This is Peter Hall’s patented dredger, Mark 3. It has a chain dangling in the mud, which is driven by the fan to agitate the silt.
Peter has high hopes for it. If it works, perhaps he can liaise with Ian Lindsay to produce a bigger version (utilising blades from Ian’s wind farms).
(The webmaster is still examining these photos for signs of skilful use of Photoshop, so far without success. Come down to the harbour to see for yourself!)