Spectra- Stonger, more durable, expensive
Polypro- weaker, less durable, less expensive
There is a new rope out now called "Max-Grip/Grabline" I have heard some people refer to it as the NFPA Throw rope (only one UL classified to meet NFPA 1983 standards a.k.a. Fire service politics). This is almost as strong as Spectra, seems to be more durable and easier to hang onto. You do lose a little bit of strength over Spectra but it is much stronger than polypro. It is significanly less expensive than the Spectra.
If you think you will be using it in any kind of mechanical advantage situation or using it for anything more than a simple throw to a swimmer then it would be a good idea to stay away from Polypro. I have had good luck with the MaxGrip. I did use it in a 3:1 to haul a completely submerged boat out from under a tree/strainer in strong current (1600cfs Narrows/Fractions ARK). In addition to the current there were three of us pulling so figure a factor of 9 against all the force being generated by the water. No sheath damage from the prusick cords and no flat spots from the knots.
Go with spectra or max grip. No need to add a weak link to a potentially critical system.
Spectre is much stronger and lighter than polypro and 2-3x the price. Spectre doesn't stretch, polypro stretches alot, especially when wet. Spectre is great when you need a static line or z-drags, but the same ridig quality makes spectre more likely than polypro to jerk out of your hands when the rope becomes taut in current.
Spectra is also more slippery than poly, so friction knots (prussiks) don't bite as firmly. It also has a lower melting temperature than poly, which actually makes it weaker in high friction situations.
In the high friction situations that boaters incounter most of the time the rope is wet so the melting issue doesn't really matter with Spectra, if it is an issure for you use real pullies not 'beiners.
I know some of you climb so maybe you can help me out...
My retriever is polypro I'm pretty sure and I'm wanting to put together a z-drag kit with spectra...I don't want to buy the ones they put together for you. I was looking at these two ropes both spectra:
The first one from nrs is a little beefy-er with a lb rating about twice the latter, the second one lets me keep my cash in state. Will it make enough of a difference to go with the beefy rope?
Also, I was wanting to use this mini traxon pulley to eliminate the need for prusiks...ease, quickness, etc. http://en.petzl.com/petzl/SportProduits?Produit=354
but the failure strength is only 4kN as compared to 32kN with their rescue pulley. I'm not so swift with newtons...is the mini traxon strong enough to deal with the forces you might generate with the z-drag?
BSOE -- Avoid using mini-traxions (or any toothed clamping device) for a mechanical system. They grip by incorporating a small tibloc into the pulley. Besides the danger of shearing through your rope (rather than having a friction not slip if the system is overloaded) they are also a bitch to get undone if they clamp under pressure. They're also pretty heavy. (Don't be concerned about the load limit. 4 kN is 900 lb-force, but that refers to the limit on the self clamping pulley -- probably the load at which some aspect of the cam fails. The more critical limit is the shear potential on the sheave bearing.)
Prussic loops weight next to nothing, and if your conserned about them being a weak link (especially the small diameter cord required for some of the smaller diameter throw bags -- remember prussic should be 60% of the main line), I suggest using a webbing sling (sewn or tied) and a kleimheist/french prussic knot.
Yonder - With respect to the tibloc, there's a good argument against any camming, rope gripping device that doesn't allow slipage on the main haul line. If one were to overload a z-drag with a tibloc rather than a friction knot, the teeth would tear the sheath causing failure of your rope. If this was a time critical situation (and very rarely does one rely on a mechanical advantage to stabalize a potential victim), the risk of failing the main line is sufficient enough to avoid using a tibloc. With that said, they're an excellent component to any expedition kit. I've used mine on simple portages over boulder sieves (black boxes), ascending "extraction lines," and in place of a prussic/kleimhiest when creating high tension lines. Just avoid them for a traveling capture.
Tiblocs jack up a throw rope no matter what kind/diameter it is, I highly recommend AGAINST them for whitewater. Throwropes are just made with more loosely woven sheaths than climbing ropes. They'll rip the sheath so fast that you'll fall over backwards onto your arse and then you won't have anything to use because the main line is just slippery core with bunched up sheat on each end. Seen it done in a demonstration to some guys brand new rope -- felt kinda bad for him.
That said, I haven't really found a type of cord that I like for prussiks yet either. Mostly just a diameter issue. I've decided that 4MM is the best because it's small enough to bite into the rope, but it isn't perfect 'cause it's still a little too big to grip perfectly and it's still not quite strong enough. What I've started doing is throwing a butterfly knot on the rope where I would normally place the prussik. This gives me a loop to clip versus a friction knot. You just have to be careful where you're placing it because it's really hard to adjust later, and like the prussik, impossible if that section of the line is under a load.
as a previous post mentioned, webbing can be a better solution. the klemheist is actually faster to tie/dress than a prussik. The webbing is as strong as the rope, instead of being the weak link, and best of all, you don't get into the diameter problem, where you need a different diameter prussik for different throwbags. maximum versatility, minimum complexity. win-win.
I've seen sewn slings 22kN strong, like 1/2 or so webbing. strong, light -- and the can double as anchor points in a pinch.
One thing that is nice in favor of poly rope is that it floats better then spectra, so it will be more visible and easier to grab onto. I'd almost say that if I was only using a throwrope as a throwrope (rather then for z-drags and such) I would go for Poly. That maxgrip stuff sounds good though, seems to be a good compromise with the added benefit of better grip. Does the better gripability affect how well it works for z-drag stuff and getting bound up?
p.s. Prussiks are about the simplest thing to apply, especially if you have the loops pre-tied. I'd say that they might take 5 seconds longer to put on then a tibloc, and do allow for some give in the system without the risk of ripping your rope up. One of the climbing companies makes a nice small rope cam device that is slightly more complex, but doesn't use teeth, but rather just some more benign grooves (like a camalot for trad climbing).
I am not a big fan of Spectra cord. True it is a high-strength cord. In fact, I met someone who once used some 5.5mm cord to tow a truck out of a ditch.
My problem is it tends to melt much easier than any other cord and it work-hardens with use (more in a second on that). Also, I have been told by several rope rescue experts that it tends to degrade (even without use) over time much faster than nylon.
Work-hardening is the tendancy of a material to become stiff with use. I have some rock climbing protection that I re-slung with Spectra. The cord is as stiff as number 12 copper wire after 5 years.
Those limitations coupled with the muchhigher cost have turned me off to Spectra. I choose to use a static (low stretch) kernmantle type of rope.
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