I'll try something simple, since the end of the contest period draws near. Another entrant sparked my interest when he noted he was annotating where his lighthouses were... I said to myself "and for some navigators, all they would need is locations and specs on the lighthouses". Well, that and any major obstacles like LAND :-).

So I grabbed some snapshots of sky-with-clouds, picked a likely one, slapped a bit of blur on it, and posterized it. I ran the number of levels up and down till I saw a pleasing set of random coastlines. If I cared about onshore topography that could have given me some semiplausible contours, but this is a dirt simple - no, saltwater-simple effort, so the zero contour would be enough: coastlines. But then one other band looked like reefs, so I kept it too. Filled lower bands with water color, upper with land-beige, and because my method gave a crisp pixellated shore, I aliased a coastline with 'find edges". Oh, after I manually etched a stretch of barrier islands on one coast - the sort of thing a simple cloud-generation won't give you.

Which gave me this:
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Click image for larger version.  Name: lighthouses-1.jpg  Views: 159  Size: 489.7 KB  ID: 55266

Now all I need is a bit more time to play, I mean map, and maybe I can finish an entry.