I had a Raymarine ST 60 system but the old instruments installed were Datamarine from the late 70's. The speed puck transducer for the Raymarine system is a Hall effect with 0-12 volt output. The output from the Datamarine was a low level signal. I contacted Raymarine for assistance and all they could tell me is that their instrument required the 0 to 12 volt signal. I called the DMI repair facility and he was less than cooperative, did not want to give any repair secrets way. The PCB that I had designed and had fabricated did not work at all. I took the datamarine speed display apart and traced the circuit board and tried another version of interface circuit. I used it and modified the circuit and it worked. The custom boards were about $75 and took a week to get, nice service available. I've redesigned the PCB's should I ever need to replace the prototype currently installed.
Cal 9.2 #19 SilverSwan