Set-Drift Control

Download SetDrift.ocx Visual Studio Control

The Set-and-Drift control plots the cumulative effects of current, leeway, and poor steering: the cumulative effect of these forces causes a boat to travel off the desired course and retards or augments the boat's true speed (that is, speed over the ground instead of through the water). The direction that effect moves the boat is called "set;" the force applied against the boat, expressed in knots, is the "drift." Helmspeople who wish to counter the effect of set and drift may choose to modify the boat's heading through the water so that the desired heading through the water and the true heading (the course over ground) coincide.

When the control is first placed upon a container such as a form, as in the example to the left, it lacks the information required to plot. One must tell the control the boat's heading and speed before the control is active. This information may come from a NMEA device such as a "Log," or it may be typed in by your end user.

With no set and drift values to plot, the course to steer matches the heading and the speed over ground (SOG) matches the boat's speed through the water.

Night and Twilight modes are programmed into the control, and the color scheme matches the rest of the NMEA Sage control suit. One may also change the colors of the plot lines and the background color of the control.

There are three ways to tell the control what the set and drift is:

  • Use the control's "SSet" and "Drift" properties.

  • Use the control's TwoFixes Method:

    The TwoFixes Method requires two position fixes: the difference between where one thought the boat was (Deduced Reckoning position) and where it actually is (via GPS fix, Lines-of-position fix, Radar fix, Celestial fix, etc.) is the set and drift. Also required is the time interval, in minutes, between the two fixes. The control requires at least ten minutes between fixes before it will plot set and drift. NOTE: Fixes that are widely divergent (i.e., inaccurate) will cause the control to plot nonsensical data.

  • Use the control's GroundVector Method:

    The GroundVector Method requires Speed Over Ground (SOG) and Course Over Ground (COG) information; when compared to the boat's heading and speed, the difference is the set and drift. This information may come from the GPS or other device that provides ground data. NOTE: Ground data that are widely divergent (i.e., inaccurate) will cause the control to plot nonsensical data.

When the data is plotted onto the control, the length of the course line (default color of green) and the length of the drift (default color is red) are proportional: if the drift is greater than the boat's speed, the red line will expand to the compass circle and the green line will retract. With little or no drift, the red line will be very small or invisible.

The broken blue line shows the "steer-to" plot derived by taking a parallel from the boat's position (the center of the control) to the end of the boat's course-and-speed line. It will always collect to the end of the set-and-drift line. The broken line may be "turned off" via the ShowParallel property.

One may "turn off" the various display functions such as the compass values, tick marks, and data. Care should be taken by the programmer to provide color schemes that will be pleasing to the end user.

With a small drift, the plot lines will bunch together. When the set is close to the boat's course, or reciprocal to the boat's course, the lines will also bunch together.

The example to the left shows several properties set to "False:"

The data at the bottom of the control may also be hidden:

Events:

SetDriftError()

Methods:

TwoFixes
GroundVector

Properties:

ShowParallel
ShowDegrees
ShowValues
ShowTicks
Course
Speed
SSet
Drift
BorderStyle
BackColor
CourseColor
SetColor
SteerColor
Night
Twilight
ErrorNumber
ErrorDescription

Error Codes

0 - No current error condition.
1 - Course must be greater or equal to zero and less than or equal to 360.
2 - Boat speed must be greater than zero and less than or equal to 200.
3 - Set must be greater than zero and less than or equal to 360.
4 - Drift must be greater than zero and less than or equal to 200.
5 - Time between fixes must be 10 minutes or more.
NMEA Sage Home Page

The Banded Compass Control
The Compass Control
The North Biased Compass Control
The Goto Control
Course and Speed (Ground)
The Position Control
Engine RPM Control
The Rudder Control
The GPS Satellite Health Control
The GPS Satellite Elevation Control
Set and Drift control
The NMEA Talker Control
Depth and Water Temperature Control
The Wind Control
The Cross Track Alarm Control
The Pilot Control
Waypoint Plotter Control
Radar Control
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