Seiwa SW AP01 User Manual
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The correct polarities are such that when the external NMEA system is transmitting, the wire
that goes positive is connected to the + terminal of the input pair. After the connection is
made, complete the other parts of the installation before checking for correct reception, as
follows:
Turn the system on and select PILOT. Press the PILOT key a second time to display the
NAV select option. Press the RIGHT ARROW key. The NAV symbol shows at the top of
the screen - both in PILOT and STANDBY. If the symbol is flashing, this means that no valid
NMEA data is being received. Wait for 15 sec. If it is still flashing, there may be some fault
with the interface. Try reversing the input wires. Then check that the NMEA device has also
been set up correctly and that a waypoint has been enterred. If it is a GPS receiver, the
message being sent will be read as invalid if the GPS has not acquired the required number
of satellites or there is no destination waypoint. Details of the navigation sentences
accepted by the system are in Chap 5. Note that, if two NMEA inputs are connected and
both contain a navigation sentence, the data in these two sentences must be the same.
The NMEA output port sends an HDG sentence containing the current magnetic
heading.
3.6 STEERING DRIVE
Four options are covered in this section: electric motor drive to mechanical steering,
coupling into a motor-drive hydraulic system, coupling into a solenoid-controlled
hydraulic system and a hydraulic linear drive.
Through the wide variety of possible drive systems and the load placed on them, the
goal is to move the rudder from 20 deg port to 20 deg stbd in not more than 15 sec.
and not less than 8 sec. Steering systems which perform outside these limits may not
give satisfactory autopilot operation.
3.6.1 CHAIN DRIVEN MECHANICAL STEERING
The drive sprocket on the steering motor matches 12.7mm (1/2 inch) British
Standard simple chain. The size of the driven sprocket on the steering wheel is
chosen to give the recommended helm response time for the length of the hull. The
sprocket size is chosen from Table 3.1 or 3.2 below, depending on the voltage. If the
sprocket is mounted on an intermediate shaft in the steering system, the ‘wheel
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