Until a few years ago it was generally the case that boat owners acquired their instruments one by one. Depth sounder, radar, compass, wind instrument, Decca, GPS, plotter, boat speed indicator and autopilot might easily be individually installed stand-alone units from several different manufacturers.
The situation today is very different, with a few major suppliers offering complete systems from which the sailor can choose as few or as many instruments as desired. Essential to this advance was the development of a specialised data bus and a data transfer protocol: functions such as the steering performance of an autopilot module can now be optimised in more demanding systems by connecting a dedicated course computer. An autopilot steering a boat between two waypoints obtained from a GPS interface can thus correct for cross-track error caused by currents running perpendicular to the boat's course.
The changing role of companies within the industry from instrument manufacturers to system suppliers explains the current extreme concentration of the market on just a few major players.
Autopilots may be divided into three groups:
1 Stand-alone systems which operate solely on the basis of a windvane or compass signal (e.g. Autohelm 800);
2 Systems which are linked to other modules via a data bus (e.g. SeaTalk from Autohelm, Robnet by Robertson) and/ or an NMEA 0183 interface;
3 Systems in which individual modules are linked exclusively by the manufacturer's data bus (B&G).
Module integration options for ROBERTSON autopilots. By courtesy of Simrad
Today most autopilots operate as one module within a complex system. NMEA (National Marine Electronics Association) interfaces offer the prospect of expanding such a system to include instruments from other manufacturers. The claim that instruments from different system suppliers could communicate with each other using the same interfaces seemed rather optimistic at one time. There were as many sailors have already discovered to their cost, several standards in existence even for NMEA interfaces, and of course no instrument manufacturer was to blame for any incompatibility; serious communication problems are always the fault of the instrument on the other side of the interface! These problems have now for the most part been resolved. Company-specific data buses do still tend to work much faster than NMEA interfaces, however, and the importance of speed cannot be exaggerated. The delay in the transmission of a steering impulse from one sensor unit to another can never be too short.
Provided with a fluxgate compass / gyrocompass signal optimised by integrated navigation modules, an autopilot is perfectly capable of steering a boat from waypoint to waypoint -assuming, of course, that the wind decides to co-operate.
Navigating down below with the AUTOHELM NAVPLOTTER 100
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