Understanding the Snatch Block
A snatch block is a commonly miss understood tool that can be a big help when stuck in a deep mud hole or when you are trying to make due with an under powered winch. A snatch block can also be used to change the direction of which the winch will pull when there is nothing directly in front of your bike (or the direction you need to pull).
A common miss conception with a snatch block is that it will double your pulling power which is close but not exactly true. (In the following When I say load I am referring to the amount of force in pounds that is required to move the object being pulled or bike).
When using one snatch block correctly you can use the equation:
1.1 x load / 2=force required from the winch.
To find the total force required from the winch you must first take the total load required to move your bike and multiply it by 1.1 to calculate for the friction added by the rope passing through the snatch block. For example a 1000lbs load pulled through a snatch block becomes an 1100lbs load due to the added friction which is calculated by using the following equation 1000x1.1=1100. By attaching the snatch block to a tree then running the winch cable through the snatch block and back to the load will create two things a slower rate of pull and less load on the winch. Now you have two points of attachment to the bike which will equally divide the total load by two. When using a single snatch block the original 1000lbs load multiplied by 1.1 and divided by 2 parts now requires 550lbs of force from the winch to be moved.
You might ask where did I get the 10%! Well it is the industry standard in the utility industry to calculate 10% for each pulley. 10% is not always exact due to the differences in pulleys and the size of the rope but it is a good base line figure..