Rope for bridge

[Tater]

I got my Mantis this weekend. After spending some time trying it out yesterday, I think I have decided I would prefer a little bit shorter bridge. So, I was considering getting some rope to make a bridge that I can modify the length of by adjusting where the knots are tied. I would like to try and keep it relatively small, maybe 8-9mm. I know Aero Hunter uses the Samson Predator, which I think is like 11.4mm, so I would definitely like to stay smaller than that.

So I know the Amsteel 1/4in is plenty strong at MBS of 7700lb, but I was wondering what does this value really NEED to be? I know there are varying opinions on this, and several different schools of thought to back this up. Here is how I have reasoned through it so far, so feel free to point out areas of concern I may be overlooking.

I had planned on trying to get some type of rope that has somewhat of an abrasion resistant sheath for sliding through my locking biner. Some of the new types of friction cordage may be good to use. I am finding most of them to be in the 4000-6500lbs ABS.

If I wanted a rope to be safe for a user upto 300lbs (I am only about 165lbs, maybe 200lbs with all boots and gear in the middle of winter), this is how I am running the calcs:

300lbs / 2 bridge legs = 150lbs per leg

150lbs x 15) = 2250lbs
(15 is a factor I have seen for fire and rescue type situations, though I saw someone mentioned this was because in rescue situations it may be used for 2 people)

2250lbs / 0.6 = 3750lbs
(60% seems to be the standard “conservative” number for amount of strength after knots are introduced, another way of saying your strength is reduced by 40%)

So it appears that these calcs would yield a WLL of 3750lbs. So if I find an 8mm or 9mm rope with abrasion resistant sheath and an ABS or MBS above 3750lbs, shouldn’t that fit the bill? Interested in thoughts.

Secondary question would be about the knots themselves. It looks like aero hunter uses a figure 8 on a bight. Could a poachers knot be used to attach to bridge loops?

Sent from my SM-G960U using Tapatalk

 

[MCDM]

Look at htp superstatic rope. It is very tough i ran it awhile back as my bridge, tether, and linemans belt. It is very durable and plenty strong. Its a tad over 9mm so its in that range. I use amsteel now for my bridge.

 

[Letemgrowitllshow]

".....2250lbs / 0.6 = 3750lbs
(60% seems to be the standard “conservative” number for amount of strength after knots are introduced, another way of saying your strength is reduced by 40%)....."

You would want to do 2250lbs. times (×) .6 (60%)

That would give you 60% of 2250, which is 1350lbs.

 

[Nutterbuster]

I would strongly recommend at least trying tubular webbing. Cheap, light, strong, and simple. I run 8mm as my linemans, and tubular webbing for my bridge and tether. So much more compact, and cheaper too.

 

[Murph4028]

I am going with a 24" climbing runner rated at 26kn doubled over connected to the saddle with delta links on each side. Should be a slim, knotless setup

 

[Tater]

".....2250lbs / 0.6 = 3750lbs
(60% seems to be the standard “conservative” number for amount of strength after knots are introduced, another way of saying your strength is reduced by 40%)....."

You would want to do 2250lbs. times (×) .6 (60%)

That would give you 60% of 2250, which is 1350lbs.

I disagree. This would leave you with less load rating. If you are starting with the load rating and figuring where it would be after knots you would be right.

I am working it backwards, from my weight TO what the load rating would need to be to account for the loss in strength due to knots.

Sent from my SM-G960U using Tapatalk

 

[Cbinderjr]

I would strongly recommend at least trying tubular webbing. Cheap, light, strong, and simple. I run 8mm as my linemans, and tubular webbing for my bridge and tether. So much more compact, and cheaper too.

This ^^, I used tubular webbing to figure out what bridge length I liked best then spliced a amsteel bridge after I found a length I liked.

Sent from my SM-G965U using Tapatalk