On the theme of creak crawling for our boats ( < 400 mm draft) , navigation is best carried out using OS maps, 1: 25000 or 50000 low water mean clearly indicates a navigable channel , not always following the geography.
I have successfully used this method in Pembroke, Cornwall, Devon and am sure it is useful in other extensive estuary .
The Plymouth, Falmouth , Milford Haven are ideal for spending nights at outstanding locations ,away from the usual mooring sites. Air draft can be a problem if > than 7m, so gunter rig is best .
Some of these areas are so tranquil that it it is a crime to use an outboard, so rowing or better still skulling, even better a Yuloh.
