What's is the load on a rope in a block in tackle?

Markup98

Markup98

New Member
Joined
Apr 10, 2021
Messages
4
Location
Oklahoma
Sorry if this isn't the best section to post this. Google cant tell me the answer to this and maybe I'm overthinking it.

To keep it simple. If I'm using a 4 to one block and tackle to pick up 100 lbs I know the force needed to pick it up is 25#. I'm wondering what's the load on the rope and the pully itself. Does the load get split evenly across the 4 ropes or do I look at it as one single rope picking up the load. I'm wondering the same thing about the pullys. Would 4 pullys @ 25, 50, or 100# be needed?

What brought this on is I can't find a b&t rated for 600+lbs for under $60 and think I might build one
 
holeycow

holeycow

Dirt, Air, Water, Sun; Seeds.
Joined
Sep 9, 2011
Messages
4,409
Location
Canada
It would be the load, plus the friction in the system that has to be overcome while hoisting the load.

so, more than 100lbs.
 

Del_

Career arborist
Joined
Feb 18, 2002
Messages
28,237
Location
U. S. of A.
Holeycow and I are on the same page.

What is theoretically a 4/1 system of mechanical advantage is more like a 3/1 in real life due to friction. Ignoring friction each strand between the two blocks sees the same load and the number of strands between the blocks determine the mechanical advantage. Four strands 4/1, six strands 6/1, etc.
 

tfp

ArboristSite Operative
Joined
Sep 29, 2019
Messages
102
Location
Australia
If you're on facebook there is a group called RopeLab which discusses these kinds of things all the time. If you can't find it already discussed there they would definitely be able to answer all your questions.
 
Tigwelder83

Tigwelder83

ArboristSite Operative
Joined
Oct 3, 2020
Messages
134
Location
16743
Ok if your using a single block to double your line, your load is split between the 2 lines, and equalized by the block. So strain is total load, + friction, ÷ by the number of blocks. So 100#'s on a 4 sheave block set is 25#'s on each section of line, plus friction, plus weight of rigging etc.
 

Latest posts

Top