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         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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