OK. Found it. And this search shall now be filed under "Sod's Law".

I first looked through "Hen Benillion" (Old Verses) by T.H.Parry-Williams; more or less the standard source for these folk verses which are 'floaters' and very popular in traditional Welsh song. Hen Benillion has some 740+ of them and, although I couldn't find "Mae yn Nefyn gwrw llwyd" in the First Line Index I was pretty sure I'd seen verses with 'gwrw llwyd' before and it was quite common to change place names; so I went through ALL the first lines, and didn't find it.

I then remembered a rather newer book, "Ar Dafod Gwerin" by Tegwyn Jones but, as I've recently undertaken an overseas move, I had to find it first! Having found it, I then undertook the same process with its 1193 First Lines. Sod's Law: it was listing 1162 in the Index.

Yn Nhy^-Nant mae cwrw llwyd,
Mae yn ddiod, mae yn fwyd;
Mi a'i yfaf lond fy mol
Nes bydda i'n troi fel olwyn trol

In Ty^ Nant there is grey (pale) beer,
It is drink, it is food;
I go there to drink my belly full
Until I spin like a cart wheel.

(I place ^ AFTER letters over which it should appear.)

TJ notes that Ty^-Nant is (was?) a tavern between Cerrigydrudion and Corwen in North Wales; and in another version it's "Drws-y-Nant", so it's common to change the place name.

Dr Price, there is ONE Welsh shanty isn't there? I'll see if I can now find THAT book (J. Glyn) to verify. It's also worth noting that crews out of ports like Newport (Pembrokeshire), Aberaeron, etc in the 1800s sang hymns ... and crews were often from a single denomination (if not from a single family). I can't for the life of me remember where I picked that up.

Spiralling even farther from the original question, I was found myself on a 'fact-finding mission' in Ireland with a crew of people including a Mrs. Williams, minister's wife, from Fishguard. I mentioned that I was interested to see how many Welsh hymns there were involving storms at sea, tempests, crashing waves, etc. and thought it involved the maritime heritage. She said, 'no', it was because of the Welsh religious orientation towards the Old Testament, and the Jewish attitude (fear mostly) to the perils of the sea. Found out later that she was some truly major Celtic scholar but she certainly didn't flaunt it! I must try to remember her first name ...

By the way Dr Price, how are you doing today? Weren't you cremated on Jan 31st 1893? You must have spent all the money you made selling tickets to the event by now ...

sian