Can #6 luff tape (aka a "bolt rope" of sorts) Shrink?

[rardiH36]

A few months ago I started a thread for info about reshaping an older but still serviceable jib by removing it's #6 luff tape and then cutting back some of the sail along the luff edge to take out some of the old sail bulge. Good responses from RichH.

Just today I started the project. (How much to cut and how to determine the curve is still a bit of a mystery (well a lot to be honest), but using some high school trig for the first time in 20 years or so I at least can trace out a consistent arc. If I need calculus to calculate a hyperbolic arc, forget it!)

My first step was to cut the stitching that joins the #6 luff tape to the sail. Planning to use the same luff tape again, so I left the tape attached at the head. I was surprised to find that without the luff tape attached, the sail naturally laid so that the bottom end of the #6 tape piece (the end near the tack) is now 7" shorter than where the end was before. The luff of the jib is (was) 43'. I am aware that real bolt ropes shrink, but I hadn't thought that #6 luff tape does the same. In the attached picture, the black mark was the original bottom end of the tape location. The red mark is where it now naturally lays unattached except at the head. The tack is about 2 feet to the right in the picture.

Either:

- the #6 luff tape was stretched before sewing when the sail was made, or:
- the #6 luff tape has shrunk like typical dacron bolt ropes can do, or;
- the sail's dacron has stretched.

Question is, after cutting the dacron back to my intended arc, should I just sew the #6 luff tape back on to the sail without any pre-stretch of the tape. I'm hoping this might be analogous to a shrunken bolt roped main sail where cutting the bolt rope stitching at the head or tack and then milking out the sail's bolt rope sleeve along the bolt rope can help restore some of the lost performance. Or should I stretch the luff tape a few inches, staple the tape to the sail along the length frequently to maintain the stretch against the naturally laying sail cloth and then sew? (Staples then removed.)

Probably not too many can answer this, but worth a try!

rardi

 

[RichH]

Most continuous support tapes dont normally shrink nor stretch over time. If the tape does shrink it is easy to stretch it out to OEM size due to the small cross section geometry of the tape with a halyard winch.
Simple speak: continuous luff support tapes dont usually shrink ... more of a probability is that the sail fabric has relaxed or has become permanently stretched.

Jib OEM support tapes arent preloaded (shortened) as are boltroped (3 strand 'ropes' inside the luff sleeve). A sail that is designed to have a continuous support tape is designed so that the point of maximum draft occurs WITHOUT the extra luff tension needed by a boltroped sail.
If your current (loosened) luff tape is shorter than the sail (laid flat) dimension, then simply add a small piece of new support tape to either the top/head or bottom/tack of the sail and 'overlap' the tape (cut away the sleeve with the braided line on the section that fits into the foil groove - you can overlap the 'secondary' sleeve, the one that doesnt fit into the foil groove) --- the overlapped remaining 'tape' (less braided line) will adequately support the loads. Melt the ends of the various sections of tape so that they dont fray or unravel.

 

[rardiH36]

RichH:

Exactly the type of info that helps. Many thanks.

Also last night I looked again at Sailrite's instructional video for converting a hank-on jib to roller furling that I found several months ago. No pre-tension was added to the luff tape when stapled to the sail cloth prior to sewing.

Now I've got to determine if the extra 7" of luff length is too long for my furler! Might have to shorten at the head a bit.

 

[rardiH36]

My sail has developed a bad case of Blue Dot Pox. Picture attached. How can I fix?

Seriously; to resume with the thread of several weeks ago, turns out that the extra 7-8" my old jib gained when I de-stitched the shrunken luff tape did indeed make it too long for the strike length of my furler extrusion. After going up the mast a couple of times this week to make repairs to the roller furler (topic was bantered about in a couple of other threads over the last week or so), today I was able to hoist the sail. Got it up, but absolutely no luff tension could be added without risk of again popping the swivel head over the top end of the extrusion. So slack wrinkles all along the luff. I have decided to shorten the luff by cutting 8-9" off at the head and then hand-sew in new head webbing. This may lead to some bad joss along the very upper section of leach ... but I'm not intending a top performance sail here. Just one that does reasonably OK.

This is the sail I also had asked for info how to cut more fabric from behind the luff to help compensate for years of sail cloth stretching and now too much belly. Today during my test sail, winds in central San Francisco Bay I would estimate were 15-20 kts. Sheeting in, the tell-tales were streaming back nicely at say another five degrees closer to the wind than they were before the mod. Restored to new sail performance? Not by a long shot. But a noticeable improvement anyway. I see I could have removed more fabric from the luff. But the project was worth doing. And I've now got Blue Spot Pox as a secondary benefit.

 

[RichH]

..... next time use 3M Super duty spray adhesive to tack down the sun cover.
;-)

 

[rardiH36]

..... next time use 3M Super duty spray adhesive to tack down the sun cover.
;-)

Hi Rich:
The sun cover sunbrella is still stitched on. So can't spray between it and the dacron. The sunbrella is old and would never withstand a de-stitch and re-stitch. Sail not worth the $'s for new Sunbrella. Better to just have fun getting creative with what's there now. At time of the Sunbrella ultimately becoming too threadbare, the next phase for the sail is the dumpster!