There is no reason not to use parasitic designs for verticals and Team Vertical has used them for several years. The most performance for the weight and using minimal space is the 2 element parasitic vertical dipole design. Making it switchable to the opposite direction covered 280 degrees on the main lobes. The plots are shown below. How to switch directions on the design was a challenge.
Salt water is terrific for antenna efficiency, but terrible on antennas and equipment.
The salt spray can cover everything and cause problems on antennas where the high voltages will arc and burn up portions of guy lines and insulators. Having been through this many times in the Caribbean enabled the right design to be developed. The guy attachment point is just above the feedpoint, which is high current and low voltage. The feedpoint impedance of a single vertical dipole is about 90 ohms. This is an attribute that makes the vertical dipole excellent for arrays.