Position Cross-Checking on ECDIS in View of International Regulations Requirements and OCIMF Recommendations - W. Legieć Gdynia Maritime University, Gdynia, Poland
With regards to GPS being a single source here is what this paper says:
Open Sea Navigation could be defined as part of the
ships voyage plan where no land is in vicinity . At
this stage ships position is obtained with use of GPS
and could be confirmed either by Celestial Fixes or by
comparison between GPS receivers. ECDIS users will
take an advantage of having two GPS receivers what
is required by IMO on every vessel equipped with
two independent ECDIS stations
Now common sense may tell us that this is unwise, GPS being a possible “single failure point”.
But the same is true in a merchant ship with a single engine. I am familiar enough with the many procedures and so forth are in place (I have an entire engine dept aboard) and thus feel confident that failure of the engine, while always possible, is sufficiently heavily guarded against such that it is an acceptable risk.
On the other hand I don’t have a solid enough understanding of GPS to evaluate on my own if GPS is robust enough to trust as a single source in open sea navigation so I have to trust the judgment of those that do know.