Vysion starting line
The starting line
screen is available on Vysion displays with a
touch screen (i.e helm displays).
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.
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
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.
||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.
||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
||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 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
||The starting line is set by
‘pinging’ the two ends of the line.
||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.
||From these, target speed and angle are determined
for the current wind conditions.
||Your ‘tactical turn radius’
is important in order to model future position and path length.
||is used in tacks and when accelerating or
decelerating to target speed.
||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.
||sets the line ends a specified distance to port
or starboard as you pass them.
||When a maneuver requires a tack, after tack
boatspeed will be reduced by this amount, and then accelerated back to
where you will cross
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
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.
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.
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.
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
- 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.
|Switches pages. Starting line continues to be
updated even if you aren't on the starting line page.
|Pings the two ends of the line (ping order is not
important). This establishes the position, length and orientation of
the starting line.
||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.
||Hides the control panel regardless of whether the
panel is locked or not.
||Brings up the starting line setup panel where the
various parameters used in modeling starts may be changed.
|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.
||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.
||If a predicted start maneouver involves a tack,
boatspeed coming out is reduced by this number, and then accelerated
back to target speed.
||Is the rate the boat accelerates (or decelerates) to taget speed.
||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.
||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
||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.
||Erases the wind and course history.
||Adjusts the length of the predictor flag and target bean.
||Turns features of fhe display on and off.
||You can rotate the line manually with these
buttons (5 degrees per). The rotation point is the line end with the
latest ping time.