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    Re: Dependence on GPS
    From: Lu Abel
    Date: 2009 Oct 29, 18:34 -0700
    Do we have specific examples of "unreliable in practice?"  

    Sure, GPSs are electronic instruments and don't like getting wet.   Sextants are high precision mechanical instruments and don't like being banged about, getting rusty, and a whole host of other forms of abuse.  And I'd sure love to hear any list member relate how they got a fix when it's been cloudy and overcast for a week.  Or how they manage to transport a Nautical Almanac in conditions that would soak a GPS.

    There have been accounts of ships hitting things "due to electronic navigation failures."  Often cited is the 1995 grounding of MVS Royal Majesty off Cape Cod.  Due to a bad antenna connection the GPS failed.   Its state-of-the-art electronic navigation system system reverted to DR navigation.  So one might call this a failure of DR navigation.  Does this make DR "unreliable in practice?"

    I don't think it's proper to eschew any form of navigation because it might fail -- there are plenty of examples of bad GPS navigation and at least an equal number of examples of bad non-GPS navigation.   If one is prejudiced against one form or the other, one can use an example of a failure as "see, I told you it's unreliable."   But, again, to me a good navigator will use (with caution and understanding of possible failure modes) ALL forms of information to help him/her guide his/her vessel to a safe conclusion of its voyage.

    On a slightly different tack:   I can fully understand why "traditional" (vs newfangled electronic) navigation can make people feel comfortable.   When I lay out a DR track, I am on a chart interacting with its record of the waters I'm passing through.  But when I "follow the bouncing ball" on my GPS, I'm not.   When I shoot a sight and reduce it, I'm can see a step-by-step evolution from my raw data to a LOP.   But when I get my position from my GPS I just see a set of numbers magically produced by some algorithms that only experts understand.   I don't blame anyone for feeling a bit nervous about being forced to "take it or leave it."  I would hope navigators would try to sanity check electronic data.   But that's way different than totally eschewing a source of valuable navigational data because it might, in some very rare instances, be "unreliable in practice"

    Peter Fogg wrote:


    frankreed wrote:
     GPS has *solved* the problem of navigation when it's used correctly. No need to un-do that!
    Not if it proves unreliable in practice.



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