ComNav Commander P2 & P2VS Installation & Operation Basic Operations
Document PN 29010074 V4.1 - 143 -
Commander P2VS Operations
The P2VS is basically a Commander P2, but with extra features – most notably, the ability to
operate without a Rudder Follower Unit, using
Virtual Rudder Feedback
(referred to as
“
VRFU operation
”). From a hardware standpoint, it is identical
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to a P2 – all the differences
lie in the firmware in the SPU & Head.
The P2VS was developed primarily for use on boats with Outboard motors or steerable
Inboard-Outboard drives, where installing an RFU is usually very difficult.
Cautions
It is important to keep in mind that – when operating without an RFU – the P2VS can
not
sense where the rudder is positioned,
nor
if it is in motion.
It can only
estimate
the rudder’s position & how far it moves while the “move rudder” signal is
being output.
Note: the word “rudder” is used in the generic sense in this section. It refers to
whatever mechanism the boat uses to control its direction of travel – e.g.,
outboard motor(s), an I/O leg, and so on.
Here is some background to, and some effects of, that “only an estimate” condition:
•
During
Drive Setup
, you enter the rudder travel limits, and then the rudder’s HO-HO
travel time is measured. Together, those give the speed (degrees per second) at
which the rudder moves.
Later, during normal operation when the P2VS is controlling the rudder (
POWER
STEER
,
AUTO
or
NAV
modes), the SPU continuously re-calculates the current
estimated rudder position – by multiplying the measured rudder speed & the length of
time it outputs each “move rudder” signal.
•
The P2VS VFRU steering algorithms also make some assumptions about the rudder
position, at certain “reference points”.
For example, it is assumed that the rudder is in the Dead Ahead position when the
boat is running on a straight Heading.
On most boats, in calm sea conditions, “dead ahead” is indeed where the rudder is at
the “dead centre” position. But that may not be so if the boat is towing something, or
in rough seas, or if there is some condition that requires the rudder to positioned
off-centre for the boat to follow a straight Track.
•
There are many factors that can cause errors in the rudder position estimation:
⇒
The only measurable effect of the rudder that the P2VS VFRU steering
algorithms can sense is changes in the Heading of the boat
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. But the rudder’s
effect on Heading varies with different boat speeds, current, tide, wind, etc.
⇒
The rudder and the associated drive mechanism (hydraulic ram, electric
solenoids, cable, etc.) typically respond to “move signals” from the SPU in a
non-linear way. The rudder’s movement may also be asymmetric – different
when moving to Port than Starboard.
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… other than the black-coloured Control Head & the product name on the Head’s LCD-protection overlay.
37
… which is why a reliable Heading source is so vital during VFRU operation.
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