Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 06-01-2014, 12:37   #121
Registered User
 
Cotemar's Avatar

Community Sponsor

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
The beauties of the soft shackle is that it is 'just a piece of rope' that anyone can make up in about a minute. And for most people, the diamond is plenty strong enough. I mostly use soft shackles made with 1/4" line on Hawk, but I realize after this testing that 1/8" line would be strong enough for almost all my applications.
Some people really get carried away with these Soft Shackles, not realizing the small ones may be over kill for their application, so they size it up.

Tests like yours may help cruisers understand what soft shackle sizes are really needed to get the job done.

Keep up the great work.
Attached Thumbnails
Click image for larger version

Name:	Large Soft Shackle.jpg
Views:	157
Size:	136.7 KB
ID:	73402  
Cotemar is offline   Reply With Quote
Old 06-01-2014, 13:22   #122
Registered User

Join Date: Jun 2010
Location: Now limited to seasonal NE sailing
Boat: PT-11
Posts: 1,541
Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
There is some indication that a shorter bury is better than a longer one (because it is hard/impossible to get equal tension on the bury and the cover), and the 'no bury' 'Kohlhoff' may be best, but it is hard to sort that out in the data from the constructional variation noise.
Although the Kohlhoff style doesn't suffer from the cover/core tension differential, wouldn't that be offset by one leg of the Kohlhoff bearing more of the load unless the two legs were EXACTLY the same length?
SVNeko is offline   Reply With Quote
Old 06-01-2014, 16:43   #123
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

I found someone else who had machine sewn and broken a lot of webbing samples, but had not done much to analyze his data. I cleaned up the data a bit and did the most basic analysis:

The overall summary number is that his samples show an average loop breaking strength = 125% of the thread tensile. However there is very significant variability, with a range from 66% to 309% and a standard deviation of 49%. There was no correlation at all with the sewing pattern/shape. And no other way to explain the big variability. I am surprised by his (and my very limited) data because I thought one of the big advantages of machine sewing was its consistency/repeat-ability.

Click image for larger version

Name:	sewing.jpg
Views:	137
Size:	17.2 KB
ID:	73407

So, I am still puzzled by our machine sewing results.
estarzinger is offline   Reply With Quote
Old 06-01-2014, 17:06   #124
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Load Testing Results

I wonder if you're seeing a chaotic chain-reaction failure here. With low-stretch line, and low-stretch thread there's going to be less load-sharing among the stitches. although the "more stitches = more strength" trend line obviously shows some load-sharing. Still, there may be more variation in the load seen by an individual stitch, and when that stitch breaks the thread slips and the whole thing unzips.

When the thread breaks do you have lost of broken stitches, or just a few and the rest pull out? If it's not obvious how the stitches are failing you might try a controlled experiment where you load up a stitched sample just under the breaking point then deliberately nick a stitch with a knife.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 06-01-2014, 18:09   #125
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

Paul,

That graph is all dacron thread in nylon webbing, so it is not really 'low stretch'.

usually when my samples break, it looks like many of the stitches break at once - eg there are lots of little pieces of thread left in the webbing rather than one or two long pieces . . . but I have not examined it closely.

I am just surprised that we are getting less 'efficiency' in machine stitching than hand stitching . . . I am wondering if there is something fundamentally weak in the geometry of the machine lock stitch.
estarzinger is offline   Reply With Quote
Old 06-01-2014, 18:16   #126
Registered User
 
Cotemar's Avatar

Community Sponsor

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Load Testing Results

Your line is pulling in a linear direction and your stitches are in shear.
Shear on a thinner thread will always go before a line in a linear direction.
It’s sort of like a scissor action on the thread.

The reason that stitches hold on strapping is because they do a box and then an x inside the box as wide as the strapping.

A line does not have the surface area to do this kind of x box stitching on.
Attached Images
 
Cotemar is offline   Reply With Quote
Old 06-01-2014, 18:17   #127
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
That graph is all dacron thread in nylon webbing, so it is not really 'low stretch'.
One of the great tragedies of life is the murder of a beautiful theory by a gang of brutal facts.
– Benjamin Franklin
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 06-01-2014, 18:27   #128
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

Quote:
Originally Posted by Cotemar View Post
Your line is pulling in a linear direction and your stitches are in shear.
Shear on a thinner thread will always go before a line in a linear direction.
It’s sort of like a scissor action on the thread.

The reason that stitches hold on strapping is because they do a box and then an x inside the box as wide as the strapping.

A line does not have the surface area to do this kind of x box stitching on.
This IS a test of stitching on webbing, not on line!

And unfortunately that's not what this data shows. That's what my comment about "no correlation between stitch pattern and breaking load" meant. The sample were stitched with a wide range of thread patterns, from all "across" to all "Down" and various box shapes in between. . . . And there was no correlation to stitch strength.

I don't know why but that's what this data set shows.

Quote:
Originally Posted by Paul Elliott View Post
One of the great tragedies of life is the murder of a beautiful theory by a gang of brutal facts.
– Benjamin Franklin
But, your comment raised the thought that the nylon webbing is stretching more than the polyester thread. It might be better if they had matched stretch or if the thread was stretchier.
estarzinger is offline   Reply With Quote
Old 06-01-2014, 18:37   #129
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
But, your comment raised the thought that the nylon webbing is stretching more than the polyester thread. It might be better if they had matched stretch or if the thread was stretchier.
Interesting! I can't think of a reason why stretchy thread wouldn't be best. It wouldn't have to match the stretch of the webbing (or line), the stretchier the better for the thread. You would just have to use a lot of stitches for strength.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 06-01-2014, 18:41   #130
Registered User
 
Cotemar's Avatar

Community Sponsor

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Load Testing Results

Or try using Tenara thread
Cotemar is offline   Reply With Quote
Old 06-01-2014, 18:57   #131
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

Quote:
Originally Posted by Cotemar View Post
Or try using Tenara thread
Tenara's big selling point is that it is UV resistant. I use it when doing sail covers and such. The sail makers I have worked with don't like it because it is slippery, and thus hard for them to get constant stitch tension on their machines.

Do you know what it's stretch characteristics are vs Dacron and dyneema? I have never seen those specs. I know that it is chemically Teflon (polytetrafluoroethylene) but I don't know what it's stretch is like?
estarzinger is offline   Reply With Quote
Old 06-01-2014, 19:08   #132
Registered User
 
Cotemar's Avatar

Community Sponsor

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Load Testing Results

estarzinger,

Yes, Tenara thread is a Teflon thread. The slippery attribute makes it great for hand stitching, but not so good on the sewing machine. I always use it for hand sewing when on the boat.
Attached Thumbnails
Click image for larger version

Name:	Tenara Thread.jpg
Views:	158
Size:	85.0 KB
ID:	73433  
Cotemar is offline   Reply With Quote
Old 06-01-2014, 19:19   #133
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

google . . .

UHMWPE
Young's modulus 113,500
Elongation 3.6%

PTFE
Young's modulus 580
Elongation 450%

Source: MatBase
estarzinger is offline   Reply With Quote
Old 06-01-2014, 19:49   #134
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Posts: 4,033
Re: Load Testing Results

I am just looking at the sewing data a little more closely.

I notice three things:

1. The very high stitch count samples all have negative residuals (eg are under the average strength). I do not have data on the length/area of stitching, but this suggests you weaken the sample by jamming too many stitches in (which sounds logical).

2. The 95% confidence interval for the breaking lbs/stitch is 24.7lbs to 30.5lbs, or (rounding a little) 110% to 140% of the thread tensile.

3. The residuals are a close fit to the normal distribution (excluding the very very low and high samples). So, the linear model is probably pretty good. We just need to find additional variables that explain more of the variation.
estarzinger is offline   Reply With Quote
Old 06-01-2014, 20:08   #135
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 10,177
Re: Load Testing Results

a. I'm not sure we've explained why the thread modulus needs to match the rope modulus. Could be true, but I've not seen a provable explanation. I can lace a tramp to a rigid boat or tie myself to unyielding rock with nylon. In fact, the nylon will have a greater ability to self-equalize, like a lacing. By the way, I've always found high mod line on tramp lacing to be pretty silly--the wrong material for the application.

b. I've broken ~ 50 samples over the last few months--line and webbing--and I have NEVER seen variation beyond 15%, high to low within a given material combination. Most of that variation was due to changes in stitch count (I presume some samples with fewer stitches had less uniformity). These were all hand sewn, and though I may be experienced, I'm not an obsessive craftsman.

c. They don't zipper. In fact, I've cut threads at full load intentionally to reduce strength. At most the efficiency drops 10-20% if the count is sufficient.

d. The scissors analogy makes no sense, the bends are not that sharp in proportion to the thread; if you see the thread pattern under load, it is more like a lacing.

e. There is plenty of area on line; I've broken lines up to 5000 pounds with only 2 inches of stitching.

f. I've seen no evidence that box stitching is magic. I think there are certain practical matters; it gives a peal resisting row at all edges and it is simple. But climbing gear is all bar tacked. I'd be happy to look at the numbers, but my testing indicates that a number of cross rows is more efficient.

g. Once zippering starts, there is no pattern that will resist it; it's fast. Better, figure out where it is starting and stop it.

h. Machine stitching depends on even tension because it is inherently unable to adjust to the load (interlocking loops). On short runs I can see that this is a challenge. Bar tack machines do not suffer from this because of the high thread count (that last is a guess).

i. Whipping twine will generally be more UV resistant than fine thread, but in any event, stitching will require protection. I can think of many proven methods.

j. Tenera thread, to my knowledge, is limited to 19#. Even after 5-8 years, plain 50# nylon twine will hold 20 #, and portions out of the sun far more. Great for awnings, but not very interesting for high load applications, IMHO. And there are heavier twines (#8 is ~ 100#) for larger lines.


Opinions, generally backed by testing. But I'd love to see more data. I'm sure I can learn more.
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Reply

Tags
loa

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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
Does Anyone Know Westsail Sailboats ? widget55 Liveaboard's Forum 130 13-01-2014 16:12
Dismasting - Why Does it Happen - How to Prevent it ArtM Multihull Sailboats 236 14-01-2013 08:59
A Second Wind for Rocna foggysail Anchoring & Mooring 209 15-12-2011 17:55
My Battery Load Test Results - Advice, Please ? Poozer Electrical: Batteries, Generators & Solar 8 21-07-2011 05:48

Advertise Here


All times are GMT -7. The time now is 23:54.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.