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    Re: US Navy and celestial...
    From: David Pike
    Date: 2017 Sep 15, 02:06 -0700

    Alexandre you wrote:

    This is frequently mentioned here:

    > In times when global navigation satellite systems may
    > be unavailable, due to natural interference, artificial interference, or a
    > failure or receivers, The Nautical Almanac remains an independent, primary
    > backup for determining the navigator's position at sea"

    Almanac remains. But the answers to these questions are unclear to me:
    How many USNavy officers are sufficiently trained to use CelNav?
    Do all Navy ships really carry sextants and almanacs? (I doubt it).

    I don’t think skills shortage would be the problem for shipping.  I think it’s more likely to be the availability of celestial on the surface at the time you require it, and is it accurate enough for Pilotage as opposed to deep-sea navigation?   There are undoubtedly places where the Sun or stars shine most of the time, but there are others where the chance of a glimpse of the sun or stars is much less predictable.  E.g. last week I was scheduled to attend a seminar in West Sussex.  Normally, I wouldn’t have bothered to attend, because it was a 400 mile round trip.  However, it’s a south facing coast unlike the ENE facing Lincolnshire coast 50 miles east of me, so there was finally a chance to try out my Hughes Mate’s Three Circle sextant on a sea horizon at a gentlemanly time of day instead of using an artificial horizon, so we decided to turn the trip into a short holiday from Sunday until Friday.  The first useable sight of the Sun was on the Wednesday, but that was the seminar day 20 miles inland, so all I could do was demonstrate the Hughes MkIX bubble sextant.  Next chance was Thursday morning, but even then there was broken cloud with patches of sunlight reflected from near the horizon and the grey sea merging into the grey cloud at the horizon.  Nevertheless, with ‘Navigator’ on my net-book doing the calcs and Mrs P hacking the clock, we eventually got our accuracy down to 1.3nm but about four days too late.  Perhaps for a warship with an astro-tracker to massage the ship’s inertial system, this wouldn’t be a problem.  It would be celestial Jim, but not as we know it. 

    Similarly, GNSS has almost replaced visual bearings for Pilotage, but in the event of the loss of GNSS, visual would be the obvious choice as a fallback procedure.

    I still think the reintroduction of a small number of lessons in celestial at the USNA is more of an ‘esprit’ sort of thing than a serious attempt to establish this skill at this level.  Just like you would expect a naval officer to know enough to get by in polite conversation on Nelson’s tactics at Copenhagen, the Nile, and Trafalgar, you would expect them to have a reasonable idea how and why people use sextants.  DaveP



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