In the article is specified, that marine ships considerable part of the operating time work in the straitened districts, in which the width of free passage-way for vessels is limited in the navigation relation by dangers, or intensive navigation. It is marked that in the case of dangerous rapprochement of vessels in the straitened waters at the choice of maneuver of divergence by an operating ship besides a dangerous target it is necessary to take into account preventing ships and navigation dangers in the district of maneuvering, and the existent methods of simultaneous account of dangerous aims and navigation dangers carry analytical character and are bulky and ineffective. The necessity of development of operative and evident methods of warning of collisions of vessels at sailing in the straitened waters is caused to these. The analysis of the last achievements and publications is resulted in work, the decision of the considered problem and selection of parts unsolved before is begun in which. It is shown that binary coordination is the basic method of description of cooperation of pair of the dangerously drawn together vessels, urgent strategies of divergence are considered, the structure of which depends on the conduct of target in the process of divergence, the analysis of procedures of account of navigation dangers is also produced by an analytical method for different types of navigation dangers. Procedure of transformation of the ship safe region set in space of relative motion is offered, in space of veritable motion, a virtual region is formed as a result. It is indicated, that basic properties of virtual regions are: rapprochements of ship with a target dangerous, when the current area of programmatic trajectory of motion of ship gets in the virtual region of target; distance of the shortest rapprochement of ship with a dangerous target will be equal to the set minimum-possible distance of rapprochement, if direction of current area of programmatic trajectory of motion of ship is tangent to the border of virtual region; equality of distance of the shortest rapprochement of ship with a target and set minimum-possible distance of rapprochement is saved at the following of ship on a virtual region tangent to the border to the moment of the shortest rapprochement. It is shown in the publication, that by the computer program dependences of position and form of virtual region on the relation of speeds of ship and target were explored, from distance between a ship and target, and also from bearing on a target. It is shown that depending on distance between a ship and target at the unchanging bearing a virtual region occupies unchanging position in relation to the line of programmatic way of ship, and position and sizes of virtual region depend on bearing on a target.