|Topic Review (Newest First)|
|01-31-2012 04:05 PM|
|smurphny||That's a good drawing. I don't think you'd get the full 8" of stretch because the boltrope is prestretched inside the luff and there is the strength of the sail material added to the boltrope once the downhaul is tightened. Still....even 1" of stretch is a significant amount for a well set up rig to be changed. Wire certainly does stretch a little. One method of rig tuning is to measure the stretch in the shrouds as you tighten the turnbuckles.|
|01-31-2012 01:33 PM|
Not a lot of people using kevlar anymore. Dacron double braid stretches a lot in comparison to modern line. Imho, no real reason to use stretchy line these days. Too many better options out there. And if you shop around, the price ain't bad either. Stop using 1/2" line for everything, and save some money.
Dyneema is probably the best (all around performer), but it does creep (which is different than stretch), not a big deal on sheets and halyards. One downside to dyneema as a core material is that the poly cover will stretch and slip over the core. Usually making it hard to hold in a clutch (the clutch holds the cover, but the core slips through). A simple lock stitch will help this or you can coat the core in maxi jacket. Also, a thicker line helps, you can add a small line like 3mm-4mm inside the core of where the clutch grabs to help hold it. I may do this on my 1/4" Endurabraid main halyard.
Everything stretches. Even wire. Here's an 'ok' chart showing some lines and their stretch under load.
Please note that the chart is not drawn to scale. This makes it look like low stretch lines are not a big deal, and in actuality, they are. This is only 8mm line at 500 lbs of load over 30' of line. Most boats will have more than 30' of line and a higher load applied. Do the math.
40'x 0.018 = 0.72'
0.72x12" = 8.64"
I don't know about you, but not having 8+" of hoist on my main, makes a HUGE difference in performance. As stated above, the stretch comes at the worse possible time, during a puff. And just think, your sail is stretching too, and your main sheet, traveler, outhaul, etc. Why not limit as much stretch as possible?
|01-31-2012 09:55 AM|
|JimsCAL||I would avoid the standard polyester double braid and go with a low stretch line. Something with a poly-dyneema blend core and a poly cover will give you good performance and still be reasonable in cost. I have used the rigging service at Defender many times. Good price on the line and quick turnaround on the splices. Remember if you get a parallel core line, you need to do a core-to-core splice which is not for beginners.|
|01-31-2012 09:54 AM|
Originally Posted by BubbleheadMd View Post
I left my old s.s. wire rope when I replaced the halyard, did away with the wire-rope splice and just put an eye/shackle to join wire and line. The bitter end can't be pulled back through the sheave and would need to be cut to get it out but it never has to pass the sheave. When hauled in, there is only about 2' of line which eliminates stretch. Wire is a PITA but does not stretch to any noticeable amount.
|01-31-2012 08:30 AM|
Originally Posted by SloopJonB View Post
...and before anyone jumps me about how stretch is only a concern for racers, that is absolutely not true. If you're caught in a blow, you want flat sails, (even when reefed) and if your halyard is stretching, you have to keep futzing with it.
I haven't actually tried it myself, but I've reviewed the splicing procedure for parallel core line (Sta-set X) and I'm convinced that "X" is the devil.
VPC is an affordable, lighter, low stretch hybird that rarely kinks and is as easy to splice as Sta-Set. Good for cruisers, day sailors and casual racers.
For racing, definitely talk to zz4gta. I've raced with him and he's done amazing things with line to make them super strong, and reduce weight aloft. 1st Place in his region and class high point series!
|01-31-2012 07:46 AM|
Originally Posted by davidpm View Post
Not true for halyards in general.
a. Given the downsizing that is possible with Kevlar, the rope/pulley ratio is quite acceptable. The requirements are the same for wire rope, which it often replaces.
b. Halyards don't run all that much. A jib sheet, winched all the time, is a different matter.
My last Kevlar halyard lasted a LONG time, and is now in service other places. Total life: over 20 years. It was 5mm in a 27-foot boat running over a ~ 2 3/4-inch pulley. Not much flexing required. But you won't find straight Kevlar anyway; it will be a blend.
|01-31-2012 01:48 AM|
Doesn't anyone use plain old Dacron double braid anymore? Still cheap and effective AFAICS.
Before hurling scorn, abuse etc, please keep in mind that when I started sailing IT was high tech line.
|01-31-2012 01:39 AM|
Originally Posted by Gary M View Post
Something like amsteel has a urethane coating and has an excellent UV resistance. Just plain dyneema is good with UV too. Vectran doesn't like UV much, but dyneema is ok. I know plenty of boats with bare dyneema standing rigging, lifelines and halyards and it does just fine.
|01-30-2012 11:18 PM|
It is not really feasible to splice Amsteel to a polyester line. You can put a cover on it but he exposed Amsteel needs to be protected from the suns UV rays.
Racers that use bare Dyneema lines pull them up into the mast when not in use to keep them out of the sun.
Originally Posted by tap View Post
|01-30-2012 09:42 PM|
|zz4gta||1/4" technora for me. but I use technora laminate sails.|
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