Probably the most important single factor governing the value which can be obtained from a given radar equipment in a ship is the presence or absence of blind or shadow sectors. This is entirely dependent, on the siting of the scanner. There is no arc of bearing on which the careful seaman does not keep a visual lookout, constant or periodic, when his ship is at sea. As radar is capable of providing him with a means of detection on all bearings, which will often be more effective than his eyes, it would be surprising if he were not prepared to go to some lengths to avoid obstructions to its ‘view’.