Rope shrinkage from splicing
 

I was making up some bowsprit shrouds from polyester-covered Vectran, and twice had my very careful measurements come up short. At last I realized that increasing the diameter of the rope by shoving rope inside of it made it shorter. I'd like to know if there's a chart or a formula available to calculate how much length is lost to a splice for a given diameter of rope. It will take out the guessing when I move on to other diameters.
Thanks
Ben

Variables
 

Hello,
We've been working on developing such a chart, but it varies according to brand, as well as diameter and, near as I can tell, the phase of the moon. So for now the best practice is to mark your tail, mark the circumference of the eye, and then beginning at the eye circumference mark that is farther from the end, measure some arbitrary distance -- say, 4ft, and mark the standing part.
Splice in your eye, and then remeasure the distance to that last mark; it will be less than it was, by the amount of shrinkage that the splice causes.
Fair leads,
Brion Toss

All right. Well, the moon was waning gibbous when I did my splices, and it seemed to take eight to eight and 1/2 inches out of 7/16 Poly covered Vectran. If I can make that stay constant, I'll be OK for most of my project.
I hope to see some updates on the shrinkage chart one of these days.
Best,
Ben

i typically layout the first splice and mark the line 10' down or something, do the first eye and measure how much i lost, use that for the other end of the line.

do this each time.

Too much
 

Better check your numbers. I don't have our notes with me, but I'd be surprised if the shrinkage exceeded 3" per end.
Fair leads,
Brion Toss

Great idea, Mr Duff, thanks.
And Brion, 8" seemed a shocking amount to me as well, but so far two splices have come out exact using that measurement. Of course I'll be constantly refiguring as I do more splices.
Ben

Really?
 

Hi again,
On reflection, it's not merely shocking, it just isn't possible to shrink 8". Are we talking about per splice? And where are you measuring from? How much bury, and how much taper?
Fair leads,
Brion Toss

Really really
 

Hi Brion

The rope is New England Vectran V-100, catalog calls it 10mm, whatever that means. I'm splicing it using the directions for core-to-core splice downloaded from NE website, using a 7/16" Samson splicing fid (you know, the pointed aluminum ones...). So total bury is three fid lengths, about 27 inches, and taper is about 17 inches. Once the splice is done, the cover is milked back over the core, and I put tension on it to make sure the bump in the core that develops as you're milking the cover over is all straightened out. But with all that, I'm losing 8+ inches per splice.
If I'm doing something wrong, I'd dearly like to know before I do too many more....
Ben

I would call 10mm 3/8 and I believe you are making the splice way too long. Check the directions again http://www.samsonrope.com/site_files...Eye_Splice.pdf
These are the instructions for the fids you are using. I know some fids are half as long and you may have instructions for those fids.
The easiest way to splice is with Brian's splicing wand, btw.
http://www.briontoss.com/catalog/tools.html

Allen

Thanks Allen,

I worried about which fid to use, and went with the bigger one for a safety margin. A pox on this metric jive! Of course the question now is: is there a detriment to a longer splice, other than wasting a few inches of rope? I am certainly not keen on pulling out all the splices I've already done, and I like the fid I'm using since the core with a wrap of tape fits snugly into its back end.
Ben

I don't think there is anything wrong with a longer splice that I can think of other than more of the line is fat. Brion talks about using rope diameters instead of fid lengths so if it were me even though I was actually using the 7/16 fid I would measure with the 3/8 one. It sounded to me like the larger problem was that your splice was twice as long as it should be and I assumed that was because the fid and the instructions didn't match. You might want to read this:
http://www.briontoss.com/education/BTR_book.pdf

I have both the Samson fids and Brian's splicing want and I prefer the splicing wand.

I think he is using 24 diameters which is 240mm or 9.5 inches. Just Google "convert 240mm to inches" for your future reference. Check the link above to make sure where that is measured to and if it applies to your core dependent line or not.

Allen

Aha!
 

Hi again,
Partly you are victim of the World's Least Logical Measurement System, aka the Metric System, partly it appears that New England's instructions are in error, and partly, you are making stuff up on your own. Splice bury length should be determined by how much friction you need to generate to assure absolute security; bury less than that and you risk having the splice slip, and bury more than that and you weaken the rope and make the splicing process needlessly difficult. On halyards, you can also limit hoist height by having the splice reach the sheave sooner.
I use 48 diameters of the rope for covered HM fibers, and this corresponds roughly with the fid-length method, but is much easier, I believe, to calculate. And the formula actually works fine with the Metric system (10mm x 48 = 480mm = about 1ft 7"; 3/8" x 48 = 1ft 6"). Even if you had been splicing 7/16" rope the tail you are using seems way long, and that is because the New England on-line instructions specify "3 full fid lengths". Samson's chart corresponds to my 48 diameters. I need to see what New England has to say. Meanwhile, going to a larger fid size for a "safety factor" is to assume that a generous safety factor doesn't already exist; why would you do that? This is like making your standing rigging one size bigger before going offshore -- it sounds prudent, but has no logical basis, and can actually make things less safe.
In this case you started with someone else's mistake, and then amplified it completely off the chart, and wound up with your 8" shrinkage. I doubt that the splices you made are actually dangerous, but in the interests of an optimal splice, please use the proportions that thousands of splices have been shown to work. By learning to splice, you are joining a great and enduring community of artisans. Work with us.
Fair leads,
Brion Toss

To make things up as I go along seems to be the theme of my whole existence.:o But who can resist such a passionate appeal? I will apply the 48 diameters and see what kind of shrinkage I get.
Cheerio!
Ben

tail news
 

Hi again,
I've spoken with NE Ropes, and they maintain that they actually use 3 fid lengths for Spectra and Dyneema, because the materials are slipperier. This is news to me, as I've been using the same length for all HM rope for decades, and with fine results, on and off the testing machine. I'll keep you posted on the conversation. Meanwhile your Vectran is definitely not Spectra, so stay with the shorter tail. Lots of taper.
Fair leads,
Brion Toss

Hi Brion,

I really appreciate your taking the time to call NE about this. This has been a really instructive thread for me, and I will forge ahead with new confidence. As to splice length, your experience carries my judgment, and I will do 48 diameters henceforth.
Thanks again,
Ben