Course To Steer
A Course to Steer is a method of calculating what heading the boat needs to be pointing in order to get successfully to its waypoint while allowing for the effects of tide and leeway.
Step 1: The first step is to plot our position fix which we label ‘A’ and our waypoint which we label ‘B’. Once both these positions are plotted on the chart, we can draw out ground track line from our position fix to our waypoint. It is best at this point to extend this line through our waypoint because we dont know what the effect of the tide will be yet.
Step 2: Once we have drawn our ground track line in, we now need to work out our tidal stream. Please have a look on our tidal steam resources page for a detailed explanation on calculating tidal streams. For the example though, we are going to use 341 degrees and 3kts of tide.
This gets applied to the start of our ground track, point ‘A’. We are for this example assuming that we are travelling for around 1 hour so there we are using 1 hour or tide and also boat speed. To identify our tidal vector, it is marked with 3 arrows pointing in the direction of the tidal flow.
Step 3: Once both our ground track and tidal vectors are plotted the last step to plot our course to steer is to plot our water track. This is done by using 1 hour of boat speed and arcing it off from the end of the tidal vector line. It will intercept the original ground track line either before or after the waypoint ‘B’ but never directly at it. In this example we have used 9 kts of boat speed.
Step 4: In order to use our course to steer line for navigation purposes we first need to measure it as a bearing in True and then convert it to either Magnetic or Compass.
In the above example, we can see that the True Bearing is 61degrees. If the variation where we are was 6 degrees west then we would be adding the 6w to create a Magnetic course to steer of 67degrees.
This is a full video on how to calculate a Course to Steer.