Bar tacking

[thinwater]

I note your tubular steel 'sheathing' on your shackle-pin, addressing the 'D:d' concern.

Why the tubing vs. a bushing vs. a thimble? Interested in the decision criteria.

• Tubing might distort under high load. But probably not at the loads you will actually see.
• The rope can slide off a bushing more easily than tubing.
• A thimble is not always stable when nylon stretches.

I've been pretty happy just padding the rope with a tubular webbing cover. But I like the tubing idea.

 

[Neeves]

Why the tubing vs. a bushing vs. a thimble? Interested in the decision criteria.

• Tubing might distort under high load. But probably not at the loads you will actually see.
• The rope can slide off a bushing more easily than tubing.
• A thimble is not always stable when nylon stretches.

I've been pretty happy just padding the rope with a tubular webbing cover. But I like the tubing idea.

Simple stuff.

Off the wall and/or lateral thinking

The tubing is, was, an accident

I had been playing with the concept of a snubber you could easily extend. The answer was LFRs - but they are expensive - or simple blocks which are even more expensive. So mulling over the LFR I wondered if a tubular sleeve on a shackle pin would rotate (and ensure abrasion was minimised).

I tried it, it worked, but LFRs are better (and if you do your homework are not so expensive). Blocks also work (but are much more expensive). I also tried long shackles with an old sheave.

This is part of an idea for an extendable snubber simply using a long shackle and an old sheave.



This is an extendable bridle where I used blocks, works well - a but pricey if you don't have spare blocks.



And this is the preferred design, simple to fabricate, not very expensive, neat - and it works.


So I dropped the idea of shackles with tubular sleeves over the shackle pin.

I finished up with little sleeves looking for a home - which they found.

I simply used tube I had, if the tube had worked I would have replaced with something more robust (a thicker walled stainless tube - which I have but was reluctant to cut until I'd tested the idea), answering the comment that the tubes might deform. I rejected thimbles for the reason you mention - difficult to attach securely and neatly.


The idea was not entirely original, or not original at all.

Shackle strength is based on straight line loading. However much loading is not straight line and the area of load slides to one side. You can source stainless tubular devices that have a 2 wedged profile, 'reversed cones', they are like a mini bow roller (and could be easily made from a tough polymer on a lathe). My sleeve was simply a derivation of this idea.

This is not a complete description of my thought processes and ideas - but I appreciate people have set ideas - just think of the people who complain of anchor threads, off the wall is just 'off' don't like thread drift, don't like threads on snubbers - so I've drawn a line in the sand..... - but sand is easy to move.....

Jonathan

 

[thinwater]

I've tried sheaves on pins like that, but the rope often jumped off. I have one on my main outhaul and it jumps off occasionally. I supose part of the problem is that they are not entirely free floating.

 

[Neeves]

I've tried sheaves on pins like that, but the rope often jumped off. I have one on my main outhaul and it jumps off occasionally. I supose part of the problem is that they are not entirely free floating.

If the shackle is narrow, the rope big enough and there is little space between sheave and shackle - there are no issues.

I am not advocating any ideas, just listing some of the options I looked at, prompted by criticism that custom, owner made, manufacture is difficult or expensive.

Its a bit like using climbing gear on a yacht - think outside the box.


Low Friction Rings are so simple - why were they not widespread 20 years ago. Soft shackles are so fashionable now and dyneema available for decades - why did it take so long for dyneema and soft shackles to be used in one sentence, silicone's non stick surface has been known for years - why did it take so long for Prop Speed to become (at least in Oz) almost a standard......don't get me started on snubbers and small chain . The corollary is - why do people persist in using swivels, raise questions about kellets/anchor angels, use no name undersized shackles for their anchors ......

Jonathan