Quote:
Originally Posted by Ekka  Common scenario where a block is installed up the tree and you are lowering sections out.
The force at the block is double whatever the weight of the section is ... that's not taking into consideration friction or any dynamic loading if the section was falling.
Imagine you cut off a 100lb section. To stop it hitting the roof you need to apply force to the other end of the lowering rope ... if you apply 100lb then the section is stopped. So you have a 100lb on one side to stop it coming down and you have the weight of the section which is another 100lb. Total is 200lb on the pulley block.
Here's a quick sketch to illustrate.  |
It is because of the doubling of the load on the suspended block that I always recommend using rope or webbing slings that are double the SWL of the load bearing line. Sometimes this is not easy due to the construction of some of the blocks. They are not wide enough at the suspension point to fit the larger size rope, especially one covered with and extra layer to help prevent wear.