Screen
detail
Numeric
MOB


Vysion starting line

The starting line screen is available on Vysion displays with a touch screen (i.e helm displays).

Features
Starting line info

The upper corners display information about the starting line – the two bearings, and the length in yards and seconds. Both tack bearings are also shown.

Favored end

shows which end is favored and by how much (in seconds to windward). This number changes with wind direction and starting line bearing and length. In the figure, the port end is favored by 15 seconds. But, the wind is currently left, so it will probably get smaller, or even switch ends.

Multiple solutions

Each starting solution shows the time and ‘overspeed’. Overspeed is how much you will be above target boatspeed when you cross the line. In this display, burn time is disabled, so the times are elapsed time.
Overspeed line is the line above which it is possible to cross the starting line above target speed. If you are running parallel and above this line at full speed, you will cross the starting line above target speed. The further you are above this line, the more you will be above target at the start.
Predictors The flag and circle in front of the boat shows where you will be in 10 seconds at current speed, and at target speed. The predictor time is adjustable.
Wind variability The wind flag is encircled by an oval showing the limits for true wind speed and direction. From these two items, you can modulate your starting strategy based on the current wind.

The dogleg start



The dogleg starting strategy involves running parallel to the starting line to build up a good head of steam and turning up just in time to cross at zero. With this type of start, you can have enough speed to pop out of the crowd into clear air and room to tack if the situation requires. The problem is, how can you determine when to turn for the crossing, and how do you adjust where on the line you will cross?

The Vysion starting line display uses these measured and setup items to predict where to turn:
Line location The starting line is set by ‘pinging’ the two ends of the line.
Environmental The stopwatch, boatspeed and heading, and true wind speed and direction are used to determine the length of the dogleg starting from your current position.
Polars From these, target speed and angle are determined for the current wind conditions.
Turn radius Your ‘tactical turn radius’ is important in order to model future position and path length.
Acceleration rate is used in tacks and when accelerating or decelerating to target speed.
GPS to bow The bow position is offset from the GPS antenna by an adjustable distance, in the direction you’re going. This keeps Vysion from recommending a start where the antenna is right on the line.
Ping offset sets the line ends a specified distance to port or starboard as you pass them.
Tack loss When a maneuver requires a tack, after tack boatspeed will be reduced by this amount, and then accelerated back to polar speed.

Adjusting where you will cross
The ‘Vanderbilt’ method

If you are going to be early at the far end, Vysion will pin the dogleg there and display “burn time”, or how much you will be early if you turned and went for it right now. The Vanderbilt method involves sailing away until the intersection is at the desired point on the line, then turning around and going for it. Note here the importance of setting turn radius so the geometry of your future path is modeled correctly.
Lurking

Another strategy would be to sit relatively still somewhere and wait for the solution to shrink down to the desired point.

Your actual strategy will probably be a combination of these.
Adjusting your crossing point after committing

Even when on your reach leg of a dogleg start, you still have control of your starting point. If you reach further away from the line, the intersection will move toward you, and vice versa.

A video demonstration of this technique is available here.
  • The clip starts at -1:53 with the boat on final, initially targeted at the middle of the line (to be adjusted as the situation changes). Wind is down, and the line has the port end favored by 30 seconds.
  • At -1:30, the dogleg has drifted left, and the boat is in danger of running out of room. The boat heads away from the line to pull the dogleg back to the right.
  • At -1:12, the boat goes back to parallel. Note the wind has increased, but the left end is still favored. The direct start path is seen converging with the dogleg.
  • At -1:04, the dogleg has disappeared in favor of the direct start, and the boat turns up for the line. The prediction at this point is 7 seconds late from 1 minute out. But there will probably be plenty of reserve speed available (note the target bead on the boatspeed predictor).
  • By -0:30, the prediction shows 1 second burn time (in other words, 1 second early). Note the wind speed is now above average.
  • At -0:20, the boat bears off a bit to burn off a couple of seconds and pick up some speed.
  • The start occurs right on the line with 0.2 knots overspeed. Vysion drops a bow marker when the stopwatch hits 0.

Controls
Prev
Next		 Switches pages. Starting line continues to be updated even if you aren't on the starting line page.
Ping <-
Ping ->		 Pings the two ends of the line (ping order is not important). This establishes the position, length and orientation of the starting line.
Default Establishes a default length and orientation of the line originating at whichever end was pinged last. The default length is a setup item, and the orientation is based on the current value of the wind direction.
Hide Hides the control panel regardless of whether the panel is locked or not.
Setup Brings up the starting line setup panel where the various parameters used in modeling starts may be changed.

Starting line setup
 The starting line setup panel controls the parameters and features of the starting line screen. The screen itself continues to be visible while setup is being adjusted.
GPS -> Bow Sets the distance between the GPS antenna and the bow. On the starting line screen, where the bow is is the important thing. The bow position is advanced from the antenna by this number, in the direction you are currently pointing.
Tack loss If a predicted start maneouver involves a tack, boatspeed coming out is reduced by this number, and then accelerated back to target speed.
Acceleration Is the rate the boat accelerates (or decelerates) to taget speed.
Turn radius This is the 'tactical' radius used to predict future position after a turn. It is certainly true that in clutch situations, you can fudge the turn radius to make up time or adjust the starting line position, but this number will be used by the prediction process for all turning.
Ping offset When pinging the starting line, the location obviously can't be where the antenna is. Vysion uses a point half way to the bow (i.e. midships) and this many feet to starboard (+) or port (-).
Default line If you don't have time to ping both ends, you can use the 'Default' button to establish a line this long from the end you did ping. Since the starting line is recorded, your first ping of a new line can produce some strange results. Using the 'Default' button sets a sensible line based on wind, to be overridden by your ping of the other end when you get to it.
Resets Erases the wind and course history.
Predictors Adjusts the length of the predictor flag and target bean.
Features Turns features of fhe display on and off.
Jog line You can rotate the line manually with these buttons (5 degrees per). The rotation point is the line end with the latest ping time.