Forming a figure of 8 in a dyneema loop

[neil1967]

I want to form a figure of 8 in a loop of dyneema so that I have two unequal loops that are joined. What is the best way of doing this and retaining the strength of the loops. The figure of 8 will be used for lifting a MOB using a handy-billy - the idea is that the large loop will be able to be picked up using a boat hook, but when lifting the MOB using the handy-billy the smaller loop would be used, so there would be quite a lot of pressure on the 'joint' between the two loops.

 

[Dutch01527]

Possibly a bowline on a bight https://www.animatedknots.com/bowlinebight/index.php.

I would sew the loose ends to the standing part for extra srength. Are you sure you want dyneema, it tends to slip more than braid on braid and the strength is not required for this application.

Another idea would be to splice 3 strand nylon into two loops, one at each end of whatever size you want.

 

[neil1967]

That could be useful - thank you. I'm using dyneema to reduce the bulk - the line will be permanently connected to the lifejacket and will be contained in the folds of the lifejacket.

 

[lw395]

We played around with hoisting MOBs a good while back.
We ended up with a lifting strop with a good long tail, so plenty of floating rope to pick up and then hang on to the tail once the tackle is attached to the lifting point. In 12mm floating rope, knots are plenty strong enough and useful for grip. A bit of whipping or seizing stops anything coming undone.
Worst case, the tackle gets released from the lifting strop, you don't want to become detached from the MOB, its good that the tail is still aboard the boat.

 

[lw395]

That could be useful - thank you. I'm using dyneema to reduce the bulk - the line will be permanently connected to the lifejacket and will be contained in the folds of the lifejacket.

You want some bulk, a thin bit of dyneema with a man's weight on it can be dangerous.
My LJs have a lifting strop built into the harness?

 

[lpdsn]

That could be useful - thank you. I'm using dyneema to reduce the bulk - the line will be permanently connected to the lifejacket and will be contained in the folds of the lifejacket.

Maybe better to reduce the bulk of the MoB. The breaking strain of cheap braid on braid is about 2 tonnes for 8mm. Use 1 tonne as the SWL and that is still a heavy MoB. You'd probably want thicker for comfort.

I'd use a bowline on a bight too. Polyester would cope better with the tight radiuses in the knot than dyneema - although again that would only apply if your MoB was a tonne or so.

PS If the MoB weight is measured in tonnes check if it has tusks - that would mean you'd rescued a walrus or an elephant by mistake.

 

[TLouth7]

I don't think a bowline-on-the-bight works here. As posed I was imagining that you start with a loop (like a climbing sling) and want to divide it in two, with the resulting loops facing in opposite directions. The bowline-on-a-bight suggestions result in two loops facing the same way, with a standing part that would be secured to the lifejacket. Which are you after?

If I read it right then you are doing what climbers do all the time when they need to shorten a sling. This is done by tying an overhand knot in the sling. Voila, you now have two loops with lengths of your choosing. Simply cow hitch the shorter loop to the LJ lifting point and you are in business.

Edit to add: The thin dyneema should not be a problem as the weight of the MOB is transferred by their harness so it will not be digging in.

 

[lw395]

....
Edit to add: The thin dyneema should not be a problem as the weight of the MOB is transferred by their harness so it will not be digging in.

It would be very easy, on a moving yacht, while grappling with the tackle, for someone to get a loop of thin dyneema around a hand or finger. With the yacht moving relative to the MOB, it seems to me a foolish and unnecessary risk.

 

[noelex]

Very few knots will hold well in Dyneema, but splices are not difficult to do (although my wife is an expert so I leave this to her).

Would two interconnected loops of Dyneema work? A closed loop is easy to do with a splice.

 

[tross]

I would create a normal loop with splicinig the ends into each other but take one end into, along and then out of the main body before splicing the two ends together. Then for security stich both splices and where it passes through the body to set the size of the loops.

 

[TLouth7]

It would be very easy, on a moving yacht, while grappling with the tackle, for someone to get a loop of thin dyneema around a hand or finger. With the yacht moving relative to the MOB, it seems to me a foolish and unnecessary risk.

True, perhaps for this reason I would look at flat or tubular webbing. Low bulk but easier to grip and less vicious than thin line.

Tying an overhand knot in a sewn loop (to make two loops) is quite safe because in the worst case the knot moves along and you end up trying to hoist the MOB via the entire loop (but this is very unlikely). As a demonstration of the validity of this approach I and many others have abseiled off such an arrangement routinely. It is also quite common in climbing to tie multiple knots along the sling to give a choice of lengths.

 

[zoidberg]

I want to form a figure of 8 in a loop of dyneema so that I have two unequal loops that are joined. What is the best way of doing this and retaining the strength of the loops.

Presuming you start with a 'loop of dyneema', then tying in a smaller loop - of whatever size - could be achieved using an Alpine Butterfly, here:

https://www.animatedknots.com/alpinebutterfly/index.php

 

[neil1967]

Zoidberg, that looks just the ticket! Many thanks

 

[colind3782]

I learned how to do what the OP is asking for in the Scouts more than 50 years ago but I can't really describe it. I'll find a piece of line and see how it goes together.

 

[TLouth7]

NB the Alpine Butterfly works best when the two ends are being pulled in opposite directions (as per the image in Zoidberg's link), which is not likely to be the situation that neil1967 will be using it in.

If neil1967 is starting with a line rather than a loop then there is scope to incorporate both ends into the knot that forms the two loops. OTOH there don't seem to be any knots that are specifically intended to do this, especially with dyneema. One option might be to stack two Double Fisherman's* to form a pair of fixed length loops. To do this you would:

1. tie a double overhand knot some distance from an end
2. thread the shorter end through the overhand and tie a Double Overhand around the standing part. This gives a Double Fisherman's forming a fixed loop (don't pull anything tight yet, but do adjust the length of the loop if necessary)
3. thread the remaining end through both knots and tie another Double Overhand around the strands that form the 1st loop
4. pull everything tight. This results in two loops, and a long, symmetrical, thin(ish) knot
5. Cow Hitch (Lark's Foot) the shorter loop to the harness

Edit to add: This is in effect a Sliding Double Fisherman's with a knot in the centre to prevent sliding. This central knot *could* be only a single overhand as it cannot pull through. https://www.animatedknots.com/slidingdoublefish/index.php

*Double fishermen's? Double fishermans'?

 

[alan_d]

*Double fishermen's? Double fishermans'?

You were right first time - double fisherman's. It's the knot that is double, not the fisherman. (Can't help with the loop, though.)

 

[TLouth7]

You were right first time - double fisherman's. It's the knot that is double, not the fisherman.

But what if there are two knots? Bowline - bowlines, double fisherman's - ?

 

[alan_d]

But what if there are two knots? Bowline - bowlines, double fisherman's - ?

Since I was rash enough to enter this debate I suppose I should continue.

The "double" tends to confuse but is irrelevant, so let us consider a single fisherman's knot and then two of them. I would write two fisherman's knots, which might be abbreviated to two fisherman's, with the knots part being understood. I think "fisherman's" is an adjective here, which in English is not required to agree with its noun in number - ten green bottles, not greens bottles. If you think the knot was named after several fishermen rather than one then it would be fishermen's in both the singular and plural. (Like goat's cheese or goats' cheese). It could never be fishermens' because that would mean of fishermens, and fishermens is not an English word, and for the same reason it could not be fishermans'.

 

[BelleSerene]

Beware assuming that knots work in dyneema. They have a tendency to slip. Splicing is far better.

More worryingly, beware a thin dyneema strip lifting a person’s weight. The pressure of the thin line into the flesh would not help. I cannot see why dyneema is indicated for this application: it’s hardly as if you would care about the stretch.

Reversing your process though, if you mount the dyneema on the MOB’s harness, you have the best solution. These [ http://westviewsailing.co.uk/livesavers/ ] do it perfectly and are being approved by more and more manufacturers. They’re easy to fit, unobtrusive, and there when required.

 

[TLouth7]

I would write two fisherman's knots, which might be abbreviated to two fisherman's, with the knots part being understood.

Ah yes, it makes much more sense if you think of it in this way. Apologies to OP for sidetracking from your original question.

Reversing you process though, if you mount the dyneema on the MOB's harness, you have the best solution.

I may be wrong but isn't this precisely what OP is proposing? The thing they intend to do differently is to also have a short loop, presumably to facilitate lifting the MOB higher.

To OP: another option to achieve the two loops starting with a sewn loop (sling) might be to create what climbers would call a "master point". Thread a bight of the sling through the tie-in point on the life jacket so that you have unequal ends. Gather up the 4 strands and tie a Figure-of-8 in the whole lot. This gives unequal, fixed loops facing forwards, and the entire long end would have to work through the Figure-8 before it would come loose. A downside would be the increased bulk in the vicinity of the tie-in, and a chunky knot.

You would end up with something like this: http://i.imgur.com/61KZRP2.jpg