Use of Celestial Navigation Today

I don’t know if you (@Kennebec_Captain) ever experienced this departing Guam but on occasion our GPS would become erratic for several hours. When it happened on successive trips in the same general area after leaving Guam the discussion between the mates was that the navy was playing games with us.

Been to Guam a few times, didn’t see that.

I can recall two times having trouble with a Sat system. Once in the Gulf of Thailand some problem with the SATNAV. I was third mate. Capt had me do a LAN. Chief mate watched over one shoulder and captain over the other while I worked it out and plotted it.

The other time was an early GPS, it switched over to DR but no alarm. Still in radar range so it had me scratching my head for a while till I noticed the tiny letters “DR” in the corner of the screen.

When I was sailing, I found the Casio analog-digital watch just perfect to find out where the North or the time was …


When I became pilot, I just bought a cheap watch to know which day it was …



I kind of like it, tbh, but most Rotterdam is a pretty… “industrial” place from my trips through there. This has got some pizzazz!

This “compass” works perfectly… if the watch shows noon at the true local noon.

The Equation of Time is not the problem, through the year the difference is only about ±15 minutes.

The time zones (and in addition the daylight time) matter much more:
From Cape Finisterre, the westernmost point of Spain, to Otranto, the Italian side of the entry into the Adriatic Sea, or to the eastern part of Hungary, the true local noon varies by two hours in the same time zone.
In higher latitudes, this is extreme: Inside Norway alone; the true noon varies by nearly two hours


A post was split to a new topic: Opinion | Ditch the GPS. It’s ruining your brain. - WP

It’s possible in navigation theory to get deep in the weeds. To help guys like us that have to solve problems on a practical level rules of thumb are used. Like the fix in the middle of the triangle. Simple and close enough.

We’ve heard don’t rely on any single aid, particularly a floating aid a million times. GPS is a different kettle of fish however. Can’t be evaluated with simple rules.

With sophisticated systems using independent verification used in the offshore industry it is impossible to spoof the GPS signal and have it pass unnoticed. If the GPS signals disappeared altogether world wide it may be a good time to pucker up and kiss your fufu valve goodbye because nothing good is happening.
If knowledge is allowed to pass from the instructor to pupil without rigour then that knowledge slowly degrades. We need the instructor to get among the weeds to lift and maintain the standards and it is not just in Navigation. There has been catastrophic failures in the operation of the main engine of a large container ship and serious damage to the switch board of a cruise ship that I’m aware of. Both cases had the senior officers who commissioned the vessel having been relieved by other officers and then these officers passing the knowledge down to others until it became like Chinese whispers and vital information was lost.


Yes, well put. I thought this tread: Interesting Article - How Technology Grows was relevant to marine engineering in the sense of having deep understanding vs work-a-day knowledge.

When I was sailing international in the 1970’s & 1980’s, I would sometimes come across a ship in the middle of the ocean flashing some kind of Morse Code at me. I have never been able to remember Morse Code so I would simply call on VHF 16 and ask them what they want. It was always somebody just wanting to practice.

I was once part of a riding crew on a tug being towed by an AHTS from Morgan City to Bombay, India. I would perform my Cel Nav every day & night and then compare my position to the position obtained by the AHTS’s Captain, a retired US Navy Commander. We usually got between 5 to 10 miles within each other, sometimes a little closer. Keep in mind that we were separated by only 1,800 feet of tow wire!


CELNAV is actually a thing. It can be completely automated and computer driven, coordinated with NMEA networks to control and helm systems. More costly than standard equipment, can be integrated into commercial navigation systems.

7 posts were split to a new topic: Lunar Distance and other From 1883 Ed of Bowditch

I was taught to not bother with LAN, just shoot a regular LOP around noon and be done with it. With modern calculators it’s actually easier to reduce a normal sun line anyway.

could see that. In the days of tables, LAN was a much much easier calculation. Spent a few months in Antarctica and we got to shoot LAM ( local apparent midnight )

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Don’t really want to revive this thread to but I’ll put is this way.

If you were put in charge of risk assessment for say 1000 ships, bulkers, tankers, container ships, RO/RO and so forth would your first memo to the fleet be that you wanted everyone to start practicing celestial in case the GPS failed?

If I was down in the trenches on a big RO/RO in shitty weather trying to slog my way though a coast-wise without killing someone I’d think that the person who sent that memo was an idiot.

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CelNav is the equivalent of throwing a log tied to a knotted line off the stern to measure your speed, (You never know when the Doppler might break!) or lead lines (never know when the Fathometer might break!), or Morse over flashing light (the radio might break!), or sails (the engines might break!), or timber raft building (the ship could sink!).

I enjoy CelNav. I enjoy baffling the kids with stuff they don’t learn in school (lunars, double altitudes, deriving longitude by moonrise without a clock). I also know these skills are oddities of a bygone time that are as likely to help me as an astrolabe.

while I agree in principal - I think it is still important for officers to be able to evaluate what is happening without being overly reliant on electronics. Watching movement of bubbles, ect alongside is still useful to see movement at slow speeds, looking for, and using natural ranges on anchor watch to check for dragging, bearing drift - nut just over the compass - but out the window, and many others. Cel Nav IMO is part of that same mind set that is just part of a healthy skepticism of electronics and an ability to confidently navigate the vessel without them.

As an example, years ago I boarded a vessel, at anchor that my company had on charter and which we believed to be aground, as an observer for our interests. The Captain insisted he was not aground and kept pointing to his electronic chart. My simple question back was, Capt if you are not aground, why are you pointing in a different direction than all the other ships at anchor.


I agree with the general mindset you’re describing here, a kind of total, constant awareness to the situation, the ship, environmental factors and so forth. But I think celnav has limited value here because unlike the bearings of landmarks or weather conditions, things that can be directly observed, reducing sights has too many steps in the process to be usable in that way.

Plugging the daily position into a spreadsheet yields useful information, days run and so forth but it’s not the same as the way a ship feels in a turn.

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“reducing sights has too many steps in the process”. There is an App for that! DR from that thumbprint on the chart while you fire up your version of a PPU with the BT GPS that reads all navigation satellites not just one system. That fails then it’s time for the sun gun. You may have to change Apps.