A new single anchor leg mooring (SALM) system has been developed through an extensive research program. The SALM differs considerably from conventional single point moorings. The mooring buoy is anchored to a base on the sea floor through a single anchor leg consisting of a pipe pivoted on a universal joint and a short anchor chain with chain swivel. Cargo passes from the base through the pipe to a submerged swivel housing at the top of the pipe. Loading hose connected to the housing rises to the surface some distance from the buoy and floats to the side of the moored tanker.
The first SALM was installed at Brega by Esso Standard Libya in 1909. A second SALM was installed at Okinawa in 1971. Experience with these facilities has demonstrated the SALM to be a very successful design. Studies have shown the SALM offers considerable investment savings compared to conventional single point moorings in water depths greater than about 100 ft. Safety and reliability are other principal advantages.
The advent of very large oil tankers in the mid 1960's resulted in a need for new concepts in tanker terminals. Standard Oil of New Jersey affiliates, including Esso Standard Libya, were faced with requirements for expanding their facilities to accommodate tankers of 200,000 dwt and larger. In 1966 Esso Research and Engineering (ERE) began a research program to develop new single point moorings (SPM). At about the same time, Esso Standard Libya requested that ERE investigate the feasibility of a new mooring concept, the single anchor leg mooring (SALM), for installation at their port at Brega, Libya.
The concept of a single point mooring is to moor the tanker by its bow to one mooring point so that it may swing freely around this point, thus minimizing forces due to wind, waves, and current. Means must be provided to transfer oil through the mooring point to or from the moored tanker. A common feature of SPM's for tankers is the co-axial arrangement of the mooring system and the oil transfer system.
The first SPM design, developed in the late 1950's and early 1960's, consists of a large flat buoy anchored by four or more chains extending in catenaries to anchor points on the sea floor some distance from the buoy. The tanker is moored to a turntable on the deck of the buoy. Floating loading hose connects through piping on this turntable to a fluid swivel in the center of the buoy. Underbouy hoses connect this swivel on the buoy with a manifold at the end of the submarine pipeline. This type will be referred to as the catenary anchored SPM in this paper. Approximately 100 moorings of this type have been installed during the last decade.
A second type of SPM now in service consists of a fixed mooring tower with a mooring turntable on its deck. One of only two examples of this tower type SPM was installed by Esso Standard Libya at Brega in 1963.
