The TCMS can be adjusted to work in a wide variety of scenarios, including shallow water. The tanker is operated and managed by Seatramp, a member of the Hellespont Group, as is Victoria Oilfield Development. The MV Hellespont Prosperity has been on station since mid-May, achieving 100% uptime. A 600,000 bbl capacity tanker, the MV Hellespont Prosperity, which has been used to carry out an EWT and EPS has been loading via a TCMS. The facility is being used currently on Texaco's Mariner Field in the North Sea.
ORCAFLEX RISER TORSION FULL
For longer term loadings, modeling and full scale tests have shown how simple and safe it is for the tankers to turn themselves around the chafe chain. For an export system where loading may typically last only 24-36 hours, this is unlikely to be exceeded. Typically, the maximum allowable rotation for a tanker on the TCMS is three turns in either direction, or a total of six turns. This eliminates the need for a swivel and thus reduces maintenance requirements and increases reliability.
The weathervaning of the tanker is made possible by the natural tendency of bonded hose to helix - or corkscrew - as twist is applied to it. The hose's low elasticity at operational loadings also reduces the reliance on the catenary profile in accommodating large node offsets. It also features additional benefits in thermal conductivity and ease of deployment. The latter has been chosen as a bonded construction which offers advantages which lie in its ability to accept torsion and is particularly user-friendly. There is now a generic layout of the chafe chain length, mooring leg top buoyancies and pretension, and the optimum type of hose to use has been identified. The load limit of the chafe chain was not transgressed. Despite harsh weather conditions), no disconnection was necessary. In two l996 system applications, uptime on the Pierce and Hermod Fields was l00%.
ORCAFLEX RISER TORSION SOFTWARE
The software package, Orcaflex, played a role in designing the TCMS, allowing the required complex modeling to be carried out and removing some of the "black art" associated with mooring design.įor example, the software package made it possible to quantify the dynamic loads which result from having one chain heaving on three mooring lines simultaneously, and to fully analyze the system in its disconnected state. The design of any individual mooring or riser system has a set of criteria and load cases to be examined and con formed to, with the integration of a mooring and riser system expanding the complexities of the design. The current system layout is the result of the develop ment work that was under taken in l995, which in volved a two day exercise in deploying and weather vaning such a system. The challenge was to modify the tripod to use traditional mooring com po nents in order to achieve l00% weather vaning capability without contact between the moor ing legs and the vessel keel, in an effort to create a safe loading path for oil. The concept is similar to the pipeline support system deployed on the Foinaven EWT in 5l0 meters of water, which incorporated a tripod arrangement l00 meters below the sea surface which served as the riser base for the tanker. The aim was to develop a mooring and loading system that could take advantage of conventional tankers - the single fixed pitch propeller tanker - rather than expensive dynamically positioned (DP) tankers that are often difficult to obtain due to restricted availability. One way to achieve this was by looking at the tanker issues normally attached to these projects.
The development of the tripod catenary mooring and loading system, also known as TCMS, arose out of Victoria Oilfield Development's desire to enhance the early production system (EPS) and the ability to perform extended well tests (EWT).
High uptime despite lack of swivel, dynamic positioning Illustration of tripod catenary loading system.
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