Decision-making made easy
4. DECISION-MAKING MADE EASY
Now you may be wondering what the purpose of all this is, especially if you’ve already worked out most of the above on the back of an envelope. This is true, and you may feel that there is little point in studying the charts or checking the tides in the almanac as your GPS chart plotter may be able to give all this when required on passage.
However, apart from any other well-known virtues of planning, the process of recording information from multiple sources in a single diagram has the added benefit of showing up any inconsistencies that might otherwise go unnoticed on your back-of-anenvelope notes.
Part of the on-passage routine aboard Mollymawk is to make an entry in the ship’s log every hour. I believe it to be good practice and it is a useful reminder to check things below deck and make a cup of tea; so whilst filling in the log and waiting for the kettle to boil I also make a mark on my graph to show the distance Mollymawk has left to run at that time.
As the hours pass, I am able to see how our actual speed compares to the planned speed. These marks are shown in red on Figure 4. You can see that initially Mollymawk was making very good progress because her actual progress line was getting closer to the 4 knots speed line; this is the speed required to get to the destination on time.
In fact her progress was too good and it was indicating that we would arrive before the strong tidal stream in Hoy Mouth had turned. However, the tide was carrying us eastwards during that evening and you can see how the speed drops after about 2000 (as did the wind) and Mollymawk’s progress falls back to the 5 knots line needed to get to the destination on time. In fact, we were only making about 3 knots over the ground for a few hours, but I knew that this was fine as there was no need to fire up the engine until the 5 knots line was reached. This was looking to be the case at about 0100 and so with a gentle 1200rpm on the Beta 50 I could motor-sail and maintain the speed to make the arrival window with ease.