NavList:

Bravo. You have recognized an important concept early on that so many students of navigation history stumble over for years: navigation manuals display the history of education resources, not navigation. They can provide insight and bakground, but they are not history. You need to look at "primary sources" when researching history. Of course, there are also other secondary sources worth digging into, and one that you must read (and should probably try to acquire in hard copy) is Lecky's "Wrinkles in Practical Navigation" originally published in 1883. It's both practical guide and memoir.

If you can make your way to Mystic Seaport Museum in Mystic, Connecticut in October, I highly recommend you join my class "Celestial Navigation in the Age of Sail" (formerly "Celestial Navigation: 19th Century Methods" which is entirely devoted to this topic and will give you direct practical experience with the methods that were used by drawing on late 19th century primary sources. 

You wrote:
"By analogy, a completely naive person looking at modern US drivers' license manuals might infer that only criminals drive over the speed limit, and would have no way of knowing that on any real world US interstate highway, driving a few mph over the limit is the norm, not the exception."

That's a really good analogy. It's always instructive to imagine how future historians two centuries from now might try to understand the world we live in today. What distorted lens would the world of youtube provide?! By the way, those "few mph over the limit" vary across the country. I spent most of my adult life driving in the Midwest (near and in Chicago) and in New England. On the interstates in this part of the country, that margin above the speed limit is comfortably 7-10 mph. Driving on I-95 out here, I normally engage the cruise control at 72mph while the posted limit is 65, and I am right in the middle of the pack. That cruising speed is only slightly above the mean driving speed on the highway, and it's highly unlikely that a driver would be ticketed, or even noticed, in New England for driving at that speed. But some years ago when I drove out to California (primarily for a little NavList gathering for in-flight aerial sextant sights organized by Gary LaPook!), as I drove across Texas and then into New Mexico and Arizona, I noticed something interesting: speed limits jumped up, but that margin of casual speeding nearly disappeared -- everyone drove at the speed limit. I was stopped by a state cop in Arizona on the way back (clearly thinking I was a smuggler...), and while he was asking me leading questions about my trip, we chatted about that speeding margin. He had a name for it, which I don't recall, and he specifically told me that he often stopped and warned drivers from other parts of the country who didn't realize that Arizona did things differently. There's a different legal standard in that part of the country. The speeding margin is 2-3 mph above the posted limited, and the average is right on the posted limit. Now there's something you would be hard-pressed to learn from a driving manual.

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA