to the Laylines
is a sin in racing. "Understanding" is a deadly sin. Many sailors have
achieved guru status by
consistently and correctly calling that last tack for the mark.
Laylines are derived from waypoint range & bearing, true wind
speed and wind
direction, target angle, boatspeed, leeway and current. With so many
inputs changing all the time, there is plenty of room for human spin.
Laylines are dynamic - the tacking point is constantly shifting due to:
- Changes in wind
- Knowing that the wind is left 10°
(see Shift & Puff below), maybe you
tack a bit shy, expecting it to come back and put you dead-bang on.
- Knowing the wind trend (see Stripcharts),
you might tack early because you expect to be lifted onto
- Changes in true wind speed affect target angle.
affects the boat's
over-ground path to the mark.
- And of course, is the waypoint
range and bearing
accurately known? If it turns out not to be, Opposite Tack (see below)
deciding whether to believe the prediction.
Shift is the amount
the wind direction differs from average; i.e. +10 means the wind is
is the amount the true wind speed differs from average; i.e. -2.6 means
the wind is in a lull.
Example: The wind is currently 10° left and you're getting
the starboard layline. Maybe you should consider tacking early because
wind will probably shift back, lifting you into a fetch.
The amount of average applied to the wind for these functions
determines how long it takes for a 'shift' to become the new 'average'.
The default is 5 minutes, but they can be adjusted with an Averages command.
mentioned above, knowing both the short and long term true wind state
is vital to calling laylines and tactics. Shift & puff provide
the short-term knowlege.
small or short changes in wind direction can produce significant
improvement in speed to weather. Read more about it on the Ockam U page and the Polar white paper. Wally is output
by BIF #4a of OckamSoft.
on the opposite tack helps with decisions about when to tack; for the
mark or whether you can clear an enemy vessel on starboard. It
also gives a heading target on the new tack or gybe. Opposite
track includes the effect of current. See Approaching the Mark for an
example of its use.
Opposite tack requires the T2 interface
(for boatspeed & apparent wind) and a heading sensor into the T1 processor, T2 interface or the 032 Heading interface. For current
compensation, GPS input is required.
Enemy range & bearing
a very, very
important thing to keep track of in match racing, because absolute
speed isn't the metric. It can also be important in fleet racing when
you need to know how you're doing against that guy who might knock you
off the bubble. Another use (sort of like match racing) is two-boat testing.
Ockam supports both Laser Range
finders and ARPA radar input which, along with wind
direction, relative gain/loss is displayed.