Here’s the results of some knot and line testing on various brands of spiderwire/stren/cabelas brands of braided super fishline. It is most commonly called Spectra braid, but is seemingly all manufactured by Honeywell under the name Dyneema. By way of preface, I have some familiarity with the use of cordage for fishing and small boats, but am far from expert in either. It turns out that any knot must be tied so as to generate equal tension among all fibers throughout. This means that when you tie, both the tag end (the leftover end) and the standing part (the line to be used) must be under tension when the knot is pulled down tight. The line should also be lubricated with saliva to get it to tighten evenly. This is not an exact process, so most really proficient fisherman tie at least a few knots for practice before the one for use is tied. For light tackle or tournament use, 10 or 20 practice knots are common.
That said, the first tests were just tensile strength of the line itself. The test rig was made up by wrapping the line around a dowel, 5 or 6 turns, and holding it in place with CA. One dowel end was clamped in a vise, between small plywood pads, and the other dowel end held between pads with a C clamp. A spring scale I use for pull tests was hooked around the free dowel and pulled by hand, and the readings recorded. For reference, it would have been better to have a slider on the scale so the reading at failure could be ‘saved’. As it was, I simply pulled slowly and watched the scale closely until failure occurred.
The lines were Cabelas Ripcord, 25lb test, yellow. This was used for all the knot tests which follow. I also pulled 20lb Stren braid and 30lb Spiderwire. All passed without difficulty, breaking at about 2 lbs over rated strength. All of these measured about .007 inch diameter. This is an estimate because the braid does collapse some under the pressure of the caliper or micrometer jaws. I elected to average the readings between when the first contact with the braid could be felt, (about .011 in.) and when under full compression (about .005 in.).
On to the knots themselves, the best website I found is the kite knots page under
http://members.aol.com/goodheavens/knots.html. For curiosity’s sake, see the following websites: Animatedknotsbygrog, realknots and thefishingsite. (If some computer guy can show me how to post a link, please feel free). Here’s the results:
Knot Result Pull CA Remarks
Improved clinch slid 3 lb no
Double larks head slid 4, 12, 15 lb no 3 tests
“ broke 16 lb yes
Albright slid 5 lb no 10 turn
“ broke 16 lb yes 10 turn
“ broke 12 lb yes 7 turn
Double larks head
With Clinch added broke 21 lb yes Hard to tie
Palomar broke 21 lb no
Note that the Albright was tied to a loop of 27 lb Dacron flyline backing, all other were tied to a wire loop simulating a line clip. I expected the cushioning effect of the softer Dacron loop would make the Albright the best choice. Not so, the Palomar is the easiest to use, and gets up to 21/25 or about 81 % of the rated line strength. Not bad for any knot.
I also opted not to test the knot sleeves the kite guys use. They put the spectra through a Dacron sleeve to add cushioning and friction to the knot. I don’t think it’s a good idea because the sleeve will prevent the user/pit boss from seeing a broken or bulged strand in the spectra line. For the same reason, my preference is to avoid the use of CA to prevent knot slippage. If you’d like to try some sleeves, they can be bought ($2.50) from the site at flyingdragonkites under sleeving kit.
As expected with anything new, you ask the wrong question at first. From all of the pulling and tugging, it feels like line stretch will be the problem, not line strength. I could feel it stretch as each test was made. For comparison purposes, a conventional set of 7 strand steel lines, .015 inch diameter, 60 feet long, stretches about 3.5 inches under a pull test tension of 30 lbs. Surprising, eh? Steel lines return to their original length when the tension is released. The test rig is simplicity itself. Fix the airplane ends of the lines to a handy anchor point. Lay a ruler on the ground, pull up the lines to get about zero tension, set the zero end of the ruler directly under the edge of the handle. Sight across the edge of the handle to the ruler when you pull the lines to tension.
Made up a set of 61’1” foot lines from 100 lb test Cabelas spectra to stretch test against the steel benchmark. The 61’1” length was the initial length, measured before any tension had been applied to the lines. All measurements of overall length were measured against a 2 lb pull to draw the slack out. Results are:
Tension Stretch under tension Overall length
10 lbs 3 in
20 lbs 7 in
30 lbs 10.75 in
After a prestretch of 25 lbs, held for 1 minute:
30 lbs 7 in 61’5”
After a prestretch of 40 lb applied for 1 minute:
30# 7.5” 61’5.75”
So the difficulty isn’t the knot strength at all. The lines have to be much stronger than the required pull test (3 times as much for this test set) in order to control the stretch. After the prestretch, this 100 lb spectra appeared to stretch just twice as much as steel. A couple of anecdotal stories: Phil Cartier let me fly a 75MPH combat ship on Spectra this spring. It turned about as well as one would turn on steel lines, I guess. The big difference in feel is that the lighter line weight is very noticeable. There is less roll in turns, and it felt like the tip weight was much less than that needed for steel. Second, Larry Scarinzi had a lot of flight time on .010 solid music wire lines in the 1950’s. He feels they were more responsive but had to give up on them when K&B greenheads got to towing his combat ships over 100 MPH. At those speeds, the thin lines stretched in turns, and the turns widened uncontrollably. So the diameters went up to .015 7 strand. Safety? Not a care in the world! My, my, times do change. Anyhow, that’s what there is so far. The next round is to learn more about prestretch and its effect on the line. I saw a mention of it on the kite sites, but nothing of much help. Anybody out there with experience on stretch and hysteresis? Help if you can, I’m way out of my element. Tom H.
Topic: Rules Proposal for Spectra(tm) Lines (Read 5129 times)