A powerboat is operating at night from which directions must the white masthead light be visible?

Rule 21 of the Navigational Rules of the Road.

(a) "Masthead light" Means a white light placed over the fore and aft center-line of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed to show the light from right ahead to 22.5 degrees abaft of the beam on either side of the vessel, except that on a vessel of less than 12 meters (39'4") in length the masthead light shall be placed as nearly as practical to the fore and aft center-line of the vessel.