Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 18-05-2016, 12:03   #1
Registered User

Join Date: Apr 2012
Posts: 570
A dyneema question...

Perhaps this has been addressed in one of the may other threads on HPME lines, but if so, I've missed it, and am wondering...

I want to install new lifelines on my cockpit area, and started researching. The guidance I've found suggests that eye splices in those lines should be taken to a thimble or ring to assure the radius of the splice is no less that eight times rope diameter, because tighter radiuses weaken the connection significantly.

This complicates the making of the lines a bit.

As I was pondering this, it occurred to me that I've seen no such caution re soft shackles. Soft shackle nooses are generally capturing a shackle "body" whose diameter is no greater than 2x the line diameter, and the shackles are used in applications that experience a much higher fatigue cycle rate and possibility of line chafe.

I realize the shackles have breaking strengths greater than the rated strength of the line itself, but since dyneema lifelines are generally oversized re strength due to selecting a larger size than needed for comfort in grabbing the line, so lifelines should generally exceed strength needed.

Is the concern in one case and not the other simply because of application...the use of the lines as "life"lines?

What am I missing? Or can I simply take the splice to a SS shackle with a quarter inch or so radius without worry (doing routine inspections for chafe or deformation, of course)?
__________________

__________________
fryewe is offline   Reply With Quote
Old 18-05-2016, 12:42   #2
Registered User

Join Date: Jan 2010
Location: Narragansett Bay
Boat: Able 50
Posts: 3,057
Re: A dyneema question...

A lot of people use soft shackles improperly. You are right that the shackles do not like sharp bends. That is because half (or thereabouts) of the fibers are being asked to take all of the load while the other half are in compression. Around a larger radius object like a thimble all of the fibers can share the load.

Soft shackles are best used to attach to something more bulky such as a thimble or a clew grommet. If you want to attach to an object that is relatively thin, such as a padeye, then several turns of a thin lashing like 1/8" would prove more reliable.


If you are making Dyneema lifelines you should terminate each line around a thimble, then attach the thimble to the pulpit, a shackle or pelican hook.
__________________

__________________
savoir is offline   Reply With Quote
Old 18-05-2016, 12:59   #3
Registered User
 
Training Wheels's Avatar

Join Date: Aug 2014
Location: Left coast.
Posts: 673
Re: A dyneema question...

As long as the turning radius is equal to or greater than the diameter of the line, your spliced eye should be 100% of the breaking strength of the line.


Sent from my iPad using Cruisers Sailing Forum
__________________
Training Wheels is offline   Reply With Quote
Old 18-05-2016, 13:21   #4
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: A dyneema question...

Fry,

On my boats just spliced the lifelines to the forward stantion, then at the aft end spliced in a thimble, with a lashing making the connection between the thimble and the aft stantion. No muss, no fuss took about fifteen minutes a lifeline.

On dyneema the bending radium seems to not be as critical as was originally thought, and I am pretty sure that down to 1:1 D/d is considered acceptable. But still there is little to no downside to making it larger. The biggest issue seems to be throat angle, when a gradual angle is prefered over a sharp bend.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 18-05-2016, 19:43   #5
Registered User

Join Date: Apr 2012
Posts: 570
Re: A dyneema question...

Thanks for the responses.

I'm still playing around with dyneema splicing, and have some spare thimbles and rings laying about. I'll probably have a go at it both ways with a line or two and then go with what seems prudent.

I like the simplicity and strength of lashings, but also the convenience of pelican hooks on the lines.

Not launching until early June, so there's time to play around with it a bit.
__________________
fryewe is offline   Reply With Quote
Old 18-05-2016, 21:52   #6
Registered User
 
Training Wheels's Avatar

Join Date: Aug 2014
Location: Left coast.
Posts: 673
Re: A dyneema question...

Use lashings rather than turnbuckles, and pelican hooks for the gates.


Sent from my iPad using Cruisers Sailing Forum
__________________
Training Wheels is offline   Reply With Quote
Old 19-05-2016, 05:09   #7
Registered User

Join Date: Jan 2010
Location: Narragansett Bay
Boat: Able 50
Posts: 3,057
Re: A dyneema question...

I'll second that.
__________________

__________________
savoir is offline   Reply With Quote
Reply

Tags
dyneema

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Eight-Year Warranty on Dyneema Trampoline Webbing fastcat435 Commercial Posts 13 14-03-2011 01:33
Series Drogue Rode . . . Dyneema ? cvondo Anchoring & Mooring 7 11-06-2010 11:18
crazy idea for those with deep pockets, spectra (dyneema) anchor line schoonerdog Multihull Sailboats 22 27-10-2008 02:46



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:41.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.