CA1134154A - Squat seabed mooring system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

For mooring a vessel such as an oil tanker, especially in shallow water, a squat base unit is located on the sea bed. The lower end of an articulated swivelling arm is built into the base unit in such a way that the upper end is free to rotate about three axes and to move vertically and horizontally around and over the base unit within the confines of a circle whose radius is defined by the geometry and weight of the arm and the height and attitude of the top section of the arm. A hawser, attached to the head of the arm, enables the head to be lifted by a tanker until the head of the arm engages into a reception chamber built into the underside of the tanker hull. By hauling in the hawser and lifting the head, the tanker locates itself within a working radius of the base unit and is moored by the arm to the base unit. The head of the mooring arm is held rigidly in the reception chamber and is able to move with the ship by virtue of its' freedom of movement. The base unit can take the form of an oil reservoir and the arm can be formed of hollow tubes which are used to transfer fluid between the base unit and the tanker. When not in use the mooring arm lies flat on the base unit on the sea bed (or within a depression in the sea bed), where it is in no danger of damage from deep keels.

Description

1134~S4 SPXCIFICATION

(Amended Maroh 14, 1982) The present invention relates to a mooring system for sea pning vessels such as oil tankereO It concerns a mooring system ~hich al80 incorporates a high capacity fluid transfer system ~ithin the mooring membersa It has the additional characteristic of having a lo~ sea bed irofile ~hen not in use~ 80 as to be neither a hszard to the keels of large ships in shallo~
~ater, nor to be exposed to the danger of damage from the deep keels of large ice formationH in polar areas. It is of particular use for loading crude oil from sea bed production facilities into ice breaking tankers in shear-zone arctic ~aters.
~ he usual ~ay of mooring and loading a tanker in an e~posed location at sea iB to attach it, temporarily, ~ith a ha~ser, to a permanently installed unlt ~hich projects above ~ater level. Flexible hoses are then connected from the unit to the tanker, and oil is transferred ~hile the tanker takes up a ~eathervaning position in relation to the permanent unit. The permanent unit is usually a large buoy anchored to the sea bed or a buoyant post attached to a sea bed base, ~ y US patent No. 4086865, dated ~ay 2nd, 1978, describes a mooring and loadlng system ~here a single ritid telescopic me~ber performe the functions of both mooring and oil transfer. The rigidity of the ~ingle member allo~ed its cross-sectional area to be great in relation to other systems and the rate of oil tranefer to be fast:- en~uring a quick transfer operat1on.
In sreaJ ~here drifting arctic ice covers the top of the ~ater a proJecting unit becomes impractical. In the same areas, very often, the base unit how ing a telescopic transfer ~ember ~ould be sub~ect to damage from deep drifting ios keels on account of its height.

Ihe deficiencies of the existing sy~tems in these circumstances ari~e rrOm their permanent occupation of space above the sea bed ~hich might at timee be in the path Or approaching deep keels, either of ~hipping, or of ice ~tructures.

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~ y the use of an improved moorlnOE system the present in~ention overco~es theae dlff1culties by an arrangement ~hlch enaW es the system to lle on the sea bed ~ith a lo~ proflle ~hen t in use, but to e%tend up to the tanker vessel's receptlon cha~ber level ~hen required; at the same time it makes possible a high rate of transfer flo~ and has the added advantage that the syste~ ~orks ~holly belo~ lce level (in polar regions) ~here the envlronment i8 acceptsble.
A further improvement of the present invention is that ~hearas, in the previous mooring post system, the mooring post ~as pivotted in the lo. reception cha~ber gate snd the head moved around ~ithin the reception chamber according to the relative movements of the ve~sel and the post, - in the present system the mooring arm head ic held rigidly in the reception chamber by uean~ of the conical top of the oring arm head bein6 secured by the stopping ring and the base of the mooring arm head being located by the reception cha~ber g~te, This is made possible by the degree of n e~ibility impàrted to the mooring arm by virtue of the joints and s~ivels.
In accordanc~ ~ith the invention there 18 provided a method of ~-moorlng a ~essel ~herein the vesse~ locates, picks up~ and hauls in a oring ha~ser ~hich is attached to the outer e~tremity of an articulated mooring anm

2~. head lying flat, ~hen not in use, on the sea bed, and the head of the mooring aro is lifted into engagement ~ith a reception chamber formed in the underside of the hull of the vessel~ the lo~er end of the arm being s~ivelly connected to a base unit.
For carrying out this method the invention provides ~ooring apparatus comprlsing a heavy squat base unit ~ith a s~ivelly attached heavy articulated mooring ar~, and haYing a mooring ha~ser connected to the outer e~tre~ity of the mooring arm head, the ha~ser having means ~hereby it can be located by the vessel to be ~oored ~hich can then haul in the ha~ser and lift the head of the aro into a reception cha~ber built into the underside of the ~essel.
~he heavy base unit can be hollo~ and can conveniently be used for the sea bed storage of oil.

The locating means can be a ~onic buoy connected to the free end of B

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~3~154 the hawser by a lanyard BO as to float at a preclse level ~ove the sea bed, but belo~ any ice coverage.
~ or fluid transfer bet~een the sea bed reservoir and the vessel the articulated mooring arm is hollo~ and performs the dual function of mooring the vessel and of carrying the fluid from the sea bed installation to the vessel, or vice ver3a.
m e mooring arm is articulated ~ith pivots and s~ivels and the bottom of the arm is swivelly connected and pivotted to the base unit ~hich is installed below the general sea bed level.
lo When not in use the mooring arm lies partly on top of the base unit and partly on the surrounding sea bed in a flat, basically horizontal, attitude.
The base unit is squat and the main characteristic of ~the system is a very low sea bed profileO
The mooring arm head is equipped ~ith loose lead-in plates and a slip sleeve. It has opening ports and port fouling guides.
Two concentric slidetracks allow the arm to slide around the centre of rotation in response to a near horizontal pull by the hawser.
The best application of the present invention is for mooring and 2 0 loading oil or liquid ga8 tankers in situations where icebergs or other ice formations may damage existing types of tanker loading installations.
Another application of the invention is for mooring, loading, and unloading oil, or liguid gas, tankers in shallow water close to land where the installation can lie flat on the sea bed when not in use and vill not form a ha~ard to shipping.
Where the sea depth is such that even ~hen lying flat on the sea bed the installation vould still form some Xind of obstruction or create a hazard, then the sea bed is dredged do~n to a lo~er level, locally, 80 as to accommodate the installation (Fhen not in use) in a hazard-free sea bed depression.

3~ Anoth~r characteristic of the present invention is that the manner of articulation of the loading arm is such that it can be very large (typically 4m. diameter) 80 that it can transfer fluid in large quantities quickly, ~.
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Thie characterlstlc 18 very n~cessary ~hen loading tankere ln the pre~ence of movlng ~lnter lce floes ln Arctlc area~. The shorter the loadlng time the smaller the risk of the tanker being pushed off station by heavy ice formatlon~.
~ further characterietic of the present invention is that the system is al~ays belo~ ~ater level both ~hen in use and ~hen at rest on the sea bed.
In Arctic regions thie is most important because in ~inter tlme the environment above ~ater (ice) level is very hostile and full of difficulties.
Working ~holly belo~ ice level in these conditions has very great advantage~. -l~ A further function of the system 18 sea bed storage. It is efficient and convenlent to store oll at a lo~ level (on the sea bed) 80 that the forces of gravity can be used to convey the oil to the ~essel. The base unit is used as a sea bed reservoir and, ~here necessary, the capacity is increaeed by surrounding it ~lth a number of simllar sguat storage units to ~hich the base unlt 18 connected.
Because the arm has a s~ivel attachment to the eea bed base unit,it can, ~hen connected to the vessel, enable the vessel to move round the ba~e unit in a ~eathervane fashlon 80 that the vessel assumee a posltion to lee~ard of the base unlt, the vessel itself ~eathervanlng about the top of ~o the arm 80 that the ~hole moo~ing system 18 in the most advantageous ~ ;-poeltion ln relation to the environmental rorces.
When the second functlon of the system 18 n uid transfer, the members of the artlculated arm and the s~ivel are all hollo~ 80 that the nUid i8 contained by them ae it moves from the base unit to the ves~el or ice ver~a, The arm has to carry very large mooring forces and 1~ constructed of alternate single and double longitudinal members in order to attaln symmetry about one a~is 80 as to reduce torsion forces and bendlng ments.
~he members are ~teel tubes.
3~ ~aslcally a vessel~ according to the inventlon, locates and lifts the head of a heavy artlculated arm ~lth one or re lanyards, ha~sers, or chains, ~hich ~e permanently attached to the end of the ar~ and are passed through a receptlon chamber located in the bottom of the vessel, untll the B

~34~L54 top end of the arm i8 ~lthin the reception chamber. The other (lower) end of the arm i~ connected to the base unit by a double ~oint ~hich allo~s the bottom section to s~ivel around a vertical a~is and rotate about a horizontal a~is. The top end of the arm also has a ~oint ~hich allo~s the top section of the a~m ~hich penetrates the reception chamber to do 90 ~ith a substantially vertical longitudinal a~is.
The arm consists of a number of alternate single and double longitudinal members connected together ~ith pivot and swivel joint3 to give the necessary degrees of flexibility required by the system.
o The top end of the arm is held rigidly in a suspended position ~ithin the reception chamber by the ha~ser. ~he vessel i~ then free to roll and pitch in the sea and can ~eathervane about the sea bed installation, but it is restrained to vement within the limited length of the arm about the sea bed base unit.
In its st useful form the arm is compo~ed of large heavy steel tube sections linked together in such a ~ay that the bottom section can rotate in its bearing~, set in the sea bed base unit, ~hile the top section, ~uspended by the vessel ~ith its head held rigidly restrained ~ithin the reception chamber, allo~s the vessel to ~ove with the ~ater and ~ave moYements but restricts it from moving outside of a radius from the centre of the bottom attachment, ~hich radius is determined by the ~eight and geometry of the arm, the draught and attitude of the vessel, and the depth of ~ater.
The system is particularly useful in the Arctic environment ~here ice floes are often ¢ontinually moving and ~here ice ridge and iceberg keels often reach do~n to the sea bed, and lo~er, scouring deep furro~s in the latter. The system is located 80 that in its lo~ered position, its top is belo~ ice keel level. Where sea bed furro~s sho~ that ice keels have previously penetrated the sea bed, a depression is formed in thc ~ea bed by dredging or other mean~ and the system is set belo~ anticipated ice keel level.

~3~15 i The invention also provides some improvements for a Yessel ~hich has mooring and oil transfer equipment for co-operation ~ith the mooring apparatus ~hen the latter is in po3ition under the sea, and this equipment on the vessel comprises a reception chamber ~ithin the hull of the vessel, an opening in the bottom of the vessel for the entry of the oring arm head into the reception chamber, means for hauling in the mooring ha~ser through the entry opening in the reception chamber, to dra~ the mooring arm head into the reception chamber, a resilient gripping ring fitted around the entry opening to engage ~ith the mooring arm 81ip sleeve and form a ~o seal~ a stopping ring, and a hawser dlrection sensing device.
In Arctic use a ded$cated icebreaker tanker is fitted ~ith a -reception chamber, aonic buoy location means, buoy retrieval means, lanyard and ha~ser ~inches, ha~er ~acking and gripping means, fast ha~ser lo~ering means, reception chamber gate, ~nflatable annular gate seal, ha~ser guides, mooring arm head stops, ha~ser direction sensor, and base unit direction sensorsO
The tanker first shatters the ice along a path upstream of the facility for a distance such as to allow it to be in shattered ice during its loading period. m e tanker then returns to the oring terminal, 2L~ locates the buoy, feeds the buoy and lanyard through its reception chamber, ~inches in the hawser, senses the direction of the mooring arm head, manoeuvres over the mooring arm head, lifts the mooring arm head into the reception chamber, and inflates the annular gate seal. Ports in the mooring ar~ head are then opened and the oil is free to flo~ into the reception chamber and out through the distribution manifolds and pumps into the ships oil storage tanks. The ~hole operation is accomplished belo~ ice le~el ~here temperatures are reasonable. Temperatures above ice level are intolerable in st Arctic ~inter conditions.
The articulation of the mooring arm is particularly important.
~k~ 'rhe sea bed installation is the base unit into ~hich the bottom ~rlrst) member Or the arm 18 located in such a manner that the bottom member has a substantlally vertical axis and has the abllity to rotate around that axis.
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- ~3~1S4 The second member i8 pl~otally connected to the top end of the bottom member, and i8 a double member, being composed of par~llel, handed, t~ins. q'he thlrd member 18 pivotally connected to the second member. The thlrd member is a slngle member ~ith a longitudinally s~ivelling ability such that one end can t~ist around the longitudinal a~is in relatlon to the other end.
The fourth member 18 pivotally connected to the third member.
Ihe fourth member is a double member composed of parpllel hsnded t~lns.
The fifth member is pivotally connected to the fourth member. The lo fifth member is a single member. 'lhe fifth member 18 generally the top member and forms the ~ooring arm head.
Nore than five members can be used if required. The system can also ~ork ~ith four members if the (slngle~ bottom (first) member is of such a size that the second member (~hich ~uld be a single s~ivelling member) can pivot lnto it. I'he third member ~ould then be a double member and the fourth member ~ould be a single member and ~ould form the mooring arm head.
The invention ~111 be described in more detail ~ith the aid of an example illustrated in the accompanying dra~ings in ~hich:-~lg. 1 eho~s an elevation and ~ig. 2 sho~s a plan of the general s$tuation sho~lng the moorlng apparatus and the tanker vessel in accordance ~ith the lnventlon.
~lg. 3 18 a re detalled plan of the mooring arm lylng horlzontally flat on the sea bed and attached to the base unit, Fig. 4 sho~s a section through the base unit, an elevation of the ~ooring arm ln three characteristic positions~ t~osho~n dotted, and transverse sectlons through the tanker vessel in t~o characteristlc positions, one ~ho~n dotted, Fig. 5 18 a sectlon through the mooring arm head suspended ~ithin the tanker vessel's reception chamber, ~X~ Fig. 6 is a diagram ehowing the typical articulations and restrictions applied to the mooring arm.

Flg. 7 is a plan on a four member artlculated mooring arm.
Fig, 8 is an elevatlon of the same arm in the loading position~

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The mooring apparatus sholn ln the dra~ings iB intended for the oring and load$ng of large ice breaking oil tankers in Arctic region~
~rhere ~rinter ice floes ~rith deep keels form a great ha~ard. The mooring and loading apparatus comprise~ a base unit 11 and mooring arm 13 enabling a ~ressel 10, such as an icebreaking tanker, to be moored in position against an advancing ice floe 15, ~ith lo-r ice keels 16, ~hile being loaded ~rith crude oil from the reservoir storage units 12.
The ice i8 flol-ing in the direction marked 18 against the tanker vessel ~hose length is marked by 19. The ice breaking tanker vessel 10 IO has to shatter the hatched area of ice 9 preparatory to loading oil in ~-order not to be pushed off station, It must shatter a length of ice 17 to attaln this. ~he base unit 11 and reservoir storage units 12 are installed belo~r seabed level 8. q~he tanker vessel floats at ~rater level 14 pushed by the ice floe 15 but ored by the mooring arm 13 which carries the oring strain, Referring no~l to Fig. 4 (a plan of which i8 sho ln in Fig. 3) it can be seen that an unladen tanker vessel 50 ~ill float high in the lrater~
it~ heiBht varying in accordance lrith the llater level 45 l-hich varies according to tidal range and ~ave height 46. A laden tanker 51 ~ill float at a much lo-rer level.
~ he characteristic attitudes of the mooring arm 53, 54, 55, 56" 57, are sholm in Flg. 4. The full line sho~s the mooring arm mooring an unladen tanker vessel 50. The mooring arm is sho~n again in dotted lines mooring a laden tanker vessel 51, and is sho~n a third time (in dotted lines), lying in a flat basicslly horizontal attitude, on the top of the base unit 11 and the sea bed supported by the inner slide track 27 and the outer slide track 26. ~he slide tracks 26 and 27 (sholm in plan in Fig. 3) enable the mooring arm to ~otate easily about its centre s~ rel ~hen pulled lsterally by the ha rser.
~0 In the typical case sho~m in Fig. 4 the lrater depth is 30 metres.
Deep ice keels such as 49 are common but ths sea bed 40 sholrs occasional deep ice keel scours Much as 41. ~he base unit 11 is installed in a dredged depres0ion 42 to enable the facility to be belo~r expected ice keels and ln a ~.

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hazard free environment.
A protectlv~ bund 44 18 bullt ~lth seabed materlal 43 out of the dredged depression 42. ~hattered lce such as 47 and 48 cover the ~ater surface ln ~inter.
~ In operation the captlve sonlc buoy 62 is located by the tanker vessel. me sonlc buoy 62, lanyard 61, and mooring ha~ser 60, are pulled through the vesAels reception cha~ber 58, ~hich 18 built into the bottom of the-vessel~ hull, and the vessel hauls in the mooring ha~er. The mooring ha~ser 60 is attached centrally to the outer extremity of the Ia mooring arm, at the top of the mooring arm head, and, as the ve~el hauls ln the ha~ser, the mooring arm head 57 and the rest of the oring arm 56, 55 and 54, are lifted by the basically vertical force until the mooring arm head 57 is ~lthin the receptlon chamber 58 and the conlcal top of the mooring arm head engages ~ith the annular stopping ring 85.
me oring anm head lncorporates a n ush ~llp sleeve 24 ~hich enables it to t~lst ln relatlon to the tanker as it 18 gripped by the gate ~eal 70.
The outer ~urface Or the mooring arm head is conical 80 as to be ~ ~
able to co-operate ~lth the annular oring head stopping ring 85. ~ ;
The mooring arm head alHo incorporates the ha~ser terminal block 73 lnto ~hlch the ha~ser 60 18 secured 80 as to emerge centrally from the outer extremlty Or the oring arm head. The terminal block 73 is secured to the outer ~all Or the mooring arm head by radlal d$aphrams 78.
The annular stopping ring 85 is mounted on radlal dlaphrams 81 ~hich are seaured to the ~all of the receptlon chamber 58. ~hese radial diaphrams also ~upport the ann~-lar OEillage 82 ~hich locate the segmented removable ha~ser guide 77 ~hlch is required to centralise the mooring ha~er as the mooring arm head 57 is lifted lnto the receptlon chamber.

The oll ~ater lnterface i8 sho~n at B7 ~here 88 18 oil and 89 is 3k~ ~ater.
~ he moorlng head ports sho~n at 72 ~closedj and 86 (open) are opened by mean~ Or a port openlng bayonet 79 ~hlch hydraulically actuates port opening ~ack~ 84 against port return sprlngs 83.

~341S4 The ports are protected by port fouling guides 80.
Fig. 5 (and thc other figures) are sho~n diagramatically for simpliclty. The mooring head is in fact sym~etrical about lt~ longitudinal central line.
Fig. 5 sho~s a ~ection through the mooring head, but fourth member of the mooring arm 56 is sho~n in elevation.
~ Ig. 6 is a diagram of the linkage system for a five member mooring arm.
ffle base unit EF i6 shoKn installed in the seabed AECD. GH is the single firet member ofthe mooring arm. It is held by bearingeUV and WX ~ith a substantially vertical axis about ~hich it can rotate. The second member HJ is a double member and i8 connected to the first member GH by a horizontal pivot at H and to the third member n ~ith a horizontal pivot at J.
The third member n iB a single member and has a longitudinal s~ivel at K enabline Joint L to rotate in relation to ~oint J about the longitudinal a%is.
The fourth member L~ is a double member and is pivoted to the third membor n at L and to the oring arm head YQ at ~.
The oring arm head ~Q is supported, ~hen in use, by the ha~ser T, ~0. restrained by the reception chamber gate NP and located by the annular stopping ring RS.
Figs, 7 and 8 sho~ 8 four section arm arrangement ~here the first member of the mooring arm 53B is a single member mounted ~ith a substantially ~ertical axis in the base unit 11 80 that it can revolve around that axis.
In thls case the flrst member is made of such a size that a double horizontal pi~ot ~olnt can be formed in its top structure to enable the second member 55~, ~hich i8 a single member, to be pivotally connected to it. The second member 55B incorporates a s~ivel 20 ~hich allo~s one end to rotate about its longitudinal axis in relation to the other end. The third member 56 is a double member and the fourth member 18 the mooring arm head 570 The moorlng apparatus sho~n in the dra~ings is intended for the moorlng and loadln6, or unloadlng, of large oil tankers in exposed locations at sea ln places ~here there is a danger of damage from deep keels. The B 1 0.

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' ' '' ' ' ~341S4 mooring apparatus comprises a base unlt 11, ~hlch 18 hollo~, 18 used for oil storaee, and 18 set ~ith lts base sub~tantlally horlzontal, Into the base unlt iB bullt the first member of the articulated oring arm 53 ~hich e~lvels about a ~ertical axis and is perforated ~ith holes 52 to allo~ oll access. The top end of 53 contains a double hor$zontal pivot 23 ~hich allo~s the t~ln second member 54 to revolve about t~o axes. ~he remote end of 54 is horizontally pivotted, at 23, to the single third member 55, 55 contalns a longitudinal s~ivel, 20, and its remote end has a double pivot 23A to the t~in fourth member 56, Pivots 23A are no longer confined to a horizontal l~ a%is by virtue of s~ivel 20 ~hich allo~s 56 and the single fifth member 57 to ve freely about three axes.
All the members, pivots, s~ivels, are hollo~ to allo~ oil to flo~
through the members from the base unit to the tanker vessel.
When the conical top of the mooring arm head 57, is lifted by the ha~ser through the reception chamber gate 59 it comes up against the annular Jtopping ring 85, Fig. 5, and the head is maintained in contact ~ith 85 by virtue of the tension in the ha~ser 60, At thls point the gate seal 70 is inflated to stop the ingress of further Hea ~ater into the reception chamber. Closed ports 72 can be opened 2~ to the position sho~n at 86 and oil can flo~ throughthe reception chamber ~nto the man~folds 74 and to the vessel's tanks.
During fluid transfer the mooringsm head is held integral ~ith the ~essel~ and moves in unison ~ith the vessel by virtue of its freedom to move about ~ a%es. Ho~ever, the articulated mooring arm also acts as a very heavy chaln and restricts ths movement of the vessel to ~ithin a radius of the centre of rotation of the arm dependant on the geometry and ~eight Or the oring 0 and height and attitude of the mooring arm head.
Because ofthe size and weight of the vessel it is necessary for the tanker's propellers and thrusters to assist in manoeuvring the vessel over ~o the ba8e unit a8 lt ~inche8 up the mooring arm into its reception chamber.
76 is B ha~ser direction sensing device ~hich enables this assistance to be ¢o-ordinated, 'l'he loose lead-in plates, 75, are threaded on the ha~serO

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3~154 When fluid tranflfer 18 complete the mooring head ports are closed~
the residue oll and sea ~ster 18 pumped out of the receptlon chamber via the scour manifold, the reception chamber and mooring head are scoured clean ~ith hot ~ater and steam ~hich is pu~ped a~ay to dirty ~ater tanXs through the scour manifold, the ~ate seal i8 released and the mooring arm i~ lo~ered to the sea bed ~ith the ha~ser. A8 the tanker sails a~ay the residue hauser ..
length is paid out follo~ed by the lanyard and sonic buoy ~hich resumes its position as marker o~er the mooring arm head.
~hereas the apparatuR has been described in relation to the storage lo. and transfer of oil it ~ill be apparent that it could also be used ~or any other flu$do ~_~~ . ` , 1q .
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-1.

Apparatus for mooring a vessel comprising a heavy squat base unit for installation in the seabed; a heavy articulated mooring arm including a head, and composed of alternate single and double rigid longitudinal members with pivot and swivel joints which lies in a flat, basically horizontal attitude when not in use, and is swivelly attached and pivotted to the said base unit; a mooring hawser centrally attached to the outer extremity of the mooring arm whereby the hawser is adapted to apply a basically vertical lifting force to the mooring arm; and means attached to the said hawser for location by a vessel to be moored; whereby the vessel is adapted to haul in the hawser and lift the mooring arm head into a reception chamber built into the underside of the hull of the vessel, the mooring arm head being held rigidly in the reception chamber of the vessel, and the mooring arm head having the necessary freedom of movement to be able to move in unison with the vessel both vertically, horizontally, and rotationally, whilst being held by the base unit within the confines of a circle whose radius is defined by the geometry and weight of the mooring arm and the height and attitude of the mooring arm head.

2.

Apparatus as claimed in Claim 1 in which the base unit is hollow and is constructed as a reservoir for fluids.

3.

Apparatus as claimed in Claim 2 in which the members of the mooring arm are hollow with fluid communication means with both the base unit and the vessel to enable the mooring arm to be used for fluid transfer between the base unit and the vessel.

4.

Apparatus as claimed in Claim 3 in which the mooring arm is in the form of steel tubes.

5.

Apparatus as claimed in Claim 1 in which the mooring arm head has a conical top for engagement with a stopping ring built into the reception chamber.

6.

Apparatus as claimed in Claim 1 in which the mooring arm head has a slip sleeve for co-operation with a reception chamber gate and gate seal built into the reception chamber.

7.
Apparatus as claimed in Claim 1 in which the mooring arm head is fitted with loose lead-in plates threaded onto the hawser.

8.
Apparatus as claimed in Claim 3 in which the mooring arm head has controllable outward opening ports to allow fluid communication with the reception chamber.

9.

Apparatus as claimed in Claim 1 in which one of the single longitudinal members of the mooring arm has a longitudinal swivel joint to enable one end to rotate in respect to the other end about its longitudinal axis.

10.
Apparatus as claimed in Claim 2 in which the base unit is installed in a shallow excavation dredged out of the sea bed such that when not in use the mooring arm and the base unit are below the general sea bed level and are in no danger from damage by deep keels.

11.
An improved method of mooring a vessel with the apparatus of Claim 1 comprising the steps of:-a) locating said mooring hawser from the vessel.
b) passing said hawser through a reception chamber built into the underside of the hull of the vessel.
c) hauling in the hawser to lift said mooring arm head into the said reception chamber until the conical top of the mooring arm head engages with a stopping ring and the base of the said mooring arm head is located by a reception chamber gate, the mooring arm head being held rigidly in the reception chamber of the vessel, and the mooring arm head having the necessary freedom of movement to be able to move in unison with the vessel both vertically, horizontally, and rotationally, whilst being held by the base unit within the confines of a circle whose radius is defined by the geometry and weight of the mooring arm and the height and attitude of the mooring arm head.

12.

An improved method as claimed in Claim 11.comprising the further step of inflating a gate seal.
13.

An improved method as claimed in Claim 11 wherein the base unit is constructed as a reservoir and a mooring arm which is hollow, said improved method comprising the further step of transferring fluid between the base unit and the vessel by means of the hollow mooring arm.

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