On Thu, 25 Jun 2009 02:30:42 -0700 (PDT), Matty F wrote:

I would certainly recommend using two gates instead of one, if that's
possible. In my case there is nowhere to swing them to. And I would
recommend steel for a 15 foot gate.

I still feel that a properly made 15' timber gate is not a problem.

http://www.flickr.com/photos/allsorts-60/3659175057/

13' timber field gate. Hinge post 5 x 3, slam post 3 x 3, top rail 4
x 3, other rails and braces 3 1/2 x 1. All rails have 3 x 1 mortises
right through the posts. The braces are overlap jointed into the top
rail and bolted right through the top thin rail and at the apex on
the bottom rail.

This gate is several years old and hasn't dropped at all, mind the
latch does take some of the weight when it is closed as should happen
with all gates.

For 15' I'd keep the same basic design but might taper the top rail
from 5 x 3 to 4 x 3 and have 3 instead of 2 sets of braces, mainly
'cause I think that would look better.

--
Cheers
Dave.