We were heading E towards Cuttyhunk and were closing on a tug/barge heading into Buzzards Bay, watching the relative bearing. It seemed we could safely cross ahead. Raised the skipper of the tug by radio, who was watching us and agreed with my cross ahead assessment. After a short moment I asked myself 'why?', altered course and went behind. Might have affected our arrival time in Cuttyhunk by 30 sec max. Why fool around???