Hi there
Sorry, I cannot find any reference giving Captain R. Butler's first name re the "Harmony".
In a book by Margaret Parkes & V. M. Williams called "Knysna the forgotten port":
"...on 13 March, 1826 the brig "Harmony" was wrecked in the channel on her way out of the port, and under his [ex-Royal Navy Lieutenant John Mackenzie Johnson's] pilotage. The vessel was taken aback in the narrows in a north-westerly wind near the outer bar. The pilot boat being insufficiently manned to tow her over to safety, she was left to drift gradually, having failed to let go an anchor, until she struck well and truly on the western rocks, and become a total wreck". [and further on it says] "But the Master of the "Harmony", which was unfortunately not insured, wrote from Cape Town to John Rex somewhat bitterly, that he felt that the Government had regarded the disaster in a "very slight manner" ....".
This makes me wonder if the reference re "R. Butler submitting a certain account of his" for 1827 on the NAAIRS site is not perhaps your man - it might give the full name in his signature?
See
www.national.archsrch.gov.za - click on RSA - key in Butler with the date 1827. Unfortunately I am not in Cape Town so cannot look it up for you.
I started tracing the voyages of the "Thomas" in 1829 but ran out of time - do you know in which month it was lost?
Regards
Sandy