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Old 20-07-2016, 16:59   #16
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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Maybe somebody can help me here. To my simple mind the load on a tack line should approximate the load at the head (halyard) just as the load at either end of a line under load is the same. What am I (and my rigger) missing? Do I really need a larger tack line than my asymmetric halyard?
The load at the tack is a combination of the load at the head plus the load at the clew.
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Old 20-07-2016, 18:45   #17
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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The load at the tack is a combination of the load at the head plus the load at the clew.
You sure? As the foil will be taking most of the load towards the sheet leaving the tack extension pointing pretty much towards the halyard where do the extra forces come from?
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Old 21-07-2016, 02:18   #18
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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You sure? As the foil will be taking most of the load towards the sheet leaving the tack extension pointing pretty much towards the halyard where do the extra forces come from?
Take a look at the link in post #11.
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Old 21-07-2016, 03:29   #19
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

If you make a Whoopie sling from 6mm Dyneema you will have an adjustable strop which is strong enough.
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Old 21-07-2016, 04:57   #20
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Headsail tack/foil extension - width and strength of Spectra or Dyneema line

Funny to notice this thread just now as 20 minutes ago I removed 15cm of dynema that I was using to raise my Genoa. Last year I had changed roller units and the tack was 15cm closer to the deck. I want to see if the pullpit will interfere with the sail or not which is why I removed it.

The dynema was looped 4 or 5 times between the tack and the roller.

Word of warning!!!!

With the extension, when sailing close hauled, because the sail tack was "free" it was pulled away from the roller and therefore where the sail entered the roller track, the sail was pulled at an angle that started to damage it. I fixed it by looping some more dynema from the tack around the roller unit.


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Old 21-07-2016, 05:21   #21
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

No one has mentioned the soft option extension is likely to twist when the furler is needed.. this can be avoided by have a 2:1 loop.
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Old 21-07-2016, 06:30   #22
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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The basic math is explained quite well here,

Calculating Halyard Loads — Rigging Doctor

What I found surprising in his worked example on a main is that the tack load is considerably higher than the head/halyard load and almost twice that of the clew/sheet load - and that all three wind loads at 25knots are several times the probable load from halyard tension.
JFYI - the calculations shown on that page are an utter and complete FAIL.
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Old 21-07-2016, 22:18   #23
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

Re. the twist on the soft option extension, a twist is good. A soft attachment (vs. ss shackle) is that when the sail is furled, the sail will lie flatter against the foil. Also, there is less damage to the alu foil.
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Old 21-07-2016, 22:59   #24
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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Take a look at the link in post #11.
They look wrong for a headsail on a foil, the tack connection will be pointing roughly parallel to the forestay with the foil taking the load towards the clew. With the halyard and tack connection pretty much in line they must take the same load, Newtons third law.
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Old 21-07-2016, 23:38   #25
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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Take a look at the link in post #11.
And after actually looking at the maths in that link Evans is right imho, it's garbage.
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Old 22-07-2016, 05:06   #26
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Re: Headsail tack/foil extension - width and strength of Spectra or Dyneema line

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Originally Posted by estarzinger View Post
JFYI - the calculations shown on that page are an utter and complete FAIL.
Yes, he needs to retake that physics class he did so well in.
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