NavList:

John,

If you plan on sailing through the Tuamotus using only CN then it would be wise to try for LOP accuracy of 2'. Table precision to the nearest minute is good enough to achieve this. Ships need to be careful not to go aground (drafts around 35 ft.). Sailboats to a lesser extent (drafts around 8 ft.).  A Bygrave is close to 1' precision so wouldn't be unsafe for CN through the Tuamotus. If using the DR position as the assumed position then Rust or Ix diagrams are plenty accurate. Pub 229 is overkill.

Greg Rudzinski

 

From: John D. Howard
Date: 2015 Jul 21, 08:33 -0700

All,

Since I first started this thread by asking what precision is needed the topic has morphed to what precision can be achieved.  I am still left to wonder what is required.  I, John, get .7', and Frank gets 2.5' then is Frank in danger?

Reading the posts it seems that if you go a day or two without a fix because of weather then get a great 3 star fix you will update your position and start your DR from your new fix.  Was the boat in danger or in violation of some law during the day of no fix?

I am not being silly with this.  When I flew over oceans the tolerance was much greater once you coasted out.  You got the best fix you could but it was not required or expected to keep on course + or - 2 miles when between LA and Hawaii.  Half way there we would check in with Ocean Station November and they would give us a reference point but even then it was a grid coordinate because November did not stay in place like a lighthouse but drifted around.  They would broadcast they were in say grid " charlie 3 " and we looked at our chart to see where the boat was.  The grid was something like 2 miles square but this was good enough to get us to within 50 mi of Hawaii.

Much discussion about compact sight reduction tables and slide rules and Bygraves and Rust diagrams.  My main question is still this - is using a Bygrave and Rust diagram at sea instead of table 229 unsafe?  From what I have learned reading the posts the table 229 will get you a much better (precise) fix than a Bygrave.  If you NEED the best possible how can you accept the use of lesser methods?

Once again forgive a pilot if this question seems silly.

John H.