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How to determine the distance to the shore

Determining the distance to the shore by a known height

Determining the distances to the shore or visible objects in the sea is a constant concern of the captain. How to determine the distance to the shore? Depending on the situation and opportunities, they use various methods, for example, using sextans and tables, but most often they estimate the distance by eye.

There is, however, a proven way to determine the distance using an ordinary school ruler, which is not much inferior in accuracy to the instrument ones. It consists in the following. In the lot or in the book Lights and Signs, the height of noticeable objects is usually indicated signs, lighthouses, towers. Knowing the height of such an object visible with boats, yachts or boats, it is not difficult to determine the distance to it.

How to determine the distance to the shore
Determining the distance to the shore by the height of the object

The proposed method is based on the well-known theorem on the proportionality of the sides of such triangles. If we know the true height of the object Hpr (m), the length of the outstretched arm(cm) and the visible height of the object hin (cm), taken on the scale of the ruler at arm's length, then the distance from the ship to the object will be

Determining the distance to the shore by a known height

Let's say the lighthouse has a height above sea level of 60 m, the distance between the ruler and your eye (the length of the outstretched arm) is 66 cm, the apparent height of the lighthouse on the ruler is 2 cm. It is not difficult to calculate that the distance to the lighthouse will be 60x66:2=1980 meters.

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