That sounds fascinating, but it's not really clear to me how imagining islands beyond the horizon can help with dead reckoning. Maybe there are changes in observable phenomena, such as ocean currents, that are associated with these unseen islands? It does sound like a very complex system based on the beginning of this article; I'm wondering if anyone here has read the books mentioned in it: https://www.jstor.org/stable/20705519
I've found a bit more information about the topic in a publicly available research article [1]:
"A depth of only 25 fathoms is quite enough to give some surface indications: coloration, wave phenomena, perhaps fauna. Is this the explanation of the ghost island? Some lost traveller, perhaps en route from Yap to Guam, seeing and remembering these phenomena, later reifying them as an inhabited land? Or is it possible that a real island once existed here, as the Carolinians say? [...] Any Carolinian navigator worthy of the name can give a whole set of radiating courses under all the navigation stars from every island of the Carolines, not just from Kaafiror. [... N]avigators do learn them, together with the courses from real islands, and they make no distinction among them. It is perhaps not altogether in the realm of fantasy to speculate that the curriculum of the schools of navigation was established in a time when Kaafifor was more than a discolored patch of water."
The explanation could be a combination of experience, details, survivor bias and true scottman.
That is with experience you can select something on the ocean far away that you can track (kelp, etc), with experience and focus to accurately track it and take into account its own movement. Then the method is obviously only promoted by those who successfully survived using it, as the potential nay-sayers who used it and failed are no longer there to give a counter-point. Finally, those who did not use it successfully are probably characterized as "not good navigators", in circular logic.
Yeah, this surprised me as well. I get how reading ocean swells, sea life, birds, ocean color (indicating depth and/or plant life below) could give a general sense of position. And I can see how stars, prevailing currents and maybe even estimates based on the relative movement of clouds (adjusted for ambient wind direction and weather conditions) could give a general sense of distance traveled. But on a completely cloudless day (or fully overcast night) gauging distance traveled seems like it could be catastrophically imprecise often enough to make for short navigation careers.
I'm not sure how the concept of tracking virtual islands over the horizon really helps. The only thing I can think of is maybe the idea of it encourages the navigator to stay focused on estimating the passage of proxy points on the far horizon based on whatever composite of wind, current and swell signs they are intuiting from. While still quite variable, I assume gauging distance estimates on the far horizon is better than the alternative of trying to estimate distance traveled from the immediate surroundings of the craft (which are only useful for estimating velocity).
> I'm not sure how the concept of tracking virtual islands over the horizon really helps. The only thing I can think of is maybe the idea of it encourages the navigator to stay focused on estimating the passage of proxy points on the far horizon
You can practice navagating against physical islands over the horizon, and when you're good at that, you've mostly gotten good at dead reckoning against a real reference point; of course, with corrections from the islands influence. Having a community shared archipelego of virtual islands lets you focus your dead reckoning skills on a point while offering a vocabulary of distance and reducing travel times between waypoints.
Go 1000 miles in this direction seems a lot harder for me to follow over many days than go X miles to A, then Y miles to B, then Z miles to C. Even if A and B aren't real. If I treat them as very small islands that will be over the horizon, no big deal that they don't influence the environment, they're small; but I can't really use them to course correct, my reckoning needs to be good.
