Is "by" here really necessary in this sentence?
Native speaker’s answer
Rebecca
"By" is necessary in this sentence because it is a part of the formal phrase "pass by". Although sentences don't always end with prepositions, it sounds better to end the sentence with "by" here since "by" is a part of the phrase "pass by". You could say "a long motorboat passed", however, it would sound much more formal and unnatural.