On Mon, 21 Aug 2006 15:39:14 GMT, Dave S
wrote:
I live on the gulf coast, and pretty much the vast majority are 200 feet
or less. Crossing a major ship channel, or the mississippi, you may find
them up to 500 feet agl though, to allow ships to pass under.

They don't need 500 ft to allow the ships to pass underneath, but
since the lines dip in the center between the towers and this is a
function of the distance between the towers, crossing a major waterway
would require the towers to be higher since the distance between
towers is greater... I'm not sure what the tallest ship might happen
to be... Probably 300 ft at the most... According to the following
link, there was a sail powered ship that had a 295 ft carbon fiber
mast... That sounds impressive...

http://www.guinnessworldrecords.com/...recordid=43706

An aircraft carrier requires about 215 ft above the waterline for
clearance of bridges and such... For power lines, you would probably
want to add another 100 or 200 ft for safety...