About July/Aug 1943, after Operation Servant to attack the Tirpitz with "Highball" was cancelled on 30 June 1943 in favour of using midget submarines in Operation Source (which took place on 22 Sept 1943) CinC Coastal Command, Air Marshall Slessor, suggested "Highball" could be used against U-boats coming out of the Baltic and transitting to the Atlantic via the Faroe Channel. As a result a series of dropping trials took place in the open water of Sinclairs Bay, just north of Wick in Scotland, by aircraft from 618 squadron based at nearby RAF Skitten. These appear to have been dropping trials only, without any target ship involvement.
These trials were, in the words of the squadron diarist "eventually abandoned in the light of existing circumstances". Whatever else he might have known was never committed to paper, probably due to the great secrecy surrounding both the weapon and the squadrons activities.
There is some film footage that may have been of these trials in this article
Read the fascinating story of how experiments were carried out during WWII with bouncing bombs that may still lie in the waters of Sinclair's Bay.
www.johnogroat-journal.co.uk
Dropping practice was also undertaken off Reculver on the north coast of Kent in 1943 and off Turnberry in Scotland, home in WW2 to a Coastal Command OTU and now part of Donald Trumps empire as a world famous golf course.
Using Highball on the open sea would have been as, or even more , difficult than trying to hit a target vessel with a torpedo. Reading the accounts of the various trials against the battleships Courbet & Malaya and the trials against land targets highlights the difficulties of getting an accurate drop, without adding in the complications of manoeuvring targets, rough seas etc.
Edit:- As for the "Upkeep" weapon used by Lancasters during Operation Chastise, it was by 30 June 1943 seen as a "one shot" weapon that had seen its time pass. Especially so since one bomb had fallen into German hands (Barlow's aircraft, AJ-E, crashed after hitting power lines but the bomb it was carrying did not explode)