Sailing

by E. F. Knight

Fig. 52.

The line joining C and D—the point where the circle and the line A B cut—represents the direction in which the vessel must be steered so as to keep on the line A B. Draw A E parallel and equal to C D. Then if the vessel be steered from A towards E, and travel the distance A E through the water she will in reality have made the distance A D in the direction of her port. In the two figures the alteration of the vessel’s course is about the same, but as the current is contrary in ([Fig. 51], A D, the distance made, is much less than A E, the distance sailed, whereas in ([Fig. 52] the current is favourable and therefore the distance made is greater than the distance sailed.

In current sailing, every advantage must be taken of the tide, and it is often possible to fetch a port dead to windward on one tack by what is termed underbowing the tide.

For instance, if we are bound for a port due north of us, and the wind is also due north, while we have a current running to the eastward, we can, by putting our vessel on the tack that directs her to the westward of north, that is, in this case the starboard tack, bring the tide on the lee bow so that the result of our north-west course and the easterly current is that our vessel travels due north.

Hence it is very necessary, while tacking across the sea, to know exactly when the tide will turn, so that we can put the vessel about to the best advantage.

If we are crossing a broad stretch of water such as the North Sea, with the wind free, and are likely to be in more than one tide, we can usually with advantage steer a course straight for our port, without paying much attention to the currents, as the effects of the ebb and flood will cancel each other, and we will be able to make a good land-fall.

The rise, rate, and direction of the tide at springs and neaps are generally given on the chart. If the hour of high water for the particular day and place are known, the speed of the current and the height above low water can be roughly calculated from the following data. Unless the conformation of the coast produces a variation from the general rule, the tide rises from low to high water in six hours and a quarter and falls from high to low water in the same time. The rise and fall are not uniform. During the first and last hours of flood the rise is smallest. During the second hour it greatly increases. At the fourth hour the tide has reached its maximum rate, and from then the rate of rising diminishes in the same proportion until high water. The same, rule applies to the ebb tide.

Fig. 53 represents the range of the tide in the open sea, which we have divided into sixteen equal parts. It has been found that the tide will rise one division in the first hour, three in the second hour, four in the third hour, four in the fourth hour, three in the fifth hour, and one in the last sixth hour and a quarter.