256 lbs? pretty light.
I'll throw my 2 cents in . Interested in whether these numbers align
with people's experiences.
(people must be using some numbers in their heads when they do this stuff?)
Be nice if you could attach at 60' out, but I suspect the tower might
bend too much.
Do people use a bridle at two attach points to prevent bending?
Probably not. Probably attach at the middle or 2/3 point?
The height of the gin pole is what's critical to reducing pull force.
(assuming it's at the hinge point, which is best)
I did a little spreadsheet out of curiosity, assuming I got it right:
It looks to me like if you only have a 10' gin pole/derrick, you need to
pull with max 800 lbs if you attach at the tower 40' out or more.
So a light 1500 lb winch with a single line should be no problem,
assuming the gin pole/derrick resists compression and bending.
The problem with no back guying on the ginpole/derrick, you're relying
on the strength of it to not bend over..so taller might not always be
better for it..(you could think of it like a wind load vs height problem
for it, if it's unguyed 25g :)
Run it over a 20' house or something that's right at the hinge point,
and you only need to pull with 400 lbs max attached at 25' out or more.
(the vertical compression on the house should be about 350 lbs). If 20'
of unguyed 25G can handle 400 lbs sideways at the top, you should be
okay. Can see why the engineer mentioned 20' being "good". Seems like
more than you need though. If you rig the winch back away from the gin
pole rather than at it's base, then you don't get so much bending force
at the gin pole..mostly vertical compressive. Can use something lighter
like a 2-1/2" pipe then (with a pulley on top).
With a 30' gin pole, attached at 48 feet out on the tower, you might
pull it up with just two guys (200 lb pull). This is like people who
throw a rope up in a tree. You don't really want a 30' gin pole
(although you see the benefit of just bolting together some long wood to
make a temporary 10-15' high big triangle..that's your cheapest
solution, and doesn't leave something in the yard permanently)
So even though the house thing sounds hooky, for this light tower, the
added height is good and reduces the overall forces you're dealing with.
Note all those max loads can be reduced by having lifting the end of the
tower to as high a support as you got, to avoid going directly from
vertical. But then you have to remember to do that when/if you lower.
-kevin
AD6Z
john@kk9a.com wrote:
> To: "F.R. Ashley" <gdadx2@clearwire.net>
> Subject: [TowerTalk] Raising Universal Tower, WAS Re: Winch for LM70 -
> Tiltover ..??
> From: John Kemker <john@kemker.org>
> Date: Fri, 04 Dec 2009 16:58:13 -0500
>
> On a similar note, anyone have any suggestions on an appropriate hoist
> to use for lifting a Universal 60 ft. tower into place? I'm planning on
> putting a "derrick" up made out of a couple of sections of Rohn 25G to
> assist in raising and lowering the tower. Universal states the tower
> weighs 256 lbs. and one of their engineers suggests attaching to the
> tower to be raised at 20 ft. While an electric hoist isn't necessary,
> it'd be nice, as long as it isn't too expensive. The derrick will be
> approximately 20 ft. away from the tower and the hoist will be mounted
> at the base of the derrick, with a pully at the top of the derrick.
> General idea is to leave the hoisting cable attached to the tower at all
> times, but not holding tension when the tower is fully raised. Other
> option is to split the raising cable between the tower and the derrick
> with a heavy-duty link and detach when fully raised and let the tower
> length hang down out of the way.
>
> --JohnK
> 73 de W5NNH
> 10X 75371/M&M 117/SMIRK 6185/Six Club 285/TRA 2499/Norcross 228 F&AM
>
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