Abstract: An apparatus for controlling the size of a wafer supporting boat such that the wafers maintained by the boat have to be positioned at predetermined distances from at least two specific utmost faces of said boat. This apparatus comprises a slanted plane (31), two reference surfaces (32), guiding means (34) arranged in order that, when the boat is laid on the slanted plane, it may slide on it in such a way that the utmost faces abut against the reference surfaces, at least one plate (50) provided with a portion of reference groove (51) arranged so as to prolong according to their plane the supporting grooves of a wafer at a determined position. Thus, when the utmost faces are abuting against the reference surfaces, a wafer can be inserted into its supporting grooves and into the reference groove only if the size of the boat corresponds to a determined standard.

Abstract: The invention describes a device for recovering oil floating on the surface of water. The device is a floating vessel which is maneuverable at will in order effectively to recover all of an oil slick floating on the surface of the water. The device includes paddle wheel means to skim the oil from the surface of the water. The oil so picked up is propelled up guide plates, and over weirs, with a plurality of said wheels being arranged in sequence. The wheels are of different diameter but rotate at the same speed in order to provide separation of oil and water picked up by the device, and the device is also arranged to discharge the oil into a means from which the oil can readily be transported away from the device.The device may be provided with an additional wheel and screen for picking up debris floating on the surface of the water, and to separate that debris from the oil and water picked up by the device by leaving it on the screen.