The only time the hydrophones were effective on the surface was if the sub was stationary.
I've commented before that Dick O'Kane did this in Tang, remaining stationary on the surface at night. Any manouevering was done on batteries only. He poved they were able to detect a submerged submarine (a US one during training prior to a patrol) before it could reach a firing position. As he put it, they could hear anything before anything could detect them, although sitting still for hours at night took some getting used to!
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