I thought I had sent this message to the reflector but apparently not . . .
Stan or Patricia Griffiths wrote:
> Yes, I am ABSOLUTELY sure. Like I said, I set up a demonstration to prove it,
> showed it at a Willamette Valley DX Club meeting with the help of W7RR and
> convinced each and everyone present that it works exactly as described.
> What I did was set up a 6 foot vertical mast made of 1 inch diameter aluminum
> tubing. Next, I rigged it with a small single pully at the top and with a
> spring scales inserted between the pully and the top of the mast showing the
> downward force on the pully which is the same as the load on the mast. Next,
> installed a known weight of 15 pounds (measured by the same spring scale
> in the demonstration) on the load rope. Next, I took up slack on the "pull"
> rope and when the weight lifted off the floor, W7RR read the scale. It said
> pounds. Why 30 pounds and not 15 pounds? Because there are TWO ropes pulling
> down on the pully, one attached to the load and the other one attached to the
> hands of the person raising the load. Both of these ropes (technically, it is
> only one rope but it has the same effect as if it were two separate ropes,
> attached to the pully, in terms of applying load to the pully and mast) have
> pounds of tension each and pulling in the same direction (down) and all of
> load (15 pounds EACH) is supported by the mast and pully.
> What I did then was make a small block and tackle with a 3:1 advantage and put
> it in place of the single pully. I again raised the load off the floor and
> read the scale in series with the pully. I now read 20 pounds instead of 30
> pounds or 2/3 of the first number. Now there are 3 strands of rope holding
> weight (15 pounds) so the tension in the rope is 5 pounds instead of 15 pounds
> and the tension in the pull rope is also 5 pounds, since it is the same
> continuous rope. So now there is effectively FOUR ropes pulling down on the
> pully (and mast) but each one only has a tension of 5 pounds each (total 20
> pounds) instead of TWO ropes with a tension of 15 pounds each (total 30
> This REALLY works. If you STILL don't believe it, you can always rig this at
> home and TRY it yourself. It is not rocket science. Also, it is not
> intuitively obvious that it works which is why there are so many
> You certainly can't deny that it is a VERY IMPORTANT concept and reducing the
> load on the gin pole by 33% could save your neck when you are lifting that 250
> pound long steel mast . . . isn't it worth checking it out?
> I have actually thought about making my demo kit available as a traveling
> program but there is nothing in it you can't get at the local hardware store
> a couple of bucks.
> You know, when we hashed this out last time here on towertalk, I went away
> the ugly feeling there were still a lot of non-believers out there and I had
> failed miserably to get this VERY IMPORTANT point across. I hope I made it
> time. The bottom line is that you can try it yourself . . . so I don't want
> hear from any nonbelievers who have not actually rigged this up and made the
> measurements themselves . . . this means I should not get ANY nonbeliever
> on this since, as soon as you try it, you will become a believer . . .
> it is absolutely TRUE.
> K7LXC@aol.com wrote:
> > In a message dated 6/12/01 11:45:50 PM Pacific Daylight Time,
> > firstname.lastname@example.org writes:
> > > A 3:1 mechanical advantage block and tackle system does, indeed, relieve
> > > about 1/3 of the load on the gin pole, in addition to reducing the number
> > of
> > > bodies required on the pull rope.
> > You sure? Isn't a hundred-pound load going to weigh 100 pounds no matter
> > how the block and tackle are set up? The load effort on the end of the rope
> > will be reduced but the dead weight of the load stays the same. You still
> > need a suitable ginpole.
> > Cheers, Steve K7LXC
> > Tower Tech
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