29. Steering With Yokogawa PT-500A
29-4
29.4.1 Characteristics of automatic route steering
Steering is course controlled with set radius between waypoints, if wind, current etc. effects the ship, the system
tries to prevent the ship from drifting away from planned route. The system has three means to prevent drifting away
from the planned route. They are most effective when used together. If cross track error is used alone, then the own
ship stabilises typically in a constant off track position. The means are:
• Measured cross track error from the center line, which is always active
• Drift compensation available from Route Parameters
• Gyro error compensation available from Route Parameters
During turns, if wind, current etc. effects the ship, the ship will drift away (inside or outside) from planned designed
turn which is displayed on radar screen.
29.4.2 Summary of route steering
GO TO WAYPOINT
Set heading
Set radius
Radius control
Dynamic waypoint position
Design before execution
Full curved EBL on radar screen
Wind, current etc. compensation in linear parts between
wp.
Wind, current etc. compensation in turns
automatic
automatic
yes
yes
yes
yes
low gain
no
Needs gyro
Needs log
Precision of position equipment
yes
yes
good
2
29.4.3 Preconditions for route steering
Route steering requires that the position filter is used. See more in chapter Filter Operations.
If you try to activate any of the route steering modes without the filter, you get alarm “2470 Disabled: Needs filter
on” and “2471 AP mode Conflict - Use AUTO”. First change mode selector back to “AUTO” or “HAND” in
Yokogawa autopilot panel and then switch Kalman filter “ON”. After that try again select “NAVI” mode.
Ship heading must point to the next waypoint and vessel must be located inside the channel limits of route,
otherwise an alarm “2468 Disabled - out of course” or “2477 Disabled: Out of channel” is given.
If you loose the filter position while you perform automatic route steering, you get first alarm “2475 Route: Needs
filter on” and then alarm “2506 Use Heading Control”
2
Precision of position is good with LORAN and GPS.
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