Headsail tack/foil extension - width and strength of Spectra or Dyneema line

[OldFrog75]

Need to raise the foot of a genoa. What is best choice of line to create a loop/extension from shackle on furling drum to tack of headsail in order to raise the tack 4" when the halyard is tightened? What lb test?

[StuM]

What boat. How big is the genoa?

[OldFrog75]

Originally Posted by StuM

What boat. How big is the genoa?

Beneteau 323. 135 Dacron and/or 125 Mylar. Could I use 850 lb test lashing line wrapped 2-3 times?

[Stumble]

Originally Posted by OldFrog75

Beneteau 323. 135 Dacron and/or 125 Mylar. Could I use 850 lb test lashing line wrapped 2-3 times?

You could, but I wouldn't. Just get a piece of 1/4" amsteel and splice it in place. Multiple passes of small stuff is far more chaff prone than one wrap of larger line.

[OldFrog75]

Originally Posted by Stumble

You could, but I wouldn't. Just get a piece of 1/4" amsteel and splice it in place. Multiple passes of small stuff is far more chaff prone than one wrap of larger line.

Thanks but two problems:

1. I don't know how to splice
2. 4" is arbitrary. Could end up being anything 2"- 6".

[donradcliffe]

Just lash it, and keep some extra lashing line on board if it starts to chafe/break.

[StuM]

New England Ropes recommend 10mm Sta-Set X for the jib halyard on a 30-35ft cruiser.

New England Ropes Line Selection Guide

Breaking strain of 10mm Sta-Set X is 5300lb.

Load on the tack is a bit more than the load on the head of a sail so up that to about 6000lb b/s for your fitting.

How you get to that 6000lb can be whatever you feel comfortable with. - soft shackle, multiple lashings, spliced loop or whatever.

Your 850lb with 3 wraps would not reach it (850 x 6 = 5100) , even if you assumed 100% strength at the turns and the join.

[Jim Cate]

Stu, I suspect that NER's recommendation is based on stretch rather than breaking strength. I doubt very much if the luff loads on his rig would ever reach anything like those numbers. Very unlikely that his halyard winch could apply much more than 500 lbs tension at the head of the sail (after friction losses, etc).

I've used a strop made of 1" tubular nylon webbing on our previous 36 foot boat for years with no failure or visible degradation. I simply hand stitched the ends together in that strop, nothing fancy, and that worked ok. And the soft eyes on our new Genoa are made from 1 inch spectra webbing... dunno what it's rated strength is, but this is a much bigger vessel with a bigish gennie.

And really, if it fails, it isn't all that serious of an issue!

Jim

[StuM]

Originally Posted by Jim Cate

Stu, I suspect that NER's recommendation is based on stretch rather than breaking strength.

Or on Safe Working Load?
.
I doubt very much if the luff loads on his rig would ever reach anything like those numbers.

Agreed. But then, you shouldn't be putting any line under loads anywhere close to the breaking strain. Safe Working Load is a different number entirely and is generally only about 20% of Breaking Strain.

ABYC recommended SWL for 3/8 (10mm) polypropylene is only around 500lbs and for Dacron it's around 750lb.

Very unlikely that his halyard winch could apply much more than 500 lbs
tension at the head of the sail (after friction losses, etc).

Which would imply a SWL of 500lbs or a BS of around 2500lbs.

But initial halyard tension is only one factor. You also have to consider the effect on head,clew and tack of the wind pressure in a gust. This may exceed the initial halyard tension considerably.

I've used a strop made of 1" tubular nylon webbing on our previous 36 foot boat for years with no failure or visible degradation. I simply hand stitched the ends together in that strop, nothing fancy, and that worked ok.

1" tubular webbing has a breaking strain of around 2500lb - when doubled into a strop, that would be close to 5000lb - similar to that Sta-Set's 5300.

And the soft eyes on our new Genoa are made from 1 inch spectra webbing... dunno what it's rated strength is, but this is a much bigger vessel with a bigish gennie.

1" spectra webbing has a breaking strain of around 5500lb - again similar to the Sta-Set.

And really, if it fails, it isn't all that serious of an issue!
Jim

Except if it fails at the most likely time - in a big gust in high winds and rough seas.

I stand by my suggestion to size it to match or exceed the recommended halyard strength. That way, everything should stay within SWLs.

[Jim Cate]

OK, I see your point Stu. I suppose that I am less conservative than ABYC in that I wouldn't worry about using a mullti turn lashing at a bit more than 20% of breaking load, but then they are lawyers and I am but a yottie! It appears that if the OP made up a strop of a single loop of 10 mm double braid with a stitched and seized join it would likely work ok for him. A double loop would be even less worrying! And using his stipulated lashing line, one additional wrap would get it up to your standard, and not involve even the minimal skills required for a stitched and whipped closure.

I have never seen any numbers relating to luff loads on a headsail. Obviously it all begins with halyard tension, but I'm curious as to how much is added by wind loading. My guess is not so much, especially compared to sheet loading, but I'd be interested in real knowledge on the subject. For instance, how much tension is lost due to friction by the time one measures it at the tack?

At any rate, his problem is pretty easily solved, and I hope he gets some good sailing in.

Jim

[StuM]

Originally Posted by Jim Cate

I have never seen any numbers relating to luff loads on a headsail. Obviously it all begins with halyard tension, but I'm curious as to how much is added by wind loading. My guess is not so much, especially compared to sheet loading, but I'd be interested in real knowledge on the subject.

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.

[Jim Cate]

Interesting link there, Stu! I'm left thinking that he oversimplifies things too much, but that the general shape of it is correct. Things that bother me: assuming that wind loading is uniform over the sail's area or even that the loading from a foil is correctly calculated by his formula. From memory, that sort of calculation is for a shape loaded solely by drag forces on a flat surface at 90 degrees to the flow... but my memory is pretty questionable!

Anyhow, thanks for posting the link. I wasn't familiar with that blog or whatever you wanna call it).

Jim

[bluewaterbill]

You shouldn't need spectra or dyneema for genoa tack or head pennant.
I've used Staset XLS 10mm on 44 ft 30,000 lb boat for years. Never a problem. In a pinch, we have also used sail ties.We do use 10 mm spectra on Code 0 tack, but that's because we need a "bar-tight" luff. Keep in mind that spectra will degrade from UV unless you have a protective poly cover.

[Dave22q]

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?

[Jetx]

Would a premade webbing dogbone or sling, like used for climbing work? Could either buy something short like this;
Mammut Crag Express Sling 24.0 | Backcountry.com

Or if not sure about the length, buy a longer sling and just double or triple wrap it to vary the distance and get the tack height that you want. Simple.. no splicing, no sewing.