Difference Between Cargo Ships And Hydrofoil
The merchant vessels of today are usually referred to as cargo ships, because of the goods they carry. Cargo ships are generally classified according to the type of cargo carried. Tankers carry oil or other fluids. Dry bulk ships carry coal, iron ore, and other bulk goods not requiring containers. Tugs are smaller ships used for helping larger seagoing ships to dock. Tugs carry no cargo, but they are often used to push barges loaded with cargo. A common combination used on rivers is the tug-barge. The unpowered barge has a notch in the stern for the tug; it can carry up to 20,000 tons. Freighters and general cargo ships carry cargo that is separately packaged in boxes or that comes in large pieces. They use hoists on the ship to load and unload cargo. The cargo is stored in holds, large open areas in the hull of the ship
“Roll-on, roll-off” ships are cargo ships that have their cargo containers placed on flatbed trucks. The cargo is then driven over ramps onto the ship through openings in the side and stern. The driver’s cab detaches and is taken back to the pier. The cargo remains on the flatbed body. These ships can carry vehicles or anything else that can be rolled aboard. They are about 700 feet (213 meters) long.
Some vacationing passengers are carried short distances in hydrofoils and air-cushioned craft. These are modern, fast ships that skim the surface of the water.
A hydrofoil uses a shaped surface similar to that of an airplane wing. It lifts the hull out of the water, enabling the ship to travel at higher speeds. The hydrofoil’s shaped surface is essentially an underwater wing. Its shape causes water to flow over the upper surface at a faster rate than over the lower surface. This creates a lower pressure on the top, which produces a lifting force. Since hydrofoils have less surface area than the hull of the ship, there is less drag on them from the motion of the water. This enables the craft to travel at higher speeds than a conventional ship. The hydrofoil ship’s hull sits fully in the water when at rest.