GPS backup switching

Many navigators decide to install a second GPS for backup, to take over from the primary GPS when it fails, for whatever reason. However, it is not always immediately known if the primary GPS stops sending data to the navigation software. If the navigation computer has been unattended for some time, the position in the electronic chart may not have been updated for a while because no GPS NMEA sentences were received.

Typically, the boat's position is checked if there is a potential navigational hazard, when an up-to date position is most needed. To discover at that time that the GPS has stopped could not be more inconvenient and dangerous. Preparing a backup GPS to replace the primary can take valuable minutes. The solution lies in using a NMEA multiplexer and have the primary and a backup GPS permanently connected. If one GPS stops, the other will still send GPS sentences with lat/lon. Chances that both GPS units fail at the same time are low.

However, permanent connection of 2 GPS units can be undesirable, because the frequency at which lat/lon is sent to the navigation software is doubled and sentences may be sent through the multiplexer with a very short time-interval, as the 2 GPS's are independent. The navigation software may not be able to handle the data from 2 GPS's and/or may slow down or even fail.

All Brookhouse multiplexers now have a feature that resolves this problem in an elegant way. One multiplexer port can be designated the "primary GPS port" and a second port the "GPS back-up port". As long as  NMEA sentences are being received via the primary GPS port, data from the back-up port is blocked. If no data is received for  30 seconds, the back-up port is unblocked and the backup GPS takes over from the primary. When the primary GPS starts sending NMEA data again, data from the back-up port is no longer sent to the computer.

This method avoids data overloading of the navigation software and makes an important contribution to safety.