Although larger boats can presumably pass the lock when the tide makes a level at any other time it's a tight squeeze for the Boston Belle:
It took only a few minutes to pen through and then the Boston Belle was away and down towards the sea.
What a shame it was a charter rather than a public trip. I'd have definitely been on board! Once the Belle was clear of the lock the flood gates were closed against the incoming tide and the lock returned to it's normal slumber.