NavList:

   

Reply

byronink@netzero.com wrote:
> Maybe I didn't make the problem clear in the write up. The gyro was fine, it 
was the yard set up that was in fault. I saw this same problem of the gyro in 
error , not because of a faulty gyro but because of reference "the AZIMUTH 
CIRCLE ERROR" and the yard set up. The Intrepid and the pilot did not know of 
the error. The ship normally would not have gone up the bay but some one mad 
a costly decision to travel in fog, pilot on board to the new home port with 
the Goveror all kind of dignitaries and other people were there to greet her.
> The other point is why use The Azimuth that is known to be at it's best not 
as accurate as the fixes required by the Navy. Navy exercises in harzard 
water uses under 50 yrd as zero error in a fix position, any thing over is 
marked againt the ship. I know that the other large ships, don't have the 
personel equipment and requirements of the Navy. They may not have the 
responsibility
> and newworth of a war ship especially a Carrier or Atomic Sub. I am really 
saying that the reference for setting gyro equipment should be the same as 
taking bearing in hazard water. Of causes I want information from others 
also. If they (INTREPID) had used my piloting tectnique, that I found the 
error with they would not have had the gyro error.    
>
>   
Even if the yard had this Utopian, absolute, error free, device that was 
used to calibrate the gyro, you would - in my opinion - still observe 
errors up to 1.5 - 2 degrees every now and then at Narragansett Bay. It 
simply is not possible to make a device more accurate by using more 
accurate calibration methods. The other problem is that you do not know 
the gyro error during its calibration in respect to the average gyro 
error. What I mean is: the gyro might be wrongly oriented in the vessel 
(say 10 degrees to starboard) and have a random error on top of that 
(say 1 degree to portside). If you now calibrate the gyro you will find 
9 degrees deviation, but that is for that moment only. When calibrating 
gyro's for survey vessels it is standard procedure to do that in two 
directions, simply because the gyro will show a different error in those 
two directions, even when using the Utopian device (and even at the same 
location at the same day and within the hour). In above example with the 
vessel in an opposite direction the gyro might still have its fixed 10 
degrees offset to starboard but 0.5 degree error to starboard on top of 
that, resulting of a 10.5 degree total error. So even when you take the 
average of the two, you will not have the gyro better aligned than to 
0.25 degrees. Then when you start sailing again the gyro will still add 
up to 1.5 degrees in each direction making the gyro producing errors up 
to between -1.25 and +1.75 degrees. In respect to this all I guess they 
were probably not able to do opposite calibrations at the yard with a 
vessel this size.

It simply comes down to this: if a device is accurate to n units at the 
1SD level (whether it is degrees, metres or whatever), it should never 
be relied on within 3n units for critical operations. So if the vessel 
did run aground due to the steered course being off at 1.5 degrees, it 
most probably was not because of how the yard calibrated the gyro.

Nicol�s

-- 
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com

   

Reply