A hydraulic tanker is an

oil tanker 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 crud ...

designed to use water as an

incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow ( isochoric flow) refers to a flow in which the material density is constant within a fluid parcel—an infinitesimal volume that moves with the flow velocity. An eq ...

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

for loading and unloading

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

cargo Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including trans ...

. 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.

Theory

Hydraulic tanker design bases: * Oil is lighter than water. * Oil and water will not mix in a full tank. * Water is an inexpensively available

hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoe ...

. * Absence of air space prevents formation of explosive gas mixtures.

Advantages

Oil

pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...

s located on an

upper deck The Upper Deck Company, LLC (colloquially as Upper Deck and Upper Deck Authenticated, Ltd. in the UK), founded in 1988, is a private company primarily known for producing trading cards. Its headquarters are in Carlsbad, California, United State ...

avoid dangerous volatile

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

accumulations in pump rooms near the bottom of a ship.

Ship stability 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 center of mass#center of gravity, centers of g ...

is improved by eliminating

free surface In physics, a free surface is the surface of a fluid that is subject to zero parallel shear stress, such as the interface between two homogeneous fluids. An example of two such homogeneous fluids would be a body of water (liquid) and the air in ...

in partially filled tanks. Ship

structural A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such ...

stresses are reduced by eliminating dynamic loading caused by sloshing of fluids in partially filled tanks. Avoiding exposure to

atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

reduces

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

within the tank, and reduces hardening of residual crude oil deposits remaining after unloading.Morrell (1931) p. 306

Disadvantages

The hydraulic system is ineffective with heavy or viscous oils and not recommended for greater than 15-degree Baumé. Heating coils must be placed near the top of tanks, where they are less efficient. An hydraulic tanker requires a larger volume of void space for buoyancy than conventionally loaded tanks, because the empty, or ballasted, condition of tanks filled with water is heavier than the loaded condition of tanks filled with oil. A heavier ballasted condition may also increase round trip fuel consumption. Many petroleum compounds have limited solubility in water. Low solubility is typically of negligible concern with respect to product loss, but toxic petroleum products may be regarded as

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

in the water displaced as a tank is loaded with petroleum. The latter disadvantage may be insignificant where navigable waters contain elevated background levels of petroleum products; and the advantages make hydraulic tankers useful

oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...

recovery ships when their storage tanks may act as

oil–water separator An oil water separator (OWS) is a piece of equipment used to separate oil and water mixtures into their separate components. There are many different types of oil-water separator. Each has different oil separation capability and are used in differ ...

Notes

Sources

* * {{cite book , last=Morrell , first=Robert W. , title =Oil Tankers , publisher =Simmons-Boardman Publishing Company , edition =Second , date =1931 , location =New York + + Ship types