US2919671A - Mooring arrangement - Google Patents

Description

2' Sheets-Sheet 1 Filed Aug. 7, 1957 INVENTORS. James G. Walvaord RichqrdvP. Knapp,

Jam 5 1960 R. P. KNAPP Erm. 2,919,671

MOORING ARRANGEMENT Filed Aug. 7, 1957 2 Sheets-Sheet 2 INVENTORS. James G. Walvoord, Richard P. Knapp,

#w27-ML( A T TORNE Y United States Patenti/ MooruNo ARRANGEMENT Richard P. Knapp, Houston, Tex., and James G. Walvoord, Grand Isle, La., assignors, by mesne assignments, to Jersey Production Research Company, Tulsa, Okla., a corporation of Delaware Application August 7, 1957, Serial No. 676,845

Claims. (Cl. 114-230) This invention relates to a mooring arrangement. More particularly, this invention relates to a mooring arrangement for floating vessels used in conducting 01T- shore operations.

Current mooring arrangements used for floating vessels, such as a rig tender, marine construction vessel, dredge or submarine mining vessel, have several disadvantages. For example, in conducting oifshore operations, such as well drilling, a drilling rig platform is used upon which the drilling equipment, such as the rigs, motors, etc., are placed. A oating vessel which is used as a rig tender is moored adjacent the drilling platform. The usual practice has been to use a plurality of chains or cables as a mooring arrangement. However, when a storm warning is sounded, it is necessary in order to avoid a collision between the tender and the drilling piatform that certain of the cables or chains be disconnected. If these chains or cables are not disconnected, there is a strong possibility that the tender will be pushed against the platform by the waves and both damaged severely.

Quite often it happens that storm warnings are given, the'desired moorings disconnected from the rig tender; and then no storm occurs. It is then necessary to recover the disconnected moorings,l and depending upon the weather conditions, it may take many days to recover the disconnected moorings. This loss of time is Very costly. If, instead of disconnecting the particular mooring lines, all of the lines were left connected and a storm did strike, it is highly possible that if the mooring lines were allowed to break at random, a collision between the tender and the platform would occur.

Our new mooring arrangement with the new type of mooringmeans utilized provides an arrangement which can be used to maintain the tender in the normal mooring position during calm weather. lf a storm warning is received, our new mooring arrangement remains intact. Hence, if the storm does not actually occur, the mooring means have not been disconnected and the time lost in recovering lost mooring means is saved. On the other hand, if a storm should occur, the specic structure of certain of the mooring means in the arrangement is such that the mooring means will not be allowed to break at random and only those mooring means will break which will minimize the possibility of a collision between the tender and the platform.

Briefly described, our new mooring arrangement includes a plurality of mooring means which are connected to anchors spaced about the rig tender. An important feature of the mooring arrangement is that some of the mooring means are purposely made with a section thereof strong enough to remain intact in normal weather and yet weak enough to break in a severe storm. Hence, if a storm should strike, the mooring means having Vthe weak section will be broken by the storm and the tender will swing about on the remaining chains in a manner such that it is kept clear of the drilling platform.

For a detailed description of a preferred embodiment of the invention, reference will be had to the accompanying drawings in which:

Fig. 1 is a plan view showing the mooring arrangement with the rig tender in normal mooring position;

Fig. 2 is a plan view showing the mooring arrangement in storm mooring position;

Fig. 3 is a plan View of one of the chains containing the frangible material;

Fig. 3a is an elevational view of the chain stopper of Fig. 3; and

Fig. 4 is a plan view showing the relative positions of the steel pile mooring anchors with respect to the drilling platform. A

Referring to Fig. l, a long narrow floating vessel 10 is shown moored in position adjacent a platform 11. In offshore operations, platform 11 contains the necessary equipment for conducting the operations, such as drilling rigs, engines, pipes, etc., with the vessel 10 used as a` tender. Though vessel 10 is shown as long and narrow, it is to be understood that the vessel may be of any other shape, such as a square.

The vessel 16 is moored by means of a plurality of mooring means 12, 13, 14, 15, 16, 17, 1S, and 19. Each of the mooring means l2 through 19, inclusive, may consist of a chain consisting of a plurality of chain links with each chain being connected to steel pile mooring anchors, 5t) to 57, inclusive. f

Chains 12 and 13 are connected to the aft short side of the vessel and extend outwardly from the aft side. Chains 12 and 13 are normally on opposite sides of a. plane passing through the longitudinal axis of the vessel.. Two other chains 14 and 15 are connected to the aft part of the vessel ltl on opposite long sides of the vessel.Y The remaining four chains 16 through 19, inclusive, all radiate from the bow of vessel 1) with chains 16 and 17 v extending substantially parallel to chains 14 and 15, and chains 13 and 19 extending outwardly from the bow on opposite sidesof a plane passing through the longitudinal axis of the vessel l0. The angular separation of chains.

- 18 and 19-from the longitudinal axis of vessel 10 is suboccurs.

` tice.

stantially greater than the angular separation of chains 12 and 13 from the longitudinal axis.

When storm warnings are given, the current practice is to disconnect some of the mooring chains, such i as chains 14 through 19, inclusive, and shorten 12 and 13 Vso as to be certain that the vessel 10 does not collide with platform 11. However, as stated, quite often after storm warnings the storm does not actually occur andl many days may be used in recovering the disconnected chains. If all of the chains are left connected and a storm does occur and certain of the chains are broken by the i storm, such as chains 12 and 13, it can be seen from Fig. 1 that a collision between the tender 1t) and plat- I form 11 is quite likely. It has occurred in actual prac-y This causes severe damage to the platform and equipment thereon and also severe damage to the vessel.

We, however, provide a storm mooring arrangement which need not be disconnected when a storm warning The new storm mooring arrangement also assures that no collision will occur between the tender and the platform. Our new storm mooring arrangement includes a section of frangible material in some of the chains 12 through 19, inclusive. The frangible material is strong enough to remain intact if a storm does not oc'- cur and yet weak enough that breaks will occur at `the points where the frangible material is located rather than at other points in the chain.

lA specic embodiment of chain or mooring meansz in which this principle of purposely placing a section in the chain of weaker breaking strength is illustrated in Fig. 3. A chain guide 2u is shown positioned on the deck 21 of the tender. The chain is payed-out and reeled in through a mooring chock 22. A chain stopper 23 is positioned across the chain guide 2t? and utilized to control the amount of pay-out of the chain. In the embodiment shown in Fig. 3, a pair of two inch heavy duty detachable links 2S and 2,6 are used to connect the frangible material to the rest of the chain. This frangible material may consist of the wrought iron links 27, 23, andA 29 shown in Fig. 3. Heavy duty detachable links 25 and 26 initially have recesses formed therein for the easy attachment and detachment of links 27, 28, and 29 from the rest of the chain, these recesses being closed after attachment of frangible material by various means.

Referring again to Fig. l, which is the normal mooring arrangement, we provide chains l2 and 13 with a new two inch high strength forged steel chain having a high breaking strength. This increased strength in mooring lines 12 and 13 reduces the probability of collisions between the drilling rig lll and the drilling rig tender 10 as a result of mooring line failures. Chains 12 and 13 may be anchored to the steel piles 5G and 51 by means of anchors 32 and 33, respectively. Steel pile mooring anchors through 57, inclusive, are driven into the hard bed of the bottom.

The wrought iron links are included in chains 14 through 19, inclusive, and are kept inboard of the chain Stoppers when the vessel is in normal mooring posiing position. Hence, during normal mooring operations the frangible material is not subject to the forces of the Wind and the wave and, hence, there is no possibility that a chain will break at the frangible material during normal operations.

By using wrought iron links of the same size as the forged steel links in the remainder of the mooring chain, handling of the mooring lines through chocks and chain stoppers is facilitated.

If a storm warning occurs, the vessel is moved away from platform 11 about 200 more feet so as to be approximately 225 feet from the front edge of the platform. The changed relative position of the mooring means 1 2 through 19, inclusive, is as shown in Fig. 2. The wrought iron links have been allowed to pay-out along with the chains 14 through 19, inclusive, so that during storm mooring arrangement they are outboard of the vessel such as shown in Fig. 3. The breaking strength of the wrought iron chain links may vary in magnitude from just below the breaking strength of the forged steel links to less than half the breaking strength of the forged steel links. Using the same materials for the strong and weak sections, the breaking strengths vary according to chain size and size of the tender. The breaking strength of the wrought iron links is high enough so that if the storm does not strike they will remain intact and it will not be necessary to connect them again. If a storm should strike and is of suicient severity, any breakage of the mooring lines will occur at the weak links. After the wrought iron links have been broken, chains 14 through 19, inclusive, will no longer restrain the movement of the vessel it). Thus, after the breaking of the chains, the vessel l@ will swing on the chains 12 and 13 regardless of the direction or change in direction of the wind. The longitudinal axis of the vessel 10 will continuously be aligned with the direction of the wind. ecause the longitudinal axis of the vessel is aligned with this direction, the smallest area of the vessel is always presented toward the main force of the winds and waves. Also, no restraint is maintained on the pivotal movement of the vessel l@ about the piles 50 and 5l. Thus, the stress upon chains l2 and 13 is minimized. Hence, chains 12 and 13 will remain intact i and the vessel will be retained out of reach of platform Fig. 4 is a plan view showing the angular relationship of the steel pile mooring anchors with respect to the front of platform il and the longitudinal axis of platform Ill. Piles 5@ and 5l are at 2 40 on opposite sides of the longitudinal axis, piles 52 and 53 are at approximately 68 47 on opposite sides of the longitudinal axis, piles 54 and 55 are at approximately 87 6' on opposite sides of the longitudinal axis, and piles 56 and 57 are at 132 lll/2 on opposite sides of the longitudinal axis.

in operation, the vessel l@ is maintained at about 25 feet away from platform 11 with the bow facing the platform. if a storm warning occurs, the vessel is moved from the platform another 200 feet. rhe movement is accomplished by pulling in chains 12 and i3, lifting chain stopper 23, and paying-out the chains 14 through 19, inclusive. The frangible links which, during normal mooring arrangement, are inboard are then passed through the chain stopper so that they are placed outboard and the chains locked by setting the appropriate chain stopper and the brake on the chain windlass.

We create weak spots of a selected magnitude lin the mooring means. The weak spots are illustrated as being weak links, such as links made of wrought iron. In some cases, links of cast steel might be used. Also, forged steel links of material identical with the remainder of the mooring means, but of a different size or partly sawed through, might he used. Accordingly, the term frangible as used herein and in the appended claims is intended to include the use of any material and any` physical configuration to produce the desired degree of weakness.

We claim:

l. A mooring arrangement for a long, narrow floating vessel comprising: four anchored mooring chains radiatf ing from each end of the vessel, with two of said four mooring chains extending outwardly from the short side of the vessel, one on each side of a vertical plane passing through the longitudinal axis of the vessel and the other two mooring chains extending from opposite long sides of the vessel, at least one of said two mooring chains extending outwardly from one short side of the vessel being made up of chain links of high breaking strength throughout their length and the other mooring chains each having at least one weak link having a breaking strength of less than one-half the breaking strength of the rest of the chain links; means for retaining the weak links inboard when the vessel is in normal mooring position and means for paying out the weak links outboard when the vessel is moved to storm mooring position.

2. A storm mooring arrangement for a oating vessel comprising: two anchored mooring means each having la high breaking strength along their entire length and extending outwardly from the stern side of the vessel;` and a plurality of other anchored mooring means radiating from the other sides of the oating vessel and each having a portion of frangible material of substantially lower breaking strength than the rest of the mooring means.

3. A storm mooring arrangement in accordance with claim 2 wherein said plurality of mooring means are chains and the portion of frangible material consists of at least one link of wrought iron with the rest of the chains consisting of forged steel links.

4. A storm mooring arrangement in accordance with claim 3 wherein the wrought iron has a breaking strength of lless than one-half the breaking strength of the forged stee 5. A storm mooring arrangement in accordance with claim 2 wherein said two anchored mooring means are chains of forged steel along their entire length with one chain being on each side of a vertical plane pasing nthrough the longitudinal axis of the vessehand the plural# ity of other anchored mooring means includes'six chains of' forged steel with each chain having a portion thereof of References Cited in the file of this patent wrought iron, with two of six chains radiating from the same end of the vessel as the two chains made of forged FOREICI PATENTS steel along their entire length, and four of said six 2,543 Great Britain of 1871 chains radiating from the other end of the vessel. 5 668,786 Germany Dec. 9, 1938

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