They were built with a welded steel hull and aluminum superstructure. The tumblehome hull and composite deckhouse reduce radar return. Vancouver Port offers discounts for ships with quiet propeller and hull designs. Polish engineering tank based on the PT-91 tank hull. Two fins were fitted on each side of the hull. Hulled barley (or covered barley) is eaten after removing the inedible, fibrous, outer hull. Ribs maintained the shape of the hull sides. A new turret went with the new hull. A double bottom extended for much of the length of the hull. Large submarines generally have an additional hull or hull sections outside. This publication attempted to classify the condition of the ship's hull and equipment. The crew tested how the long, narrow, flexible hull withstood the tough ocean waves. Using iron construction for warships offered advantages for the engineering of the hull. Southwest has had nine accidents, including two aircraft hull losses. An example of a conventional hull mounted sonar is the SQS-56.