Выпишите из текста задания сказуемые, определите время и залог глаголов. Navigation requires the use at different times of two different kinds of technique. For finding the way across the oceans, the techniques of deep- sea navigation using celestial observations are essential. Electronic navigational aids such as long-range direction-finding, or satellite station can also be used for this. But as long as he is in contact with the land or with outlying seamarks, the navigator must use the techniques of coastal navigation and pilotage. That is to say, he must manage his course by a mixture of observation and dead reckoning .
The ship’s position in coastal waters is known, in broad terms from the time she leaves her birth until she takes her departure into the oceans. It depends on the frequency with which known object can be observed and on the accuracy of the technique used in making the observations.
The task of a helmsman is to steer the ship precisely according to the instructions of the officer of the watch. On passage, these instruction take the form of a course to be held. A good helmsman uses the least rudder deflection to maintain a steady course. He must learn quickly at the beginning of each trick whether the ship is carrying port or starboard helm.

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