You were right, a fathom is 6'. However for most practical purposes that's 2m for those who prefer Napoleonic units to Christian ones.*
- 45 = 4.5 m
- 26 = 2.6 m drying height.
- 42 = 42 m, note that the 2 is full size.
Heights and depths are referenced to the Lowest Astronomical Tide (LAT) which is the lowest that the tide can get purely due to astronomical effects, though weather may take it lower. The predicted low tide at 2320 today is 1.5m, so you need to add that to the charted depths.
A very interesting set of guesses about my career! After a short period in Middlesbrough Public Libraries I worked for 5 years at Whitley Bay High School as a lab technician. Most of my life though has been working with computers, rising from operator through system programmer to system management. Virtually all the work has been on behalf of the MoD, so any more information is inappropriate here. We were taught about maps at school, in the scouts, ATC and OTC. I've studied a bit about surveying just for interest. I seriously considered the Senior Service when at school, but there were questions about my health. I've tried to spend time on boats as much as possible, without a lot of success until I was made redundant when I bought an old yacht. I've trained as Day skipper (theory and practical) and Yachtmaster (theory) but can't really take it further due to failing health. Thinking me RN! That's must rank as today's best complement.
*Sarcy comment nabbed from "The Model Engineer".