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Re: [TowerTalk] rope strength - Knot Expert

To: Gedas <>
Subject: Re: [TowerTalk] rope strength - Knot Expert
From: Edward Mccann via TowerTalk <>
Reply-to: Edward Mccann <>
Date: Mon, 9 Dec 2019 10:44:58 -0800
List-post: <>
And finally, what knot did you use to secure the carabiner into the loop?

Sent from my iPhone

> On Dec 9, 2019, at 7:56 AM, Gedas <> wrote:
> Grant TU for the very useful write-up and description. Yesterday before solid 
> rain and below freezing temps set in today my wife and I managed to put 
> everything in place and raised up both towers. Each now has my 2x4 with 
> pulleys arrangement attached & threaded and I really like the way it turned 
> out. Running up the loop with attached SS Carabiner clips up & down worked 
> out so well.
> I provided a couple of URL's showing the 99% finished setup. Images do not 
> show the SS pulleys attached to those clips. The images may look a little 
> confusing but I tilt over my 70' Universal towers (with 22' mast) using a 
> system I designed and have been using for over 35 years. The black poles are 
> a pair of 6"x6"x18' PT timbers bolted together and set into 7' deep concrete 
> (same as the HD tower bases). A double pulley system and geared winch allows 
> me to tilt up & down the towers in about 10 minutes since I do not climb.
> The images show I used a simple square knot to join the rope ends but these 
> will be replaced with a double fisherman's knot in the next day or so. Thank 
> you again to everyone who helped out and provided input.
> Gedas, W8BYA
> Gallery at
> Light travels faster than sound....
> This is why some people appear bright until you hear them speak.
>> On 12/1/2019 11:40 PM, Grant Saviers wrote:
>> I looked at your 2x4's with pulleys jpgs.  If rope strength is a concern, 
>> then consider that going around a sheave (pulley) significantly compromises 
>> strength in two ways. I thought a comment would be appropriate given the 
>> discussion about knot strength.
>> The rope fibers are compressed inside and stretched outside in the sheave 
>> wrap so the strength can be degraded 50% or more.  The pulleys you appear 
>> have a tiny radius.   Repeated passage is cumulative for damage. Check rope 
>> specs for the recommended sizes. 
>> (might be 
>> for wire rope, same problem, bigger loads and life safety = bigger concern)
>> The second problem is there is a lot of friction in the pulleys. I've seen 
>> tests for hardware store ones where the output tension is only half of the 
>> input tension.  I use a good sailing block, the best have polymer ball 
>> bearings.  It's amazing the difference low friction makes.
>> Sailboat pulleys are also made to minimize chafe, so if the load moves or 
>> the rope stretches in the wind you will be much happier in the long run 
>> spending $20 for the good ones.  I figure a tower climb costs much more than 
>> $20 if the rope breaks or the pulley fails.  Harken, Lewmar, Ronstan, are 
>> all great.  Here is the one I am currently using
>> Also, I went back to your original post to understand the goal. You mention 
>> 30# load.  The actual load in a rope pulled from the side is greatly 
>> affected by the angle the rope makes with the a line between the ends.  i.e. 
>> at halfway actual rope tension is load/sine(angle).  That means at zero 
>> degrees the tension multiplier is infinite for a load 50% between the 
>> support points. Obviously, that never happens since the rope stretches or 
>> something fails.  When your hoist point gets to the top pulley then that 
>> pulley will take all the load and the other line part can be slack, so not a 
>> problem.  Be aware that when hoisting,there might be a larger tension then 
>> expected halfway up if the hoist is a tight loop.  And the loop force on the 
>> supports is twice the tension. So a better solution is to put a lot of slack 
>> in the hoist loop.  I always use a loop through my permanent sailboat blocks 
>> in trees, just to never lose an end, but they have a lot of slack, also to 
>> reach the antenna on the g
 round partway out.
>> Grant KZ1W
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