Start Line - RacePanel series with Mark Chisnell: Part 2

The start can be one of – and sometimes – the single most important part of the race. It’s vital to get it right tactically, strategically and in the execution. The RacePanel software provided by Zeus and Vulcan series chart plotters is there to help you do all of these things.

• Develop a strategy for the first leg.
• Find the right place on the line to start.
• Hit the line at full speed, on the gun and going the right way.

It will simplify our look at the software if we take these jobs separately. First up, let’s have a quick look at general strategy for the course – for instance, if there’s a big current or wind advantage to one side of the leg. A lot of strategic decisions become easier when you can see the start line clearly positioned on the chart. It will flag up all sorts of things that can be important, like a difference in depth of water (and therefore current) from one end to the other; or the shape of the land might hint at geographic wind shifts.

Fortunately the Vulcan or Zeus chartplotter will allow you to display the start line on the chart, so you can get the full lowdown on any possible geographic advantages, and can start thinking about the strategy for the first leg.

Once the line is set, then when you go to the Start Line Data screen, it will look something like this:

There’s lots of useful information here, but the number we’re interested in at the moment is in the bottom left corner; Bias. In this example it says six degrees. So what does that mean?

Imagine that we had to do this the old fashioned way, with a hand bearing compass and some mental arithmetic. We’d start by taking a bearing along the line. Then, if we took the bearing from the starboard end we would add 90 degrees to the line bearing. Or, if we took the bearing from the port end we would subtract 90 degrees.

The value of that simple sum is what’s called the neutral line wind direction. It’s the wind direction that is completely square to the line, ie. there is no advantage to starting at one end or the other. If the wind veers from this direction, then the starboard end will be favoured, and if it backs the port end is favoured.

In our example with a line bias of 6 degrees, this means that the port end is favoured by 6 degrees – we know it’s the port end because the start line widget in the middle of the screen has the arrow point to the port end.

If we look at the number in the bottom right hand corner we can see that the value for the Bias Adv is now 22.9m. So anyone who starts at the port end of the line is going to be nearly 23m closer to the windward mark than someone who starts at the starboard end – and that’s definitely an advantage worth having.

A word of warning: any wind shift will change this value, and potentially make the other end of the line advantaged. It’s important to keep an eye on the shifts and the chartplotter has tools to help with this that we will come onto later in the series.

To calculate the position of the Zero Burn Line accurately, the Start app will need an accurate Polar or Performance table. If you don’t have one for your boat, then talk to the manufacturer or designer. If you don't have access to a set of Polars, you can use the Target table to input basic information - find it in Settings > Chart Settings > Laylines. Once the data is input, your chartplotter will know what speed the boat will travel at in the relevant wind speed, and at the relevant wind angle to the line. And after that it’s a straightforward calculation of time and distance to display the Zero Burn Line.

 The way to use the Zero Burn Line is on final approach to the line. The real boat needs to hit full speed through the water, just as the Zero Burn Line catches up with the virtual boat on the screen. The human brain is extremely good at judging differing speeds and accelerations of two  objects (otherwise we’d walk into each other a lot more on busy pavements, not to mention crashing at motorway intersections) – but the part you will need to practice is communicating the speed adjustments required to the helmsman and trimmers.

 This is something we always worked on a lot when training for America’s Cup pre-starts, but with a bit of practice and a clear line of communication, you will find the Zero Burn Line a really useful tool.