An advantage of artificial turf over grass is supposed to be that it’s less affected by rain. But after a light-but-persistent rain on Saturday, following heavy rains on Friday, the new FieldTurf field at Pier 40 was unplayable and closed to use. A boat in front of Pier 40, below, could have come in handy. By Sunday, however, the field was back in commission. Tobi Bergman, a Greenwich Village youth sports advocate, said he believed the field’s drainage problem is getting worse. Before the Pier 40 courtyard field officially opened last May, there had been concerns with snow drainage on the field during the winter, which was said to have delayed the opening. The problem was reportedly fixed at that time.