Wind And Current Effects; Figure 2 - Heading Change In Auto Mode - ComNav Commander P2 Installation & Operation Manual

ComNav Commander P2 Installation & Operation
Operator selects new
desired heading of 135° (SE)
Figure 2 – Heading Change in AUTO Mode

Wind and Current Effects

If your boat encounters a crosswind, and/or a tidal current, at some angle to the Desired
Heading, it will be constantly pushed away from that heading, in the direction of the wind or
current. So the autopilot will constantly be making course corrections.
As that condition persists, the SPU will gradually begin to maintain the rudder a few degrees
to Port or Starboard of the centred position, to counter the effect of wind, and/or current. This
feature, known as trim, will keep your boat pointed in the right direction, despite the wind or
current.
However, one side-effect of trim is that your boat may not follow the Track you want – it will
maintain your Desired Heading, but the track will "slip" sideways in the direction of the
crosswind and/or current. This potential problem can be solved by using another mode that
ComNav Autopilots provide: NAV mode, described next.
Document PN 29010074 V3.1
Autopilot is steering vessel
on a heading of 225° (SW)
Typical response is for the
Autopilot to "over-shoot"
the new heading slightly,
then straighten out
Autopilot is now steering
the vessel on the new
heading of 135° (SE)
- 21 -
Autopilot responds to the
change in desired heading
by moving the rudder to
Port -- vessel begins to turn
As the actual heading
approaches the new desired
heading, the Autopilot starts
to move the rudder back
towards mid-ships position
How Autopilots Work
N