A Fixer Assassination (Hook, Line and Sinker) edited in a cinematic fashion and in High definition with subtitles, enjoy.

Description:
The target is on a boat, use a boat to get closer and give chase, shooting the boat until it explodes
A much easier way is to use a boat to get only a little closer and snipe the target. This is easiest when positioned behind the target's boat as the target's head can be covered by windshield from other directions.
Note: You don't have to kill both occupants, just the driver (left seat).