On Fri, 25 Feb 2005 17:38:51 GMT, Rich Hampel
wrote:

My perceptions of WAAS, turned off selective availability, etc. is
that you in many cases are still using and co-relating to charts that
were constructed using hand thrown lead lines and surveying instruments
(sometimes on a pitching deck). Especially when using vector charts the
magnification possible with such charts completely overwhelms the
'resolution' accuracy .... and can very quickly put yourself firmly
onto a reef, rock, or channel berm. Jeeze, most of the coastal charts
used in the USA are based on the NAD27/29 data (many of which were
simply transcibed from pre-colonial charts .... and were NOT verified
by 'modern' means).

Running an unfamiliar channel, close approach to a hazzard, etc. by the
sole means of GPS (even with WAAS etc.) is GOING to 'catch you'.

Charts in areas of heavy commercial use, like NY, Boston, and Portland
harbors are mch more recent, and waas is really good. Jonesport is
more like prerevolution Admiralty charts. However, the locations of
Nav Aids are checked by DGPS every time they are serviced.

NAD 27/29 is not common in the Northeast.



Rodney Myrvaagnes NYC J36 Gjo/a


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