Jeff:
Anything is feasible, given enough time and money. And I wasn't being flippant
with that comment, either. There must be a few Cellular towers in the vicinity
of your property; they had to be designed for similar conditions.
Given your acknowledged issues with the site, including the soil, ocean
proximity and wind record, a Registered Civil Engineer ought to be familiar
with all of these limitations and be able to design a tower installation that
will survive nature's worst. If you're serious about installing a tower, pay
the money and do it right - you'll sleep much better during windy nights.
Good luck.
73 de
Gene Smar AD3F
On 10/23/13, Your Name<ks4tl@rodentranch.com> wrote:
I am trying to determine if it would be practical to safely install a 40
to 50 foot free-standing or bracketed (not guyed) tower in my location.
I would like to hear from anyone who has erected a tower in a similar area.
My location is Chincoteague Island, Virginia, Zip Code 23336. If I am
reading the �three second gust speed� maps correctly, this location is
in a 120 mph area on the Exposure �C� maps. However, the location is
also about a quarter-mile from open water (an inlet off the Chesapeake
Bay), so it is possible that it should be considered Exposure �D�. The
location is flat and barely above sea level, with no significant
features to obstruct wind.
The soil quality is about as poor as possible from a support standpoint.
It is silty sand, and during the course of a year varies from dry/loose
to completely waterlogged. It is also mildly salt-contaminated(from
seawater flooding in 2012), and so rather corrosive. The ground water
table is high - holes deeper than 3-4 feet tend to fill with saltwater.
One good thing: winters are relatively mild, frost depths never exceed
an inch or so. Ice storms are rare. Icing would not be expected to
exceed 1/4 - 1/2 inch at most, and ice storms have not been known to
occur at the same time as high winds.
One final feature of the site: it is subject to tidal flooding during
severe tropical storms and nor�easters. Every 2 or 3 years, the base of
any tower at this site will be immersed for several hours in seawater,
to a height of up to 4 feet. (Most houses here, if you are wondering,
are elevated on pilings or perimeter walls.)
Guying of the tower is absolutely not possible. Bracketing to my
residence (modern construction, concrete walls from the ground to four
feet, frame above four feet) may be possible.
The total wind load of all equipment would be about 10 square feet.
I would install either a K4KIO Hex-Beam, a 2-element Steppir Yagi, or a
small tribander (Force 12 C-3S or similar) on the shortest practical
mast at the top of the tower. All of these have rated wind loads below
6 square feet. A medium-sized rotator (Yaesu G-800 SA or equivalent)
would be used. I would probably also attach 1-2 fixed, omnidirectional
VHF/UHF antennas to the tower.
My initial idea is to simply overengineer - select a tower rated for 120
mph at *double* my planned windload, and go up a step or two on the
usual foundation size. I'm also inclining toward an aluminium, rather
than steel, tower due to the saltwater corrosion issue.
Any thoughts would be much appreciated. I might end up turning to a
Professional Engineer for final planning, but I'd like to check to see
if this is even remotely feasible before I incur that expense.
Thanks,
Jeff / KS4TL
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