An apparatus and method of preparing and coating a large structure such as a ship's hull while in a dry dock wherein a plurality of spray guns disposed in an array are positioned by a robotic arm in a spaced relationship along the surface to be treated so that their spray patterns overlap. The array of spray guns is traversed downwardly a thus painting a strip whereupon the spray guns are secured, move horizontally and then activated to be moved upwardly until another strip adjacent to and overlapping the first strip is painted. These steps are repeated until the surface area is substantially entirely painted. A shroud is provided for collecting paint oversprays and other excess paint is mounted in the array assemblage. An auxiliary spray gun may be positioned and its spray pattern adjusted to apply paint to areas which were missed by the original spray pattern emanating from the array of spray guns. Travel of the system along the work surface is accomplished by a reference track, which may be virtual or actual along which an unmanned platform travels. An articulated computer controlled arm is carried by the unmanned platform which in turn carries the assemblage. Other tools may be selectively operatively connected to the arm for cleaning the hull before a coating is applied thereto.