in terms of deadweight tonnage to its weight when empty is one way to measure its efficiency. A small Handymax ship can carry five times its weight. In larger designs, this efficiency is even more pronounced: Capesize vessels can carry more than eight times their weight. Bulk carriers have a cross-section typical of most merchant ships. The upper and lower corners of the hold are used as ballast tanks, as is the double bottom area. The corner tanks are reinforced and serve another purpose besides controlling the ship's trim. Designers choose the angle of the corner tanks to be less than that of the angle of repose of the anticipated cargoes. This greatly reduces side-to-side movement, or "shifting," of cargo which can endanger the ship. The double bottoms are also subject to design constraints. The primary concern is that they be high enough to allow the passage of pipes and cables. These areas must also be roomy enough to allow people safe access to perform surveys and maintenance. On the other hand, concerns of excess weight and wasted volume keep the double bottoms very tight spaces. Bulk carrier hulls are made of steel, usually mild steel. Some manufacturers have preferred high-tensile steel recently in order to reduce the tare weight. However, the use of high-tensile steel for longitudinal and transverse reinforcements can reduce the hull's rigidity and resistance to corrosion. Forged steel is used for some ship parts, such as the propeller shaft support. Transverse partitions are made of corrugated iron, reinforced at the bottom and at connections. The construction of bulk carrier hulls using a concrete-steel sandwich has been investigated. Double hulls have become popular in the past ten years. Designing a vessel with double sides adds primarily to its breadth, since bulk carriers are already required to have double bottoms. One of the advantages of the double hull is to make room to place all the structural elements in the sides, removing them from the holds. This increases the volume of the holds, and simplifies their structure which helps in loading, unloading, and cleaning. Double sides also improve a ship's capacity for ballasting, which is useful when carrying light goods: the ship may have to increase its draft for stability or seakeeping reasons, which is done by adding ballast water. A recent design, called Hy-Con, seeks to combine the strengths of single-hull and double-hull construction. Short for Hybrid