Sink a ship

Sink a ship is a guess making game which is virtualized as a battle occurring between the player’s ship and the three pirate ships. The battle arena is a Sea of 7x7 grid. The objective of the game is to make guesses of cells of the sea grid where the pirate ships are positioned. By Sinking down all the three pirate ships at or within 18 guesses makes the player to win the game. Each time the game starts the ships will have their own new positions which is generated randomly.

Try making least number of guesses to kill all the three powerful pirate ships and defend your home ship!!!