Friction device

RBJtree

Well-Known Member
I've never heard of anyone using a ratchet strap as an anchor for a portie. You would need one serious ratchet strap to match the working load of a pow and I don't think ratchet straps are designed for shock loads. I know some of the fixed bollard types use straps, but they are huge straps. Myself and others use ratchet straps to hold a stein or regular buck type pow in a vertical position from the top, not load bearing. A woopie or a dead eye is usually 3/4" or larger tennex, 3/4 I think is 22,000 lbs tensile and no metal mechanism to wear and break plus millions of hours of use through out the world to prove it works and is safe when used properly
 

Bango Skank

Well-Known Member
Alot of it is personal preference and what someone is used to. Fixed bollard type gets strapped to the tree. Porty types need a rope sling.

Sean was just mentioning a tip on using a small ratchet strap to keep the portys out of the mud I think. The strap sees none of the rigged load.

I've always used a fixed bollard strapped to the tree. It's what I learned on and what I'm used to. The one I posted on page 1 is close in size and weight to large porty I reckon, so smaller and lighter than other bollard devices, but it is a custom made, and not readily available to buy. Most (all?) strap on lowering devices that you can buy are pretty big and heavy and can take 2 guys to set-up. The porty style ones are relatively inexpensive, available through many vendors, set up with one guy, and tested by manufacturer to be bomber.

If you're on the fence about what to buy, nobody really regrets owning a port a wrap with a big dead-eye sling.
 

TimBr

Well-Known Member
I prefer the design of the Stein unit, that I think was designed by Reg Coates. Having the ability to hang it upright makes things easier, to my way of thinking. I use a dead-eye sling and a cow hitch to secure the bottom of the device. I love how secure the cow hitch feels, and how easy it is to tie it.

Tim
 

KevinS

Well-Known Member
Thanks guys that’s what I always thought. I’ve never bothered with a ratchet to hold it up out of the mud I just move my sling up 6” so it’s clear.
I’ve never used the bollard type I’ve always been a porti guy
 

southsoundtree

Well-Known Member
Thanks guys that’s what I always thought. I’ve never bothered with a ratchet to hold it up out of the mud I just move my sling up 6” so it’s clear.
I’ve never used the bollard type I’ve always been a porti guy
It isn't too keep it out of the mud, which it does.

It keeps the POW from flopping around.

Easier to load,
easier to pretension,
When negative-rigging a top, the Floppy POW drops and pops up (possibly damaging a safe-tree), but much more importantly, the rope can get messy. I've read if people having the POW lock-up from sloppy ropes getting twisted up, after the flip down and flip up.


The ratchet strap (I keep 5-10 onsite between trucks and trailers, often, to secure loads) is onsite and simple.


A ratchet straps can hold a heavy, fixed bollard to the tree from the top, while one person sets up the webbing anchor belt.
 

Stephen Moore

Well-Known Member
View attachment 59694

Accomplished welder is essential. The bottom right was the first, only had a small picture in the Sherrill catalog to go by,
cool looking devices, The pipe thickness has lots to do with heat dispersion, one of those looks mighty thick! The reason most manufacturers use thin walled stuff is to bleed of heat caused by enormous amounts of friction. When you by a device they have tested the design, plus steel and rod are not cheap either, nor is my time!
 

*useless info*

Active Member
Pulls up the trunk, or any pull 'lenghthwise'(ABoK) rather than right angle across host mount should be double bearing at least(prefer self adjusting), especially with taper, especially taking hits in flat rope( webbing) or round rope as most mechanically correct against worst angle of pull/lengthwise on rope/flexible devices.
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Prefer round rope for Porty. People use round ropes because round is correctest in so many ways . i prefer Backhand Turn based hitch that pulls from center of tree/anchor, long eye with seam buried in turns presented for loading.
>>Pile Hitch always amazingly simple, yet powerful strategy; really shines here too i think. Laced Pile Hitch (1st cross is over against load pull, Round Turn here is strength upgrade)) around anchor tree +half hitch of 1 leg as stopper around the other leg(of Pile) to Porty very nice. Can cheat last tuck 1 less step than Pile and safely half hitch around leg to Porty, especially if Round Turn upgrade (that also can buffer loading to buried 'seam' of eye) .
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Take three wraps
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i think best to count in half circles to be clearer if 3 or 6 half circles of contact. AND really to be closer to key mechanical aspect here (somehow)
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In faded memory(edit:http://www.jrre.org/att_frict.pdf )there is some report,
of smooth steel pipe brake, showing brake force more as a degrees of contact than inches of contact (especially accentuated to be sifted out here in low texture/friction devices w/o much other explanation especially small pipe..).
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(i believe)They said :
3 half circles as 10x multiplier of controlling Hand Hold as brake force achieved against load
5 half circles as 50x multiplier of controlling Hand Hold as brake force against load
7 half circles as 250x; whereby even the free hanging weight of the rope on the control side is significant.
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rappelling rack etc. play off this same cumulative degrees of contact geometry etc.
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Rope folk sometimes argue on what constitutes Round Turn; always viewed as 3 half circles(540 degrees) personally. And a TOTALLY different thing than simple Turn in the way each plays out over and over. The simple Porty lessons and Bollards thru history, viewed thru this math is amazing, but could very well be fair! (A Radian x Pi is a half circle i think is somehow key here. )
 
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*useless info*

Active Member
Traced this link down for what i think is very key vision into brakeForce mechanics on bollard type simple pipes like Porty. But would then extend to cranking capstan, why to always keep at least 2 turns on drum of winch (so no raw force possible to termination) and even inside the secret life of knots..
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http://www.jrre.org/att_frict.pdf
Technical Paper: The Mechanics of Friction in Rope Rescue presented to International Technical Rescue Symposium 1999
by Stephen W. Attaway:GA.Tech Masters Structural Engineering + Computational Mechanics (modeling stresses, displacements) Ph.D
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i believe this fully explains what we 'feel' in working with Porty AND turns of Friction Hitch, any Round Turn + etc.
>>very powerful strategies, that math/geometry offers explanation for.
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*useless info*

Active Member
Important note, the eye can be fooled.
A single Turn and Half Hitch has only 1 radian Pi power arc of Nip and Brake forces and Round Turn has 3 such power arcs. On the graph above jumping backwards on the exponential growth rate shows single Turn left way behind; not in the running... This carries into all kinds of systems and knots.
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i think a base knot of 1 Turn just hangs on, But Round Turn(RT) different class if performed on the mount (also Crossed Turn base of Clove is Round Turn with more enforced friction) or on the Standing Part is great increase in knot forces.
>>But not RT or Crossed Turn on host mount, followed by RT on Standing Part because the RT (or Crossing RT) on host consumes the 'power' needed to get strength return from RT on Standing.
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The 3+ half circles this way, or upgrading Square Knot to Surgeon's (as linear 3 half circles are close to more perfect knot of long eye splice) i think is an extension of the above 3 half circle arc on bollard theory above; only 3 arcs now alternating/opposing/self balance used to apply to linear pull as some key to knot workings.
 
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