Not to be pedantic, but it’s electric field, not EMF, lightning not lightening, and shear not sheer.
EMF is simply voltage. Lightening is the process of making something lighter, and sheer is the curve made by the upper edge of a hull.
Electric field, in this case, is determined by the potential difference over (divided by) the distance between the two sources of charge. Move one source closer to the other (the charge-bearing clouds are blown your way) and although the voltage difference remains the same, the field increases up to the point of (dielectric) breakdown, and electrons leave the mast and go streaming up to the clouds.
Yeah, I’m an engineer, bo no one truly understands all the mechanisms of lightning. ;-)
Mike
On Oct 25, 2015, at 3:12 PM, taladorwood@yahoo.com.au [harryproa] <harryproa@yahoogroups.com.au> wrote:
First off, it is important to install a very pointed static discharger, (or the fuzzy balls with hundreds of needles) that is electrically bonded to the boat.Unlike what everyone normally thinks, me included, lightening rods (Static dischargers) are designed to bleed off static electricity, (coronal discharge), before the EMF builds up large enough for a lightening strike, not attract a lightening strike.However they don't always work : (So onto fabricating a rotating mast or wing spar.Let's start off simple and use an H beam for example. Lets say the beam is being pushed to the right. The left side of the H is in tension, the center is in sheer and the right side is in compression. It is the compression side that is the problem and why carbon (or wood, or metal) is needed to prevent BUCKLING, glass compresses fairly easily. If the beam was always deflected to the right it would be easy to put glass on the left, foam in the center and carbon on the right side, for the lightest, strongest, most economical beam.Sadly reality is never that simple and on a rotating mast the buckling forces are going to come from every direction. The first casualty is the foam and glass, they just aren't stiff enough weight wise. That leaves Carbon as the last man standing and carbon is expensive and potentially tricky to lay up.A wing though is a little different.Only two sides of the box spar need to be carbon, because that is where 99% of the deflection forces are. A wing has comparatively small fore and aft forces and less force overall.A wing spar is going to be comparatively lighter than a mast and easier to build which means cheaper.I think it might be possible to hand layup the carbon and vacuum bag it.Talador
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Posted by: Michael Gehl <mike@vail.net>
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