One absolved by Inland Revenue essentially boarded fabulous ship (5,5)

'fabulous ship' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'one absolved by inland revenue essentially boarded' is the wordplay.
'one' becomes 'i' (Roman numeral).
'absolved' becomes 'shrove' (I can't justify this - if you can you should believe this answer much more).
'by' means one lot of letters go next to another.
'inland revenue' becomes 'ir' (abbreviation for Inland Revenue).
'essentially' indicates the central letters.
The central letter of 'boarded' is 'r'.
'i'+'shrove'='ishrove'
'ishrove' after 'ir' is 'irishrove'.
'irishrove'+'r'='IRISH ROVER'

Can you help me to learn more?