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Old 22-03-2023, 15:07   #1
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Soft shackle for old block

I have those double blocks on my dinghy Davits and yesterday the shackle on one of them failed. I couldn't find a shackle that would fit, so I'm wondering how to do a soft shackle that wouldn't slip not chafe.

The one on the second pic is just a length of 7/16" dyneema with figure 8 knots on both ends. Would it be enough to change those figure 8s to a stopper knot appropriate for dyneema (which?) and some rubber hose around the middle of the dyneema, where it touches the shackle? Or is there a better way?

FWIW, I no longer plan to leave my dinghy hanging from those blocks; once the dinghy is hoisted I will lash it to the davits with a separate line and release tension on the line running through the blocks. Click image for larger version

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Old 22-03-2023, 16:11   #2
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Re: Soft shackle for old block

Please just buy new blocks. You deserve them.
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Old 22-03-2023, 16:31   #3
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Re: Soft shackle for old block

^^^^^

Why would a dyneema soft shackle not work in this fairly low load application? I use them to hold sheet fairlead blocks to a perforated toe rail where the loads are much greater and with greater chances for chafe... and they have survived for several years now.

His application seems quite within a soft shackle's capabilities.

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Old 22-03-2023, 17:20   #4
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Re: Soft shackle for old block

These blocks only get used to raise or lower the dink. Hardly an effort on the part of the block or the impromptu fix.
The breaking strength of 7/16" dyneema is around 21,000 lbs.
A rough guess on the dinghy load is maybe 150-200 lbs for each leg of the davit, hardly a strain for the dyneema.
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Old 22-03-2023, 17:34   #5
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Re: Soft shackle for old block

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Originally Posted by LifesBetterWhenYoureBeating View Post
Would it be enough to change those figure 8s to a stopper knot appropriate for dyneema (which?) and some rubber hose around the middle of the dyneema, where it touches the shackle? Or is there a better way?
Your quick fix sounds easy and reasonable to me. Maybe someday you'll find a 2nd hand block at a great price. For a more interesting solution, take a look at Seaworthy Lass's detailed descriptions of making a soft shackle.
https://www.cruisersforum.com/forums...ml#post1957966

I enjoyed learning how to do this, and put my new soft shackles to use routinely.
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Old 22-03-2023, 19:16   #6
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Re: Soft shackle for old block

I would sand and/or file smooth where the dyneema goes through. That’s a thin piece and dyneema can chew through quickly.

I have my whole dinghy (with the motor on) held up by 4mm dyneema wire rope replacement lines. There was a chain but it wouldn’t work on our new aluminum rib without messing up the paint. Switch to dyneema. See some slight chafe after 6 months, so going to go up 2 mm just for more chafe guard.
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Old 23-03-2023, 04:56   #7
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Re: Soft shackle for old block

Quote:
Originally Posted by Jim Cate View Post
^^^^^

Why would a dyneema soft shackle not work in this fairly low load application? I use them to hold sheet fairlead blocks to a perforated toe rail where the loads are much greater and with greater chances for chafe... and they have survived for several years now.

His application seems quite within a soft shackle's capabilities.

Jim
The Dyneema will work perfectly; but a block that's starting to lose parts should be on the replacement list, IMO. As a thrifty cruiser, I can see the value in getting one's money's worth out of everything: I have stay'sl sheets more than 12 years old, but those blocks don't owe anyone anything.

Granted, their failure here would be no big deal, but what if someone were encouraged by this to keep mainsheet blocks beyond their time, and a sheave collapsed right when you needed to sheet it in quick in a west Greenland katabatic, jamming the whole system?
I only mention this scenario because it actually happened, with blocks whose replacement I had strongly urged.
Keeping failing equipment is bad practice, unless there's a compelling reason not to replace it. I wouldn't consider $60 a good reason.....
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Old 23-03-2023, 05:03   #8
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Re: Soft shackle for old block

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Originally Posted by Benz View Post
The Dyneema will work perfectly; but a block that's starting to lose parts should be on the replacement list, IMO. As a thrifty cruiser, I can see the value in getting one's money's worth out of everything: I have stay'sl sheets more than 12 years old, but those blocks don't owe anyone anything.



Granted, their failure here would be no big deal, but what if someone were encouraged by this to keep mainsheet blocks beyond their time, and a sheave collapsed right when you needed to sheet it in quick in a west Greenland katabatic, jamming the whole system?

I only mention this scenario because it actually happened, with blocks whose replacement I had strongly urged.

Keeping failing equipment is bad practice, unless there's a compelling reason not to replace it. I wouldn't consider $60 a good reason.....
It looks like the blocks load bearing is done primarily with the steel cage, so that should still be ok.
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Old 23-03-2023, 05:41   #9
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Re: Soft shackle for old block

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Originally Posted by JoeRobertJr View Post
Your quick fix sounds easy and reasonable to me. Maybe someday you'll find a 2nd hand block at a great price. For a more interesting solution, take a look at Seaworthy Lass's detailed descriptions of making a soft shackle.

https://www.cruisersforum.com/forums...ml#post1957966



I enjoyed learning how to do this, and put my new soft shackles to use routinely.
I've made several soft shackles as well, but can't fit one on the pinhole of that block, that's why I've used a single length of dyneema

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Old 23-03-2023, 05:44   #10
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Re: Soft shackle for old block

Ok, so it seems I can keep the dyneema until I'm somewhere where I can get a new shackle or block, but I've read the figure 8 stopper is likely to slip on dyneema so I'm looking for alternative stopper knots. Any suggestions?

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Old 23-03-2023, 05:56   #11
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Re: Soft shackle for old block

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Originally Posted by LifesBetterWhenYoureBeating View Post
Ok, so it seems I can keep the dyneema until I'm somewhere where I can get a new shackle or block, but I've read the figure 8 stopper is likely to slip on dyneema so I'm looking for alternative stopper knots. Any suggestions?
I understand the barrel knot (aka triple overhand knot) to be more slip resistant than a figure 8 knot.
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Old 23-03-2023, 06:01   #12
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Re: Soft shackle for old block

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Originally Posted by LifesBetterWhenYoureBeating View Post
Ok, so it seems I can keep the dyneema until I'm somewhere where I can get a new shackle or block, but I've read the figure 8 stopper is likely to slip on dyneema so I'm looking for alternative stopper knots. Any suggestions?

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This one is designed for use on dyneema


https://www.animatedknots.com/estar-stopper-knot
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Old 23-03-2023, 06:05   #13
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Re: Soft shackle for old block

Quote:
Originally Posted by LifesBetterWhenYoureBeating View Post
Ok, so it seems I can keep the dyneema until I'm somewhere where I can get a new shackle or block, but I've read the figure 8 stopper is likely to slip on dyneema so I'm looking for alternative stopper knots. Any suggestions?

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Knots will begin to slip at a relatively high % of BS, or thousands of pounds. It will not be a factor in this application. Each knots it only carrying ~ 30% of the load, or less than 500 pounds, even with dynamic loads.


Yes, a triple overhand is better. But if you really don't want slip, Use the Estar stopper, above. Tested slip proof in Dyneema.
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Old 23-03-2023, 06:52   #14
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Re: Soft shackle for old block

Thanks for the info on that estar knot. I am going to add that to my repertoire.
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Old 23-03-2023, 11:37   #15
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Re: Soft shackle for old block

The UHMWPE line will work fine for that use case. If those axle corners are too sharp, consider sliding that portion of the line through some Dyneema chafe sleeve. Works great!

Alternatively, consider lashing using a smaller diameter UHMWPE line, and doing it with two seperate lines for redundancy.

I installed a 12 V DC ATV winch on my davits. I use the Harken T2 blocks designed for soft attachment, and UHMWPE line on the winch for all lifting.

I mention this not to suggest you switch blocks or add a winch, but to demonstrate mounting blocks using soft attachments (UHMEPE) is a standard- and holds up over time.

In my case I use a double loop strap typically used with a dog bone- with the loops being captured by a shackle. Everything is in its 4th year of full time use. (Granted, the T2 blocks are designed to use line for attachment, but proof of concept still applies.)

In case this is helpful.

Cheers, Bill

PS: The white line with the red trace in the photo below is the safety line that takes all the strain once the dink is raised in the davits- as you were describing adding to your set-up...
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