Radio contact over the Irish sea
My experience is that you can always contact someone while at 2000' over the Irish sea, at least on the Holyhead - Dublin route. The problem is that the advertised London Info frequency 124.75 doesn't (or didn't) work right where it is printed in big letters on the 1/2 mil map West of Anglesey!
This is possibly because it is located down at Clee Hill and shadowed by Snowdon. I have pointed this out to London Info, but don't know if any changes are planned.
However, the northern London info freq 125.47 does work, as I suspect might Warton, Liverpool, etc.
I have been able to work Dublin from overhead Caernarvon and Llanbedr or Aberporth from overhead Arklow, but not perhaps at 2000'.
However part of the Irish Sea problem is that the military stations are often closed. I have had to skirt around danger areas because London info say they are active, but the controlling agencies don't answer and have clearly gone home!
Airliners would clearly relay a call on 121.5 and I have a radio set to 121.5 when I suspect I am out of range, but more significant perhaps at least one of the ferries has 121.5 permanently on the bridge. I know this because I once got a ride 'up top', granted perhaps because they misinterpreted my request for a visit when I explained that I was 'a pilot'.