NavList:

         Azimuth of the sun and gyro/compass error                                                                             
While I was crew on NAVY Ships undergoing overhaul in the Shipyard, the yard 
worker align the gyro and related systems.  The azimuth of the sun is the 
preferred reference to setup the system and my pet peeve.
The Azimuth Circle used to align the gyro is a delicate instrument that is with 
mirrors and a prism that throws a beam of light on the compass for a reading of 
the compass/ gyro. The Azimuth is timed and the true bearing of the sun is 
worked out using reduction tables for a tabulated Azimuth. The light beam on to 
the compass card has a thick beam of about .3 degrees, the Circle leveling 
bubbles must be level to get a good reading.   There exists a reasonable error 
of 0.5 degrees of error when the sun is high. Even so, the delicate, mirrors and 
prism may be unknowingly out of alignment (small knock can do this) for 
additional error.  After the ship is out of the yards and underway, the Azimuth 
circle is use to further check on the compass/gyro error.  At sea everything is 
fine, the ship may often correct course to close the Dead Reckoning (DR), 
because of set and drift found by underway fixes. There is no problem. After the 
ship enters  to the hazard waters and the ships is to transit for a distance to 
the birth or anchorage, another set of rules are in place, large NAVY ships are 
to take on a pilot to advise the conn of harbor up dates , recommend courses and 
place tugs.  The navigation team will use visual, radar, and electricronic fixes 
ever three minutes, every third fix must be of different equipment (according to 
naval instructions.) The compass, helmsman and the visual bearing s are a big 
part of the navigation aids used in these more dangerous, waters. The bearing 
takers for visual bearing are stationed with telescopic Alidades not the Azimuth 
circles. The bearing taker with Alidade can call in a round (3 or more) of 
bearing in a few seconds, with the accuracy of 0.1 or .2. (Looking back, a good 
azimuth accuracy may set the gyro to 0.5 + or -.)  The Azimuth Circle used in 
the yard to set up the gyro is known to be inaccurate. Bowditch "it is 
reasonable to round calculations to the nearest half or perhaps whole degree for 
most purposes."   We have the Alidade that can take bearings to 0.1 or 0.2 and 
helmsman that can steers less than 0.5 and we introduce large error because of 
past azimuth practice. I have seen the results many times in my past, when I 
evaluated piloting problem aboard both submarines and surface ships. My best 
example was the USS INTREPID.She left the Philideliy Yards after overhaul. 
Sailed to her home port of Norfolk VA. Sailed to her new home in RI. And ran 
aground in Narragansett Bay RI. Than to her birth at the pier. She ran aground 
in heavy fog, I am sure that is the main reason. After I went aboard and she got 
underway, I saw two small triangles on the chart, her second fix. What I saw was 
an east error of approximately 1.5 degrees. I requested to the Navigator that he 
add 1.5 degrees to the next round of bearings. With that correction the next fix 
was a three point intersection, that 1.5E correction was used for fixes until 
months later when the gyro error was manually corrected. The AZIMUTH CIRCLE use 
at the overhaul was the original problem. The grounding in the fog was due to 
the visibility, although the bottom INTREPID hit was to the right of the center 
channel. With a 1.5 East error the ship will track you to the right of your 
ordered course (17 YARD FOR EVERY 1000 YDS TRAVELED.)  INTREPID traveled the 
ordered course for about 6000yrds and tracked 150 yds to the right of the 
desired track. The Pilot didn't know this compass error nor did the crew.  I 
found it after the grounding. Reconditions, don't use the Azimuth to set the 
compass. Use the Alidade and bearing to chart NAVAIDS to a three point fix. (Use 
the two Alidades (use in transiting hazardous water,) to ensure they are the 
same. See Franklin piloting technique. I may rewrite this for the naval 
proceedings (a naval Magazine.)I would like to get Merchant / Navy /every one, 
ideas and experience on this subject.


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