a hydrodynamically streamlined , towable sonar apparatus is described charerized by a housing , including a central frame having a circular planar web portion from which extend a plurality of annular coaxial ribs which cooperate with similar ribs extending inwardly from top and bottom concavo - convex cover members to define annular chambers and to provide compressive load bearing support . transducers are arrayed on the periphery of the frame and enclosed in a curved plastic fairing thereabout . electronics are accommodated in the annular chambers .