Alf: "Ok then .. all our theories are only guess work but perhaps mine are wide of the mark. 729 would have been ideal for a test from New Ross though, as the frequency had probably only just been vacated by ABC .. if that is actually the case"

The Cork RTE transmitter moved to 729kHz sometime in I believe late-1982 (old RTE guides, which may be on line, or whatever would indicate exactly when).
It would have been unworkable for ABC to have used 729 after that, so they would have been well gone from 729 by 1984.

However the ship (when at new Ross) could well have tested in the small hours of the morning on 729 though... after RTE radio had closed overnight anyway and it would not likely have attracted any attention for other reasons ...

Radio Nova in Dublin did incidentally very briefly operate on 729 in May 1984 before moving frequency again. Maybe the same crystal(s) for 729 briefly used by Laser found their way to Nova ?
I assume being co-frequency with the Cork RTE transmitter was the main cause of grief with Nova's very brief use of 729 ???

https://dxarchive.com/downloads/irish/nova/840507_1747_729_nova_greg_g_c90_863_kb.mp3

they (Nova) seem to have moved between SIX different AM frequencies in the 700-900 region
(info on the DX Archive site)!