[Towertalk] Re: mast disaster avoidance

[Mike Gilmer, N2MG]

Jim,

Wrong pulley/wrong place.  A "movable" pulley, located at the mast 
(load) in a common "block and tackle" arrangement serves to reduce the 
force necessary to lift the mast (by 2:1).  This reduction benefits the 
ginpole as well since the downforce on the ginpole is the total of the 
dead weight of the load plus the lifting force.

In the most simple ginpole arrangement, and ignoring friction, a 100lb 
mast requires the rope be pulled with 100lb downforce to get the mast 
to just lift off the ground. Together, these apply 200lb downforce on 
the gin pole.

However, we can employ one additional pulley: lift rope goes from the 
pulling personnel up the tower through the ginpole pulley, down to the 
load and through its attached pulley and back up to the top of the 
ginpole where it is anchored.  This pulley moves with the load - thus, 
a "mavable" pulley.  This setup allows the lifting crew to pull with 
50lb of force to get the load to move.  Total force on ginpole is 100lb 
downforce from the load (distributed across the two lines on the load 
side), plus 50lb downforce from the lifting crew = 150lb. load on 
ginpole.

Mike N2MG

N2EA wrote:

> If you had a ginpole with a 2 wheel block on top (never seen
> one, myself. Do they exist?), you would reduce the load on each 
> run of line, proportional to the number of lines.  
> 
> But the load on the axle is still the sum of the line-loads.
> i.e., unchanged.  
> 
> The compressive load on the ginpole itself is thus still the 
> same, and the out-of-column bending loads are the same.  
> 
> 
> Jim/N2EA
> 
> 
> -0-
> From: "Mike  Gilmer"<n2mg@eham.net>
> Date: Thu, 11 Jul 2002 12:16:03 -0300
> Subject: [Towertalk] Re: mast disaster avoidance
> 
> I agree with most of N2EA's post except:
> 
> > Solutions using added pulleys still leave the same load on 
> > the ginpole material itself
> 
> This is not true.  As has been oft-discussed on this reflector in the 
> past (and still misunderstood), judicious use of "added pulleys" can 
> reduce the total load on the ginpole.
> 
> Mike N2MG