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## [TowerTalk] Re: An Engineering Question

 To: [TowerTalk] Re: An Engineering Question k6ll@juno.com (David O Hachadorian) Sat, 31 May 1997 13:59:52 EDT
 ```On Sat, 31 May 1997 13:32:01 +1200 Martin Ellis writes: >Hi, > >Just reflecting on the problem of placing guy anchors >closer to the base of the tower... > >Interesting how yachting designers plan their rigging to >keep 100+ foot masts upright, when they are limited >by the beam of the yacht. And how many square feet >of sail area? > >Martin ZL1ANJ > That _is_ an interesting thought. There are some differences between the two problems though. I'm not a sailor, but I think the following observations are at least partially correct: Many of the sails are triangular, with the center of pressure fairly low on the mast. Ham antennas have a big blob of surface area at the very top. The boat heels in the wind, spilling some of the air. You'd better hope your ham tower doesn't do this! The sails are not orthogonal to the wind in most cases. You can't count on this for ham antennas, which are frequently "sailing" unattended! Isn't there a wind speed limitation, above which the sails must be lowered? Pressure exerted by wind is a nonlinear function: 5mph = 0.1psf 10mph = 0.4psf 20mph = 1.6psf 40mph = 6.4psf 50mph = 10psf 60mph = 14psf 70mph = 20psf 80mph = 26psf 90mph = 32psf 100mph= 40psf I think sailboats lower their sails just as the curve starts to get interesting for ham antennas! Dave Hachadorian, K6LL k6ll@juno.com -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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