Preferred Lashing Methods - starting and finishing

[yoyo]

Mostly throwing this out for discussion and to clarify a few things that nag me about lashings.  I'm looking for observations / suggestions from the brain trust here on best methods for high load lashings. In the back of my mind the attachment point starting the lashing (eye splice) seems like it may be the weakest link.  I'm also interested in which finishing method people prefer for high load lashings.

Those nice Colligo terminators have individual passes for each run of the lashing line.  With that setup I would assume each leg of lashing will become similarly loaded.  If my math is right each lashing loop gives approx 1X load rating of the lashing.  4 loops is then 4X rated load.  So if the 4 passes share the load = 1/4 load per loop.  For this example, does the eye splice really only see 1/4 the load?   It always nags me that the eye splice is approx 1X rated for the lashing but we multiply the load rating because of the extra loops.  I'm sure someone has done destructive testing - is there a resource with results somewhere?  Same idea for load rating as the multi pass covered dyneema loops I suppose.

When you lash between two eyes the tensioned lashings are forced into a bind.  I would assume the binding creates some imbalance between individual passes which will have an effect on rated load and the load seen by the eye splice.  Any comments on this?

For finishing the lashing there seems to be two trains of thought; create an hourglass (Colligo) or two parallel paths.  They both are proven to work.  Anyone have input on what they have seen to be the best?

I like the half hitch method shown in this video (about 10:00 in) with two parallel paths.  Not sure I like the use of a cow-hitch/larks foot (maybe that was just for the sake of the video).

https://youtu.be/BqrJ2d4aXWE

Thanks in advance for the input.

 

[slug zitski]

Not sure what you are doing

 I avoid lashings and prefer continuous loop dog bones for highly loaded soft attachments 

 

[yoyo]

Not sure what you are doing

Trying to educate myself.  Along with a bit of forward thinking for potential future projects.

One might be lashing between hydraulic ram and fixed length synthetic backstay.  Lashing should allow some adjustment for messing with different rake settings.

Another example might be adding a sprit with bobstay that is tensioned via lashing.

 

[MultiThom]

I had a similar thought about the beginning eye splice so I used a sailmakers thimble to distribute the load on that as well as my first lashing separator.  While the colligo terminations are nice, I chose to use ronstan shocks (1K swl) as separators and load distributors.  I do a couple wraps for friction (and to keep the knots from being so tight I have to use a marlin spike to undo), then I use half hitches to finish--two one way, one the other; then because I'm anal, tie a few more then I tie a bowline with the remaining excess line.    SO far, the first three half hitches have always held.  But my boat is small; but, being a trimaran, those knots have to survive on lines that are slack, then are slammed taut as I tack or gybe.  

 

[MultiThom]

https://www.translatorscafe.com/unit-converter/en-US/calculator/pulley-mechanical-advantage/

In case you want a refresher on mechanical advantage calculations.  

I just wanted to add that when I finish with half hitches I tie close to the spread caused by the spreaders so as the tension in the system increases. the tension in the half hitch also increases.  

 

[DDW]

Not sure I follow your explanation but if there are 4 loops then you have 8 strands of line sharing the load, or nominally 8x the line strength. The eye splice will see the same load as the rest of the line, it may be 80% of the line strength.

 

[yoyo]

Not sure I follow your explanation but if there are 4 loops then you have 8 strands of line sharing the load, or nominally 8x the line strength. The eye splice will see the same load as the rest of the line, it may be 80% of the line strength.

Thanks for the info.  I was going by what I read about constructing covered loops with multiple passes of thin dyneema.  Each full loop under the chafe cover adds 1x rated.  I was assuming that each full loop (back and forth) of the lashing would be similar to that since the completed lashing essentially makes a loop.    

So to confirm what you are saying.... For a lashing each strand on a lashing adds 1x rating of the lashing.  With 8 strands you get 8X rated capacity for completed lashing.  The eye splice is 1 of 8 so it would only see 1/8 the load on the lashing.  And since its a splice it should only be rated at 80% rated capacity of the lashing for safety factor.   Does that sound right?

 

[SASSAFRASS]

I would try to find a manufacturer reccomended process.  Lashing is about as old as you can get and very strong but also very easy to mess up.  On commercial fishing gear sections are connected via Benzel or lashed think 1 1/2 dynema eyes connected with 5/16 nylon, so definitely a proven method.  Dynema is so slippery I would want to go with a process  that has been load tested and proven.  As a rule of thumb smaller and more turns is better in any circumstance but in all cases getting even tension is crucial.  I use dynema seine twine for all sorts of stuff. I would be reluctant to advise what I do though as it is pretty easy to screw up and I have no bench testing to back it up.  Maybe Evans will chime in with some field testing he has done.

 

[DDW]

Thanks for the info.  I was going by what I read about constructing covered loops with multiple passes of thin dyneema.  Each full loop under the chafe cover adds 1x rated.  I was assuming that each full loop (back and forth) of the lashing would be similar to that since the completed lashing essentially makes a loop.    

So to confirm what you are saying.... For a lashing each strand on a lashing adds 1x rating of the lashing.  With 8 strands you get 8X rated capacity for completed lashing.  The eye splice is 1 of 8 so it would only see 1/8 the load on the lashing.  And since its a splice it should only be rated at 80% rated capacity of the lashing for safety factor.   Does that sound right?

Depends on what "rated" means. Each strand carries approximately equal load and the load is split between them. So in a perfect world if the line breaks at 1000 lbs, 8 lines breaks at 8000. It isn't a perfect world, and the load sharing won't be perfect, the eye splice won't be perfect, there is some load concentration at the bend which won't be perfect, age makes everything less than perfect. I'd assume it would break at 60 or 70% of the 8000 lbs, and so I would plan a working load of perhaps 30% of the 8000 lbs. Maybe that' what you are reading about, 1x the breaking strength of the line for each full loop would be nominally a 100% safety factor but in real life perhaps only a 20 - 40% safety factor. That's less than I'd be comfortable with for anything at all critical, but I am a big believer in overkill. 

 

[thinwater]

In fact, Colligo has done failure testing and so have I, and we got similar results.

NO, an 8x lashing is NOT 1/8 per leg. It is about 0.17 for a Colligo block and about 0.25 for a low friction ring, with some variation depending on the materials and number of passes. The reduction is due to imbalances in tension, not splices or terminations, and it gets too complicated to answer here. The bottom line is a safety factor of 2:1 over the total number of passes is a good starting point.

https://www.practical-sailor.com/sails-rigging-deckgear/lashing-for-strength

This boat has been sailed a good ways, and one leg is still not nearly equal.

The other thing to remember is that you can't use a lashing to tighten something like a multi-part purchase. You will get some mechanical advantage, but not more than about 3:1, no matter how many passes you use, due to friction. The tension must be supplied by other means.

Curiously, the photo appeared in a sail mag, and the own later came to me and said that was not true, that all of the passes were equally tight (the other passes were rod-tight, couldn't budge them 1/16 of an inch). How he thought I faked the picture I have no idea. I was not straining. I didn't debate him.

 

[Zonker]

+1 to uneven lashing tensions. I used those on some inboard shrouds. The leg at one end was easy to pull out by hand, the other end was bar taut. So my solution is use lots of light line and really overkill it with the number of turns. Or just assume a 4 leg lashing has 4x the rating of the rope, not 8. Dyneema is so strong it's very easy to make sure the lashing is much stronger than the thing it is lashing.

 

[DDW]

So, the world is just about as imperfect as I estimated (1/8 / 70% = 0.17)  .

 

[thinwater]

So, the world is just about as imperfect as I estimated (1/8 / 70% = 0.17)  .

Yes, that was a very good guess! However, that is the very best case, using Dyneema with Collego blocks. Every other case (low friction rings, thimbles, lashings multiple layers thick) is less efficient, in some cases much less.

Going 2x is the rule of thumb for general lashings.

 

[DDW]

By 2x do you mean: allowable load = 1/2 * line breaking strength * number of loops? Or allowable load = 1/2 * line breaking strength * number of stands? Former is 400% of ideal line strength, latter is 200%. 

Nice to know someone has done the tests and taken the data.

 

[Robc]

Here’s my method....

eye splice the first end of possible, always spec the line diameter for load to achieve ideally 4 -6 wraps max on the lashing, any more and there is no way it will level out the loads due to friction.

apply the wraps as evenly as possible. Then take the tail though the middle of the lashing, and create a figure of 8 around it (not hitched) then continue with figure of 8s hitched under themselves.

3 or 4 figure 8s is plenty.

this gives two advantages, 1. It keeps things as evenly loaded as possible and minimises friction for things to level out.

2. You can always undo the figure of 8s as it won’t bind in the bottom 8 that has no hitch...

 

[yoyo]

Great info.  Thanks everyone for all the input and load testing info.  The inability to get even tension (shared load) across each pass and what that might impart to the eye splice has always nagged me.

Thinwater - out of curiosity during your testing can you comment on the common failure point?  Was it the lashing line itself (early wraps or late wraps) or the eye splice?

My take away from this is that the eye splice should be fine as long as the lashings are done neatly, somewhat equally loaded and sufficient combined rating to get a healthy margin of safety (2X).  

After all that I guess the final tie off method is up to whatever method you like.  As long as it holds, either one will work, especially with the built in safety factor.

 

[estarzinger]

you all have correctly agreed on the leg imbalance issue (eg all our testing suggests you should assume they are about 1/2 as strong in the real world as one would expect in a perfect world mostly because of imbalance). So . . . if you really want to be sure of a 2x safety factor you need to make them 4x the ideal world theoretical.

I will comment that the imbalance depends in part on how you finish the lashing.  It is a greater imbalance if you constrain (like with half hitches) several legs together, and less if you only constrain the tail around only one leg (or to the other end, as loups does). It is also less the number of turns you take (when made by hand - made by machine is different), and less the smoother and greater bend radius at the ends.

Starting with an eye splice loop is just fine.

There is a specific 'highest strength' way to do these lashings (which is not very commonly done in 'yachting'), but typically they are so over strength it does not really matter.

 

[longy]

What if you have a spliced eye in the starting end, and the bitter end is brought back to that eye & tied off? So the lashing is not pinned anywhere, but is a series of loops??

 

[estarzinger]

What if you have a spliced eye in the starting end, and the bitter end is brought back to that eye & tied off? So the lashing is not pinned anywhere, but is a series of loops??

That is essentially what loups does. It is stronger than the typical half hitch about all legs because it allows much more equalization. This approach tends to work/test relatively better with more round turns than less (eg the knot hurts the least when there is friction at the ends buffering shock loading)

But the 'tied off' part does create a bit of (theoretical) weakness (rather more than the splice) vs the theoretical ideal best practice. 

Ideally, you primarily avoid constriction of the strands all together. And also secondarily avoid knots. Sewing, dogbones, end to end 'quick tuck' splices (my personal favorite) and similar solutions do this. This path is easy if you can unload the lashing while you are finishing it, but are trickier (the quick tuck splices can be done then tensioned and then sewn) to do well if you have to hold high tension while finishing.  In that case, a practical solution is to bleed shock load off (with extra friction) before the knot (turns on one end before half hitching back on one leg does this).

I believe the theoretically best solution (if you need to create under tension) is a 'cascade lashing' - eg you have a lashing, with a scaled-down lashing joining the two spliced eye ends. and you can repeat. But I have only ever seen that in extremely exotic applications.