Follow Kim with the boat. Attackers in black boats will soon move in from both sides. Use L1 to shoot the boats. Aim for the attackers inside the boats. If the boats take enough fire, they will blow up, killing all occupants. At one point you'll need to stand up using the triangle button to use the rocket launcher and take out the enemy helicopter. When aiming at the helicopter, lead it off a bit, as the rocket travels fairly slow. Once the helicopter and all of the boats have been destroyed, the mission is essentially complete. Follow Kim back to the dock to end the mission.