The saga of tilting over my UST HDX-5106 continues. The
raising fixture shipped with a Fulton K2550 winch rated at 2500 lbs.
That seemed overloaded, so I replaced it with a Fulton
KW3000 worm drive winch rated at 3000 lbs. That replaced
the brake overheating problem with a worm drive overheating
problem. And I needed two hands to turn the crank.
I don't know why I waited so long, but I recently estimated
the force on the winch cable. It is something in the
neighborhood of 4000 lbs, even with no rotor, mast, or
antenna. And I want to be able to tilt with all those
in place. No wonder I had all these problems. How
many other hams with smaller towers have replaced a K1550
with a K2550 due to the same underdesign situation?
In defense of UST, there is no simple fix for this. There are
no larger hand winches available from Fulton or any other
vendor and even motor driven ones top out around 3 or 4
thousand lbs. It is also not possible to increase the mechanical
advantage above the current value of 4 because no winch
will hold the additional cable needed after adding even more
pulleys.
In light of the winch being underrated, it is curious
that UST chose to use 5/16 inch galvanized cable. This is
rated at well over 10,000 lbs. Well, it doesn't hurt to
have extra design margin, does it? Actually, it turns out
that it does. First, the cable barely fits on the drum.
Second, the increased stiffness of the cable makes it
difficult to manage when the tower is near vertical and
the cable is not under much tension. Third, a thicker
cable means a large winding radius which increases the
stress on the winch.
I am working with Lunmar Boat Lifts to use a motorized
winch. (Thanks to W4ABC for turning me on to these
guys.) The off the shelf winch drum is large enough
to hold 50 feet of 1/4 inch cable. That happens to be
a perfect match for my tower, which shipped with 50 feet
of cable. Lunmar tells me that I should use 1/4 inch
stainless cable because it will be much more flexible
than 5/16 galvanized, yet it is still rated at around
8,000 lbs, so there is a 2X safety factor. Apparently
they use this all the time on their boat lifts. The
alternative would be to have a custom drive drum made
that could hold the larger cable. This is entirely
possible, just takes time and money.
Does anyone know of a reason why I should not convert
to 1/4 inch stainless cable and violate the K7LXC
prime directive? For example, the pulleys seem perfectly
sized for 5/16. Lunmar says that it is no problem to
keep those pulleys and use 1/4 inch cable, however, it
seems like the cable would get flattened slightly.
How critical is this?
Rick
N6RK
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