Crossword Genius

Unwelcome on a ship but they pay for accommodation (8)

Ross

I believe the answer is:

boarders

I'm a little stuck... Click here to teach me more about this clue!

'ship but they pay for accommodation' is the definition.
The definition suggests an adverb but the answer is not.

'unwelcome on a' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
The remaining letters 'borders' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for boarders that I've seen before include "Live-in school students" , "Students staying at school" , "group of schoolchildren?" , "ones who get on" , "Resident pupils in school" .)

I've seen this clue in The Globe and Mail.
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