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Comment by nradov | Hacker News Reader

GPS is only a supplement for maritime collision / allision avoidance. All you actually need are: radar, eyes, horn, flags, lights, VHF radio, and charts. Of course GPS is certainly helpful as a backup and provides some protection against human error.

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Allision - my maritime word for the day

https://gcaptain.com/maritime-word-of-the-day-allision/

...and control over your ship motor + steering without computers. I’m not sure that is true on newer larger ships.

Edit: Would of course not be a spoofing attack.

Airplanes also use Inertial Navigation Systems.

I think the military can go even further and verify that the GPS data is correct.

The military has additional codes available to them (P(Y) and M per [1] et seq.).

[1]: https://www.e-education.psu.edu/geog862/node/1741

I don’t believe all of those are strictly necessary.

Charts, sextant, and regular visual observations are all strictly necessary.

Some kind of semaphore would probably be handy too.

The COLREGs (as well as local supplemental rules) are rather complex. All of the additional items I listed are implicitly required at least for certain vessels in certain conditions.

All you "need" are the stars and some way to track time (a basic implementation conveniently provided by the sun). Everything else just increases accuracy. ;)

There was an interesting youtube video a while back on the SR-71 that could navigate via the stars years and years ago.

Of course the SR-71 probably never had cloud cover problems. :)

edit: I think this one: https://www.youtube.com/watch?v=tj9UwKQKE3A

The SR-71 also had an excellent clock on board.

> (a basic implementation conveniently provided by the sun).

No. You need an actual clock and charts. The sun and stars are completely useless for determining longitude without a clock.

The Moon on the other hand is marginally useful because its phases can be looked up. But its resolution is poor.

> The sun and stars are completely useless for determining longitude without a clock.

This is not completely true. The stars (and planets) provide for a very nice clock when viewed with sufficient resolution.

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