Sings the praises of former partner lost at sea (6)
I believe the answer is:
extols
'sings the praises of' is the definition.
(I've seen this before)
'former partner lost at sea' is the wordplay.
'former partner' becomes 'ex'.
'at sea' indicates an anagram.
'lost' is an anagram of 'tols'.
'ex'+'tols'='EXTOLS'
(Other definitions for extols that I've seen before include "'Praises, lauds (6)'" , "Sings the praises of" , "Praises highly, lauds" , "Enthusiastically praises" .)