He knows what's going to happen next—the steam makes him easy to find—so he whips out of there. A second later, the yacht gets simply forced under the water by a burst from the big gun. Hiro runs for a few seconds, finds a pontoon where he can steady himself, and opens up again with a long burst; when he's finished, the edge of the Enterprise has a jagged semicircular bite taken out of it where the Phalanx gun used to be.