CA1227379A - Floating offshore structure - Google Patents
Floating offshore structureInfo
- Publication number
- CA1227379A CA1227379A CA000507928A CA507928A CA1227379A CA 1227379 A CA1227379 A CA 1227379A CA 000507928 A CA000507928 A CA 000507928A CA 507928 A CA507928 A CA 507928A CA 1227379 A CA1227379 A CA 1227379A
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- Canada
- Prior art keywords
- hull
- hole
- vertical
- floating
- tubular body
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE:
A floating offshore structure for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected at the end thereof, for conducting a sub-marine excavating operation by an excavating drill pipe. The structure comprises a hull; a vertical through-hole formed in said hull; and means for preventing floating objects such as broken ice from entering the vertical through-hole, comprising a tubular body projecting downwardly from a bottom of the hull substantially coaxial with the vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through the vertical through-hole and tubular body to the sea bottom. The tubular body in an operative position projects below the hull bottom a sufficient distance to prevent the floating objects from entering the vertical through hole, but without reaching the sea bottom.
Means are provided for suppressing oscillation of the floating offshore structure, comprising an overhanging member projecting radially outwardly from an outer periphery of a lower end of said tubular body.
A floating offshore structure for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected at the end thereof, for conducting a sub-marine excavating operation by an excavating drill pipe. The structure comprises a hull; a vertical through-hole formed in said hull; and means for preventing floating objects such as broken ice from entering the vertical through-hole, comprising a tubular body projecting downwardly from a bottom of the hull substantially coaxial with the vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through the vertical through-hole and tubular body to the sea bottom. The tubular body in an operative position projects below the hull bottom a sufficient distance to prevent the floating objects from entering the vertical through hole, but without reaching the sea bottom.
Means are provided for suppressing oscillation of the floating offshore structure, comprising an overhanging member projecting radially outwardly from an outer periphery of a lower end of said tubular body.
Description
37~
The present application is a division from the appli-cation No 425,226, of the same inventors, filed on April 5, 1983.
1. Field of the Invention - 5 The present invention r~lates to a floating of-s.^ore structure and more particularly to a structure floa.ing offshore and moored so as to be positioned at ~ subs~antially fixed position, such as a floating deck structur~ usa_le for submarine excavation, for example.
The present application is a division from the appli-cation No 425,226, of the same inventors, filed on April 5, 1983.
1. Field of the Invention - 5 The present invention r~lates to a floating of-s.^ore structure and more particularly to a structure floa.ing offshore and moored so as to be positioned at ~ subs~antially fixed position, such as a floating deck structur~ usa_le for submarine excavation, for example.
2. Description of the Prior ~rt With a st~e3 ris~ in sem2nd for oil, submarine Gi;
fields have been visorousl-~ developed. Also, othe~
submarine resources have k~en energetically investiga~~d and developed. As a mo~ahle excavating apparatus 'oz effecting these deJelopments, for example, a floating offshore structure is ~mployed. The floating offsho~e structure of this ~ype is a larg~-sixed structure hav ng a diameter or longi~udinal or lateral dimension of ne 1~
100 ~, for exa~nple, and a displacement of nearly fr~m 30 to 40 thousand tons. Such a structure employes a large n~er (e.g., 12) of mooring hawsers so as to be moor~d a;
a fixed position on the sea by means of anchors connec.ed to the ends of these moo~i n g hawse r 5 r e spe c t i ve 1~ .
The floating offshor3 structure of this type w~ich is ~ , ~ ~73~ ' employ~ad in an icy sga ar~a in csld wa~srs wbere floating ice is present conven onally has a pianar shape which is a circle or a poly~on close to 2 circle. Therefore, in case of conducting exca~ation in a Crozen sea, this structure is made to have no dir-ctional property with respect to tne floating ice force (the collision force of floating ice) and, henco, is independent of the flowing direction o- the floating ice. On the other hand, however, sinco the structure has a circular section, the width allowing floating ice to collide is large relatively for a giJon effective deck area, so that the structure rcceives a correspondingl~ la~ge collicion force of floating ice.
For the same reason, the mcvement o.- the structure due to waves is larger.
~oreover, in a floating offsncre struc.ur2 for submarine excav~tion, such as an oil rig, a vertical through-hole is formed in the structure body, i.e., the hull, and an excavating drill pipe driven by an excavator on the deck is passed through the tnrough-hole and ex_ended to the sea bottom to carry out operation. In the floating offshore structure of this kind, the vertical througn-hole is hitherto formed as a hole opened in the hull bottom.
Therefore, in case of using the structure in a f~o2en sea, such as cold waters where floating ice is present, some of blocks of ice broken by the outer wall of the hull on the for side (the side with which floating ice collides) scatter in the sea around the hull bottom and may undesirably enter the vertical through-hole from its opening formed in the hull bottom, resulting in damage to the excavating drill pipe and mooring hawsers extending through the through-hole.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a floating offshore structure capable of preventing floating ice from entering the through-hole for receiving the exca-vating drill pipe.
According to the present invention, there is there-fore provided a floating offshore structure for mooring at a fixed position on the sea by means oE a mooring hawser having an anchor connected at the end thereof, for con-ducting a submarine excavating operation by an excavating drill pipe, comprising:
a hull;
a vertical through-hole formed in said hull;
means for preventing floating objects such as broken ice from entering said vertical -through-hole, comprising a tubular body projecting downwardly from a bottom of said hull substantially coaxial with said vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through said vertical through-hole and tubular body to the sea bottom, said tubular body in an operative position projecting below said hull bottom a sufficient distance to prevent said floating objects from entering said vertical through hole, but without reaching said sea bottom and means for suppressing oscillation of said floating offshore structure, comprising an overhanging member pro-jecting radially outwardly from an outer periphery of a lower end of said tubular body.
One or more than one mooring hawser may be used for mooring.
~ ~7~
Preferably, the tubular body can be wi-thdrawn from its projecting operative position to a withdrawn position substantially within said hull.
Preferably, the hull has a mooring hull part for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected to an end thereof, and a movable hull part rotatably fitted about said moorage hull part, said vertical through-hole being formed in a central part of said moorage hull part.
The movable hull part may have a substantially oval horizontal cross-section near its water plane.
It is another object of the present invention to provide a floating offshore structure allowing the forces of floating ice, waves, tide, and wind received by the struc-ture to be smaller for a given effective deck area than theconventional floating offshore structures thereby decreasing the pitch and roll of the structure, as well as capable of smoothly rotating in response to the change in the flowing direction of floating ice or the like so as to prevent the increase in the forces of floating ice, waves, tide and wind, thereby overcoming the above-mentioned problems of the prior art.
According to this object there is provided a floating offshore structure having a floating body with a deck on an upper surface of the floating body and adapted to float while being moored at a fi~ed position on the sea, comprising a fore draft part being a front portion of the floating body, having near its water plane a hori20ntal section, said fore draft part being moored to the sea bottom;
and an after draft part being a rear portion of the floating body, having neax sald water plane a substantially smaller width than said fore draft part, said after draft part being connected to said fore draft part so as to be ~ -4-7~7~
rotatable within a horizontal plane about an axis located about at the center of said fore draft part.
Preferably, the after draft part taperingly projects aft from said fore draft part so that a horizontal section of said floating offshore structure near said water plane is substantially oval.
Preferably, the fore draft part has near said water plane a substantially circular hori,zontal section, while said after draft part has near said water plane a substantially circular horizontal section with a diameter smaller than that of said fore draft part.
Above and other objects and features of the invention will be apparent from the following description given as example without limitative manner when the same is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a floating offshore struc-ture in accordance with a first preferred embodiment of the invention;
Fig. 2 is a sectional view taken along a line II-II
of fig. l;
Fig. 3 is a sectional view of the floating offshore structure shown in Fig. 1 taken along a line III-III of Fig. 2, i.e., a water plane thereof;
Fig. 4 is a sectional view of the floating offshore structure shown in Fig. 1 taken along a water plane thereof, particularl~ illustrating the state of floating ice around the sarne;
Fig. 5 is a sectional side elevational view of a floating offshore structure in accordance with a second preferred embodiment of the invention;
Fig. 6 is a sectional view of the f loating of f shore structure shown in Fig. 5 taken along a water plane 7~37g thereof;
Fig. 7 is a sect_onal sice eievational view of a floating offshore structure in accordance with a t~ir~
preferred embodiment of the in~ention;
S Fig. 8 is a sectior.al view of the floating offshore str~lcture shown in Fig. 7 'a~en along a water plane thereof;
Fis. 9 is a sectional side elevational vie~ of a floating offshore structure in ac^ordance wi_h a four h preferred embodiment of the invention;
Fig. lO is a sectional ~iew cf the floating off_hore structure shown in ~,g. 9 ta~.sn along a line X-~, i.e., a water plane therecf;
Fig. ll is a p~an vie~ o_ a floating offshore structu~e in accordar,~:e with a fifth preferred embodiment of the invention;
Fig. 12 is a sectional view ta~en along a line XII-XII
oE Fig~ 11;
Fig. 13 is a plar. view of a floating offshore structur~ in accordance with a sixth preEerred em~od~ment of th~ inv2ntion;
Fig. 14 is a partially cutaway side elevational view of the Eloating offshore structure shown in Fig. 13i Fig. lS is a plan view of a floatinq offshor~
structure in accordance with a seventh preferred embodiment ,, .
of the invention; and Fig. 16 is ~ ?ar~ially cu_away side elevational view of the floating of_shore structlre shown in Fig. 15.
DESCRIPTION OF THE i??.~ ;) E.4'BODIMENTS
Preferred em~odiments of the invention will bz described hereinunder with reference to the accompanving drawings.
Figs. 1 thru 4 show a floating offshore struc-urz in accordanc~ with a firs. preCe~r2d embodiment of the in~ention.
Referring to Figs. 1 t;.ru 3, a moorage hull par~ 3 is moored at a fixed ?ositic~ Gn he sea by means of a plurality (e.g., -~e'-Je) cf mooring hawsers 1 radial~y extending to the sea bct~om from their respective positions su~stantially ~auali~ spaced ir. the circumferential direction, together with anchors 2 connected to the ends of the mooring hawsers 1, respectively. The moorage hull part 3 has a substantially cylindrical shape with an overhanging upper ~nd surCace~ on which winches 4 for win~ing and unwin?irg the respective mooring hawsers 1 are installed. As illustrated, the mooring hawsers 1 are pa~sed through a vertical through-hole 5 formed in the moorage hull part 3, and stretched in the sea, b~ing guided ~y pulleys 6 disposed nzar the through-hole lower end, resQ~ctively.
1~Z7~7~
P. ~.o-~able hull 2ar~ ~ is fi-~ed around tAe moorage hull part 3 through low-C-ictio^.al means 7 such as bearings so as to be rotatabi~ hin ~ horizontal plane, i.e., about a vertical a~is. In the illustrated embodiment, a mcorage hull part rGceivins hole 9 as a vertical through-hole is formed at a posilion closer to the bow of the mova~le hull part 8 (closer to the left side as viewed in Fig. 1), and the mo~rable hull part ~ and the moorage hull par 3 are connected togethGr with the latter inserted in the receiving hole 9. In ct;.er words, the movabie hull part 8 is constituted as a hull de ining the outer wall of the floating of snore st uct-lr-, which is assembled havi.~ the moorage hull part 3 re~eiv--s in the receiving hole 9 formed inside the hull.
Thus, as shown in Figs. 1 and 3, both the planar shape of a deck 10 formed on the upper surface of the movable hull part 8 and a water plane thereof (a section tak2n along a water surface W) 11 are substantially oval.
Particularly, the water plane, i.e., a horizonal section near the water surface has an oval shape including a fore draft part 12 in the shape of a substantially circular arc (radius R) with the moorage hull part receiving hole 9 as a center and an after draft part 13 taperingl~ projecting aft from the fore draft part. ~lthough the after draft part 13 has a shape of a circular arc with a radius r smaller :J 8 7 Q /~
than ~he radius R OL- _he C3re dr~ ~ part 12 in the illus~rated embodim~nt, the snape o. the aft-r part can b~
formed into a r~ctilinear or any other desired shape.
~oreover, although ~he fore draft part 12 has a sha?~ of a circular arc wi_h a r~dius ~, tnis shape is not exciusive and ma~ be a pollgon.
The outer wall of the movable hull part 8 is i-.-lin~d downwardly in-~ard, similarl-~ to conventional hulls.
Especiall-~, th~ ou er wall near tne fore dr~f~ part 2 is inclined in order to lessen the collision force (floa_ing ice force) against the hull of the floating ice flow ng in the direction of an ar.ow ~ rcm ~he 'ront of th~ bow.
In Fig. 2, t-e d~c~ 1~ for~ed on the u~per su~face of tne movable hull par ~ is a working deck for carrying out lS submarine excavaticn such as oil excavation. On t:~ deck 1~, various equi~nen~s ar.2 ap~aratus are installed ~.icb are required for oper~tion, such as a derrick 14 for installing an excavator (not showni. From the exca~ator, an excavating drill pi~e lS ls ~xzended toward the sea bottom through the vertical through-hole 5 of the moorage hull part 3. Exca~atiQn is conducted by means of a drill provided on the end of the pip~
According to th~ embodiment described above, in an excavating operation by means of the floating offshore structure moored in a frozen sea, when floating ice _g_ (thickncss: 1 m, for exam31e) .low, in the direction o, the arrow A as shown in F g. ~, al':n^ugh the floating ice .orce applied to the floating offshor- struc~ure is aimost e~ual to that ~pplied to a ci~c~llar structure shown by a t-~o-dot chain line in Fi~. 4, i' is possible to allow the dec:Y area and the displace.~ent to be largeE correspondingly to ~:~e portion projecting to~ard the stern. In other wors,, the floating ice force can b~ reduc~d for a given effect~e deck area or displacement, so that it is pcssible to obtain an efficient floating Grfshor- structure.
In addition, since the water plane has the fore a.aft part 12 formed i~to a circu a arc with a pr-scri`æ d -~dius and the a.ter draf_ ~ar~ ~i-h a smaller width and projected, when the flowin~ direction of the fioating ice lS changes and it flO~a in t`ne direction of an arrow B, ~he ~ovable hull part 8 ~an smoothl~v rotate about the moorage hull part 3, as shown in Fig. 4. In other words, since there is no need for breaking ice when the flowing direction of the floating ice changes, the movabl~ :~ull part 8 can change tne direction to the direction or 'he arrow 3 or even to a great~r angle in accordance wi~ the flowing direction of the floating ice, without receiJing a substantial resistance. It is to be noted that when the movabl~ hull part 8 changes the direction, a side thruster 16 can be used, if necessary. As illustrated, the side 7~7~
t~rus.er 16 is yene.ally cons~ t2~ by a propeller mounted at ~n underwater par_ near t;~e s~err. of the movable hull part a.
~oreover, it is possiblo to reduce the value of resistance offered by floating ice, since the outer w~ll of the movable hull ~art 8 is inclined downwardly inw~ ~ at least in the region near the fore draft par~. The larger the inclination angle ~, the smaller the resistance ~alue.
~owever, the inclination angle ~ is practically wil-. n a range from 15 tG 70 deJreeS.
It is to be noted that ~lthough the fore draft sart 12 has a circular shape in th~ 2bove description, practically, there are cases where t:~e shaDe Oc the fore draft par_ 12 is a ?olygon ~ h a lar~e n~m~er of vertexes. It is to be ur.derstood that the circular fore draft part a~cor~ing to th~ ;nvention includes the abov~-mencioned polygon as long as t~ere is no nindr~nce to the wor`~ing of the invention in view of the objects or action and effect thereof, although it depends on th- number oE the vert2xes, the roundness of each vertex or the hardness of ice, t3 say more ?recisely.
?igs. 5 thru 10 show other various preferr~d embodiments of the invention. In the Figures, the parts corres~onding to those of the first embodiment descrioed with reference to Figs. 1 thru 4 are d~noted by ,he same rerer~nce numerals.
7~
Figs. 5 and 6 in c^mbina'ion show a second pre.erred embodiment of the in-~;entior..
In this embodiment, a hull defining the outer w~11 of a floating offshore structure is composed of both the moorage hull par~ 3 ar.d the movable hull part 8.
The moorage hull part 3 having tne vertical through-hole 5 for receiving the excaJating drill pipe 15 and the mooring hawsers 1 has ~ shape of a rotatable bod~ (a substantially truncated cone, according to the illus~-ated embodiment) with the 'hroug:~.-hole axis as a center. The upper surface of the moorage hull part 3 serves as ~ fore stationary deck 17. The ~inches 4 for the ooring hawsers 1 and the derrlck 14 for 'h~ exoa-~ator are installe~ on the stationary deck 17.
lhe movabl~ hu i part a is connected to the moorage hull part 3 so as to be rotatable about the center of the through-hole 5. In this embodiment, a hole 18 is formed in a hull bottom extended par~ 17A projecting toward the bow at an underwater position of the movable hull part 8, and the moorage hull part 3 is inserted in the hole 13 through the bearings 7 to assemble the floating offahor-st~ucture. In greater detail, the moorage hull part 3 has at an underwater part thereof a neck part 3A with an outer peripheral wall vertically ext2nded, and this neck par~ 3A
is ~itted in tt-e hole 18.
~ ~737~
~ s shown in Fig 5, a hor zontal section of the null near the water surfac2 W has a substantiall-~ ova: sha?Q
including the circul~- fore dra.t part 12 defined by 'he moorage hull part 3 and the n-rrower-width after dr~f' par.
13 defined by the movablQ hull part 8 and taperingl-projec.ing from the ~ore draft part 12 Moreover, the moorage hull part 3 has su~stant_a ly a truncated cone shape, ~hich upwardl~ enlarges, and -hQ fore outer ~all thereof is inclined downwardl~ inward (ang:Q ~) As descriced above, thQ lcating offshore s'ruc~-rQ
shQwn in Figs 5 and ~ differs from that shown in ~.gs thru 4 in that the hull is compcsed of both thQ moor~-e hull part 3 and the mclJa'_le hull ~art 8, but the t-~o structures are practicall~y the sz~e in other res?Qc's ~ccordingly, this e~bcdiment also permits the 'cating icD rorce to be redlicQd for a given effective decc area or displacernent similari~ to the case described above, ~h~n the floating offshore structure is ~oored in bloc~s of - floating ice Moreover, it is posaible to attain _~ch an advantage that the mo~Jable hull part 8 can smoothly -hange the direction without any need for breaking ice whan the floating ice changes its flowing direction It is to be noted that since in this embodi~an- 'hQ
deck fore half on the moorage hull part 3 and the dec'~
after half on the movable hull part 8 rotate in th2 7~
opposite directior.s ~ ea~h ~ :ne_ when the direction changes, it is necessar-i to dis?ose the various equi?..ent and apparatus on t:~e ~Qck in consideration of t'nis ?o'qt Figs. 7 and 8 shc~ a thi--~ prQferred embodimen' of the invention.
This embodiment differs from that shown in Fis~. 5 and 6 in that the movabie hull par. 8 is rotatably conn--~ed ~o the rotatable bod~ shaped mo~r~qe hull part 3 a~ove -h-water surface and that t~e drat part of the movable -.ull part 8 has a substantially ~ r-ular section, but th2 t-~o embodLments are prac sally the same in other respec~s.
In more detai;, t:.e rec.~ part 3A is for~ed in t:he upper part of the su~s ar.tial'y truncated cone shape~
moorage hull part 3, i.e., above the water surface '~, and the ex~ended part 8~. of the movable hull part a is rotatably fitted wi~.h the nec~ part 3A through the ~arings 7. The movable hull part 8 is formed into substantially an inverted truncated cone shape ha~Jing a smaller diæ~eter than the moorage hull part 3, an~ the extended part ~.' is horizontally extended ~rom an upper end surface 8B ;her-of.
Therefore, a horizontal section 11 near the water plan~ has a shape with two se?arate parts, i.e., the moorag- hull part 3, as the fore part, having a radius R and t~e m~vable hull part 8, as the after part, having a radius r, as shown in Fig. 8.
; -14-~ o~7~.~7~
This e~bodiment also offers the sa~e advantage as t'n~
embodiment shown in F~s. 1 thru ~ or that shown in ~ics. 5 and 6.
Fiss. 9 and 10 snow a fourth preferred embodime..t of the invention.
This embodiment differs from the embodiment show.. in Figs. 7 and 8 in tha~ the movable hull part 8 is conne-~od to the moorage hull part 3 at two positions, abo~e ar.~
below the ~ater surf~ce and '..at the deck is defined by the upper surfac~ of the mo~Jable hull part 8 as well as t'nat oxpanded parts i9 and 20 for suppressing heaving and dipping are formed ~ t'-.e bo _om parts of the mooras~ hull part 3 and the mo-JaDle hull p2rt a, respectiv21y, bu; the two embodiments are practically the sa~e in other respects.
More specif.ca71~, the moorag2 hull part 3 has ~ first neck part 3A and a se^ond neck part 38 for~ed at the upper end par' thereof and a position thereof below the wa~er surface respectiv~l~. A first extended part formed by - horizontally extending the deck part of the movable hull part 8 is rotatabl~ fitted with the first neck part 3~, while a second extended part 22 forming a yoke shape by horizontally ext~nding from an underwater position of tne movable hull part 8 is rotatably fitted with the second neck part 38. In this embodiment, the first ext2nded part 21 is defined as the deck of the floating offshore structure.
~ .ccording to this s.~bsdime.~, besides the above-.~entioned advantages, it becomes -elatiJely easier to design, in consideration of strsng h, the connection structurs or the movable hull part 3, i.e., the first and second ext2nded parts 21 and 22. Accordingly, such an effect can be attained that it is possible to ef'fectively su?~ress oscillations in the directions of 6 degrees of freedo~, suc'n as hoaving, pitching ~nd rolling of the hull in 2 stor.~y weather.
Figs. 11 and 12 ahO~ a Fiffh preferred embodlmen~ of the invention.
According to this e~bod ~ent, a hull 31 of a floating offshore structure~ l.e., the ~.ain body is formed in one body and has a ~ertical through-hole 32 formed in a substanti~lly central part thereo. The floating ofFshore structure is ,~oored at a fixed position on the sea by ~oans of a plurality of mooring hawsers 35 extending through the through-hole in the sea from a plurality (e.g., twelve` of .20 winches 34 installed on a deck 33 around the through-hsl2 and anchors 36 connected to the ends of the mooring ha~s~rs 35 respectively.
A derrick 37 for installing an excavator tnot shown) is secured onto the deck 33. An excavating drill pipe 38 driven by the excavator is passed through the vertical ~ -16~
7~
through-hole 32 and e~ ~..szd t^ t..e sea bottom.
A tubular body 39 dcwn-~ard'y ?ro,ec~ing from the hull bottom is disposed arour.~ the opening of the vertic~l through-hole 32 OpenQd in tne hu l bottom. An ove.nanging part 40 is formed on the outer periJhery of the lower end of the tubular body 39.
In addition, pl~lleyc 41 for s~iding th2 respectiv-mooring hawsers 35 are disposed on the inner sur~ace of ~.~2 tubular body 39 in order to prevent the mooring ~.awsers '5 from contacting the wall of ~_he through-hole 32 or the tubular body 39.
Moreover, the ou~er ~ the hull 31 is inclinec downwardly inward by 2n an~le ~ at ieasi at a part nea- ~ne water surface W (~a~r plane).
In case of emplo~in~ the above-described floating offshore structure .n a frozen sea, wn~n floating ice 42 floating near the water surface W ~nd flowing in the direction of an arrow A ~Gllides aga ns~ the hull outer wall, the floating ice breaks into a large num~r of ice 2p blocks 42A, as illustrated. hlthough the floating ic~
force applied to the hull 31 is reduced correspondingl~ to the inclination angl~ O of the outer wall, some of th~
broken ice blocks 42A scatter under~ater and flow near the hull bottom.
However, since the tubular body 39 is provide-d in this ~ ~7~37~
embodir.ent, it is pos a ible .o p re vent the ice blocks 42A
frcm entering the ve~tical thr~,ugh-hole 32 or dir-c~ly colliding with t;~e e~ca~Jating drill pipe 38 and the ~ooring hawsers 35, thereby allowing ~he excavating drill pipe 38 and the mooring hawsers 35 to be protected from dam.age.
Moreover, since the overhanging part 40 is for~ed on thP outer periphery of the lower end of the tubular body 3g, also such an eff2ct can be obtained that it is possible to suppress oscillations of the ~loating ofCshore structure, i.2., oscillations in the direction of 6 ~egrPes of freedom, such as heaJing, pitching and rolling.
Figs. 13 an~ 14 show a sixth preferred embodi~ert of the invention.
This embodiment dif ers from the above-described e.~bodimGnt in tnat the hull 31 is constituted 'Dy a ~oorage hull p~rt 43 which s moored at a fixed position or th~ sea by means of the mGoring hawsers 35 and the anchors 36 connected to tne ends thereof respectively and a movable hull part 4i rotatably fitted with the moora~e hull 2art 43 through bearings 44 and that the tubular body 39 provided around the opening of the vertical through-hole 32 formed in the hull bottom can be adjusted to the illustrated projecting position and a w~ithdrawing position inside the hull 31 by means of cylinders 46 driven by means of oil pressure or the like. The two embodimets arP, however,
fields have been visorousl-~ developed. Also, othe~
submarine resources have k~en energetically investiga~~d and developed. As a mo~ahle excavating apparatus 'oz effecting these deJelopments, for example, a floating offshore structure is ~mployed. The floating offsho~e structure of this ~ype is a larg~-sixed structure hav ng a diameter or longi~udinal or lateral dimension of ne 1~
100 ~, for exa~nple, and a displacement of nearly fr~m 30 to 40 thousand tons. Such a structure employes a large n~er (e.g., 12) of mooring hawsers so as to be moor~d a;
a fixed position on the sea by means of anchors connec.ed to the ends of these moo~i n g hawse r 5 r e spe c t i ve 1~ .
The floating offshor3 structure of this type w~ich is ~ , ~ ~73~ ' employ~ad in an icy sga ar~a in csld wa~srs wbere floating ice is present conven onally has a pianar shape which is a circle or a poly~on close to 2 circle. Therefore, in case of conducting exca~ation in a Crozen sea, this structure is made to have no dir-ctional property with respect to tne floating ice force (the collision force of floating ice) and, henco, is independent of the flowing direction o- the floating ice. On the other hand, however, sinco the structure has a circular section, the width allowing floating ice to collide is large relatively for a giJon effective deck area, so that the structure rcceives a correspondingl~ la~ge collicion force of floating ice.
For the same reason, the mcvement o.- the structure due to waves is larger.
~oreover, in a floating offsncre struc.ur2 for submarine excav~tion, such as an oil rig, a vertical through-hole is formed in the structure body, i.e., the hull, and an excavating drill pipe driven by an excavator on the deck is passed through the tnrough-hole and ex_ended to the sea bottom to carry out operation. In the floating offshore structure of this kind, the vertical througn-hole is hitherto formed as a hole opened in the hull bottom.
Therefore, in case of using the structure in a f~o2en sea, such as cold waters where floating ice is present, some of blocks of ice broken by the outer wall of the hull on the for side (the side with which floating ice collides) scatter in the sea around the hull bottom and may undesirably enter the vertical through-hole from its opening formed in the hull bottom, resulting in damage to the excavating drill pipe and mooring hawsers extending through the through-hole.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a floating offshore structure capable of preventing floating ice from entering the through-hole for receiving the exca-vating drill pipe.
According to the present invention, there is there-fore provided a floating offshore structure for mooring at a fixed position on the sea by means oE a mooring hawser having an anchor connected at the end thereof, for con-ducting a submarine excavating operation by an excavating drill pipe, comprising:
a hull;
a vertical through-hole formed in said hull;
means for preventing floating objects such as broken ice from entering said vertical -through-hole, comprising a tubular body projecting downwardly from a bottom of said hull substantially coaxial with said vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through said vertical through-hole and tubular body to the sea bottom, said tubular body in an operative position projecting below said hull bottom a sufficient distance to prevent said floating objects from entering said vertical through hole, but without reaching said sea bottom and means for suppressing oscillation of said floating offshore structure, comprising an overhanging member pro-jecting radially outwardly from an outer periphery of a lower end of said tubular body.
One or more than one mooring hawser may be used for mooring.
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Preferably, the tubular body can be wi-thdrawn from its projecting operative position to a withdrawn position substantially within said hull.
Preferably, the hull has a mooring hull part for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected to an end thereof, and a movable hull part rotatably fitted about said moorage hull part, said vertical through-hole being formed in a central part of said moorage hull part.
The movable hull part may have a substantially oval horizontal cross-section near its water plane.
It is another object of the present invention to provide a floating offshore structure allowing the forces of floating ice, waves, tide, and wind received by the struc-ture to be smaller for a given effective deck area than theconventional floating offshore structures thereby decreasing the pitch and roll of the structure, as well as capable of smoothly rotating in response to the change in the flowing direction of floating ice or the like so as to prevent the increase in the forces of floating ice, waves, tide and wind, thereby overcoming the above-mentioned problems of the prior art.
According to this object there is provided a floating offshore structure having a floating body with a deck on an upper surface of the floating body and adapted to float while being moored at a fi~ed position on the sea, comprising a fore draft part being a front portion of the floating body, having near its water plane a hori20ntal section, said fore draft part being moored to the sea bottom;
and an after draft part being a rear portion of the floating body, having neax sald water plane a substantially smaller width than said fore draft part, said after draft part being connected to said fore draft part so as to be ~ -4-7~7~
rotatable within a horizontal plane about an axis located about at the center of said fore draft part.
Preferably, the after draft part taperingly projects aft from said fore draft part so that a horizontal section of said floating offshore structure near said water plane is substantially oval.
Preferably, the fore draft part has near said water plane a substantially circular hori,zontal section, while said after draft part has near said water plane a substantially circular horizontal section with a diameter smaller than that of said fore draft part.
Above and other objects and features of the invention will be apparent from the following description given as example without limitative manner when the same is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a floating offshore struc-ture in accordance with a first preferred embodiment of the invention;
Fig. 2 is a sectional view taken along a line II-II
of fig. l;
Fig. 3 is a sectional view of the floating offshore structure shown in Fig. 1 taken along a line III-III of Fig. 2, i.e., a water plane thereof;
Fig. 4 is a sectional view of the floating offshore structure shown in Fig. 1 taken along a water plane thereof, particularl~ illustrating the state of floating ice around the sarne;
Fig. 5 is a sectional side elevational view of a floating offshore structure in accordance with a second preferred embodiment of the invention;
Fig. 6 is a sectional view of the f loating of f shore structure shown in Fig. 5 taken along a water plane 7~37g thereof;
Fig. 7 is a sect_onal sice eievational view of a floating offshore structure in accordance with a t~ir~
preferred embodiment of the in~ention;
S Fig. 8 is a sectior.al view of the floating offshore str~lcture shown in Fig. 7 'a~en along a water plane thereof;
Fis. 9 is a sectional side elevational vie~ of a floating offshore structure in ac^ordance wi_h a four h preferred embodiment of the invention;
Fig. lO is a sectional ~iew cf the floating off_hore structure shown in ~,g. 9 ta~.sn along a line X-~, i.e., a water plane therecf;
Fig. ll is a p~an vie~ o_ a floating offshore structu~e in accordar,~:e with a fifth preferred embodiment of the invention;
Fig. 12 is a sectional view ta~en along a line XII-XII
oE Fig~ 11;
Fig. 13 is a plar. view of a floating offshore structur~ in accordance with a sixth preEerred em~od~ment of th~ inv2ntion;
Fig. 14 is a partially cutaway side elevational view of the Eloating offshore structure shown in Fig. 13i Fig. lS is a plan view of a floatinq offshor~
structure in accordance with a seventh preferred embodiment ,, .
of the invention; and Fig. 16 is ~ ?ar~ially cu_away side elevational view of the floating of_shore structlre shown in Fig. 15.
DESCRIPTION OF THE i??.~ ;) E.4'BODIMENTS
Preferred em~odiments of the invention will bz described hereinunder with reference to the accompanving drawings.
Figs. 1 thru 4 show a floating offshore struc-urz in accordanc~ with a firs. preCe~r2d embodiment of the in~ention.
Referring to Figs. 1 t;.ru 3, a moorage hull par~ 3 is moored at a fixed ?ositic~ Gn he sea by means of a plurality (e.g., -~e'-Je) cf mooring hawsers 1 radial~y extending to the sea bct~om from their respective positions su~stantially ~auali~ spaced ir. the circumferential direction, together with anchors 2 connected to the ends of the mooring hawsers 1, respectively. The moorage hull part 3 has a substantially cylindrical shape with an overhanging upper ~nd surCace~ on which winches 4 for win~ing and unwin?irg the respective mooring hawsers 1 are installed. As illustrated, the mooring hawsers 1 are pa~sed through a vertical through-hole 5 formed in the moorage hull part 3, and stretched in the sea, b~ing guided ~y pulleys 6 disposed nzar the through-hole lower end, resQ~ctively.
1~Z7~7~
P. ~.o-~able hull 2ar~ ~ is fi-~ed around tAe moorage hull part 3 through low-C-ictio^.al means 7 such as bearings so as to be rotatabi~ hin ~ horizontal plane, i.e., about a vertical a~is. In the illustrated embodiment, a mcorage hull part rGceivins hole 9 as a vertical through-hole is formed at a posilion closer to the bow of the mova~le hull part 8 (closer to the left side as viewed in Fig. 1), and the mo~rable hull part ~ and the moorage hull par 3 are connected togethGr with the latter inserted in the receiving hole 9. In ct;.er words, the movabie hull part 8 is constituted as a hull de ining the outer wall of the floating of snore st uct-lr-, which is assembled havi.~ the moorage hull part 3 re~eiv--s in the receiving hole 9 formed inside the hull.
Thus, as shown in Figs. 1 and 3, both the planar shape of a deck 10 formed on the upper surface of the movable hull part 8 and a water plane thereof (a section tak2n along a water surface W) 11 are substantially oval.
Particularly, the water plane, i.e., a horizonal section near the water surface has an oval shape including a fore draft part 12 in the shape of a substantially circular arc (radius R) with the moorage hull part receiving hole 9 as a center and an after draft part 13 taperingl~ projecting aft from the fore draft part. ~lthough the after draft part 13 has a shape of a circular arc with a radius r smaller :J 8 7 Q /~
than ~he radius R OL- _he C3re dr~ ~ part 12 in the illus~rated embodim~nt, the snape o. the aft-r part can b~
formed into a r~ctilinear or any other desired shape.
~oreover, although ~he fore draft part 12 has a sha?~ of a circular arc wi_h a r~dius ~, tnis shape is not exciusive and ma~ be a pollgon.
The outer wall of the movable hull part 8 is i-.-lin~d downwardly in-~ard, similarl-~ to conventional hulls.
Especiall-~, th~ ou er wall near tne fore dr~f~ part 2 is inclined in order to lessen the collision force (floa_ing ice force) against the hull of the floating ice flow ng in the direction of an ar.ow ~ rcm ~he 'ront of th~ bow.
In Fig. 2, t-e d~c~ 1~ for~ed on the u~per su~face of tne movable hull par ~ is a working deck for carrying out lS submarine excavaticn such as oil excavation. On t:~ deck 1~, various equi~nen~s ar.2 ap~aratus are installed ~.icb are required for oper~tion, such as a derrick 14 for installing an excavator (not showni. From the exca~ator, an excavating drill pi~e lS ls ~xzended toward the sea bottom through the vertical through-hole 5 of the moorage hull part 3. Exca~atiQn is conducted by means of a drill provided on the end of the pip~
According to th~ embodiment described above, in an excavating operation by means of the floating offshore structure moored in a frozen sea, when floating ice _g_ (thickncss: 1 m, for exam31e) .low, in the direction o, the arrow A as shown in F g. ~, al':n^ugh the floating ice .orce applied to the floating offshor- struc~ure is aimost e~ual to that ~pplied to a ci~c~llar structure shown by a t-~o-dot chain line in Fi~. 4, i' is possible to allow the dec:Y area and the displace.~ent to be largeE correspondingly to ~:~e portion projecting to~ard the stern. In other wors,, the floating ice force can b~ reduc~d for a given effect~e deck area or displacement, so that it is pcssible to obtain an efficient floating Grfshor- structure.
In addition, since the water plane has the fore a.aft part 12 formed i~to a circu a arc with a pr-scri`æ d -~dius and the a.ter draf_ ~ar~ ~i-h a smaller width and projected, when the flowin~ direction of the fioating ice lS changes and it flO~a in t`ne direction of an arrow B, ~he ~ovable hull part 8 ~an smoothl~v rotate about the moorage hull part 3, as shown in Fig. 4. In other words, since there is no need for breaking ice when the flowing direction of the floating ice changes, the movabl~ :~ull part 8 can change tne direction to the direction or 'he arrow 3 or even to a great~r angle in accordance wi~ the flowing direction of the floating ice, without receiJing a substantial resistance. It is to be noted that when the movabl~ hull part 8 changes the direction, a side thruster 16 can be used, if necessary. As illustrated, the side 7~7~
t~rus.er 16 is yene.ally cons~ t2~ by a propeller mounted at ~n underwater par_ near t;~e s~err. of the movable hull part a.
~oreover, it is possiblo to reduce the value of resistance offered by floating ice, since the outer w~ll of the movable hull ~art 8 is inclined downwardly inw~ ~ at least in the region near the fore draft par~. The larger the inclination angle ~, the smaller the resistance ~alue.
~owever, the inclination angle ~ is practically wil-. n a range from 15 tG 70 deJreeS.
It is to be noted that ~lthough the fore draft sart 12 has a circular shape in th~ 2bove description, practically, there are cases where t:~e shaDe Oc the fore draft par_ 12 is a ?olygon ~ h a lar~e n~m~er of vertexes. It is to be ur.derstood that the circular fore draft part a~cor~ing to th~ ;nvention includes the abov~-mencioned polygon as long as t~ere is no nindr~nce to the wor`~ing of the invention in view of the objects or action and effect thereof, although it depends on th- number oE the vert2xes, the roundness of each vertex or the hardness of ice, t3 say more ?recisely.
?igs. 5 thru 10 show other various preferr~d embodiments of the invention. In the Figures, the parts corres~onding to those of the first embodiment descrioed with reference to Figs. 1 thru 4 are d~noted by ,he same rerer~nce numerals.
7~
Figs. 5 and 6 in c^mbina'ion show a second pre.erred embodiment of the in-~;entior..
In this embodiment, a hull defining the outer w~11 of a floating offshore structure is composed of both the moorage hull par~ 3 ar.d the movable hull part 8.
The moorage hull part 3 having tne vertical through-hole 5 for receiving the excaJating drill pipe 15 and the mooring hawsers 1 has ~ shape of a rotatable bod~ (a substantially truncated cone, according to the illus~-ated embodiment) with the 'hroug:~.-hole axis as a center. The upper surface of the moorage hull part 3 serves as ~ fore stationary deck 17. The ~inches 4 for the ooring hawsers 1 and the derrlck 14 for 'h~ exoa-~ator are installe~ on the stationary deck 17.
lhe movabl~ hu i part a is connected to the moorage hull part 3 so as to be rotatable about the center of the through-hole 5. In this embodiment, a hole 18 is formed in a hull bottom extended par~ 17A projecting toward the bow at an underwater position of the movable hull part 8, and the moorage hull part 3 is inserted in the hole 13 through the bearings 7 to assemble the floating offahor-st~ucture. In greater detail, the moorage hull part 3 has at an underwater part thereof a neck part 3A with an outer peripheral wall vertically ext2nded, and this neck par~ 3A
is ~itted in tt-e hole 18.
~ ~737~
~ s shown in Fig 5, a hor zontal section of the null near the water surfac2 W has a substantiall-~ ova: sha?Q
including the circul~- fore dra.t part 12 defined by 'he moorage hull part 3 and the n-rrower-width after dr~f' par.
13 defined by the movablQ hull part 8 and taperingl-projec.ing from the ~ore draft part 12 Moreover, the moorage hull part 3 has su~stant_a ly a truncated cone shape, ~hich upwardl~ enlarges, and -hQ fore outer ~all thereof is inclined downwardl~ inward (ang:Q ~) As descriced above, thQ lcating offshore s'ruc~-rQ
shQwn in Figs 5 and ~ differs from that shown in ~.gs thru 4 in that the hull is compcsed of both thQ moor~-e hull part 3 and the mclJa'_le hull ~art 8, but the t-~o structures are practicall~y the sz~e in other res?Qc's ~ccordingly, this e~bcdiment also permits the 'cating icD rorce to be redlicQd for a given effective decc area or displacernent similari~ to the case described above, ~h~n the floating offshore structure is ~oored in bloc~s of - floating ice Moreover, it is posaible to attain _~ch an advantage that the mo~Jable hull part 8 can smoothly -hange the direction without any need for breaking ice whan the floating ice changes its flowing direction It is to be noted that since in this embodi~an- 'hQ
deck fore half on the moorage hull part 3 and the dec'~
after half on the movable hull part 8 rotate in th2 7~
opposite directior.s ~ ea~h ~ :ne_ when the direction changes, it is necessar-i to dis?ose the various equi?..ent and apparatus on t:~e ~Qck in consideration of t'nis ?o'qt Figs. 7 and 8 shc~ a thi--~ prQferred embodimen' of the invention.
This embodiment differs from that shown in Fis~. 5 and 6 in that the movabie hull par. 8 is rotatably conn--~ed ~o the rotatable bod~ shaped mo~r~qe hull part 3 a~ove -h-water surface and that t~e drat part of the movable -.ull part 8 has a substantially ~ r-ular section, but th2 t-~o embodLments are prac sally the same in other respec~s.
In more detai;, t:.e rec.~ part 3A is for~ed in t:he upper part of the su~s ar.tial'y truncated cone shape~
moorage hull part 3, i.e., above the water surface '~, and the ex~ended part 8~. of the movable hull part a is rotatably fitted wi~.h the nec~ part 3A through the ~arings 7. The movable hull part 8 is formed into substantially an inverted truncated cone shape ha~Jing a smaller diæ~eter than the moorage hull part 3, an~ the extended part ~.' is horizontally extended ~rom an upper end surface 8B ;her-of.
Therefore, a horizontal section 11 near the water plan~ has a shape with two se?arate parts, i.e., the moorag- hull part 3, as the fore part, having a radius R and t~e m~vable hull part 8, as the after part, having a radius r, as shown in Fig. 8.
; -14-~ o~7~.~7~
This e~bodiment also offers the sa~e advantage as t'n~
embodiment shown in F~s. 1 thru ~ or that shown in ~ics. 5 and 6.
Fiss. 9 and 10 snow a fourth preferred embodime..t of the invention.
This embodiment differs from the embodiment show.. in Figs. 7 and 8 in tha~ the movable hull part 8 is conne-~od to the moorage hull part 3 at two positions, abo~e ar.~
below the ~ater surf~ce and '..at the deck is defined by the upper surfac~ of the mo~Jable hull part 8 as well as t'nat oxpanded parts i9 and 20 for suppressing heaving and dipping are formed ~ t'-.e bo _om parts of the mooras~ hull part 3 and the mo-JaDle hull p2rt a, respectiv21y, bu; the two embodiments are practically the sa~e in other respects.
More specif.ca71~, the moorag2 hull part 3 has ~ first neck part 3A and a se^ond neck part 38 for~ed at the upper end par' thereof and a position thereof below the wa~er surface respectiv~l~. A first extended part formed by - horizontally extending the deck part of the movable hull part 8 is rotatabl~ fitted with the first neck part 3~, while a second extended part 22 forming a yoke shape by horizontally ext~nding from an underwater position of tne movable hull part 8 is rotatably fitted with the second neck part 38. In this embodiment, the first ext2nded part 21 is defined as the deck of the floating offshore structure.
~ .ccording to this s.~bsdime.~, besides the above-.~entioned advantages, it becomes -elatiJely easier to design, in consideration of strsng h, the connection structurs or the movable hull part 3, i.e., the first and second ext2nded parts 21 and 22. Accordingly, such an effect can be attained that it is possible to ef'fectively su?~ress oscillations in the directions of 6 degrees of freedo~, suc'n as hoaving, pitching ~nd rolling of the hull in 2 stor.~y weather.
Figs. 11 and 12 ahO~ a Fiffh preferred embodlmen~ of the invention.
According to this e~bod ~ent, a hull 31 of a floating offshore structure~ l.e., the ~.ain body is formed in one body and has a ~ertical through-hole 32 formed in a substanti~lly central part thereo. The floating ofFshore structure is ,~oored at a fixed position on the sea by ~oans of a plurality of mooring hawsers 35 extending through the through-hole in the sea from a plurality (e.g., twelve` of .20 winches 34 installed on a deck 33 around the through-hsl2 and anchors 36 connected to the ends of the mooring ha~s~rs 35 respectively.
A derrick 37 for installing an excavator tnot shown) is secured onto the deck 33. An excavating drill pipe 38 driven by the excavator is passed through the vertical ~ -16~
7~
through-hole 32 and e~ ~..szd t^ t..e sea bottom.
A tubular body 39 dcwn-~ard'y ?ro,ec~ing from the hull bottom is disposed arour.~ the opening of the vertic~l through-hole 32 OpenQd in tne hu l bottom. An ove.nanging part 40 is formed on the outer periJhery of the lower end of the tubular body 39.
In addition, pl~lleyc 41 for s~iding th2 respectiv-mooring hawsers 35 are disposed on the inner sur~ace of ~.~2 tubular body 39 in order to prevent the mooring ~.awsers '5 from contacting the wall of ~_he through-hole 32 or the tubular body 39.
Moreover, the ou~er ~ the hull 31 is inclinec downwardly inward by 2n an~le ~ at ieasi at a part nea- ~ne water surface W (~a~r plane).
In case of emplo~in~ the above-described floating offshore structure .n a frozen sea, wn~n floating ice 42 floating near the water surface W ~nd flowing in the direction of an arrow A ~Gllides aga ns~ the hull outer wall, the floating ice breaks into a large num~r of ice 2p blocks 42A, as illustrated. hlthough the floating ic~
force applied to the hull 31 is reduced correspondingl~ to the inclination angl~ O of the outer wall, some of th~
broken ice blocks 42A scatter under~ater and flow near the hull bottom.
However, since the tubular body 39 is provide-d in this ~ ~7~37~
embodir.ent, it is pos a ible .o p re vent the ice blocks 42A
frcm entering the ve~tical thr~,ugh-hole 32 or dir-c~ly colliding with t;~e e~ca~Jating drill pipe 38 and the ~ooring hawsers 35, thereby allowing ~he excavating drill pipe 38 and the mooring hawsers 35 to be protected from dam.age.
Moreover, since the overhanging part 40 is for~ed on thP outer periphery of the lower end of the tubular body 3g, also such an eff2ct can be obtained that it is possible to suppress oscillations of the ~loating ofCshore structure, i.2., oscillations in the direction of 6 ~egrPes of freedom, such as heaJing, pitching and rolling.
Figs. 13 an~ 14 show a sixth preferred embodi~ert of the invention.
This embodiment dif ers from the above-described e.~bodimGnt in tnat the hull 31 is constituted 'Dy a ~oorage hull p~rt 43 which s moored at a fixed position or th~ sea by means of the mGoring hawsers 35 and the anchors 36 connected to tne ends thereof respectively and a movable hull part 4i rotatably fitted with the moora~e hull 2art 43 through bearings 44 and that the tubular body 39 provided around the opening of the vertical through-hole 32 formed in the hull bottom can be adjusted to the illustrated projecting position and a w~ithdrawing position inside the hull 31 by means of cylinders 46 driven by means of oil pressure or the like. The two embodimets arP, however,
3.~ 7~
practically the same in othGr respects. Accordin~ly, liks or corresponding parrs are deno e~ by like rerer2nce nume-als respectivel~, and a detailQd description ~hQreof is omitted.
According to this embGdimQnt, in case of employi.ng the floating offshore st-ucture in a frozen sea, i' is ?ossible to obtain the same ad-~antages as the above-d~s^ri'~d embodiment. Moreover, since ths hull 31 is consti~ tQd by both the moorage hull part 43 and the movable null pa.~ 45, it is possible to obtain an e~fect that the moS~able hull part ~5 can change the di.ection in accordance with tne dir~c~ion of the floa-ing i~s force applied thereto and the force can be lessened corres2ondingly. In addition, s~lch an effect can b- obtainQd that it is possible ~o reduce resistance in towing, sinse ~he tubular bod~y 3~ can ~
adjusted to the ~ithdrawing position.
As will b~ apparent from the a~ove description, according to the fifth and sixth em~odiments, it is possi~le to obtain a floating offshore structure capable of protecting the excaJating drill pipe and mooring ha-~,ers disposed through the vertical through-hole fro~ floating ise by preventing floating ice from entering the through-hole, as ~ell as suppressing the heaving and dipping or the hull.
Finally, a seventh pre~errea embodiment of the invention is shown in Pigs~ 15 and 16. This embodim~nt is ~ 19--~ ~7~
constituted by combining thD embsdimPnt shown in ~l~s. l and 2 and that shown n Figs. 13 a..d 14. P~rts identical or corresponding to those shown in Figs. 13 and 14 ~re denoted by the same referenc_ numerals as those in ~igs. 13 S and 14, and a detailed description thereof is omitted. In other ~ords, this emDcdiment differs from the above-dPscriced sixth embodiment in that the movable hull par' 45 has a substantiall~ oval planar shape at the deck '3 and -fs wAter plane similArl~y to the first embodiment so that the movable hull part 45 c~n smoothly rotate in response to the change in the flowing direcfion of floating ic~ or the like and moreove- the d~c~ ~rea can be inc~eased without receiving a larser f'oating lce force. The sixth and seventh embodiments are, however, practically the same in o'he~ respects. mherPfore, according to this emb^dimDnt, it is possible to o~,cair. th~ effect orrered by the first embodiment, toge~her with that presented by the six~h embodiment.
~lthough the invention has ~een described through specific terms, lt is to be noted here that the descri3ed embodiments are not exclusive and various changes and modifications ma~ be imparted thereto without depar~ing from the scope of th~ invention which is limited solely by the apponded claims.
practically the same in othGr respects. Accordin~ly, liks or corresponding parrs are deno e~ by like rerer2nce nume-als respectivel~, and a detailQd description ~hQreof is omitted.
According to this embGdimQnt, in case of employi.ng the floating offshore st-ucture in a frozen sea, i' is ?ossible to obtain the same ad-~antages as the above-d~s^ri'~d embodiment. Moreover, since ths hull 31 is consti~ tQd by both the moorage hull part 43 and the movable null pa.~ 45, it is possible to obtain an e~fect that the moS~able hull part ~5 can change the di.ection in accordance with tne dir~c~ion of the floa-ing i~s force applied thereto and the force can be lessened corres2ondingly. In addition, s~lch an effect can b- obtainQd that it is possible ~o reduce resistance in towing, sinse ~he tubular bod~y 3~ can ~
adjusted to the ~ithdrawing position.
As will b~ apparent from the a~ove description, according to the fifth and sixth em~odiments, it is possi~le to obtain a floating offshore structure capable of protecting the excaJating drill pipe and mooring ha-~,ers disposed through the vertical through-hole fro~ floating ise by preventing floating ice from entering the through-hole, as ~ell as suppressing the heaving and dipping or the hull.
Finally, a seventh pre~errea embodiment of the invention is shown in Pigs~ 15 and 16. This embodim~nt is ~ 19--~ ~7~
constituted by combining thD embsdimPnt shown in ~l~s. l and 2 and that shown n Figs. 13 a..d 14. P~rts identical or corresponding to those shown in Figs. 13 and 14 ~re denoted by the same referenc_ numerals as those in ~igs. 13 S and 14, and a detailed description thereof is omitted. In other ~ords, this emDcdiment differs from the above-dPscriced sixth embodiment in that the movable hull par' 45 has a substantiall~ oval planar shape at the deck '3 and -fs wAter plane similArl~y to the first embodiment so that the movable hull part 45 c~n smoothly rotate in response to the change in the flowing direcfion of floating ic~ or the like and moreove- the d~c~ ~rea can be inc~eased without receiving a larser f'oating lce force. The sixth and seventh embodiments are, however, practically the same in o'he~ respects. mherPfore, according to this emb^dimDnt, it is possible to o~,cair. th~ effect orrered by the first embodiment, toge~her with that presented by the six~h embodiment.
~lthough the invention has ~een described through specific terms, lt is to be noted here that the descri3ed embodiments are not exclusive and various changes and modifications ma~ be imparted thereto without depar~ing from the scope of th~ invention which is limited solely by the apponded claims.
Claims (4)
1. A floating offshore structure for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected at the end thereof, for conducting a submarine excavating operation by an excavating drill pipe, comprising:
a hull;
a vertical through-hole formed in said hull;
means for preventing floating objects such as broken ice from entering said vertical through-hole, comprising a tubular body projecting downwardly from a bottom of said hull substantially coaxial with said vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through said vertical through-hole and tubular body to the sea bottom, said tubular body in an operative position projecting below said hull bottom a sufficient distance to prevent said floating objects from entering said vertical through hole, but without reaching said sea bottom; and means for suppressing oscillation or said floating offshore structure, comprising an overhanging member pro-jecting radially outwardly from an outer periphery of a lower end of said tubular body.
a hull;
a vertical through-hole formed in said hull;
means for preventing floating objects such as broken ice from entering said vertical through-hole, comprising a tubular body projecting downwardly from a bottom of said hull substantially coaxial with said vertical through-hole such that the mooring hawser and the excavating drill pipe can be extended through said vertical through-hole and tubular body to the sea bottom, said tubular body in an operative position projecting below said hull bottom a sufficient distance to prevent said floating objects from entering said vertical through hole, but without reaching said sea bottom; and means for suppressing oscillation or said floating offshore structure, comprising an overhanging member pro-jecting radially outwardly from an outer periphery of a lower end of said tubular body.
2. A floating offshore structure according to claim 1, wherein said tubular body can be withdrawn from its pro-jecting operative position to a withdrawn position substantial-ly within said hull.
3. A floating offshore structure according to claim 1, wherein said hull has a mooring hull part for mooring at a fixed position on the sea by means of a mooring hawser having an anchor connected to an end thereof, and a movable hull part rotatably fitted about said moorage hull part, said vertical through-hole being formed in a central part of said moorage hull part.
4. A floating offshore structure according to claim 3, wherein said movable hull part has a substantially oval horizontal cross-section near its water plane.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000507928A CA1227379A (en) | 1982-04-16 | 1986-04-29 | Floating offshore structure |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57-63628 | 1982-04-16 | ||
| JP57-63629 | 1982-04-16 | ||
| JP57063628A JPS58180393A (en) | 1982-04-16 | 1982-04-16 | Mooring structure |
| JP6362982A JPS58180394A (en) | 1982-04-16 | 1982-04-16 | Mooring structure |
| CA000425226A CA1213788A (en) | 1982-04-16 | 1983-04-05 | Floating offshore structure |
| CA000507928A CA1227379A (en) | 1982-04-16 | 1986-04-29 | Floating offshore structure |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000425226A Division CA1213788A (en) | 1982-04-16 | 1983-04-05 | Floating offshore structure |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1227379A true CA1227379A (en) | 1987-09-29 |
Family
ID=27167335
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000507928A Expired CA1227379A (en) | 1982-04-16 | 1986-04-29 | Floating offshore structure |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1227379A (en) |
-
1986
- 1986-04-29 CA CA000507928A patent/CA1227379A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |