How to Graph Tidal Currents
The graphing of current velocity information is generally the same as
graphing tide data. The most important difference is that tide height
changes at a fairly constant rate. Current velocity on the other hand is
related to many factors; for complete information on current velocity,
refer to Duttons, chapter 10.
We can use the times between slack water and maximum current to plot
our data. Table 4 can help us determine the amount of time a current is
weak and it should also help us make an educated guess of how steep a
curve must be plotted.
You may want to overlay the current data on the same graph as the one
that has tide data for the same period. If this is the case, it is normally
acceptable to omit drawing curves for the current data. Instead, you
would draw straight lines between slack water and maximum current.
At the intersection of each line, annotate SW for slack water and MC for
maximum current respectively. If you do choose to overlay, make sure
you use different colors of ink, one that represents tide data and one that
represents current data.
In our next chapter youll learn how the Quartermaster keeps track of
the ships position.