On Friday, April 02, 1999 7:37 PM, Stan Griffiths
[SMTP:w7ni@teleport.com] wrote:
> Here is what you are missing: The gin pole has to support
> TWICE the weight of the load since the load pulls down on
> one side of the gin pole and the rope you are pulling on to
> raise the load is pulling down on the other side of the gin
> pole. The gin pole sees both of these down pulls and has to
> hold them BOTH, or twice the weight of the load.
>
> By using a block and tackle, you can reduce the pull on the
> rope you are using to lift the load. If you use a 3 to 1
> block and tackle, you reduce the pulling force to 1/3 of the
> weight and reduce the total load carried by the gin pole.
> Here is an example:
>
> Supposing your big mast weights 200 pounds. Pulling it up
> with a normal gin pole with nothing but a pully at the top
> means it must support 400 pounds. If you use a block and
> tackle, you can cut the pulling force
> down to 67 pounds and the gin pole now has to support only
> 267 pounds instead of 400 pounds.
Wrong. Just plain wrong. While the block and tackle gives
you a mechanical advantage, the gin pole is carrying
*only* the weight of the antenna (200 pounds), either with
a single pulley at the top, or with the multiple pulley
arrangement of the block and tackle. In fact, the added
weight of the extra pulleys and rope places a greater
strain on the gin pole than just a single pulley at the
top.
73, Hans, K0HB
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