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    Re: The development of bubble sextants
    From: Hanno Ix
    Date: 2009 Aug 15, 09:19 -0700

    I did indeed commit an error interpreting the dynamics of the bubble in the spirit level, and I thank all of you who took such an interest into that question.

    This error triggered all kinds of other questions and ideas. I will follow up and report in time.

    Best regards


    --- On Sat, 8/15/09, frankreed@HistoricalAtlas.com <frankreed@HistoricalAtlas.com> wrote:

    From: frankreed@HistoricalAtlas.com <frankreed@HistoricalAtlas.com>
    Subject: [NavList 9528] Re: The development of bubble sextants
    To: NavList@fer3.com
    Date: Saturday, August 15, 2009, 8:53 AM

    Gary L, you wrote:
    "I have been a flight instructor for 37 years. We demonstrate to all student pilots that they can't use their natural balance sense to determine which way is "up" while in flight. We demonstrate this by having the student close his eyes and then we maneuver the aircraft and ask the student to tell us what the airplane is doing. We then tell them to open their eyes and they are then surprised that they were completely wrong in their estimate based on their semi-circular canal senses."

    And this reveals a fascinating cultural difference between traditional mariners and traditional aviators. From the earliest lessons, aviators are taught that the instruments, the "black box" instruments (!), can be trusted while the "mark one accelerometers" in our heads cannot be trusted at all. By contrast, as we've seen in a number of posts in the past few months on NavList, many mariners believe that the "black box" instruments should be treated with suspicion while the "mark one eyeball" is always your friend.

    For mariners, in today's increasingly electronic navigational world, I have a feeling that the experience of aviators is going to become more relevant. The electronic navigational tools work 99.99% of the time. What's required is not more "mark one human sensor" instrumentation, but rather the error-detection skills, which depend heavily on the last redoubt of the skilled navigator -- the human brain itself, that let us identify those rare circumstances when either the electronics or the biological sensors are giving us incorrect information. The key is knowing that there is something wrong. And if you can detect an instrument problem, you can switch to backups.

    This all leads to the subtle problem of false alarms. Reading more on the grounding of USS Port Royal, it appears that the "Voyage Management System" aboard these vessels is notorious for frequent alarms. When the VMS warned them that the inertial system and the GPS did not agree, the navigators that day did what experience had taught them to do: they ignored the alarm. It's a case where the vessel had thee complete, highly accurate systems which could almost instantly read out position: GPS, radar, and inertial (while there were no radar repeaters on the bridge, the radar was active and functioning). Unfortunately, the crew for some reason (random bad luck? poor training? deliberate sabotage of a commander they disliked?) chose to trust the one system that wasn't working that day. They didn't have, or didn't use, the skills that would have allowed them to detect the failure of one of their navigational systems.


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