At 05:18 PM 5/31/97 -0700, you wrote:
>
>The thing that is different about crankups is that they are the ONLY type of
>tower I have ever seen advertised or speced for windspeeds of only 50 MPH.
>I think the reason is obvious: If you really speced them for the winds they
>will actually experience, they are too weak to hold up much of an antenna
>with any safety factor at all. If the manufacturers speced them
>conservatively, they wouldn't sell any of them.
>
>Stan w7ni@teleport.com
>
Aloha from Kauai,
My US Tower, MA-550, on the fixture which allows it to rotate,
survived Hurrican Iniki in the late Summer of 1992 out here.
It was carrying an oversized antenna: a 4-element quad on a
30 foot boom. The quad became a pretzel in the winds which reached
Cat. IV or V stregth depending upon your spot here on the island;
probably peak gusts of 150 mph here near Koloa in a pretty exposed
setting.
I had the tower retracted as low as it would go, probably down to
23 feet tall or so. I through ropes over the quad boom in hopes
of lashing the thing in place -- didn't work. The winds were so
strong the entire structure was vibrating at a terrific rate,
and moving (swaying ?) about 8 inchs peak, enough to hit the
house at the roof line about 10 feet or so above the mounting
base of the tower! You would think there would be no way that
thing could move that far. My son climbed up as the
winds were intensifying and put some towels between house and
tower, but they blew away, and it went ahead and hammered on
the house for another 30 or 40 minutes before the winds calmed
down while the eye passed. During the second act, of course the
winds came from the opposite direction, the West, this time,
but they were not so strong, maybe 100 or so on the back side
of the hurricane, so not nearly the vibration of the tower.
Anyway, the 550 survived, and is holding up my Mosley
TA-34-XL tribander now; and has been through lots of
strong trades these last 4+ years since Iniki blew
through. Bought the Mosley after being told it was
probably the strongest antenna made for wind survival.
For example, no one, so far as I know, can keep
a KLM up out here!
73, Jim, KH7M
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