How to Tie a Button Knot Soft Shackle
- Oct 13, 2013
- 129
- #1
- Nov 8, 2010
- 11,385
- #2
- Nov 8, 2010
- 11,385
- Jul 13, 2004
- 88
- #5
Evens Starzinger came up with a very easy way to make a soft shackle that involved only an overhand knot on the end. It is dead-simple to make, but requires almost twice as much line as all the others. I think he called it "improved soft shackle" or similar. He took down his website, so the instructions aren't available there anymore, although you could probably search for it.
I don't worry much about the strength of the knot because all the applications I use the shackles for generally have much lower loads than the strength of the line used in the shackle. I look for cheap cutoffs and ends of dyneema whenever I'm in chandleries and pick up any odd 1/4" or 5/16" for shackles. With 8,000-13,000lb breaking strength, my needs are covered. Even if the knot was half the strength of the line (which it never is), it is usually still much stronger than any load they are used for.
Mark
- Aug 10, 2014
- 532
- Dec 30, 2010
- 188
- #7
- Aug 10, 2014
- 532
- #8
Actually, probably not. UHMW Polyethylene (sold as Dyneema / Spectra / etc.) is much stronger than steel (especially 316 stainless) of the same diameter. For example, 1/4" Amsteel Blue (Samson's brand) has a rated breaking strength of 8600 lbs; and that's for a single line - since a soft shackle is a loop, they usually break well above line strength (120%-230%, depending on the design and knot used). Whereas Wichard rates their 1/4" stainless shackle (model 1403) at a breaking strength of 2200kg = 4840 lbs.Obviously the soft shackle offers the advantage of allowing for a bit of movement... but ultimately isn't a hard shackle stronger?
But - safe working loads for soft shackles are usually more conservative than for hard shackles (that actually applies to most if not all fiber vs metal comparisons - e.g. standing rigging). So a normal safe working load of a soft shackle might be 20% of breaking strength. For the 1/4" example, assuming soft-shackle with a good knot and a breaking strength at 150% of line strength, we'd get 8600 * 150% * 20% = 2580 lbs SWL. Wichard rates their 1403 at 680kg = 1496 lbs (~31% of breaking strength). You can play with those assumptions, but I think you'll generally find that safe loads are at least equal to that of a hard shackle of similar thickness.
But - the hard shackle will always be smaller, which can be a deciding factor in some applications (the loop has to fit over the knot, so there's a limit to how small you can make a soft shackle). Also chafe: UHMW fibers are surprisingly resistant to chafing (see @thinwater's experiments), but you still probably want to stick with steel in locations that might see significant abrasion.
- Dec 30, 2010
- 188
- Aug 10, 2014
- 532
- #10
Oooh - good point about UV. I live here in the Pacific NW, where any day with enough sun to even think the word 'UV' is grounds for communal celebration. And except for a short few months in the summer, my boat spends most of her life parked in the shop, so I can't say that I've put much thought into UV on my soft shackles.What about UV protection? A soft shackle needs some sort of cover for protection... a hard metal shackle does not.
Here is a link from Practical Sailor talking about "coating" soft shackles.
http://www.practical-sailor.com/issues/37_49/psadvisory/UV-Protection-for-Dyneema_11591-1.html
But I should probably replace the ones on my jacklines (those are important!), and get a bottle of UV protectant. Thanks for the advice!
- Dec 30, 2010
- 188
- #11
In the PNW, I worry about rain intrusion and mold, and that damn green stuff that grows everywhere. (even on the rear view mirrors of my truck...) sigh. I think I saw the sun yesterday... but I'm not sure. I forget what it looks like.
- Jul 13, 2004
- 88
- #12
Mark
- Oct 13, 2013
- 129
- #13
- Dec 30, 2010
- 188
- #14
When I was a racing crew on a J-105, we always "skyed" our dyneema halyards to prevent exposure to UV after the races. By "sky" I mean we would attach a line to the shackle end of the halyard and pull the halyard into the mast to reduce UV exposure. Yup, the line was uncovered for half it's length, "to save weight aloft."Dyneema is very UV stable. There is no problem with uncoated or uncovered dyneema in the tropic sun. Our trampoline is laced with it and we live mostly in the tropics. We also have several soft shackles and runners out in the rigging. None of the dyneema has shown any signs of UV degradation. Racing boats routinely use uncovered dyneema running rigging, and lots of boats use it as standing rigging.Mark
- Oct 13, 2013
- 129
- #15
This is just my opinion.
The reason the Diamond is not as strong is in the thickness of the neck.
If someone has the equipment to test my knot I would love to know the results. For now my knot's strength is theoretical based on the data from the button knot's neck thickness.
- Jul 13, 2004
- 88
- #16
Or just replace the shackle every couple of years - $1 worth of line and 15min of time.Untreated dyneema retains 60% strength after 5 yrs in extreme sun conditions like Arizona, New Mexico. If a concern go up one size. Dyneema lifelines should be replaced after 8 yrs as a rule.
In our applications, the shackles are way stronger than necessary just because the dyneema would be too small to easily work with if sized for the loads. Probably many applications on most boats are this way.
Scary how many quality SS shackles we have had fail or about to fail after 5yrs...
Mark
- Jul 13, 2004
- 88
- #17
Mark
- Feb 11, 2017
- 121
- #18
- Dec 30, 2010
- 188
- #19
Wouldn't abrasion, in the case of using these shackles for some part of the anchoring system, be an issue?That will be a piece of cake and not much of a test for a 1/4" soft shackle. We have been anchoring our 40' (heavy) catamaran on a 3/16" soft shackle for a full year now. A couple of 50kt blows and heavy fetch, as well as 30kts for weeks and it looks like new. Being a catamaran, we anchor in shallow water and the shackle spends much of its time dragging around in sand and rubble. Still looks like new.Mark
- Jul 13, 2004
- 88
- #20
But the thing to remember is that a soft shackle costs $1 and 15min of time. I keep several around and can just replace one at any sign of weakening, or just on a routine basis.
Mark
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How to Tie a Button Knot Soft Shackle
Source: https://forums.sailboatowners.com/threads/an-easy-enhanced-soft-shackle.184511/