[Posted on November 17, 2015 by Bill Stewart]
A single point mooring (SPM) is a buoy or floating platform that resides offshore for the purpose of keeping tankers and other large vessels on station at all depths, for the offloading and handling of petroleum products when a storage facility is not available. An SPM serves as a link between onshore storage facilities and the tanker. The SPM is permanently attached to the sea bottom in such a way that it can move freely within certain parameters. They are designed with wind, rough seas, deep water, currents, and weather conditions in mind. Consulting firms such as Stewart Technology Associates provide mooring analysis services for the design of powerful moorings.
Advances in mooring technology and analysis have led to the unprecedented development of materials, designs, and construction that is used in the manufacture and implementation of mid-ocean floating platform stations for connecting oil tankers to pipelines. The environment is taken into account during design and analysis so that the materials themselves will pose no threat to marine life and so that failure, if it occurs in any part of the structure, will be contained. This includes anchor, mooring line, and connector materials and construction. The material used depends on the type of mooring and may be wire, chain, or fabricated fiber rope.
An SPM works in such a way as to facilitate the on-loading or off-loading of oil products via seafaring ships. They are primarily large buoys with decks where a ship can moor. Anchored to the floor of the ocean and attached to a pipeline and manifold at the center of the float, they are designed to be used in all weather conditions.
There are hundreds of SPMs operating across the globe. There are numerous benefits of using SPMs to safely and economically convey petroleum products to tankers in mid-ocean.
Negates the Need for A Ship to Make Port
There are oil discoveries in remote locations where pipelines are not financially or technologically practical. Ocean depth or the distance to the nearest onshore facility often requires alternative ways to deliver crude oil. Since a tanker can offload or take on cargo mid-ocean using an SPM, there is no need for the vessel to sail to a port. This is a tremendous savings in time and fuel costs.
Large Amounts of Cargo Can Be Handled
By nature of the SPM design, the buoy can be approached by a vessel and docked and connected in calm seas or even severe weather. It has fenders to protect its structural integrity from the movement of the ship. Connections are made via floating hoses from the submerged pipeline to the tanker, and a series of valves are controlled by an electrical substation. A swivel in the buoy enables the transfer of fluid between the geostatic section and rotating part of the float in most types of climate conditions. The amount of crude oil that is transferred depends on the size of the vessel. Since even a massive tanker is able to dock to the buoy, vast quantities of crude can be on-loaded for transport.
Extra Large Vessels
An SPM can accommodate huge ships. The design allows ships to “weathervane” around the single mooring point. If the sea is large, or there is wind, the SPM can absorb energy through stretchable ropes and anchor chains.
Very large carriers require a high draft to maneuver, which makes it difficult for them to navigate close to shore. SPMs can be constructed and set up in deep water, thereby eliminating the need for jetty construction and storage facilities. This allows deep water vessels to approach, take on cargo, and sail away much faster than having to navigate a deep-water port.
Due to the nature of the design, an SPM allows fluid transfer in most weather and sea conditions that are not considered severe or gale force. However, in adverse climatic conditions, a vessel can make its approach, connect to the buoy and initiate the fluid transfer. This allows tremendous flexibility in scheduling the transport.
An SPM is considered an instant port and can be installed in deep water. This presents tremendous cost savings, since there is no need for jetty construction or port dredging to accommodate deep water vessels. This also offers a faster turnaround for tankers to approach, moor and take on crude. They can arrive, load or unload relatively quickly, and move on. Even in high winds and big seas, an SPM can accommodate a large number of ships in this fashion. All of these factors combine to create an economical and safe way to transport crude oil.
A single point mooring system design must be compliant with and adhere to certain standards and requirements within the offshore industry and the American Bureau of Shipping. The buoys and hoses and accompanying materials have to be durable enough to withstand combined wave, current, and wind forces generated by the severest of storms. This is essential for the protection of the environment. The tanker connects to the buoy via floating hoses. These hoses are fitted with breakaway couplings that have a predetermined break load. Should they break for any reason, an internal valve is activated to close automatically and prevent an oil spill.
Hydrodynamic analysis and dealing with the motion of fluids has evolved from using scale models in water tanks to advanced computer modeling. SPM technology and the progress that has been made in this area has made the disbursement of crude oil around the world safer, cleaner, environmentally sound, and much more economical.
As long as crude oil is the primary source of fuel and energy, we will need to make sure it gets from point A to point B as quickly and as safely as possible. Research, analysis, and planning are ongoing, with great strides being made in safety and efficiency. SPM stations are a vital part of that strategy and have changed the face of crude oil delivery.