Captive Column . Com

arrow1.gif (893 bytes) Time Line - 1980: Captive Column Dielectric Tower...
Finished NATO Tower   The finished Captive Column Dielectric Tower in use. (32k)

NATO had an urgent need for a portable dielectric (non-conductive) antenna system. According to IRT Corporation of San Diego California, this tower was needed for testing the EMP (Electro Magnetic Pulse) survivability of military aircraft around the world (extremely high level EMPs are given off by nuclear bombs). The tower therefore needed to be both highly portable and dielectric to prevent it from affecting the test results.

Due to the very stringent specifications required for this tower, IRT was unable to purchase it from existing tower manufacturers -- conventional construction methods simply could not do the job.  IRT therefore turned to Mr. Bosch and the Captive Column to fill their needs. As you will see, Mr. Bosch not only solved their problems, but also produced a unique tower system that greatly exceeded their specifications.

Here are the design requirements submitted to Mr. Bosch by IRT:

"This Firm Fixed-Price Purchase Order covers the purchase of one (1) seventy (70) foot tall antenna tower, which shall have (1) a minimum 'dead load' capacity of 500 lbs. and have a maximum Tower Weight of 300 lbs., and (2) be 'field executable' by four (4) men in a minimum of 8 hours, requiring only hand tools for such erection. Tower is to be constructed from non-metallic materials with the possible exception of vendor's use of small metal fittings. Seller is to furnish all materials and supplies required to fabricate the above units."

Mr. Bosch took these specs and proceeded to produce a Captive Column tower with the following characteristics:

  1. The tower was 70 feet tall and weighed 70 pounds (1 pound per foot). 
  2. The tower could be erected by 3 men in less than 1 hour.
  3. The tower could support a load in excess of 500 pounds.
  4. The tower was completely non-metallic, with the exception of 3 metal turnbuckles at the base (acceptable to IRT).
  5. The tower was packaged in two 10-foot boxes when disassembled, reducing the effort required for transportation.
  6. The only tool required to erect the tower was a hand wrench to tighten the turnbuckles.

When comparing the delivered product to the IRT specifications, you can see that Mr. Bosch had eliminated the need for 1 man and shaved 7 hours off of the erection time -- improving on specifications that were already too tough for any other construction technique to satisfy. The second-generation tower was expected to weigh about 50 pounds.

The following photos show some construction stages of the Captive Column NATO tower.

Winding Machine Semi-automated Bosch winding machine wrapping a Captive Column vertical compression element of the NATO tower. (34k)
Close Up Of Winder Close up of the winding heads. (37k)
Finished Beams Some finished NATO Captive Column tower components. (30k)
Taking Shape The tower begins to take shape. The finished tower consisted of 7 vertical components, 18 radial components, a mylar rope tension cage, and miscellaneous hardware for assembly. Turnbuckles at the base, weighing 12 pounds, made up a good portion of the 70-pound total weight of the tower. (28k)
Assembled Assembled tower can be held at any point without bending or twisting out of spec. Billiard balls were used for joints to provide flexibility under extreme loads. (54k)
Packed For Transport The entire NATO tower fit into two ten-foot boxes for air transport. The mylar tension cage had to be designed so that it wouldn't snag. (41k)
The Fargo Shop The Fargo North Dakota shop where the NATO tower was built. (18k)

It should be mentioned here that Mr. Bosch did not go to all of this effort to design and build just one tower (sold to IRT for $11,000). IRT had told Mr. Bosch at the start of the project that there was a definite need for towers of this kind, and that IRT would purchase some more. Mr. Bosch therefore believed that he was in fact building the prototype for a fledgling business. Although the tower met and exceeded the needs of IRT and remained in use for the duration of its scheduled multi-year service period, IRT never purchased another tower. This was interesting considering this communication from IRT Corporation:

"... I would like to say that IRT is excited about the potentials for this technology. We are looking forward to working with you in the future in helping to bring the Captive Column technology to the market place in the form of practical devices such as this tower." -- Thomas W. Buckman, Ph.D., IRT Staff Engineer

IRT has never offered an explanation for their actions, which put Mr. Bosch out of business again.

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Copyright 1998-2004 by Lawrence R. Bosch.