How Safe Is Digital Navigation

[barnakiel]

DISCLOSED: VOR participants Team Vestas missed the mark!

We would have never discovered this if all we had were our rusty sextants!

b.

[transmitterdan]

Is this a "known fact" from the RC or just discovered from the track data? To be sure one would have to know how often the track data is updated. It could be they rounded the mark but the track points don't show it.

[GrowleyMonster]

I have seen a lot of sextants but never a rusty one.

[skipmac]

Did you mean rusty sextant or trusty sextant?

So what does this mean. Is team Vestas disqualified or will they just add a penalty to their time.

[skipmac]

Originally Posted by GrowleyMonster

I have seen a lot of sextants but never a rusty one.

Nope, no rusty sextants but have seen one or two that were turning green.

[MarkJ]

Looks like the data was intermittent and the guy went around the mark. You can see the data points

[barnakiel]

OK guys, the riddle solved, here:

http://mmb.smugmug.com/Other/Miss-Gr...ha%20TQI-L.jpg

;-)

b.

[GrowleyMonster]

Even with electronic navigation, the human element must be considered, and a human navigator must be available to at least keep a proper DR track either on paper or manually on an electronic plotter. Manually putting an electronic fix on a paper chart. Whatever. Systems can fail. Humans can fail. Redundancy is essential.

Once, not long after GPS came into widespread use, I was sailing as AB on a ship, on the 12 to 4 watch with the 2nd mate, who of course is the navigator. I used to amuse myself on long ocean passages either practicing celestial to keep my skills fresh or trying new and way out stuff. One day I took an LAN and was like 5 miles off... quite outside my normal error even in marginal conditions. I KNEW the shot itself was good... we had a cadet aboard who also shot LAN and our shot times were maybe 2 seconds apart and agreed almost exactly. I went over and over this very simple and straightforward problem and always got the same latitude. At 1500 I grabbed a sun line. Actually I took 4 or 5 shots so I could average, so once again I was confident in the actual observation. This time, my LOP was I don't remember, maybe 35 miles from our position by DR from the 1500 GPS fix on the plot sheet. I pounded on my calculator furiously, trying to find my error before my relief came up, and at the last minute noticed that my estimated position from crossing the DR track and my LOP was almost exactly a full degree of longitude from the shot time DR position. Closer investigation revealed that the 1500 GPS fix as logged and the fix on the plot sheet were a degree apart. On switching from the Noaa chart to plot sheet a couple days earlier, the Chief Mate had put the initial fix down a degree to the East of our position. Subsequently, everyone had entered the L/L correctly but only got the minutes of longitude right on the plot sheet, perpetuating the error in longitude until someone finally broke out a sextant and stubbornly refused to give up finding why an LOP was so far off. So the Electronic Navigation was faulty, but only because humans still are involved and still make errors.

Now, all ships have ECDIS, supposedly taking navigation errors out of the Mates' hands, but in truth errors still occur, and when I next see a particularly funny one I will try to remember it and share. I might point out, though, that every ship I have been on since ECDIS became universal, also had paper charts out on the chart table, and the mate on watch still plots hourly fixes.

The GPS position is gonna be right on the money. Pretty much always. Electronic navigation is safe, assuming a reasonable level of redundancy. Humans are not.

I no longer insist that celestial navigation skills and equipment are necessary for ocean passagemaking, but I do believe strongly that multiple means of determining position and course/speed are necessary. These multiple means should not share any component... gps receiver, antennae, power source, nothing; total redundancy, so no matter WHAT, there is still a fully functioning system.

I will also point out an observation of mine that will irritate some... A good racer is not always a good sailor and a good sailor is seldom a good racer. It's a matter of priorities.

[nautical62]

I know how accurate and safe my sextant and DR skills are. Digital navigation is much safer than either, though I still find eyeball navigation essential.