Pitch is how far in inches the propeller would travel in one rotation with no slippage. Higher number means that the propeller would travel further, lower number means that the propeller would not travel as far.
Example: 26x32 = 26 inch diameter, 32 inches of pitch (boat would move 32 inches/revolution)
26x34 = 26 inch diameter, 34 inches of pitch (boat would move 34 inches/revolution)
In practice this takes the test vessel from 32 mph to 38 mph, same rpm range.
Without enough torque however, one might not be able to wind in additional pitch willy nilly and the boat ends up going slower since it cannot spin fast enough.