'unberthable' originates from English, specifically formed from the prefix 'un-' + the word 'berth' + the suffix '-able', where 'un-' meant 'not', 'berth' meant 'a place for a ship; a ship's assigned place', and '-able' meant 'capable of'.

'berth' was used in Middle English as 'berthe' meaning a place or allotted space for a ship; the negative prefix 'un-' is from Old English, and the adjectival suffix '-able' comes via Old French/Latin formation meaning 'capable of'. These parts were combined in modern English to form the compound 'unberthable'.

Initially the compound-form simply conveyed 'not capable of being given a berth'; over time its use has remained essentially the same, used to describe vessels or situations where berthing is not possible.