|
Day Skipper - Part 6
- Course to steer
 Probably
the one topic that gives Day Skipper students the most grief is calculating
a course to steer. If only it were possible to anticipate the effect of
wind and tide, we could calculate a course that would take us over safe
ground.
We need to decide our start and finish positions and the approximate
distance between them - let's say 16 miles. We know that our cruising
speed is 15 knots and we have calculated that the tidal stream is setting
200° at 1.5 knots. It is a calm day so there is no leeway involved.
You should start by laying off the tide direction from the start point.
We know that the passage will take about one hour, so the length of the
tide line will be 1.5 miles. Once the tide is marked on the chart, add
three arrows to the line to indicate tide. Then, using a pair of compasses,
open them to 15M (the distance we will travel in one hour). Place the
pointed end on the outer edge of the tide line and draw an arc on the
planned track. Join the end of the tide to the point where the arc cuts
the planned track and this is the course to steer to compensate for the
tide. It is extremely unlikely that your compass arc will pass through
the finish point. If it does, check that you have done it correctly.
When calculating speeds and distances you don't always need to use one
hour. So long as the tidal speed and vessel's speed is calculated for
the same time, you will always get the same course to steer.
Helpful hints
 |
Tide tables are only a prediction. Many meteorological factors can
affect their accuracy. |
|
