I'm trying to get a land-based VHF marine monitoring station up and
need to make my antenna have some degree of directionality. I need to
know if there is a "simple" way for me get about a 180 degrees of
coverage versus 360 (in hopes of increasing my range in the right
direction).

The antenna (a 9db whip-type) will be mounted along side a
free-standing antenna tower and have a tip height of about 80 ft asl.
Without any directional feature that should give me a range of
somewhere between 16 and 17 miles (assuming the distant end antenna
height is 8 ft asl).

If there is aneasy way to make it somewhat directional and gain another
mile or two range (at least) that would be great.

Any ideas or am I "all wet?"

Ken