North U. Tactician iPhone app

How-to Example

Ideally, you have sailed out to the race course area well before the scheduled time of the warning signal. When sailing closehauled with the sails trimmed for and steering for best upwind progress, use the keypad to enter the boat’s heading.

On the next screen, you specify whether the heading is for upwind or downwind, port or starboard tack. You also use the sliders to set the tacking angle and the true wind speed. The boat in our example, a Beneteau 36.7, sails at an optimum true wind angle of 39 degrees in 17 knots of true wind. The two sliders will remain at whatever value you last entered. The “Upwind/Downwind” button also remains at whatever value you last used. In this data entry point, we confirmed that it was set to “Upwind”. Once you tap one of “Port” or “Starboard” (“Starboard” in this case) the observation is saved.

It is important to be as accurate as possible with the upwind tacking angle for the boat in the prevailing conditions. The North U. Tactician app makes inferences about the true wind direction from your port or starboard heading inputs and the tacking angle you specify. Using a tacking angle that is inaccurate by a few degrees will result in calculated true wind directions that will fluctuate subtly as you tack from port to starboard tack, even if the wind has held perfectly steady in direction in the interim.

The goal before the start is to discover the full range of the oscillations in the wind direction, from the furthest left to the furthest right, and measure this full range in terms of the headings that result on both tacks.

In the North U. Tactican app, the time axis has the most recent observation at the top.

After you have gathered a sufficient number of upwind headings on port and starboard, tap the compass button.  

The “Upwind medians” calculator finds the mid-point between the recorded highs and lows on port and starboard. The calculator will also tell you the angle between the two mid-points.

With the port and starboard upwind headings gathered in this example, the two mid-points happen to be 73 degrees apart. We know from experience (or from consulting the polars supplied by the boat’s designer) that this is too narrow of a tacking angle for the boat in the prevailing conditions. What probably happened is that the boat didn’t get fully headed on one tack in the pre-start data gathering period. Remember that the goal is to discover the full range of the oscillations in the wind direction, from the furthest left to the furthest right, on both tacks. But time in the pre-start is not unlimited, so don’t worry if you cannot gather a full range of headings on both port and starboard tack.

With the tacking angle unlocked, manually adjust the port and starboard median headings with the plus and minus one degree buttons until you have both a tacking angle (78 degrees) and a median true wind direction (255) that seems right to you. It is more important to get the tacking angle correct for your boat’s performance characteristics in the prevailing conditions, as the tacking angle that is set by the upwind medians calculator screen will be used thereafter as the default tacking angle for all subsequent observations. The median true wind direction can be adjusted later quite easily, as you will see in a moment.

Tap the unlock button to change it to locked, which locks in the tacking angle. Once the tacking angle is locked, a tap of +1 or -1 on one tack moves the other tack as well.  With the tacking angle unlocked, port and starboard are free to vary independently. Tap “Set” when you are finished selecting the median true wind direction.

The History page will now show the MED values that you picked with the upwind medians calculator.

Remember that these MED headings are no longer going to be mid-points of the two ranges, because these have been overridden by the upwind medians calculator. But the two MED headings represent the headings on port and starboard at which the true wind direction is at the mid-point of its range. It is precisely this median true wind direction that, as a tactician, you want to be able to identify in order to stay in phase with the wind shifts.

A vertical line will now appear on the graph at the median true wind direction.

The vertical white line should evenly split left and right the true wind direction readings. You can use the left and right arrows on either side of the top of the white vertical line to adjust the median true wind direction in one degree increments. Here is the result of nudging the median true wind direction to the right by one degree.

Nudging the median true wind direction to the right by one degree adjusts the port and starboard medians by the same amount. The tacking angle remains at 78 degrees.

Now it is time to return to the starting area for the 1400h warning gun, finalizing rig tune on the way. A quick head-to-wind shot just after the five-minute gun (a white “W” on the graph) confirms that the wind direction has not varied since the pre-start data collection period and that the median true wind direction as selected is in the right ballpark.

You can use the “Mark” button on the keypad to denote the start time as well as any mark roundings. A mark icon will appear on the History page, and a white horizontal line will appear on the graph at the right time. Remember that this happens in real time as you tap the “Mark” button.

In this race, the boat got off the start line with the true wind direction in a slight right phase, as indicated by the green Ss to the right of the median line between 1405 and 1410. A few minutes up the first beat, the wind swung abruptly left, which converted into a nice lift on port.

Once you have set the upwind medians, every upwind heading you enter will be followed by a pop-up message that tells you how you are doing at that moment -- lifted, or headed, and by how much.  The shift midway up the first beat was a six degree lift on port.

The pop-up analysis also works out for you some of the other angles and bearings that are useful to know from a tactician’s point of view.

The opposite tack number is that which you would expect if your boat was on other tack in that same wind. This is helpful for judging laylines. If you took a bearing on the windward mark and found that it was very close to this opposite tack heading, then you know you are at risk of overstanding.  

The two bearings of equality identify your current “ladder rung” -- the line passing through your boat and perpendicular to the true wind direction as implied by your most recent closehauled heading, on which any other boat is theoretically tied with your boat at that moment in the race to the windward mark. You can use a handbearing compass to take bearings on the competition on your weather quarter and on your leeward bow to see if they are to the left or right of the bearings of equality that the pop-up analysis gave. This will give you an idea of how you are doing in the beat, and whether to expect any close crossing situations.

The tactician’s goal is to sail as much as possible on the lifted tack upwind. When the wind is left of its median direction, your goal is to be on port tack; when the wind is to the right of its median direction, your goal is to be on starboard tack. This will appear on the graph as having all red Ps on the left of the white vertical line, and all green Ss on the right of the white line vertical.  See in this example from 1405 and onwards how the boat is staying nicely in phase with the oscillations in the wind direction.

Of course, other boats may prevent you from always sailing on the lifted tack. The course geometry may also conspire to force you sail on the headed tack. Always sailing on the lifted tack may take you to a layline earlier than you intended. Don’t sail over laylines.

Tap the “Mark” button as you round the windward mark.

You can use the North U. Tactician app to keep track of boat headings on port and starboard on the run downwind. Tap the heading into the keypad, and then tap Downwind on the next screen.

The Upwind/Downwind button will remain at whatever you last set it at. Remember this as you round the leeward mark to go back upwind.

Downwind numbers will appear in the History table in grey.

In its current version, the North U. Tactician app shows you your downwind headings on port and starboard, but it does not make any inferences about the true wind direction. You have to read the downwind numbers carefully for any clues about the state of the true wind direction and what left or right phase it might be in. In the example, the boat was lifted on port from 060 to 055, headed on starboard from 090 to 085, and later lifted on port to 050. This suggests that the true wind direction is backing, to the left of 255.

Because the North U. Tactician draws no inference about true wind direction from port and starboard downwind headings, downwind legs will appear on the graph as blank swaths.  In this image, the first downwind leg is the area between the two horizontal lines, from 1415 to 1425.

Because of the evidence of the wind shift to the (course) left, the boat in this example rounded the starboard-to gate mark. Again, remember on your first upwind reading after the leeward mark to change the “Upwind/Downwind” setting on the second data entry screen to “Upwind”.

If you did forget to switch to the upwind setting, the number you entered will appear in the history, but in the light grey -- which may initially be easy to overlook. On the other hand, you probably will notice that there is no green S or red P for the observation you just entered. You will also probably notice that you do not get the tactical pop-up analysis after you enter a heading. This is because you have by mistake entered an upwind number as a downwind number, and in the current version of North U. Tactician, downwind numbers do not result in plots on the graph or the analysis pop-up.

To correct this situation, you can always edit a data point and change it from a downwind to an upwind reading. To make corrections to an observation, tap and hold on its row in the History table. This opens up the record; make any required changes and click Save. Once you have changed the mistaken data point from downwind to upwind, it will appear in the History table in white (not grey), and a point for that observation will appear on the graph. You will still have to remember to get the Upwind/Downwind setting right on the data entry screen, because it stays on the last value that you entered. If you forget again, you may find yourself having to open, edit and save many records.

The initial starboard upwind reading on the second beat was a 4 degree header, confirming that the wind was in a left phase. The boat tacked to stay phase, and later up the leg tacked back to starboard to take advantage of a right shift. This set the boat up for a big left shift that came midway up the beat. The North U. Tactician app alerts you to major developments like a shift that has gone further than what has been observed up to that point with messages like “New high”. Good thing we protected the left.

When you switch to the graph, the axis of compass headings will be centered on the most recent implied true wind direction. The 14 degree lift on port is plotted here by the red P far to the left of the vertical line, so you get a good idea of how large a left shift it was.

You can drag left and right, and scroll up and down on the graph.

Near the top of the second beat, the boat’s starboard heading coincided with the selected median heading for that tack. The North U. Tactician app alerts you to this development with “Median” in the pop-up message.

The run to the finish again showed more signs of a course-left shift, with starboard gybe headings lower than the first run.

The boat finished at 14:46, with an easy win.

If there is another race in the day, it is a good idea to use the “Mark” button to record the time of your finish, and to continue to monitor the state of the wind direction, perhaps with periodic head-to-wind observations, and a new period of sailing upwind on port and starboard tacks. If there has been a major shift in conditions between races, you can update the tactical analysis by changing the baseline time that the North U. Tactician app uses.