Identify the tense and auxiliary verb: The original sentence "When did you buy the boat?" is in the simple past tense, and the auxiliary verb is 'did'.
Identify the object of the active sentence: The object is 'the boat'. This will become the subject of the passive sentence.
Identify the subject of the active sentence: The subject is 'you'. This will become the object of the passive sentence (often omitted or placed after 'by').
Use the correct form of 'to be' for the passive voice: For simple past, it's 'was' or 'were'. Since 'the boat' is singular, we use 'was'.
Use the past participle of the main verb: The past participle of 'buy' is 'bought'.
Maintain the question word: 'When' remains at the beginning.
