A variable area trim tab which is adjustable to control its effective area of the trim tab for use on boats having any of several propulsion methods. Area control is used to vary the effective lift area of the trim tab and to control the water flowing to, or flooding, the propeller. Flood doors and flood gates may be water blocking style, or water passing style to control water flow to the propeller. Area control and flood control components are also used as propeller guards, or propeller screens. Tunnel propellers use sliding and hinged tunnel closures to control water flow to the propeller. Sliding closures serve as propeller guards when the propeller is in the raised position. Side inlet water flow pipes allow water to fill propeller tunnels and serve as a side thruster propeller housing.