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Advanced WindPlot with Mark Chisnell

Mark Chisnell explains how to get the most from the new Advanced windplot feature on Zeus2 and Zeus3 chartplotters (Coming soon to Vulcan)

Advanced WindPlot

Advanced Wind Plot is a vital Zeus and Vulcan chart plotter app (coming to Vulcan in a late 2018 software update) that gathers together True Wind Direction (TWD) and True Wind Speed (TWS) information onto one screen and presents it for maximum clarity. And when it comes to winning sailboat races, understanding the wind is the magic sauce.

What’s what with the Wind Plot

 The Wind Plot app shows us two vertical strip graphs side by side. The one on the left is TWD and the one on the right is TWS. The most recent information is at the top, and the time intervals run down the middle; so that’s two-minute intervals showing 10 minutes of data in total.

 If we take the TWD graph first, we can see that at the top by the title we have the most up to date reading (286 degrees). Below it are the lower, mid and upper bounds of the graph – in this case that’s 255, 294 and 335 degrees respectively.

 The advantage of orientating the graph like this is that it shows the wind pattern as though looking into the wind: left-hand shifts are on the left of the graph, and right-hand shifts are on the right of the graph.

 The graph line is red when the boat is on port tack, and green when it’s on starboard tack. The dashed yellow line is the trend line. This smooths out the noise in the data and shows clearly whether the wind is in a left or right-hand phase. In this example the boat is on port tack in a left-hand phase – so good tactics!

 The right-hand strip graph shows us TWS in the same manner. The up to date reading (4.6kts) is beside the title and under that are the lower, mid and upper bounds of the graph – in this case that’s 0.0, 5.5 and 10.0 knots. The TWS is plotted in grey against the black background, and the trend line is a white dashed line. In this example, the wind is just starting to ease after a sustained puff.

Help with the TWA

The Wind Plot also provides us with help on the True Wind Angle (TWA) that the boat has been sailing. This information is contained in the coloured bar on the right-hand side of the TWS plot.

 The circle with the boat in the middle provides a legend for the coloured bar. The red and green lines show the time on starboard and port tack. The colours in the middle bar indicate the TWA; yellow is downwind, light blue is reaching and dark blue is upwind.

 So in this example, ten minutes previously the boat was reaching (light blue central bar) on starboard tack (green line to the right of central bar). The boat slowly bore away until it was edging between downwind VMG angles and reaching (interspersed sections of light blue and yellow) and then gybed to port and sailed a steady VMG angle downwind (yellow central bar and now a red line to the left of it).

 In the final two minutes the boat started to luff up and the yellow turned to a light blue central bar, which then flicked to dark blue to show that the boat was briefly sailing upwind.

Lots to take in

There is a lot of information here, but when the wind is plotted out like this, it’s remarkable how obvious things become –patterns emerge in graphically displayed data that remain hidden in raw numbers.

 A slow permanent wind shift might appear in a sea breeze, or a geographical shift might give itself away by popping up every time the boat is close to a particular part of the race course.

 For example, in the images above we can see that the sustained increase in wind speed has come with a left-hand shift. So next time there’s a patch of dark water and more breeze coming towards the boat, think about getting onto port tack just in case it comes with another left-hand shift.

 The Wind Plot will provide lots of useful information that can be fed into the What If? app – input about changes in wind strength and direction will show how they impact the wind angles and layline times. This is invaluable information for any tactician.

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