O'Docker nicely pre-empted the second part of this weekend navigation puzzlers, by raising the very valid question - does it matter?
For as you see above the PLA vessels that was surveying the Thames to ensure charts are up to date (and hence was displaying the restricted ability to manoeuver shapes) sped off at the end of the day no doubt to have a refreshing cup of tea without taking down the shapes.
And they are not alone as I don't think in all my sailing I've ever seen the sailing vessel under power shapes, despite often seeing and being in yachts motoring along.
There are two schools of thought. Firstly there is Commodore of the fleet (retired), owner of the Pedant of Cowes, author of many a letter to Yachting magazines complaining of the lax behaviour of the youth of today in not flying the correct signals.
Then there is the O'Docker school of thought - look, we're grown up, we have eyes, for heaven sake this is meant to be an escape from the button down rules on land (I paraphrase, maybe a spokesman or alumni of this school could chip in some words of wisdom).
So which side of this fence do you sit?