Originally Posted by Pyxis156
And out of curiosity, why will the VHF
be kept independent of the instrument network? Mine is on the network with the AIS disabled, but if something went wrong with the XB-8000 it is a simple matter to reactivate the AIS functionality and once again have it displayed on the chartplotter
. Just curious if I am missing something.
Pyxis, here's a better answer on why independent redundant systems may be better than single
integrated systems. It's all in combinational probability.
To keep the math simple and for illustration purposes only, let's assume that any electronic system has a 50% chance of failure. For a somewhat critical function, say, gps
coordinates, AIS positions of other boats, and VHF communications
failure would be serious.
If 2 systems are separated (independent of each other) and each system still has a 50% chance of failure, the probability of both systems failing is .50 * .50, the probability of failure in system 1 times the probability failure in system 2. Thus the probability of being without a critical system is .25 or 25%.
Second Star will have at least 4 GPSs on board, the Zeus2, the XB8000, the VHF, and a handheld. If each of these has a 50% probability of failure, the probability of all of them failing simultaneously due to device failure (not to the whole GPS
system going down) is .5 * .5 * .5 * .5, or .0625 or about a 6% chance that I would not have any functioning GPS. If the systems were completely integrated and not independent of each other, the probability would remain at 50%.
There are of course places where there might be a single
point of failure that could take down all of the systems. Something like the GPS satellites all going quiet or a massive electrical
failure onboard with dead batteries. Those events
are difficult to account for. Electrical
failure can be mitigated with the handheld and by placing the other electronics
on separate circuits.
A long wonkish answer to a simple question. That's what we retired guys do, think up long answer to short questions.