Didn’t know the right term for the point I was trying to make with this thread:
We don’t need no stinking compass’
The first meaning of the word “redundant” in the dictionary is "exceeding what is necessary or normal, superfluous". But the third meaning, as used in engineering, is
serving as a duplicate for preventing failure of an entire system* but there are other forms: For example Dissimilar redundancy
Aboard ship in the engine department having one ship’s service generator (SSG) running with another on standby is a duplicate, the emergency diesel generator (EDG) is a partial redundancy, the batteries for the GMDSS is dissimilar redundancy.
On the deck side, on the bridge there might be two compasses, two radars, two VHFs, threes modes of steering etc. With methods of navigation and collision avoidance there’s visual, radar ranges, bearings, AIS, ARPA and so forth.