the tide is six miles an hour. In the last chapter I have explained that in the open sea at half-flood the tide is at its strongest, rising then as much in one hour as it does in the first two hours of the flood. From this we can therefore calculate that the drift of the flood has been about eighteen miles during the four hours since we took our departure. From E we draw on the chart a line parallel to the arrow which indicates the direction of the current, and with the dividers we measure out upon it, from the scale of miles on the chart, E F equal to eighteen miles. Then F is our true position, and C F is the distance we have made. What we have gained by putting our vessel on the port tack, and so underbowing the tide, now becomes very apparent; for our true course has been north-easterly, that is, we have travelled over the ground right in the teeth of the wind and directly for our destination, being now about half-way to it; whereas, had we laid the yacht on the starboard tack, we should in the same time have only reached the point Y.
Supposing that the wind had been favourable for our port when we left C, we should have employed the following method of ascertaining the course to be steered so as to make allowance for current. Let L in the diagram, at the foot of Fig. 69, represent the vessel's point of departure, and let P be her destination. With the dividers we take from the scale of miles the number of miles the current runs in one hour, and lay this distance down from L to
