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.
https://drive.google.com/open?id=1VLLuLA9e7lridHe3BgwfX34fbRPZeKti
https://drive.google.com/open?id=12aRNdm-8hnw31shSPDEoO-Lz7QGm4J-R
https://drive.google.com/open?id=1hn2NeCGb5lYBqMVq4dqbvomNpWM0836T
Gedas, W8BYA
Gallery at http://w8bya.com
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.
https://www.mazzellacompanies.com/portals/0/Images/Page206_3.png
(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
https://www.amazon.com/Ronstan-Ball-Bearing-Orbit-Block/dp/B002NSSCF2/ref=sr_1_6?dchild=1&hvadid=3527191554&hvbmt=bp&hvdev=c&hvqmt=p&keywords=ronstan&qid=1575260910&sr=8-6
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 ground partway out.
Grant KZ1W
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