How do find him? *COMPLETED*

[wonkiewidge]

Hello,

I've just come across an Irish ancestor amongst my English heritage.
His name was Daniel Mulvey, and from the National Archives Trafalgar Ancestors database I have found this information:

Daniel Mulvey aged 25 born in Limerick, Ireland.
Ship: HMS Conqueror
Rank/Rating: Able Seaman   
     
  Service details   
    HMS Conqueror
Ship's pay book number: (SB 331)   
     
  Sources used   
    Catalogue reference: ADM 36/16250
 

This information was dated 1805, so from this he was born around 1780.

My question is, how do I go about finding him and his parents in Ireland before he came to England.

Oh, and why would an Irish man join the British Navy?

Any help would be greatly appreciated.

Linda