Abstract Principles in Familiar Waters

I think this sort of thing is interesting. Start in familiar waters and apply what’s been learned elsewhere.

In his book Intuition Pumps and other Tools for thinking Daniel Dennett uses the example of an assumed position in celestial navigation. It’s basically the same technique used to do long division, start out by making a guess at the right answer and then refining from there.

In celestial navigation the AP used is an exact latitude and longitude that matches a problem solved in the tables.

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Every time somebody is squawking about changing nav practices I just imagine how much shit those guys got.


A nautical chart is a representation of reality, specifically an abstract and simplified representation of specific elements of the marine environment.

The celestial sphere is a ‘conceptual tool’, it’s more abstract than a chart.

Lest anyone forget … Fred Noonan.

The dying breed of paper charts, (and electronic charts to a lesser extent) are “good enough” estimate that can be used to get the job done. The day I wrote this was the day I learned from the president of Ocean Graphics that scale isnt uniform, apparently 1:10,000 can be +/- several millimeters, which really killed the mood for the day for my OCD ass. But beyond that, I’ve seen numerous cases where coast pilot disagrees with the light list on bearings of ranges, the position of a buoy on a chart compared to its actual position is only a concept, and while I’m not planning to go scuba diving to prove a point, i suspect there are loads of ghost obstructions cluttering charts everywhere. Comparing the light list to looking out the window I have my doubts to its accuracy as well. Also considering some of the survey data dates back to some guy with a lead line in the 1800s in some places, to reported depths from 30 years ago else where, charts are really only a rough aproximation of depths.

While i understand why they arent updating land on paper charts anymore, there have been years where the ENC shows different land than the chart. And I wont be able to really confim this while I’m at work, i have a strong suspicion that Oceangrapix charts have different land shapes than NOAA charts.

Then you look at the accuracy of publications like the coast pilot, which have a lot of outdated and conflicting information. Just try to find the nearest repair facilities in Florida, no two ports say the same thing, and for some reason Miami cites container gantry cranes in Port Everglades as a repair facility?

While we aren’t exactly assuming the earth is the center of the universe, there are a lot if assumptions made on nautical charts. I was trying to echo and agree with this guy more than anything:

(Sorry ive been editing this on the fly, I pressed post on accident too quick)

The diagram illustrating the celestial equator and pole, zenith and declination shows the observer as a pencil point on a flat earth - seems to work.

Captain Thomas Sumner died in a asylum.

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Amelia’s navigator? The one that signed off on flying to an island into the rising sun? It wasn’t until I had to do that myself in the pre-GPS era I realized how dumb that was, you are lucky if you see the island while directly over it, you sure as shit aren’t seeing it ahead of you.

  • I had gas to go back at least :roll_eyes:

Old school paper charts were usually very good as far as being relatively accurate from one bit to the next. It wasn’t until we had some GPS-induced wrecks that it became obvious some were quite a bit off the GPS datum. In the old days you just wanted to get close enough to identify something for landfall, no one was looking at a display to make the actual channel.
Now it is considered poor form for sailboats at least not to have GoogleEarth georeferenced photos for navigating some areas of the Pacific, no charts are as accurate.

The Celestial Sphere. May It Rest in Peace. - David Burch Navigation Blog

It must be true then that not just astronomers but also astrologers use the celestial sphere, and sure enough most cel nav books start right out with a discussion of it. But all that time is wasted. We do not deal with navigation in the sky, we navigate on earth, and all the coordinates that might be used in the sky to describe the location of a star, have a counterpart on earth that is much easier to comprehend and thus use in our work.

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I would love to be able to toggle to google earth on the ECDIS like you can on google maps, that would be so rad.

Datum issues are one thing, but I was having a bad day when I realized 1:10,000 is +/- a couple mm for the same POD chart number, between suppliers. Drivin’ me bonkers.

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You can do that on a computer for sure, maybe not on an “official” ECDIS.


This is, according to the ancients, because the charts and pubs describe the imperfect, changing sublunary realm of the cosmos as opposed to the perfect, unchanging celestial realm.

In the sublunary realm imperfect ‘representation’ is the best you can do.