Constructive Criticism Request on my Dyneema Lifelines

[Chichiflys]

Good evening all,
My lower LL on our ‘82 Hunter36 were in desperate need of replacement. I replaced the uppers a few years ago with a Suncor DIY “kit” but I wasn’t very happy with it so will probably replace them (again) next if this Dyneema idea pans out.
I used 6mm (1/4”) Amsteel (SK78) for most of the lifeline, Brummell spliced 6mm heavy duty thimbles on each end and have 5/32” Spyderline (Dyneema core) to tension the ends with three wraps around the thimble and pulpit. I also have 6mm thimbles on the inside of the gate areas. For the gates I Brummell spliced the thimble to one end and then fed the tail around the stanchion (since I couldn’t fit a buried section through the stanchion hole) and then Brummell spliced it after going around the stanchion (see picture, hard to describe). For the actual gate I used 3/16” Amsteel because my gates aren’t wide enough for a proper bury on each end using 6mm line. I used an Estar hitch to attach one end of the gate line to a thimble and have a Whoopiesling arrangement on the other end with the Pelican hook, this allows me to fairly easily tension it all. Please ignore the long tail on my Estar hitch, I’ll dress that up later….
My initial thoughts are this arrangement should be as safe as the original pvc coated SS wire lines, but I was hoping for some critique from the community if I have overlooked something glaring. I realize my weakest link is probably the gates since I’m using smaller dia Amsteel and a knot on one end (reducing strength considerably). I also have a sharp bend in the other end of the gate line attaching to the Pelican hook….I may up the gate to 1/4” line as well if I have enough room for a proper bury on the Whoopiesling portion. Anyway, hopefully these pictures make sense of my ramblings. Any thoughts/inputs welcomed.

[Don C L]

Welcome aboard Chichiflys!
I feel very confident that, were I thrown against that, it would hold, no problem.

[s/v Jedi]

Originally Posted by Chichiflys

Good evening all,
My lower LL on our ‘82 Hunter36 were in desperate need of replacement. I replaced the uppers a few years ago with a Suncor DIY “kit” but I wasn’t very happy with it so will probably replace them (again) next if this Dyneema idea pans out.
I used 6mm (1/4”) Amsteel (SK78) for most of the lifeline, Brummell spliced 6mm heavy duty thimbles on each end and have 5/32” Spyderline (Dyneema core) to tension the ends with three wraps around the thimble and pulpit. I also have 6mm thimbles on the inside of the gate areas. For the gates I Brummell spliced the thimble to one end and then fed the tail around the stanchion (since I couldn’t fit a buried section through the stanchion hole) and then Brummell spliced it after going around the stanchion (see picture, hard to describe). For the actual gate I used 3/16” Amsteel because my gates aren’t wide enough for a proper bury on each end using 6mm line. I used an Estar hitch to attach one end of the gate line to a thimble and have a Whoopiesling arrangement on the other end with the Pelican hook, this allows me to fairly easily tension it all. Please ignore the long tail on my Estar hitch, I’ll dress that up later….
My initial thoughts are this arrangement should be as safe as the original pvc coated SS wire lines, but I was hoping for some critique from the community if I have overlooked something glaring. I realize my weakest link is probably the gates since I’m using smaller dia Amsteel and a knot on one end (reducing strength considerably). I also have a sharp bend in the other end of the gate line attaching to the Pelican hook….I may up the gate to 1/4” line as well if I have enough room for a proper bury on the Whoopiesling portion. Anyway, hopefully these pictures make sense of my ramblings. Any thoughts/inputs welcomed.
Attachment 250796

Attachment 250797

Attachment 250798

Attachment 250799

Attachment 250800

I like it. Mine are alike using same dyneema. I used low friction rings instead of thimbles to eliminate the stainless steel.

I like the whoopie sling in the gate. I tried that as well but could not loosen it after tensioning. I guess you open the pelican hook for that, but I don’t like pelican hooks…

[Celestialsailor]

What's that white stuff all over the decks?

[OldManMirage]

[QUOTE=Celestialsailor;3549799]What's that white stuff all over the decks?[/QUOTE


LOL !!!

[Benz]

You could make the whoopee sling bury a lot less, and have room for a splice at the other end instead of the Estar hitch. A brummel with a 6" bury is more than enough. Under the loads you're putting on it, cutting the length of the whoopee bury in half wouldn't cause any splippage.
The rest looks pretty elegant. Couldn't you get gray for the gates as well?

[Chichiflys]

Thank you all for the quick and insightful input. Once all the cold white stuff is off the deck I’ll get the sails on and test out the design. Perhaps, March? Although we’ve seen it fall from the sky then as well. I’ll play around with a shorter bury on the whoopsie sling and the fixed end as well. I was intent on keeping the 72x bury lengths, but I guess the stanchions would fail long before the Dyneema would break if it was a full strength bury?
I only had blue in the 3/16” size so I went with that…looks funny, but for now it’ll do. Jedi, I’m on the fence with the pelican hooks, this version was very affordable and seems to allow my first mate ease of use. She struggled with the older type hooks that were on the original lines, and the newer style that I have on the uppers, while also easy to operate, will need an adaptor for use with Dyneema and that will make them even longer reducing my useable Dyneema length, so for half the cost of the Dyneema adaptor alone, these work well. Time will tell.
Thanks again everyone, I’ll stick with this design for the most part and move on to the 17 other winter projects I have lined up….cheers.

[Dartanyon]

My thoughts (just an opinion) is that ... if you happened to have a 250# friend who fell 8' from the high side of the boat in some sporty wind and hit that; I'd be concerned about the hitch and whoopie sling slipping. I think I'd build the gates from a continuous loop spliced in place. You loose the tensioning ability that the whoopie affords you but tensioning could be done at the whipping anyway.

[guyrj33]

I like it. Nice job, particularly the splices at the gates.

[Chichiflys]

Originally Posted by Dartanyon

My thoughts (just an opinion) is that ... if you happened to have a 250# friend who fell 8' from the high side of the boat in some sporty wind and hit that; I'd be concerned about the hitch and whoopie sling slipping. I think I'd build the gates from a continuous loop spliced in place. You loose the tensioning ability that the whoopie affords you but tensioning could be done at the whipping anyway.

Thanks for the idea - that's something I didn't think of. While I like the ability to quickly adjust tension with the whoopie, it's noncritical, and after initial "break in" I shouldn't have to mess with tension too often. That should also allow (in theory) me to retain more of the 3/16" strength, as the whoopie retains 70% of strength (according to Samson) and I assume the Estar hitch retains only 50% (I don't have a source for that so I'm going by a general rule of thumb of 50% loss with knots in dyneema). Im not sure what the sharp radius bend in the pelican hook (less so in the thimble) does, but I figured cant be worse than the knot?

But since its cold outside and I'm teleworking I decided to do some math based on your scenario. Disclaimer, I'm no engineer, but I do own a calculator :-). My best run at the scenario is that 250#(113kg) human in freefall for 8' (2.4m) has 2.7KN of kinetic energy. Assuming a lifeline deflection of 6 inches (.15m), that equals 17.7KN (~4000#) of force against the lifeline. 3/16" Amsteel breaks at 5400#, cut that in half due to the hitch and I "only" have 2700# to play with, so it looks like it'll break, but the reality is the crew member won't produce anywhere near that energy since they wouldn't be in freefall..more like tumbling from a 30-45 deg heel angle...I have no idea what that equates to, but i have to think it's significantly less than freefall energy?

Nonetheless, I like the continuous loop idea and will certainly try it out, perhaps luggage-tagged on the thimble and pelican hook so I can remove it if needed. Thanks again.

[Benz]

Originally Posted by Dartanyon

My thoughts (just an opinion) is that ... if you happened to have a 250# friend who fell 8' from the high side of the boat in some sporty wind and hit that; I'd be concerned about the hitch and whoopie sling slipping. I think I'd build the gates from a continuous loop spliced in place. You loose the tensioning ability that the whoopie affords you but tensioning could be done at the whipping anyway.

The stanchions would deform before the dyneema broke.

[s/v Jedi]

Yeah, I think it is plenty strong. The knot can be replaced by a splice.

Instead of the pelican hook, maybe a dogbone/toggle would work to open the gate while tensioned?
https://www.amazon.com/Tylaska-DB10-...8-2&th=1&psc=1

[Chichiflys]

Yes Benz, the stanchions would surely give way, softening the blow even more....alas they are 40 years old so probably wouldn't take much. Jedi I'll take a look at the dog bone idea, seems like it would afford more room for splicing. Neat idea, thanks.

[kdeemer]

Very professional! I’m planning a similar one. My question, though, is why isn’t the total strength limited by that of the Spyderline? Breaking a single wrap would bring the whole thing down.

[thinwater]

Originally Posted by Chichiflys

Thanks for the idea - that's something I didn't think of. While I like the ability to quickly adjust tension with the whoopie, it's noncritical, and after initial "break in" I shouldn't have to mess with tension too often. That should also allow (in theory) me to retain more of the 3/16" strength, as the whoopie retains 70% of strength (according to Samson) and I assume the Estar hitch retains only 50% (I don't have a source for that so I'm going by a general rule of thumb of 50% loss with knots in dyneema). Im not sure what the sharp radius bend in the pelican hook (less so in the thimble) does, but I figured cant be worse than the knot?

But since its cold outside and I'm teleworking I decided to do some math based on your scenario. Disclaimer, I'm no engineer, but I do own a calculator :-). My best run at the scenario is that 250#(113kg) human in freefall for 8' (2.4m) has 2.7KN of kinetic energy. Assuming a lifeline deflection of 6 inches (.15m), that equals 17.7KN (~4000#) of force against the lifeline. 3/16" Amsteel breaks at 5400#, cut that in half due to the hitch and I "only" have 2700# to play with, so it looks like it'll break, but the reality is the crew member won't produce anywhere near that energy since they wouldn't be in freefall..more like tumbling from a 30-45 deg heel angle...I have no idea what that equates to, but i have to think it's significantly less than freefall energy?

Nonetheless, I like the continuous loop idea and will certainly try it out, perhaps luggage-tagged on the thimble and pelican hook so I can remove it if needed. Thanks again.

A few engineering thoughts to help you.


The units on energy, as calculated, are actually KN-meters or kilojules. Thus, equating this to line strength is not direct.



To determine fall energy, assuming no friction, you use only the vertical component. At 30 degrees, this is 1/2 of the 8' horizontal distance. But there was friction and he also fell from standing height to something lower. 2 meters should be about worst case, or 2 KN-meters.


Then there is the impact. If severe, the stanchions will bend and it will take about 0.3 meters to stop. At first the force is low, reaching a peak at the end. To catch 2 2KJ in 0.3 meters the average force (energy = force x distance) must be 6.7 KN and the peak must be > 13.3 KN. To know the line tension you would need to know the angles the lifeline formed, but assuming 10 degrees, on each side, the peak lifeline tension will be about 38 KN, perhaps a little higher. Of course, this will be taken across both lifelines, the body will flop, and the result will be a lot lower. But yeah, you need the full rated strength.



You can do this all in US units with fewer conversions. 250 pounds times 6' = 1500 ft-pounds. Stopping in 1-foot = 3000 pounds peak load (that will leave a mark). Taken at a 10 degree angle on each side about 10,000 pounds tension. But lifelines do not break unless chafed, so obviously the fall is not that bad. The stopping distance must be great, the fall slower, and the load shared.


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Finally, always tie the string of half hitches around the entire lashing bundle. This makes them easier to adjust (knots do not jam) and reduces the tendency for the whole thing to unwind if one strand breaks. This is another reason to use a LOT of hitches (at least 10).