Tonnage is a measure of the cargo-carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine. In modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. Tonnage should not be confused with displacement, which refers to the actual weight of the vessel. Tonnage is commonly used to assess fees on commercial shipping.
The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger metacentric height implies greater initial stability against overturning. The metacentric height also influences the natural period of rolling of a hull, with very large metacentric heights being associated with shorter periods of roll which are uncomfortable for passengers. Hence, a sufficiently, but not excessively, high metacentric height is considered ideal for passenger ships.
A double bottom is a ship hull design and construction method where the bottom of the ship has two complete layers of watertight hull surface: one outer layer forming the normal hull of the ship, and a second inner hull which is somewhat higher in the ship, perhaps a few feet, which forms a redundant barrier to seawater in case the outer hull is damaged and leaks.
A tanker is a ship designed to transport or store liquids or gases in bulk. Major types of tankship include the oil tanker, the chemical tanker, and gas carrier. Tankers also carry commodities such as vegetable oils, molasses and wine. In the United States Navy and Military Sealift Command, a tanker used to refuel other ships is called an oiler but many other navies use the terms tanker and replenishment tanker.
Marine engineering includes the engineering of boats, ships, oil rigs and any other marine vessel or structure, as well as oceanographic engineering or ocean engineering. Specifically, marine engineering is the discipline of applying engineering sciences, including mechanical engineering, electrical engineering, electronic engineering, and computer science, to the development, design, operation and maintenance of watercraft propulsion and on-board systems and oceanographic technology. It includes but is not limited to power and propulsion plants, machinery, piping, automation and control systems for marine vehicles of any kind, such as surface ships and submarines.
A ballast tank is a compartment within a boat, ship or other floating structure that holds water, which is used as ballast to provide stability for a vessel. Using water in a tank provides easier weight adjustment than the stone or iron ballast used in older vessels. It also makes it easy for the crew to reduce a vessel's draft when they enter shallower water, by temporarily pumping out ballast. Airships use ballast tanks for similar advantages.
The free surface effect is a mechanism which can cause a watercraft to become unstable and capsize.
A Kingston valve is a type of valve fitted in the bottom of a ship's plating that connects the sea to the ship's piping and storage tanks.
The Zubr class is a class of air-cushioned landing craft (LCAC). This class of military hovercraft is, as of 2012, the world's largest, with a standard full load displacement of 555 tons. The hovercraft is designed to sealift amphibious assault units from equipped/non-equipped vessels to non-equipped shores, as well as transport and plant naval mines.
Ship stability is an area of naval architecture and ship design that deals with how a ship behaves at sea, both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of gravity, centers of buoyancy, the metacenters of vessels, and on how these interact.
USS Chehalis (AOG-48) was a Patapsco-class gasoline tanker acquired by the United States Navy for the dangerous task of transporting gasoline to warships in the fleet, and to remote Navy stations. The vessel was named in honor of Chehalis, Lewis County, Washington State.
A heavy-lift ship is a vessel designed to move very large loads that cannot be handled by normal ships. They are of two types:
An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. For example, moving crude oil from oil wells in Nigeria to the refineries on the coast of the United States. Product tankers, generally much smaller, are designed to move refined products from refineries to points near consuming markets. For example, moving gasoline from refineries in Europe to consumer markets in Nigeria and other West African nations.
The displacement or displacement tonnage of a ship is its weight based on the amount of water its hull displaces at varying loads. It is measured indirectly using Archimedes' principle by first calculating the volume of water displaced by the ship then converting that value into weight displaced. Traditionally, various measurement rules have been in use, giving various measures in long tons. Today, metric tonnes are more used.
The MACS3 Loading Computer System is a computer controlled loading system for commercial vessels, developed by Navis. Prior to October, 2017 it was offered by Interschalt maritime systems GmbH, before by Seacos Computersysteme & Software GmbH.
Ship measurements consist of a multitude of terms and definitions specifically related to ships and measuring or defining their characteristics.
Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, submarine, or other floating structure that holds water is called a ballast tank. Water should move in and out from the ballast tank to balance the ship. In a vessel that travels on the water, the ballast will remain below the water level, to counteract the effects of weight above the water level. The ballast may be redistributed in the vessel or disposed of altogether to change its effects on the movement of the vessel.
CMA CGM Benjamin Franklin is an Explorer class containership built for CMA CGM. Delivered in November 2015, she is named after United States Founding Father Benjamin Franklin. She is one of the largest container cargo vessels, capable of carrying 18,000 TEU.
An hydraulic tanker is an oil tanker designed to use water as an incompressible fluid for loading and unloading petroleum cargo. Each cargo tank is kept full at all times so oil floating on water will be pressed against the top of the tank. A cargo tank initially filled with water is loaded with the desired quantity of oil by pumping oil into the top of the tank displacing water which overflows through an opening at the bottom of the tank. The cargo tank is unloaded by removing oil from the top of the tank as water is admitted at the bottom.
