Below is a picture of my biggest HF antenna. The antenna was a 5BA from Force 12, it was a 15 element 5 band yagi.
The antenna was mounted on top of a 15M (50 feet) tower.

The antenna was unfortunately brought down by a heavy storm in the beginning of 2002....
 

The boom of the 5BA was about 11 M long (34 feet) and the longest element was 11 M long.
The antenna had 3 feed points, one for 20M, one for 15/18M and one point for 12/10M.
Gain on each band was approx 6-7 dBd.