Soft shackle, which size do I need?

[Quidi Vidi]

Having read a recent thread on soft shackles, I have decided to try them out. Unfortunately I don't think that i have the skills to make one up so have been looking at ready made ones online but I'm really not sure which size I need, they appear to be measures in tonnes! They also appear to come in different materials and lengths but having never seen one in the flesh or tried one out, I am unsure which would be best for connecting my jib/genoa sheets. Could someone advise me please?

 

[Rossynant]

I'd use same diameter line as for tying sheets to sail normally, the old ways. Worked for ages so should still
Or a minimum diameter of sheet, if you know this - actual sheets are over-sized for easy handling.

 

[Quidi Vidi]

Thanks, I was confused by the tonnes breaking strain figures! They also quote rope diameter and finished diameter, ie 5mm Dyneema producing a finished shackle of 10mm, I presume if I match finished diameter to my 8mm sheets, then I should be ok? Should I only consider Dyneema or would normal braid be ok?

 

[Rossynant]

I would not know, nor would I care.
Yes, they write a lot about breaking strengths, but this is irrelevant - it's for loading once. -
As from climbing - rope submitted (once) to high a load was discarded immediately.

Working load is what you shop for, this in fact can be assumed to be about the same for any rope - for instance sisal is same as dacron though there are some stronger. But then easy to remember what diameter is for what, rule of thumb, other particulars aside. In shackle I guess you take the small diameter in consideration, in the loop.

Would be harsh (tis' the word? ) :

"Dyneema® is a registered trademark of DSM B.V.

CAUTION: Break Strength: The breaking strength of a rope is the load at which a new rope will break when tested under laboratory conditions. Break strength should not be mistaken for safe working load.
Safe Working Load: Because of the wide range of rope use, rope condition and the degree of risk of life or property, it is not possible to make a blanket recommendation for safe working load. It is ultimately dependent on the rope user to determine what percentage of break strength is their own safe working load. [ ]
Wear: Ropes wear out with use; the more severe the usage, the greater the wear. It is often not possible to detect wear on a rope by visible signs alone. Therefore, it is recommended that the rope user determine a retirement criteria for ropes in their application. For assistance in developing safe working load and retirement criteria for each application please call or write Phillystran, Inc.

All printed statements, data and recommendations are based on reliable information and tests, and are presented without any guarantee or warranty."

Their own words - guess you can trust them

 

[knuterikt]

You don't write what kind of sheet's you have

But here ate some typical numbers for breaking strength (BS)
10mm Polyester/Polyester braid has a BS of 2000 kg = 2 ton
12mm Polyester/Polyester braid has a BS of 2500 kg = 2.5 ton
14mm Polyester/Polyester braid has a BS of 3800 kg = 3.8 ton

10mm Polyester/Dyneema (Dyneema core, poly cover) BS 5800 kg = 5.8 ton

Sizing the Soft shackle for the BS of your sheet mean that that you are not introducing a weak link in your system..
But as other wrote sheets are normally oversize to get better grip.
You can use the Genoa sheet load calculator here http://www.harken.com/Calculators/ to find a load figure for your boat.

For soft shackles I have seen that the BS is 1.5x the BS of the rope it is made of as a rule of thumb.

SWL (Safe working load) is normally not given for rope as the safety margin required is different for different applications.

 

[Rossynant]

Yeah, all right. "normally not given..." Depends what someone considers normal.
It's not Top Secret, for Christ's sake...

But some knowledge may be of use. Quite safe margin may be 1/3 of breaking for natural fibres, 1/5 for high melting synthetics, 1/8 -1/10 for low melting. More in important situations.

" It may surprise you to find out that the working load for most kinds of rope is between 15% and 25% of the tensile strength. Now consider the fact that any time you tie a knot in a rope you effectively cut the tensile strength in half. The knot when tensioned cuts the line. While certain kinds of knots damage the line less than others, the 50% loss of tensile strength is a good general rule to live by. Research has shown that the figure 8 knot reduces the tensile strength by approximately 35% instead of 50% for other common knots tested."

For dyneema the biggest drawback is low melting point. As rope works, there is friction, on outside as well as inside, just stretching it result in friction inside, which raises temperature and destroys the filaments. They get weakened even well below melting point, any temp raise has effect.
Temps, comparisons here http://www.marlowropes.com/technical/physical-properties.html

Good tables for loads and use:
http://www.unols.org/publications/winch_wire_handbook__3rd_ed/12_useful_info.pdf

 

[knuterikt]

Yeah, all right. "normally not given..." Depends what someone considers normal.
Manufacturers give this data, of course, sometimes they are legally obliged to do so. It's not Top Secret, for Christ's sake...

Most sources I have seen (For yachting rope) only give breaking strength, not SWL.
The BS is no secret the figures in my previous post is from this site http://www.teufelberger.com/en/products/marine/fse-robline.html

But some knowledge may be of use. Quite safe margin may be 1/3 of breaking for natural fibres, 1/5 for high melting synthetics, 1/8 -1/10 for low melting. More in important situations.

" It may surprise you to find out that the working load for most kinds of rope is between 15% and 25% of the tensile strength. Now consider the fact that any time you tie a knot in a rope you effectively cut the tensile strength in half. The knot when tensioned cuts the line. While certain kinds of knots damage the line less than others, the 50% loss of tensile strength is a good general rule to live by. Research has shown that the figure 8 knot reduces the tensile strength by approximately 35% instead of 50% for other common knots tested."

Yes and that is why I always use splices if possible.
Even more important when you use Dyneema..
Reason for using Dyneema rope is the low stretch properties and strength.

For dyneema the biggest drawback is low melting point. As rope works, there is friction, on outside as well as inside, which raises temperature and destroys the filaments. They get weakened even well below melting temp. Most damage in place rope goes through something solid, less in sheaves.
Temps here http://www.marlowropes.com/technical/physical-properties.html

More data:
http://www.lanex.cz/en/marine-ropes-technical-parameters
Good tables for loads and use:
http://www.unols.org/publications/winch_wire_handbook__3rd_ed/12_useful_info.pdf

High friction can damage Dyneema rope that is true.
For soft shackles the melting point is not that important.

 

[Gwylan]

Diameter of eye in your jib - genoa is a good place to start.
P.m. me with that dimension and the diameter of your sheets and I'll send you one.
We have been making them for a couple of seasons and can and do make virtually any size.

Generally for your sort of use they will be stronger than the sheet.

 

[temptress]

Thanks, I was confused by the tonnes breaking strain figures! They also quote rope diameter and finished diameter, ie 5mm Dyneema producing a finished shackle of 10mm, I presume if I match finished diameter to my 8mm sheets, then I should be ok? Should I only consider Dyneema or would normal braid be ok?

A rope 10mm diameter rope shackle is made from looping 5mm diameter rope back through itself. The weak point is the 5mm loop. Use the lower diameter to calculate breaking strain.

 

[onesea]

Having read a recent thread on soft shackles, I have decided to try them out. Unfortunately I don't think that i have the skills to make one up so have been looking at ready made ones online but I'm really not sure which size I need, they appear to be measures in tonnes! They also appear to come in different materials and lengths but having never seen one in the flesh or tried one out, I am unsure which would be best for connecting my jib/genoa sheets. Could someone advise me please?

Seriously they are very easy to make. I would by some cheap braid on braid, polyester for a few pounds and look on you tube.

I have not bothered about the dyneema thread to help release it, you do not need it.

The hardest thing you will have to do without the proper fids is threading the core back in on its self...

I would melt the end nice and smooth and use a knitting needle or similar length of metal. To push or tape the end to a knitting needle to pull...

If the boat you are talking about is your aviator then almost any size would do. It does not have to be Dyneema if it is not it just has to be a bit bigger.

 

[Topcat47]

I have them on my Parasail sheets. Get ones that fit the cringles in your sail and give you a decent sized working loop. The one's you buy are almost certainly going to be dyneema and as a result you'll not need to worry about strength. Mine are probably the strongest "link" in my parasail rigging.

 

[Quidi Vidi]

Thanks for the kind offer Gwylan, I will measure the diameter of the cringe when next down the boat. Thanks all for your replies, I'm a little wiser now and hopefully can make a better informed decision.