hmm, lemme try this idea out for you with the group's input....
LONN (lack of nads necessary) could possibly be overcome by the following....
I am assuming you will be able to completely build your stack of beams onto
the mast....and, it can be lifted up in one fell swoop.....that does sound
awfully nice...c'mon lotto!
MOST IMPORTANTLY Have the rotor ready to receive the boom....upon its
slipping into place, sock it down....once this is done I wonder if the
following combination might work for you:
I witnessed an interesting phenomenon recently when we took down the 25G at
W1CW. The man on top (K1 Top Of) was fastening the carabineer to the mid
point of the section to be lowered and also took a second caribeener and used
it as a loop which encompassed a rung of the tower and the lifting
rope....the weight was being controlled by the lower attachement point....but
the floating carribeener (how do you spell this word correctly?) kept the
tower sections near vertical as they were lowered....the weight pof the
section encouraging the rope to be vertical and the caribeener in turn
forcing the top part of the section to be pretty much so above the attachment
point.
Borrowing on this theme - we need to create a similar scenario for you - with
the weight being carried at the attachment near the lower antenna....a sling
around the boom to mast assembly of the lower antenna, perhaps.
Now, to make it go up "vertical" without tipping over you will need to have a
way to keep the lifting cable close to the upper boom to mast mount.
Since the lift cable will have some kind of a counterweight on it and that
will be near the lower antenna, the idea of some kind of hoop for the that
ball has to pass through is out....
Why not do the following (I think this a real good idea and am feeling very
pleased with myself for visualizing it)
At a height along the lifting line above your lifting point which is just
below the top beam securely tie a loose fitting loop of rope onto the lifting
line....this will go around the mast just below the upper antenna...
everyone with me so far?????
After the load has been lifted into place and is bolted into the rotor,
disconnect the lifting ball and sling assy and have the crane operator
proceed to continue lowering the lifting ball.....it will drop and as it
drops the "magic loop" of rope which was just below the upper beam will come
down to just above the lower beam...a height I believe you can work at
without suffering LONN.
The only down side I can see to this involves your feedline/beamtail for the
upper beam....since you will not be able to get to it, due to LONN (don't
feel bad...a LOT of guys don't go any higher than the top of the
tower...standing on the top plate is indeed a pleant relief for those arches
after a few hours in the air...) .
Since you will have to pre-install a beam tail that will come down to the top
of the tower and then barrel into your line to the shack (or go to your
remote coax switch if it is at the top), that piece of coax will need to be
taped onto the mast in between the two beams....this is the area that the
loop will ride along....if the weight of the antenna places strain on the
loop and the loop is over your coax it might crush it.....pre comitting to
having the lifting line run up the "North side" of the antennas and the coax
ALSO running on the "North side" of the mast will minimize this
possibility....the lifting line will be constrained by your upper boom from
wanderring and hence the the "magic loop" will bear on the opposite or "South
side" of the pipe.
As I am writing this I have a further refinement that comes to mind.....I
think this might be even smoother......have the lifting ball's hook or loop
on its underside be the location for the "magic loop".....also at this point
drop a HD sling to the real lifting point at the lower antenna's boom to mast
plate......by having the lifting cables weight at the "magic loop" you KNOW
it will slide down the mast as the crane lets out the cable!
Towers are cool, even for those suffering from LONN....I think that your
crane guy may have a short sling that will work for your "magic loop"....or,
fashion it from a short length of nice rope....go to the Home Depot and shell
out for a cut length of that really nice stuff....heah, I know you are
strapped for cash if you bought some SSV but the "magic loop" will only be
what....a 2 foot piece, you can handle that!
el jugo
k4oj
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