These are windlasses, or lock-keys. On canals and rivers with locks (to move the boats up or down levels) they are used to operate the paddles on the lock gates which allow you to empty (or fill, as appropriate) the lock once the boat is securely in the lock.
Many of the paddles are quite stiff, and the lock gates themselves can be very heavy. You tend to return from a week on the canal feeling like you've done 4 weeks in boot camp!
I like it! Good focus on the key and enough out of focus background information. I have enjoyed your boating shots Peter even if i haven't made a comment on all of them.
@kimcrisp Thanks so much, Kim.
@yogee246 Gita, yes, canal boats tend to be very colourful, luckily!
@yrhenwr Well, thanks, David, appreciate that.