[CA] [CA11] Loran TDs input on Axiom setup help

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum jmleonard,

I suspect that you may have selected the Chain and one or both Slave settings incorrectly. The Time Differential (TD) settings should be configured to the same settings used within the LORAN C system which had initially recorded them. Should the LORAN C coordinates for locations in the Jupiter, FL area, then I suspect that the Chain had been configured to 7980, Southeast US. The Slave 1 and Slave 2 settings are selected based upon the first two digits of the LORAN C coordinates (i.e. the first 2 digits of first LORAN C coordinate will be matched the range of one of the listed slaves, which will then be selected for Slave 1. Similarly, the first 2 digits of second LORAN C coordinate will be matched the range of one of the listed slaves, which will then be selected for Slave 2. Appendix B of the USCG's LORAN Handbook includes listing of Loran C data sheets and coverage diagrams to further aid in Chain and slave selection.

Unlike level of accuracy which can be achieved by GPS receivers of different manufacturers (typically 3 meters or less), maximum accuracy of LORAN C was typically dependent upon use of the same LORAN C unit to record positions and then again to return to those positions. While the ability of the same LORAN C receiver to accurately place the vessel on a location based upon saved LORAN C coordinates was quite good, similar accuracy would not typically be able to be repeated with another LORAN C receiver. When other LORAN C units were later employed and LORAN C coordinates from another receiver had been used, accuracy was typically about 250 feet. Conversion of LORAN C coordinates to Lat/Lon coordinates will typically yield similar results. Accordingly, it would be recommended that such conversion be used to get the vessel in the ball park of the desired location and that other aids (sonar, radar, etc.) be used then determine and mark the desired location using GPS coordinates. It is not be uncommon for fishermen, divers, etc. to use multiple waypoints to mark the boundaries of a reef, wreck, etc.