Seiwa SW AP03 - Manual (Page 35)

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 NAV key. The top right of the display may
now show:
NAV WAIT
and may remain for up to 15 sec. If it stays longer, there is 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. For existing hydraulic systems
using a helm pump, instructions are given below for adding a Coursemaster/Hydrive
pump motor. But for systems supplied by other manufacturers, installers should
consult the data supplied by the manufacturer.
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 revolutions’ in the
table apply to that shaft.
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