Lakeboat, from an early play by David Mamet — he wrote it in the early 1970s, based on his experiences as a college student doing a summer internship on a steel freighter in the Great Lakes — is brought to the screen awkwardly but ardently by Mamet-actor supreme Joe Mantegna in his feature-directing debut. There are updated references, including one to — yikes! — Steven Seagal. Still, the piece is a theatrical curio, but no less fascinating for that as the shipmates reveal their dreams and delusions to the student (Tony Mamet, the playwright’s brother). Among the sterling cast — including Peter Falk, George Wendt and Denis Leary — Robert Forster (Oscar-nominated for Jackie Brown) stands out in a blazing, award-caliber performance as Joe, whose speech about his youthful goal to be a ballet dancer and the dashed hopes that led to his near-suicide is as pure and potent as anything in the Mamet canon.