Multiple knot effect on rope strength.

Reread the bold part as many times as necessarily.

OP: First off, you're fine.

If you need the technical reason: A good rule of thumb is that knots reduce the strength of rope by 30%. Some knots more than others, but don't worry about that, if Technical Rescuers can use the 30% rule, so can you.

Added knots will not will not reduce the strength any further. Each knot reduces the strength the same. More knots adds more weak(er) points, but the overall reduction is still just 30%.

Now let's do the math: 11.1 mil static rope is good for 6,000 lbf. (Usually more, for example sterling 11.1mm superstatic has a minimum breaking strength of 6850lbf).

Subtract 30% for the knots = 4000lbf remaining.

You weigh, let's assume 200lbf. If you are hanging in free space, you have a factor of safety = 20:1.

Now, since you're just using it to downclimb, let's say a 45% slope, then your force on the rope is only your weight times cosine of 45% or 141 lbf (assuming 200 lb). So actual factor of safety = 28.

You're fine.

you didn't account for the hog-rider effect

rocknice2 wrote:Reread the bold part as many times as necessarily.

Oh, I forgot that bolding something makes it much more convincing!

Using a doubled rope as a handline isn't something I recall doing much and probably wouldn't elect as my go to technique.

I think the OP would be better off choosing a different rope for his purposes, something that's easier to hold onto than 11 mil static, so that knots wouldn't be needed. The excess strength of the 11 mil doesn't contribute to safety at all. Hemp rope would probably be strong enough and might work better in this application. Even clothes line would probably be better than static rope.

If it was me, I would choose a rope that would allow me to hold onto a single strand and use a biner block.

Regardless, I don't have any first hand experience (at least that I can remember!) with knots on a retrievable doubled rope and couldn't say for sure what combination of knotted and unknotted would be most usable and safest. DVan may want to experiment in a low consequence environment. Or maybe he actually knows something on the subject, as opposed to you and me.

Hi All,

:) I love the heated debate. Thanks for all the advice!

Mark Dixon: Your idea was exactly what I had in mind, but I take it from the response that might not work.

It can get pretty steep in some places, not all, 45 degrees to small vertical drops (10 ft). Usually we just brake down the slope and move from tree to tree (they tend to be spaced very close together, say 3-5ft on average). Sometimes we drop 500 ft + elevation this way.

The main reason I was thinking 11mm rope was to have something thick enough to comfortably grip while light enough to carry around. I'll check out the ski rope though.

I've considered body rappelling, but with a backpack on that seems like it might be unpractical.

The "trails" we hike on ridges are too narrow for hiking poles, and too overgrown to strap to a backpack just for downslope. I sometimes cut a strong sapling for a pole on the downhill, but that doesn't cut it for support on many steep sections.

Anyway, I was certainly interested in the technical assessment about the knots, so thank you to those who did the analysis for me.

I attach a few pics to give you an idea of where I was coming from with the question.

Enjoy the weekend!

D.Buffum wrote:Where is it? It looks tropical.

Hawaii

Having gotten ropes stuck with one knot pulling them I'd think seriously whether you'll be able to free one with many being pulled in the terrain you're talking about. If it's a real concern a lightweight harness, rappelling device and 7mm rope may be the way to go.

A lightweight bod harness and a munter w/ a biner would also solve your problem if the dulfer isn't desirable.

Don't get caught using technical gear in Hawaii, you'll be executed as an insurrector of public safety...

Stopper knots would not have nearly enough effect to reduce the strength of any rope for you to ever be able to break it by simply using it for descending.