Note: Descriptions are shown in the official language in which they were submitted.
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.
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
79
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
,, .
--6--
379
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_
79
(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.
-12-
~ ~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
79
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
-17-
~ ~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.
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