I was looking at the report into the grounding of HMS Trafalgar in 2002 during a Perisher.
The board of inquiry report can be read here:
http://www.mod.uk/NR/rdonlyres/FB21A...strafalgar.pdf
Copies of the chart can be seen here:
http://www.mod.uk/NR/rdonlyres/11837...enc_q6220a.pdf
I would guess that DR.Sid is probably closest at the accuracy of a fix decreases with time and motion.