Redundant Navigation Systems

Back-up systems are essential in my book.  Many of our friends now have electronic charting systems and many have them interfaced to everything you can think of.  We have electronic charts too and we interface a spare GPS to the computer so we can track the boat real time on the screen but there ends the integration.  We also have a cockpit GPS mounted so the helmsman can see it.  It is interfaced to the cockpit Radar display but that's all the integration on that leg of our systems.  Then we have paper charts for everyplace we're going.  Am I overdoing it?  Maybe but this level of redundancy has saved our bacon more than once.

Generally, I plan our route out using the computer charts.  Since there's no interface between the computer charts and the cockpit GPS or Autopilot, I must then manually transfer our planned route into the cockpit GPS.  Most often, in the Bahamas, I'll use the Explorer paper chart book to key in their waypoints to the cockpit GPS.  (we've found their waypoints to be very good) This provides a double check on the planned route as each waypoint must be reentered and checked.  If we're going to be offshore and out of sight of land for a while then we also plot everything on the paper charts as well.

Now, when we're under way, we have the computer on in the nav station displaying the chart we're on and the position of the boat ... sometimes we'll also turn on the tracking feature if we want to save the route for future use.  We also have the cockpit GPS and radar on.  We steer by the cockpit GPS and manually enter course changes and corrections into the autopilot if we're using it.  Offshore we'll also plot our progress on paper charts, on an hourly basis, just in case we lose power or something else happens to the electronics.  By having a plotted known position less than an hour old, I can easily pick up a DR plot and not get lost.

If there's any doubt about where we are or even if there isn't any doubt, a quick glance below at the computer chart readily confirms that we're near our planned track.  Or in a recent case, off course.  I had mis-keyed a waypoint into the cockpit GPS that put us off our course.  Well, you might say that if I had them interfaced, I wouldn't have fat fingered the coordinates ... true but what if the planned point was off 3 miles ... then we'd have had the same error in both systems ... this way they serve as a check on each other.  

The radar figures in because it shows the same data as the cockpit GPS but it also displays the next waypoint in a target on the screen.  It's often helpful to see that the blip representing a channel marker or other reference is actually inside the target.  If not, we know we have a problem.  Recently, I plotted a waypoint off Three Rooker Bar just south of Anclote Key.  The waypoint was pulled from a paper chart of the area.  It was dark that night so we're navigating blind.  The radar however showed our waypoint to be on land.  Sure enough, the waypoint was on land.  The chart is wrong.  Hurricanes in recent years no doubt rearranged Three Rooker Bar so that the chart isn't even close anymore. Radar and redundant navigation systems once again saved our bacon.