Ferry with two paddles docked (2-2)

I believe the answer is:

ro-ro

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'ferry' is the definition.
(short for roll-on/roll-off)

I can't explain the rest of the clue.

(Other definitions for ro-ro that I've seen before include "Transport for vehicles with drivers" , "Class of ferry/cargo ship" , "Kind of ferry" , "Type of ferry transport for vehicles" .)

I've seen this clue in The Independent.

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