Posted by bruce in CO from 63.186.39.23 (sdn-ap-004neomahP1801.dialsprint.net) on Wednesday, March 27, 2002 at 10:05AM :
In Reply to: Re: Snatchblock - what is it? posted by Guy(NH) from 198.22.15.73 (drc19825073.drc.com) on Wednesday, March 27, 2002 at 8:49AM :
The term "snatchblock" refers to the pulley mechanism that allows a change in direction of the path of the winch cable. The unit is typically a pulley in a casing attached to a hook. One side of the pulley casing is typically made to unlock, pivot out of the way, then pivot back and relock. This allows the winch cable to be threaded through the pulley and keeps the cable from popping out of the pulley.
The mathmatical theory is that by attaching the hook of the snatchblock to the load to be pulled, and returning the hook end of the winch cable back to the bumper of the winch truck (or a separate anchor point close to the truck), that you will create a 2:1 ratio in the pulling power of your winch as opposed to the 1:1 setup of hooking the hook end of the winch cable straight to the load.
In theory if you used a second snatchblock hooked to the winch truck and returned a third run of the winch cable back to the load, you could create a 3:1 ratio and would be simulating a block-and-tackle type of load-reducing pulley system. The tradeoffs of increasing your pulling power in this manner is that 1). the winch takeup speed is reduced, 2). you need a lot more winch cable, 3) The winch cable gets used up faster in the pulling process possibly requiring mulitiple resettings of the system to gain the same pulling distance. 4) It can be complicated and if not monitored properly can put large amounts of physical stress on the componants of the system leading to break points and potential danger.
The snatch block can also be used as a simple change-of-direction tool if the angle of the the load is not lined up in a direct line with the winching truck AND if a suitable anchor-point exists or can be placed in usable location from which to anchor the snatchblock.
All of this theory applies to roped uphauls and rescue procedures in the world of rock and glacial climbing and rescue as well as to truck winching.
Sorry to ramble on Guy, the simple answer to your question is: A PULLEY!!!
Bruce
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