Functions
Page 3
Next
Previous
Real world sailing
Main page

Jump to:
True Wind
Targets
Stripcharts
Performance
Trim & Steer
Navigation
Status
Calibration
Stats

Tactics

Time to the Laylines


Overstanding 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 direction.
    • 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 the layline.
  • Changes in true wind speed affect target angle.
  • Current 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) can help deciding whether to believe the prediction.

Shift & Puff

Shift is the amount the wind direction differs from average; i.e. +10 means the wind is 10° right.
Puff 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 close to the starboard layline. Maybe you should consider tacking early because the 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.

As 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.

The Wally

Taking advantage of 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.

Opposite Tack

Knowing the heading 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

This is 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.

WordPress Appliance - Powered by TurnKey Linux