In a standard game of battleships, what is the minimum number of strikes you will need to make to guarantee hitting at least one boat?

Battleships is played on a 10x10 Grid,
You are allowed:-
1 Battle Ship (4x1)
2 Cruisers (3x1)
3 Destroyers (2x1) and
3 Submarines (1x1)

NOTE:-These rules are slightly different than those of the board game, I am using these so that all members can give the same answer.