B&G Blog – RacePanel Series with Mark Chisnell – Part 2Uncategorized
Zeus2 series chart plotter – Starting Software
Not just a simple software upgrade, more like a whole new era – combine the Zeus2 series chart plotter with an H5000 CPU and the latest product launch from B&G brings America’s Cup-level tactical software to this not-so-humble chart plotter. In this article we look at the tools provided in the start line software.
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 new starting software provided by the Zeus2 series chart plotter upgrade 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 new 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 Zeus2 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.
If there’s a really big strategic advantage to one side of the leg, then it may make sense simply to start at that end, and get going the right way as soon as you can. But if not, then most of the time on upwind or downwind starts this decision depends on what’s called the line bias; finding the end of the line that’s closest (upwind starts) or furthest away (for downwind starts) from the direction the wind is blowing from.
Before Zeus2 and the H5000 can calculate the line bias the system will need to know where the start line is located. This can be done in several ways, setting the port and starboard ends individually via:
• A “Ping” to the yacht’s current position
• Set at a waypoint position (using a waypoint from the chart and/or from your waypoint list)
• Set at the cursor position on the chart
• Set one end as a range and bearing from the other end
• And finally, by ‘nudging’ one end of the line up or down to make minor adjustments
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 starboard end of the line is going to be nearly 23m closer to the windward mark than someone who starts at the port 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 Zeus2 has tools to help with this that we will come onto later in the series.
So, now we know which end of the line to start, all we have to do is be there on the gun at full speed! When it comes to trying to hit the start line at pace, the most useful screen on the Zeus2 is the Start Line Scaled View, which is shown below. This has the same numbers as the Start Line Data screen but gives you some extra and very important visual cues. Note that that bias advantage and distance behind the line are now shown in boat lengths.
The main one that we can see in the illustration is the Zero Burn Line. This is the line that tells you that you have no time left ‘to burn’. In other words, when your virtual boat appears on this line, if you are sailing at full speed, and you keep going flat out, you will be right on time at the line – there’s no more time to waste/burn!
To calculate the position of the Zero Burn Line accurately, the system will need an accurate Polar or Performance table. If you don’t have one for your boat, then talk to the manufacturer or designer. Once it’s installed in the H5000 CPU, then the system knows 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.
That’s it for this time around, I’ll be back in a couple of weeks with some thoughts on setting a race course up in your Zeus2.