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A RADICALLY NEW CONCEPT FOR LOADING ORDISCHARGING LIQUEFIED GAS SHIPS

UN CONCEPT RADICALEMENT NOUVEAU POUR CHARGER ETDECHARGER DES NAVIRES TRANSPORTANT

DES GAZ LIQUEFIES

Bertrand LanquetinTechnical Manager, LNG Shipping

TOTALFINAELF2, Place de la Coupole

La Défense 6 – 92078 Paris La Défense Cedex - France

ABSTRACT

This paper presents successively:

- The state of the art of loading/unloading systems for liquefied gas ships: conventionaljetties, SPMs and unconventional schemes developed by TOTALFINAELF in years1999-2000, associated with GAZ DE FRANCE, EURODIM and ITP INTERPIPE.These unconventional schemes are based on following criteria: serving non dedicatedships, reducing significantly the overall cost, allowing the system to be at somedistance from the coast, allowing the use of flexible hoses for products transfer.

- Then, and in line with the above criteria, the paper presents a radically new concept ofloading/unloading system based on a rotating quay for which a patent is pending.

This system, as well as other loading/unloading systems, are now studied in detail byTOTALFINAELF in association with GAZ DE FRANCE and EURODIM, with theobjective to have in hand by end of 2001 different systems available for differentenvironmental conditions and depths, with all the components fully tested.

RESUME

Ce papier présente successivement:

- L’état de l’art des systèmes de chargement/déchargement pour des navirestransportant des gaz liquéfiés: appontements, SPMs et les schémas nonconventionnels développés par TOTALFINAELF dans les années 1999 – 2000 enassociation avec GAZ DE France, EURODIM et ITP INTERPIPE. Ces schémas nonconventionnels sont basés sur les critères suivants: servir des navires non dédiés,réduction significative des coûts, terminaux pouvant être déportés à quelque distancede la côte, terminaux pouvant accomoder des flexibles de transfert de produits.

- Ensuite, et en accord avec les critères ci-dessus, le papier présente un conceptradicalement nouveau de chargement/déchargement basé sur un quai tournant pourlequel un brevet a été déposé.

Ce système, ainsi que d’autres systèmes de chargement/déchargement, sontactuellement à l’étude par TOTALFINAELF en association avec GAZ DE France etEURODIM, avec l’objectif d’avoir en mains à fin 2001 différents systèmes disponiblespour différentes conditions d’environnement et de profondeur et dont l’ensemble descomposants aura été entièrement testé.

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A RADICALLY NEW CONCEPT FOR LOADING ORDISCHARGING LIQUEFIED GAS SHIPS

PART 1: STATE OF THE ART

Conventional design of loading / unloading jetties:

All the loading/unloading jetties for liquefied gases today (mainly LNG – LiquefiedNatural Gas and LPG – Liquefied Petroleum Gas) use very similar designs including:- A trestle between the jetty and the shore, which supports the liquid and vapour lines and very

often an access/egress road.- A loading (or unloading) platform often with two or three levels, which supports the loading

(unloading) arms and the fire protection.- Two to four breasting dolphins for berthing the ships.- Six to eight mooring dolphins for mooring the ships.

These jetties necessitate a very large number of piles and a lot of civil work, the costof which becomes rapidly prohibitive when the distance to the coast increases.

The above design presents several drawbacks such as:- Proximity of the coast is necessary- The site has to be sheltered- The breasting dolphins have to be dimensioned so that one dolphin only has to absorb

all the berthing energy of the ship, which generates a reaction force on the dolphin of250 to 350 tons for 135,000 m3 ships

- The mooring dolphins have to be dimensioned to withstand the efforts of wind, wavesand current on the moored ship. For indicative purpose the lateral force generated bya lateral wind of 30 m/s (60 knots) is in the range of 500 tons for a 135,000-m3 ship.Accordingly such forces require typically 16 to 18 mooring lines (4 spring lines andtwo groups of 3 to 4 breast lines fore and aft)

- A limited depth- Four tugs of approximately 4,000 HP (sometimes three but more powerful) are

required for turning, berthing and unberthing manoeuvres of 135,000 m3 ships.These constraints make difficult the research of an appropriate site for the loading

(unloading) jetty. Very often it is necessary to provide an access channel withnavigational aids and a turning circle in front of the jetty, which may have to be dredged.In some instances a breakwater has to be provided as well in order to provide a calmstretch of water in front of the berth. Further information related to siting problems ofconventional liquefied gas jetties is given in References [1] and [2].

- An artist view of a loading jetty is given on Figure 1.

SPM (Single Point Mooring):

To palliate the above drawbacks, the liquefied gas industry (gas companies, systemsvendors) considers and invests in studies of loading (unloading) facilities based on SPMsassociated to submarine cryogenic lines (or alternately tunnel) for the liquid and thevapour transfer between the SPM fixed part and the coast. This technique is widely usedby the oil industry and the number of SPMs installed worldwide reaches several

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hundreds, all types included. This technique allows – and this is its main advantage – theship moored by the bow to weathervane and to reach an equilibrium position in thedirection of the smaller environmental efforts. In turn this excludes the conventionaltrestle, at least in the vicinity of the SPM (say a manoeuvring radius of 1,852 m - onenautical mile). The SPM allows therefore working in more difficult weather conditionscompared to the classical jetty described above and allows deeper waters as well.Accordingly the SPM can be installed at some distance to the coast (limitation given bythe pressure drop) minimising the disturbance to the local environment, particularly incongested areas, and solving the navigational constraints (channel, turning circle andtraffic).

Figure 1: Artist view of Bontang 3rd LNG/LPG dock (operational 1999)(Source, see Reference [3])

TOTAL, now TOTALFINAELF, has been associated in the past (more than twentyyears ago) in the CHAGAL program (CHAGAL for chargement de gaz liquefies). Theproject was based on the development of a cryogenic SPM for loading GPL, whichrequired sub-sea flow-lines and PLEM (Pipeline End Manifold), flexible hoses and acryogenic swivel to be designed and tested. 8” cryogenic hose was designed and tested byCOFLEXIP while a 16” cryogenic swivel was designed and tested with butane. Thepatent of the swivel initially with EMH of France (Entreprise d’Equipements Mecaniqueset Hydrauliques), was taken over by SBM (Single Buoy Moorings Inc.) and the swivelwas further tested for LNG application.

The SPM design, although very attractive, presents also some drawbacks for handlingliquefied gases:- Because a floating cryogenic hose (length 200 to 300 m typically) cannot be

envisaged, the ships must be dedicated with a forward manifold for the connection ofthe transfer system. It has to be mentioned that some designs incorporate floating orsubmarine pontoons (or barges) between the SPM and the ship manifold in order to

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avoid having dedicated ships. However these devices are complicated: articulationswith jumper hoses, ballasts, etc. None of them have been installed.

- The ships will have most probably to be equipped with a propulsion assistance formooring to the SPM and keeping the station once moored to the SPM. This is to avoida possible collision to the SPM during berthing or in case of the reverse of current.This assistance will be done in the form of semi-dynamic positioning (one or morebow thrusters) and/or at least one tug.

- Finally, and this is probably the main difficulty, the transfer system of the liquefiedgas between the SPM and the ship is not yet operational. Several designs are studiedand proposed: the BTT from FMC (Boom To Tanker), the cryogenic hose, the LNGoffloading arm from SBM, the articulated transfer arms with jumper from Kvaerner,the systems based on boom and cryogenic hoses from EXXON-MOBIL and fromSTATOIL-NAVION, etc. There is no doubt that such systems will be installed in thenear future, starting most probably on transfer systems from FPSOs, FSRUs, orbarges, if not immediately on SPMs. It must be noted that these systems will have arather big size taking into account the movements of the ship moored by the bow andthe loading (unloading) rates required (10,000 m3/h for LNG ships). The question ofcoupling/uncoupling the device to the ship manifold in routine and emergencyoperations and of the ship/shore links such as ESD link (Emergency Shutdown) needsalso further studies so that the systems gain the same level of reliability as classicaljetties.

The fact to have dedicated ships will remain a major constraint for loading(unloading) systems based on SPM techniques because it will exclude spot or mediumterm sales contract for LNG (those contracts are developing quickly since a few years)and further it will eliminate all other liquefied gases requiring non dedicated ships (likeLPG ships, which are multi-ports users). An example of a LNG carrier moored at an off-loading terminal of SPM type is given on Figure 2.

Figure 2: Illustration of a typical LNG carrier as it is moored at an off-loading terminal(Source: patent WO99/47869 23 September 1999 “regasification of LNG aboard a transportvessel”, MOBIL OIL CORPORATION)

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Unconventional schemes developed by TOTALFINAELF associated with GAZ DEFRANCE, EURODIM and ITP INTERPIPE:

In years 1999-2000 a loading (unloading) facility using cryogenic sea-lines andcryogenic hoses has been developed by an association of French companies, namelyTOTALFINAELF, GAZ DE FRANCE, EURODIM and ITP INTERPIPE. The governinglines for this project were:- To be able to have the facility at some distance from the coast, i.e. with no more

navigational and siting problem (major criteria).- To be able to load (unload) non-dedicated ships (major criteria).- To obtain significant cost reduction, particularly beyond some distance from the

coast (say beyond 2,000 m) by replacing a costly trestle by submarine lines (majorcriteria) and by using cryogenic hoses for the product transfer as an alternative tohard arms.

- To take advantage of the transfer cryogenic hoses flexibility (ability to accept abigger envelop of ship flange connection) to derive a more compliant system for theloading/unloading jetty. An illustration of this unconventional scheme is given inFigure 3 and the system is fully described in Reference [4]. The architecture itselfand the connection system placed onboard the LNG ship have been developed byEURODIM.

Figure 3: Artist view of an unconventional scheme for loading/unloading LNG ships(Developed by TOTALFINAELF, GAZ DE FRANCE, EURODIM AND ITP INTERPIPEin 1999-2000)

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We give hereunder a short description of the major components of this unconventionalscheme.

Ø Patented novel cryogenic sub-marine cryogenic pipe developed by ITP INTERPIPE:Main features area follows:

- A double wall technology currently used on sub-sea HP/HT projects (the doublewall type technology has been first developed for TOTAL by ITP INTERPIPE onDunbar in 1992, then used as well on Shell Etap and Elf Tchibeli projects).

- An internal pipe in INVAR (nickel alloy with 36% Ni) with no loops or expansionjoints (this material has an extremely low dilatation coefficient, which combineswith its mechanical strength, a high tenacity and good welding characteristics).

- The best insulating material IZOFLEX thus reducing the size of external pipe (theIZOFLEX material has been developed and patented by ITP INTERPIPE. Thethermal performances of this material were recently confirmed by full-scalethermal tests carried out in Houston by a JIP led by TEXACO associated with BPAMOCO, EXXON MOBIL and TOTALFINAELF. Since, mechanical testing ofthis material in cryogenic environment has been carried out during the designphase of this project and has confirmed the suitability of the material for LNGtransport operations).

- The annular is continuous annular.- The external pipe is made of regular carbon steel to handle massive external

aggression for additional protection and pipe stability.

A representative spool of internal diameter 800 mm and length 8 m will be tested withLNG in April 2001 in GAZ DE FRANCE cryogenic test premises in Nantes (France).

Figure 4 gives the composition of the double wall cryogenic sub-sea pipe.

Figure 4: Composition of the double wall cryogenic sub-sea pipe(developed by ITP INTERPIPE in 1999-2000, to be tested with LNG in spring 2001)

Ø cryogenic transfer hoses:- An 8” cryogenic flexible was designed and tested in the past by COFLEXIP.

More recently COFLEXIP STENA OFFSHORE has promoted a JIP for thedevelopment of a 16” cryogenic hose to be used for offshore LNG transfer. Thishose has been tested in cryogenic condition in autumn 2000 and the Figure 5 givesa photo of the hose during the test in Le Trait (France). It is expected that thetechnique can be extended to 24” while keeping the similar design of hosecomposition.

Insulation materialIZOFLEXTM

100 mm

Outer PipeCARBON STEEL

48” / 20.6 mm

Inner pipeINVAR

36” / 6mm

Concretecoating

sealing barrier

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- The length of the hose required in the design described on Figure 3 is around 45m, which is well within the capabilities of the COFLEXIP manufacturing plant(16” cryogenic hoses up to 100 m in length can be manufactured).

Ø Hoses connecting/disconnecting system:A multi-function cryogenic connection system has been studied with the followingfunctions:

- Normal connection (flexible hot).- Filtering of stresses induced by the physical motions and the loads induced by the

flexible line at cryogenic temperature in order to cope with the limited stresspermissible at the ship manifold flanges.

- Normal disconnection (flexible cold).- Emergency closure of the valves.- Emergency disconnection of the flexible assembly from the ship manifold.

A patent application by EURODIM has been launched.

A prototype of a full-scale module 16” will be built and fully tested in 2001.

Figure 5: Cryogenic test of a 16” cryogenic hose by COFLEXIP STENA OFFSHORE(autumn 2000)

As a conclusion of our joint studies by TOTALFINAELF, GAZ DE FRANCE,EURODIM and ITP INTERPIPE:

All the components of a coastal loading/unloading system for LNG – and moregenerally liquefied gases - have been already tested in year 2000 or will be tested in year2001 with the aim of:- Serving non dedicated ships.

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- Reducing significantly the overall cost compared to conventional jetty design.- Eliminating in the same time the navigational, traffic and neighbouring constraints by

allowing the system to be at some distance from the coast.

A limited number of other vendors/manufacturers have also (or are in the process todo it) developed and tested cryogenic sub-sea pipes, cryogenic hoses and cryogenicswivels.

In our opinion the remaining key component - in order to make the system even moreattractive - is now:

“How to achieve a general architecture of a loading (unloading) system, which willimprove the operating thresholds of the conventional systems (unberthing necessary

when significant wave height reaches 2.0 to 2.2 m and wind 20 m/s)”.

This research is now the heart of the present studies carried out by a group of Frenchcompanies in 2000 to mid-2001, namely TOTALFINAELF, GAZ DE FRANCE andEURODIM. Several systems are tested against mooring calculations using powerfuldynamic computer models. At the same time the connecting/disconnecting procedureswill be further studied in 2001 and tested on a full-scale prototype in order to insure thesame functions and the same level of reliability as on a conventional jetty.

The common objective of this group of companies is to have by end of year 2001 one orseveral loading (unloading) systems available, applicable to different environment anddepth conditions, fully studied with regard to ship behaviour and operating thresholds, andwith the technology related to all the components of the systems in hand (all thesecomponents being fully tested in the research programme 2000-2001).

It is time to describe now in the present paper one of these systems, for which a patentby TOTALFINAELF is pending. Studies like dynamic calculations are presently inprogress, that is the reason why detailed calculation results cannot be presented in thispaper. Only preliminary estimations will be therefore provided with more details given atthe time of the presentation of the paper in May 2001 in Seoul.

PART 2: A RADICALLY NEW CONCEPT FOR LOADING ORDISCHARGING LIQUEFIED GAS SHIPS

General description of the system:

We have imagined and developed a system, which combines the advantages of:- A conventional jetty: safety, reliability, components using a proven technology, non

dedicated ships.- And a SPM: remoteness from the coast, cheaper cost, higher operating thresholds.

Without having the disadvantages of these systems:- For the conventional jetty: siting and navigational constraints, high cost, low

operating thresholds- For the SPM: reliability (predictability) of the transfer system between SPM and

ship, requirement for having dedicated ships.

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In the system we propose, the jetty is replaced by a revolving quay, which is mountedaround a vertical axis on a fixed supporting structure. The fixed structure is connected tothe shore by sub-sea cryogenic lines. The system allows a tug to position the quay parallelto the ship approaching direction, then to maintain the ship in the direction of lessenvironment efforts. In case of emergency, quick departure can be achieved with a veryhigh level of safety and reliability. An illustration of the system is given on Figures 6 and7 (gangway if required and fire fighting equipment, hydraulic unit, nitrogen cylinders andmiscellaneous equipment are not represented).

Figure 6: Artist view of the rotating quay for loading/unloading LNG ships

Figure 7: Artist view of the rotating quay for loading/unloading LNG ships(developed by TOTALFINAELF in year 2000, patent pending)

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This concept is in line with the objectives given above for unconventional schemes, i.e.:- Serving non dedicated ships.- Applicable for both loading and discharging terminals.- Able to handle any type of liquefied gas.- Flexibility with regard to depth.- More compliant than a conventional berth with regard to weather operating thresholds- Reducing significantly the overall cost compared to conventional jetty design.- Eliminating in the same time the navigational, traffic and neighbouring constraints by

allowing the system to be at some distance from the coast.

In addition it present several remarkable advantages:- All components are standard and the same as the ones used on conventional jetties:

mooring hooks, fenders, arms, gangway, etc.- The system uses the same rules, standards and guidelines for design as the ones used

for conventional jetties (OCIMF guidelines for mooring, PIANC or BSRA standardsfor fender selection, OCIMF specification for loading arms, all SIGTTO guidelines,etc.).

- The rotating quay can support either hard arms or flexible hoses for the producttransfer; the shape of the rotating quay can be adapted accordingly as shown later inthe paper.

- The supporting structure and the rotating quay have similar lattice structures (jacketand lattice beam) allowing a yard to build both structures at the same time.Transportation to the site can be made on two barges and installation isstraightforward (installation and piling of the jacket similar to offshore techniques,followed by installation of the beam by lifting or alternately by barge ballastingsimilar to topsides installation in offshore). Although this has not been estimated indetail, there is an important reduction of the construction and installation timecompared to a conventional jetty, which requires a lot of civil work and piling. It mustbe noted that the supporting structure can have also as well the form of a towerstructure.

The various components of the system are now described hereunder.

Ø Rotating quay:- The lattice beam has a length of 75-80 m, i.e. 25 to 30 % of the length overall of

the biggest LNG ship (LOA # 300 m). The width is either in the range of 30 m incase hard arms are used for product transfer or 35-40 m in case flexible hoses areused (in order to have sufficient span for a better catenary effect). The height ofthe beam is in the range of 4-5 m, sufficient for the beam to offer enoughhorizontal rigidity.

- The lattice structure contributes to the rigidity of the structure, to a weightreduction while offering little resistance to the extreme waves and to the wind.

- The elevation of the top of the beam is sufficient in order to keep the equipmenton deck out of the water as it is done on a conventional jetty design.

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Ø Supporting structure:- The structure is designed to absorb the horizontal force generated either by the

berthing of the ship (reaction force versus berthing energy) or by the forcesgenerated by the moored ship under the effect of the wind, waves and current.Due to the possibility of 360° orientation of the rotating quay, the structure hasisotropic properties and is preferably hexagonal (or alternately can be of towertype).

- The structure is piled to the seabed in order to achieve a good stability.

Ø Mechanical part allowing a 360° rotation of the quay around the vertical axis of thesupporting structure:- The rotating quay is mounted in the base case in its centre of gravity on the

supporting structure (alternately an offset can be given on the quay in order tohelp the ship to weathervane but in such case the pulling requirement of the tugwill be higher, which is not recommended)

- The mechanical part allowing such free rotation is available on the market in therange of efforts considered: it can be a system of either roller bearings, or self-lubricating bushings or boogies or any other mechanical device allowing freerotation of the beam.

We will give now a description on how the three main functions of the loading(unloading) system are achieved. These three functions are:- The ship berthing and unberthing (cast off) including unberthing in emergency situation.- The mooring of the ship.- The transfer of liquefied gases and of the vapour (if required).

Ø The ship berthing and unberthing (cast off) including unberthing in emergencysituation:- On a conventional jetty it is necessary to turn the ship with usually four tugs each

having a power in the range 3,800 to 4,500 BHP prior berthing. This manoeuvrerequires a turning circle of about 700 m for big ships, free from every obstacle andwith a depth of 14 to 15 m. In several places this require dredging and installationof navigational aids. Once the ship is parallel to the berthing line, the tugs arepushing the ship along side the fenders with a berthing speed not exceedingtypically 15 to 20 cm/s. The tugs loss quickly their efficiency when the sea statedeteriorates. The berthing thresholds are limited to waves significant height of 1.2to 1.5 m and to winds 12 to 15 m/s.

- The recommendations for conventional jetties requires that one single breastingdolphin absorbs all the berthing energy while two to four breasting dolphins areusually provided. This is due to the difficulty to achieve a berthing with the shipexactly parallel to the berthing line. The dimensioning case for breasting dolphinsis in most cases the reaction force resulting from the ship berthing and not thedolphin solicitations from the ship all fast alongside under the wind, waves andcurrent. As a result the breasting dolphins are very strong and expensivestructures.

- The rotating quay has a system of fendering similar in principle. Four fenders(possibly two might be enough) are mounted on the berthing side of the beam inorder to protect the beam during berthing and absorb the berthing energy, then to

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support the ship when moored alongside. However the rotating quay presentsseveral advantages compared to a conventional jetty:a) A tug will position the beam parallel to the direction of ship approach. The

ship not having to be turned, the manoeuvre is simplified and it is expectedthat a ship can be able to berth with higher berthing thresholds and with onlytwo tugs for assistance.

b) During the berthing manoeuvre, as soon as the shipside is in contact with afender, the beam will naturally turn under the efforts of the ship and rapidly allthe fenders will be in contact with the shipside. In turn it means that the fourfenders, and not a single fender as for a conventional jetty, will absorb theenergy. This will allow using smaller and cheaper fenders. The reaction forceon the supporting structure of the rotating quay will be in the same order ofmagnitude as the one on a single breasting dolphin on a conventional jetty,resulting in a similar sizing. The cost saving becomes an evidence in theconcept of rotating quay: there is only one fixed structure between the surfaceand the sea bed compared to two to four structures similar in strength forbreasting dolphins and six or more mooring dolphins plus the catwalks.

- Once the ship is at berth the system is not stable under the forces generated by theelements; a tug has therefore to be tied up to the bow of the ship in order tocontrol in permanence the orientation of the beam in the direction of less efforts.The ship unberthing manoeuvre in these conditions either in normal circumstancesor in emergency is straight forward because:a) The ship is already heading in the right direction.b) The tug is in attendance.

This is illustrated in Figure 13.

As a result the only thing the ship has to do is to start the engine and the tug willhelp the ship to keep away from the berth. The manoeuvre is safe and there is norisk that the ships cannot be unberthed as on a conventional jetty under adverseweather conditions.

- To complete the description of the berthing/unberthing function, it can be said thatmanoeuvring time will be saved as well.

Ø The mooring pattern of the ship:- On a conventional jetty big LNG ships are moored by generally by 14 to 18 wire

mooring lines in order to provide a sufficient restraining force. The mooring linesare divided in several groups of lines in order to restrain the ship movement underlongitudinal force component: spring lines, and under lateral force component andthe moment: several groups of breastlines. Each group of spring lines has twolines and each group of breastlines has two to four lines.

- The mooring of big ships on a conventional jetty requires therefore in average sixmooring dolphins, each being designed to support an effort of three (in case ofthree-hook assembly) to four times (in case of four-hook assembly) the SWL ofthe mooring lines, this represents an effort of 300 to 500 tons depending on thejetty design.

- In the concept of the rotating quay only eight mooring lines are necessary: twogroups of two spring lines connected to hooks on the side of the beam close to theship and two groups of two other mooring lines connected to hooks on the

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opposite side of the beam. This simple arrangement results from the fact that a tugis used to keep permanently the ship heading in the direction of the less effortsfrom the environment. Some allowance around this direction is acceptable and thepreliminary calculations have shown that the heading should remain within a +/-20° sector (moderate to severe weather conditions) or within a +/- 30° sector (mildweather conditions) around the ideal position to be on the safe side. Outside thesesectors the transversal component of the efforts are beyond the capability of themooring pattern.

- Here again the cost saving is evident compared to a conventional jetty: nomooring dolphins, only four sets of two-hook assemblies are required.

- Quick release hooks (QRH) are used like on conventional jetties. In case that thetug has a failure, the second tug (two tugs are required for berthing the ship),which is on stand-by during loading (unloading) operation of the ship, willprovide the necessary assistance. In the improbable case where the two tugs havea failure or that the ship cannot stay in the required sector for the direction, thenthe ship will have to be disconnected in emergency using the ERS (EmergencyRelease System) for the hard arms (or flexible hoses) followed by the quickrelease of hooks. There is therefore a way to protect the facility even in case of acatastrophic scenario as described above.

- Finally it has to be mentioned that it is not necessary to apply a big pre-tension inorder to maintain the ship “stuck” to the fenders. At the contrary the system has tobe compliant in order to absorb as much as possible the high frequencymovements of the ship in the waves. As a consequence the preliminarycalculations have shown that it is possible to stay moored alongside without anyproblem in 3.0 to 3.5 m significant wave height depending on tug efficiency(compared to 2.0 to 2.2 m for a conventional jetty). At the time this paper iswritten, more sophisticated calculations are in progress in order to assess thelimits of the system.

- Preliminary mooring calculations are given at the end of the paper.- A view of the mooring arrangement is shown on Figure 8.

Figure 8: Artist view showing the mooring pattern and the tug pulling

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The transfer of liquefied gases and of the vapour (if required):- The transfer of the products between the plant storage and the ship (or between the ship

and the plant storage) is illustrated in Figure 9 and include:

Figure 9: Side view showing the overall transfer system

a) The sub-sea lines, which have been described already above in the descriptionof unconventional schemes.

b) The vertical risers in the fixed supporting structure (similar pipes as the sub-sea lines are used).

c) The cryogenic swivel already described above as well. To achieve 10,000 m3a 24” swivel is required for which the technology can be derived from alreadytested and working 16” swivels. Should it be decided to install a vapour returnsystem then an elegant solution could consist in having a two-path concentricswivel with the liquid circulating in the central passage and the vapourcirculating in the annular space and acting therefore also as a leak recovery,should the liquid swivel presents some defect (similar swivels are proposed bySBM in their LNG off-loading arm concept). Other arrangements are ofcourse possible.

d) The transfer system between the swivel and the ship manifold is done eitherby hard arms or by flexible hoses as illustrated on Figures 10 and 11. This ispossible thanks to the width of the rotating quay allowing sufficient space forthe hoses. The most compliant hose configuration is a catenary shape allowingan extended flexibility with regard to ship manifold envelop of movements,which in turn should allow more severe operating thresholds for the ship atberth. The studies are in progress at the time this paper is written. Typicallyhoses 45 m in length are used with a span of about 33 m (horizontal distancebetween the hose fixation on the beam and the ship flange). The beam lengthallows having as much hard arms or flexible hoses as necessary.

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Figure 10: Artist view of the rotating quay with hard arms

Figure 11: Artist view of the rotating quay with hoses

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Ø Miscellaneous:The concept of rotating quay allows receiving also several equipment similar to the onesmounted on a conventional jetty:

- A hydraulic unit for the arms or hoses and the gangway if required.- Nitrogen cylinders for the purge of the arms or hoses and for N2 bleeding in the

arms swivels.- Fire detection and fire protection.- Navigation light and fog horn.- Lighting- Lightning protection.- Various ship/shore links like ESD, communications and data from berth

monitoring system (approach distance and speed and mooring lines tension).A sub-sea cable and an electric swivel unit can provide the electric power.

Finally the side of the quay opposite to the ship is equipped with a boat-landingallowing access to the quay from the sea.

Mooring lines tension calculations and estimation of the tug pulling requirements:

Preliminary calculations have been done with OPTIMOOR and main results are givenhere under. They are presently completed by dynamic calculations (results are not yetavailable at the time of this paper preparation).

The ship used for the calculations is a 4 tanks LNG ship of Moss Rosenberg type andcapacity 137,800 m3 and fully loaded (draft 11.27 m) of Mubaraz type. MBL (MinimumBreaking Load) of the mooring lines is 110 tons with 7 tons pre-tension, wire cables withno tail ropes in these calculations. It is assumed that the winches start to pay out at 75 %of the breaking strength. Water depth is 20 m for the calculation.

The following hypothesis have been considered for the environment parameters:

HYPOTHESIS H1 (see note 1) H2 H3 H4 (see note 2)wind 20 m/s 25 m/s 25 m/s 30 m/scurrent 1 m/s 1 m/s 1 m/s 1 m/sHs (significant waveheight)

2.0 m 3.0 m 3.5 m 3.5 m

Note 1: corresponds to maximum operating thresholds for a LNG ship to stay moored at berth ona conventional jettyNote 2: corresponds to the deemed maximum operating thresholds for the LNG ship to staymoored on the rotating quay (the wind being 60 knots as per OCIMF recommendations)

The wind, current and waves are supposed to be co-linear and calculations have beendone with incidences of 0°, 10°, 20°, 30° and 40° from the ship heading.

The pulling angle of the tug line is taken at 60° from the ship heading as shown onFigure 12 in a normal situation.

Figure 13 shows the lines paying out because of an excessive incidence angle of theenvironment exceeding the mooring capability.

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Figure 12: Mooring arrangement, incidenceof the elements 20° (environment H2), tugpulling angle 60°; normal circumstances

Figure 13: Mooring arrangement, incidenceof the elements 40° (environment H4), tugpulling angle 60°; abnormal circumstances,lines paying out

Results of mooring calculations are given on Figure 14 for environment H1, H2, H3and H4 as a function of the incidence of the environment conditions and for a tug pullingat a 60° angle, H being the tug pulling requirements and T the maximum tension. It canbe seen that:- The tension remains within 55% of the breaking load if the ship heading remains

within a sector of +/- 30° from the environment incidence for hypothesis H1(environment conditions similar to the ones of a conventional jetty).

- This safe sector has to be reduced to +/- 20° for more severe conditions H2, H3 andH4.

- The tug pulling requirement is in the range of 45 to 48 tons for conditions H2 and H3but 63 tons are required for condition H4 at 20° incidence. This kind of tensionremains reasonable for such moderate to severe environmental conditions.

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Figure 14: Results of mooring calculations (tug pulling angle 60°)

Figure 15 gives the tug pulling requirements as a function of the pulling angle forenvironments H2 and H3 at incidence 20°. One remarkable result is that the tug-pullingrequirement is almost constant in a wide range of pulling angle (say 40 to 90°).

Figure 15: Tug pulling requirements as a function of the pulling angle

As a general conclusion it appears that the operating limits of the system will behigher than the ones of a conventional berth. The following conditions seem to be safe:- Rotating quay: weather H2 with wind < 25 m/s, waves Hs < 3.0 m, current moderate

(say 1 knot), sector for environment incidence +/- 20°, tug pulling requirement 45 to47 tons.

- Conventional jetty for comparison purpose: weather H1 with wind < 20 m/s, wavesHs < 2.0 to 2.2 m, current moderate (say 1 knot).

At this stage we have limited the operating thresholds of the rotating quay toconditions H2 because the tug efficiency is reduced as soon as the sea state deteriorates.The choice of the type of tug and propulsion will have to be looked at in detail. Analternate using ship bow thrusters is also envisaged.

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Integrated marine monitoring system (MMS) and automatic elaboration of pullingorders for the tug

It is similar to the one on a conventional jetty. The integrated MMS for the ship atberth measures:- The environment parameters (wind, waves and current).- The tensions in the mooring lines.- In addition, the orientation of the quay orientation is given as well.

With the above data it is easy for a computer software to calculate the pullingrequirements for the tug. Necessary instructions can be then transmitted by telemetry tothe tug wheelhouse on a console showing pulling direction and pulling force instructionsto the master. An audible alarm is provided in case these instructions are not followedaccurately before reaching a situation of potential danger.

A typical illustration of such system is given on Figure 16.

SENSORS

v WIND

v CURRENT

v WAVES

v LINES TENSION

v ANGLE OF BEAM

TELEMETRY

CONSOLE ON TUG(TENSION & DIRECTION)

MEASURING AND CONTROL

Figure 16: Automatic elaboration of pulling orders for the tug

PART 3: GENERAL CONCLUSION

This paper has presented successively:- The state of the art of loading/unloading systems for liquefied gas ships: conventional

jetties, SPMs and unconventional schemes developed by TOTALFINAELF in years1999-2000, associated with GAZ DE FRANCE, EURODIM and ITP INTERPIPE.

- Then, and in line with the criteria set-up for unconventional schemes, a radically newconcept of loading/unloading system based on a rotating quay (patent pending).

This system, as well as other systems are now studied in detail by TOTALFINAELFin association with GAZ DE France and EURODIM, with the objectives to have in handby end of 2001 different loading/unloading systems applicable in different environmentalconditions with all the components fully tested.

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Figure 17 (next page) proposes a classification of the various systems described inthis paper based on two parameters: environment conditions and cost.

It can be seen that a reduction of 50% of the cost compared to a conventional jetty canbe expected, while offering higher operational thresholds, accepting non dedicated shipsand eliminating all navigational, traffic and siting constraints.

Figure 17 shows the classification of the various systems described in the paper. (See next page.)

REFERENCES:

[1] LNG JOURNAL – January/February 2000 issue: “Siting of LNG/LPG Terminals,”Bertrand Lanquetin TOTALFINAELF

[2] LNG TECH Asia 2000 – Kuala Lumpur – May 10-11, 2000: “Siting of LNGTerminals (Case Study), ” Bertrand Lanquetin TOTALFINAELF

[3] LNG 12 – Perth- May 4-7, 1998: “Bontang Future 3rd LNG/LPG Dock: a Designwhich Achieves Very High Levels of Flexibility, Safety and Reliability,” BertrandLanquetin TOTALFINAELF and Yosua Sitepu PERTAMINA PKP

[4] GASTECH 2000 – Houston – November 14-17, 2000: ”Ship/Shore LNG Transfer:How to Cut Cost?” Chris Thomas and Bertrand Lanquetin TOTALFINAELF,Emmanuel Flesch GAZ DE FRANCE, Bernard Dupont EURODIM and MichaelOffredi ITP INTERPIPE

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Figure 17: Classification of the various systems described in the paper