Such barges need to be towed by tugboats or pushed by towboats. Barges are usually unpowered and must be moved by tugboats or towboats. Navigation locks allow towboats, barges, and other vessels to transit the dams. Towboats moved the dredge and sand barges around as needed. Towboats push barges lashed together to form a "tow". Smith also built a substantial number of steam vessels, including steamboats, towboats and tugs. Post-war, the shipyards built customized crafts, but specialized in barges and towboats. Private capital followed these improvements with heavy investments in towboats and barges. River tugs are also referred to as towboats or pushboats. Other new vessels included the freighter/towboats "F.B. Jones", and "M.F. Henderson". Ellet converted several powerful river towboats, heavily reinforcing their hulls for ramming. These towboats travel between ports and are also called line-haul boats. In the United States, the industries that use these vessels refer to them as towboats. Five "Ellet"-class rams were converted from civilian towboats at Pittsburgh. Most towboats have a very small hull and a flat bottom to minimize wake.