard on the wind not to be able to harden the vang without first oversheeting the main.

When the sheet is subsequently eased, the vang will come under extra load (resulting in more line tension than any crew can pull) because of the leverage of the boom.

Even then, I imagine it's rare for non-winched vang lines to break. I've not heard of a case....
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Old 09-05-2013, 16:03   #17
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Re: High-end vs. low-end line?

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Originally Posted by Andrew Troup View Post
Jim
Here's what I was driving at, and it's counterintuitive, which is why I thought it worth raising, and why I'm 'quibbling' now:

A multipart tackle doesn't amplify the tension in the line, it multiplies the line tension at the attachment of the block, by the number of standing parts. Each standing part is only subject to the tension you can apply, until you cleat it.
Dang, Andrew, I think that you are right about that! And in fact I have never broken a main sheet, but I have broken a few attachments to the boom.

Still, in the real world I think that dynamic loads on sheets are what break them in most cases, but such breakage is pretty rare.

Cheers,

Jim
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Old 09-05-2013, 16:13   #18
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Re: High-end vs. low-end line?

Spinnaker sheets and halyards, more than any other sheets / guys / halyards on the boat, should have a little stretch in them. Unless you have a boat that "pops out" and planes easily (and given that this is a cruising site, I'm guessing not many do), then when you experience a gust with a kite up, it can really load up the spinnaker because cruising boats are relatively slow to accelerate. By having some stretch in your kite halyard and sheets, you reduce the load on the spinnaker and thus reduce the chance of blowing up an expensive sail.
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Old 09-05-2013, 20:19   #19
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Re: High-end vs. low-end line?

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Originally Posted by FlyMeAway View Post
Agreed -- but does that mean you're saying that I can go even less than the ~4-5k lbs. that Catalina recommends for these sheets?

Is the real issue here that I should want larger-sized sheets just because they are easier to handle, and not because I actually need the strength?
I'm not saying that exactly. What I'm saying is to look it up (which you have -- 4k to 5k is the answer) I don't mean that to sound flip so let me explain a bit.

A friend of mind needed to change some of his lines on his '77 Tartan 30. A good thing about Tartan's is they have a large owner's group (I bet Catalina does too). On on of the pages of the manual was a what came with the boat had been rigged for and I think the breaking strength of lines too. Either that or I looked it up, it's been a while.

In other words, his boat had been engineered to a certain set of loads. No surprise there, every boat is. Rarely is everything exactly the same because everyone else who does engineering puts in fudge factors. The dacron in your sail, the lines, standing rigging, the terminals -- pretty much everything. You realistically can't know all the factors in order to optimize. You can however satisfice the process by looking up either what originally came with the boat or what most of your class use. More often you find that, if the boat is older, even the very cheapest line is much stronger that what came with them years ago.

One more thing about link size -- there is a point of RAPIDLY diminishing returns. Case in point was about 1/2 of his lines were over sized to the point where they caused the sheaves to bind. Now, in your case of jib lines and not say a jib halyard, that's less likely but it may be a factor depending your setup.
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Old 09-05-2013, 21:03   #20
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Re: High-end vs. low-end line?

Whenever I used lightweight sheets the breeze comes up and I regret it. But heavy spin sheets are a drag in light air. As a compromise I sprung for 3/8" sheets with a Dyneema core and a polypro, non-absorbent cover (NE Ropes Flightline).

You may want tapered sheets. You can strip the cover off sheets like mine, or you can make your own tapered sheets by splicing a smaller dyneema / spectra single-braid into a larger double-braid line. Either way you can have lightweight sheets near the chute and line in the cockpit that's comfy on the hands.
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Old 10-05-2013, 05:58   #21
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Re: High-end vs. low-end line?

Even on our small boat, all the major lines are 3/8" or larger for reasons of handling. (boom vang is 1/4" on a 4:1 reduction)
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