DYNAMIC VESSEL MOORING SYSTEM AND METHOD

Abstract

An example is directed to a mooring apparatus for mooring a vessel via a mooring buoy to an anchor under weather conditions from a light weather condition up to a preset maximum weather condition. A single-bouncer mooring apparatus includes a bouncer connected via an anchor line to the anchor having an anchor weight, the bouncer having a bouncer weight; and a catenary section line connected between the mooring buoy and the bouncer, the catenary section line having a catenary section length and a catenary section weight. The bouncer weight, the catenary section length, and the catenary section weight are selected to place the bouncer just touching the bottom of the body of water in the preset maximum weather condition for the vessel having the vessel length and the vessel weight. A multiple-bouncer mooring apparatus includes two or more bouncers connected in series via respective catenary section lines to the mooring buoy.

Claims

1. A mooring apparatus for mooring a vessel having a vessel length and a vessel weight, via a mooring buoy to an anchor disposed at a bottom of a body of water under weather conditions from a light weather condition up to a preset maximum weather condition, the mooring apparatus comprising: two or more bouncers connected in series to the mooring buoy and including a distal bouncer which is connected via an anchor line to the anchor having an anchor weight, the two or more bouncers each having a bouncer weight; and two or more catenary section lines including a first catenary section line connected between the mooring buoy and a proximal bouncer which is a first bouncer of the two or more bouncers; the first bouncer being connected sequentially to an i-th bouncer as the distal bouncer in series via the two or more catenary section lines from the first catenary section line to an i-th catenary section line as a distal catenary section line; and the two or more bouncers each having a bouncer weight and the two or more catenary section lines each having a catenary section length and a catenary section weight, which are selected to place the distal bouncer just touching the bottom of the body of water in the preset maximum weather condition for the vessel having the vessel length and the vessel weight.

2. The mooring apparatus of claim 1, wherein the preset maximum weather condition adds to a maximum of MLLW (Minimum Lower Low Water) by a tidal range and a storm surge to form a total water depth for placing the distal bouncer just touching the bottom of the body of water in the preset maximum weather condition.

3. The mooring apparatus of claim 2, wherein a total weight of the two or more bouncers has a limit of F.sub.Vmax, a comfortable vertical force, provided by a moored facility and the mooring buoy, and associated with an acceptable, relatively small longitudinal inclination or trim which would not affect the facility's function.

4. The mooring apparatus of claim 3, wherein the buoy end tangential force T, when the proximal bouncer is bouncing, is determined based on a unit weight in water of the proximal catenary section line q, the water depth h, and the bouncing bouncer's tangential force T.sub.bouncer, i.e., T=q*h+T.sub.bouncer, here T.sub.bouncer being a combination of a weight in water of the bouncer W.sub.1 and the horizontal force F.sub.H, T.sub.bouncer=sqrt (W.sub.1.sup.2+F.sub.H.sup.2).

5. The mooring apparatus of claim 1, wherein a number of the two or more bouncers, the bouncer weight of each bouncer of the two or more bouncers, and the catenary section length and the catenary section weight of each catenary section line of the two or more catenary section lines are determined using a catenary analysis, involving an iteration process running through each chain/hawser segment for each catenary section, to add up cumulatively the two or more catenary section lines sequentially from the first catenary section line to the distal catenary section line until the distal bouncer just touches the bottom of the body of water in the preset maximum weather condition.

6. The mooring apparatus of claim 4, wherein a distal catenary section length of the distal catenary section line may not be preset as that of a previous catenary section, but is tried out using an iteration process to add up cumulatively all of the segments on the tried length of the section to see if the distal bouncer just touches the bottom of the body of water in the preset maximum weather condition.

7. The mooring apparatus of claim 5, wherein a length of a proximal catenary section line is not preset but is determined using the catenary analysis involving an iteration process that runs through every segment until the proximal bouncer at the last segment just touches the bottom of the body of water in a light weather condition (e.g., the condition that generates the of the moored ship's maximum weather horizontal resistance, for the catenary section of a 3,000 lb proximal bouncer).

8. The mooring apparatus of claim 1, wherein the two or more bouncers each includes at least one of (i) a plate-like shape or (ii) a damper plate coupled thereto.

9. The mooring apparatus of claim 1, wherein the anchor comprises an array of ground anchors connected to the distal bouncer via their respective anchor lines, slack on seabed, with different length in different directions from the distal bouncer.

10. A mooring apparatus for mooring a vessel having a vessel length and a vessel weight, via a mooring buoy to an anchor disposed at a bottom of a body of water under weather conditions from a light weather condition up to a preset maximum weather condition, the mooring apparatus comprising: a bouncer connected via an anchor line to the anchor having an anchor weight, the bouncer having a bouncer weight; and a catenary section line connected between the mooring buoy and the bouncer, the catenary section line having a catenary section length and a catenary section weight; the bouncer weight, the catenary section length, and the catenary section weight being selected to place the bouncer just touching the bottom of the body of water in the preset maximum weather condition for the vessel having the vessel length and the vessel weight.

11. The mooring apparatus of claim 10, wherein the preset maximum weather condition adds to a maximum of MLLW (Minimum Lower Low Water) by a tidal range and a storm surge to form a total water depth for placing the bouncer just touching the bottom of the body of water in the preset maximum weather condition.

12. The mooring apparatus of claim 11, wherein the weight of the bouncer has a limit of F.sub.Vmax, a comfortable vertical force, provided by a moored facility and the mooring buoy, and associated with an acceptable, relatively small longitudinal inclination or trim which would not affect the facility's function.

13. The mooring apparatus of claim 12, wherein the buoy end tangential force T is determined based on a unit weight in water of the catenary section line q, the water depth h, and the bouncing bouncer's tangential force T.sub.bouncer, i.e., T=q*h+T.sub.bouncer, here T.sub.bouncer being a combination of a weight in water of the bouncer and the horizontal force.

14. The mooring apparatus of claim 10, wherein the bouncer weight and the catenary section length and the catenary section weight are determined using a catenary analysis, involving an iteration process running through each segment of the catenary section line until the bouncer just touches the bottom of the body of water in the preset maximum weather condition.

15. The mooring apparatus of claim 10, wherein the bouncer may be (i) a plate-like shape or (ii) a damper plate coupled thereto.

16. The mooring apparatus of claim 10, wherein the anchor comprises an array of ground anchors connected to the bouncer via their respective anchor lines, slack on seabed, with different length in different directions from the bouncer.

17. A method of mooring a vessel having a vessel length and a vessel weight, via a mooring buoy to an anchor disposed at a bottom of a body of water under weather conditions from a light weather condition up to a preset maximum weather condition, the method comprising: connecting two or more bouncers in series to the mooring buoy, the two or more bouncers including a distal bouncer which is connected via an anchor line to the anchor having an anchor weight, the two or more bouncers each having a bouncer weight; connecting a first catenary section line between the mooring buoy and a proximal bouncer which is a first bouncer of the two or more bouncers; connecting the first bouncer sequentially to an i-th bouncer as the distal bouncer in series via two or more catenary section lines from the first catenary section line to an i-th catenary section line as a distal catenary section line; and selecting the two or more bouncers each having a bouncer weight and the two or more catenary section lines each having a catenary section length and a catenary section weight, to place the distal bouncer just touching the bottom of the body of water in the preset maximum weather condition for the vessel having the vessel length and the vessel weight.

18. The method of claim 17, wherein the preset maximum weather condition adds to a maximum of MLLW (Minimum Lower Low Water) by a tidal range and a storm surge to form a total water depth for placing the distal bouncer just touching the bottom of the body of water in the preset maximum weather condition.

19. The method of claim 18, wherein a total weight of the two or more bouncers has a limit of F.sub.Vmax, a comfortable vertical force, provided by a moored facility and the mooring buoy, and associated with an acceptable, relatively small longitudinal inclination or trim which would not affect the facility's function.

20. The method of claim 19, further comprising: determining the buoy end tangential force T, when the proximal bouncer is bouncing, based on a unit weight in water of the proximal catenary section line q, the water depth h, and the bouncing bouncer's tangential force T.sub.bouncer, i.e., T=q*h+T.sub.bouncer, here T.sub.bouncer being a combination of a weight in water of the bouncer W.sub.1 and the horizontal force F.sub.H, T.sub.bouncer=sqrt (W.sub.1.sup.2+F.sub.H.sup.2).

21. The method of claim 17, further comprising: determining a number of the two or more bouncers, the bouncer weight of each bouncer of the two or more bouncers, and the catenary section length and the catenary section weight of each catenary section line of the two or more catenary section lines using a catenary analysis, involving an iteration process running through each chain/hawser segment for each catenary section, to add up cumulatively the two or more catenary section lines sequentially from the first catenary section line to the distal catenary section line until the distal bouncer just touches the bottom of the body of water in the preset maximum weather condition.

22. The method of claim 20, further comprising: trying out a distal catenary section length of the distal catenary section line, which may not be preset as that of a previous catenary section, using an iteration process to add up cumulatively all of the segments on the tried length of the section to see if the distal bouncer just touches the bottom of the body of water in the preset maximum weather condition.

23. The method of claim 21, further comprising: determining a length of a proximal catenary section line, which is not preset, using the catenary analysis involving an iteration process that runs through every segment until the proximal bouncer at the last segment just touches the bottom of the body of water in a light weather condition (e.g., the condition that generates the of the moored ship's maximum weather horizontal resistance, for the catenary section of a 3,000 lb proximal bouncer).

24. The method of claim 17, wherein the two or more bouncers each includes at least one of (i) a plate-like shape or (ii) a damper plate coupled thereto.

25. The method of claim 17, wherein the anchor comprises an array of ground anchors connected to the distal bouncer via their respective anchor lines, slack on seabed, with different length in different directions from the distal bouncer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The attached drawings help explain the embodiments described below.

[0015] FIG. 1 is a schematic view of a mooring system according to an embodiment illustrating a single-bouncer configuration.

[0016] FIG. 2 is a table presenting a summary of the available mooring diameter of an area and an estimated free-swing diameter when a 154 cutter is attached to the mooring buoy according to one example.

[0017] FIG. 3 is a table presenting environmental design conditions for the single-point mooring system according to one example.

[0018] FIG. 4 shows an example of an anchor holding power calculation methodology used for determining the maximum anchoring/single-point mooring design load.

[0019] FIG. 5 shows details for typical concrete block sinkers including (A) a top view, (B) an elevational view, and (C) a table presenting weight and dimension details for typical concrete sinkers.

[0020] FIG. 6 shows an example of (A) a Dor-Mor anchor and (B) a table containing details on weight and holding power for typical Dor-Mor anchors.

[0021] FIG. 7A shows a buoy selected for the mooring system according to one example.

[0022] FIG. 7B shows an example of a coupling mechanism between the buoy and the proximal end of the first section chain in the mooring system.

[0023] FIG. 8 shows a swivel including (A) a front view, (B) a side view, and (C) a table presenting weight and dimension details for typical swivels.

[0024] FIG. 9 shows examples of (A) a split key shackle assembly and (B) a rivet pin shackle assembly, including (C) a front view and (D) a side view of a shackle body, (E) a section view and (F) a side view of a pin, and tables (G), (H), and (I) containing typical details of the components.

[0025] FIG. 10 shows examples of a split key and a split key pin, including (A) a top view and (B) a side view of the split key and (C) a table containing typical details thereof; and to the split key pin, (D) a top view, (E) the section view of the top view, (F) a side view, (G) the section view of the side view, and (H) a table containing typical details thereof.

[0026] FIG. 11 shows an example of a mooring bridle.

[0027] FIG. 12 shows an example of a table of components of the single-point mooring system.

[0028] FIG. 13 is a schematic view of a mooring system according to an embodiment illustrating a two-bouncer or double-bouncer configuration.

[0029] FIG. 14 is a flow diagram 1400 illustrating an example of a process for determining the length of a first catenary section with a first bouncer just touching the seabed.

[0030] FIG. 15 is a flow diagram illustrating an example of a process for determining the length of a next catenary section with the next bouncer just touching the seabed.

[0031] FIG. 16 shows an example of the values of parameters, properties, and characteristics that may be used in the processes described in the flow diagrams of FIGS. 14 and 15.

[0032] FIG. 17 shows an example of the values of parameters, properties, and characteristics selected for use in the process in the flow diagram of FIG. 14 to determine the length of a first catenary section of a double-bouncer mooring system.

[0033] FIG. 18 is a graphical plot of the result of the bouncer catenary chain length for the first bouncer versus the water depth illustrating the bouncer catenary chain shape using the values of FIG. 17 in the calculation.

[0034] FIG. 19 shows an example of the values of additional parameters, properties, and characteristics selected for use in the process in the flow diagrams of FIGS. 14 and 15 to determine the length of first and second catenary sections of a double-bouncer mooring system.

[0035] FIG. 20 is a graphical plot of the result of the bouncer catenary chain lengths for the first and second bouncers versus the water depth illustrating the entire double-bouncer catenary chain shape using the values of FIGS. 17 and 19 in the calculation.

DETAILED DESCRIPTION

[0036] A number of examples or embodiments of the present invention are described, and it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a variety of ways. The embodiments discussed herein are merely illustrative of ways to make and use the invention and are not intended to limit the scope of the invention. Rather, as will be appreciated by one of skill in the art, the teachings and disclosures herein can be combined or rearranged with other portions of this disclosure along with the knowledge of one of ordinary skill in the art.

[0037] Embodiments of the invention are directed to a single-point-mooring (SPM) system including an SPM anchor and a relatively lighter bouncer sinker connected between the SPM buoy and the SPM anchor. The portion of the chain between the buoy and the bouncer is a first catenary section chain in the single-bouncer embodiment. Additional bouncers may be added in series via respective catenary section chains between the buoy and the SPM anchor to form multiple-bouncer embodiments. The one or more bouncers each have a bouncer weight and the respective catenary section chains or lines each have a catenary section length and a catenary section weight, which are selected to place the distal bouncer just touching the bottom of the body of water in the preset maximum weather condition.

[0038] FIG. 1 is a schematic view of a mooring system according to an embodiment illustrating a single-bouncer configuration (Example 1). The mooring system 100 includes a mooring buoy 102 connected to a ship 104 via a mooring bridle 106 which is attached to an upper portion of the mooring buoy 102. A lower portion of the mooring buoy 102 is connected to a sinker referred to as a bouncer 110 via a first section chain 112. The bouncer 110 is connected to an anchor 120 via a second section chain 122. The anchor 120 rests on the seabed 130. The bouncer 110 is configured to rest on the seabed 130 under light to mild weather conditions. The characteristics of the components of the mooring system 100 are designed or selected based on a maximum water depth 140 at a design weather condition (e.g., tropical storm), as well as the size of the ship 104. The bouncer 110 may have a bouncer weight that is smaller than the anchor weight of the anchor 120.

[0039] The mooring system 100 employs double sinkers: a holding sinker or set sinker or anchor which is to be set at a designated location without moving, and a bouncing sinker or bouncer which is designed to bounce around the set sinker in the design weather condition such as a tropical storm condition. This configuration of double sinkers reduces the total chain length as compared to the single sinker configuration and significantly minimizes the risk of chain's knotting with itself. The bouncer also increases the initial resistance to sudden pulls in the mooring system and absorbs shock in the response.

[0040] The bouncer 110 may have a plate-like shape. The bouncer 110 may include a damper plate coupled thereto or added to it for increasing the initial resistance to sudden pulls in the mooring system and absorb shock in the response. The anchor 120 may include an array of ground anchors connected to the distal bouncer via their respective anchor lines (chain/hawser) with different length in different directions from the distal bouncer. This suits a mooring system with a response stiffness variable by direction such as in a narrow channel that restricts the moored ship from swinging to channel walls.

[0041] In the embodiment shown, the mooring buoy 102 may be a cylindrical buoy which is generally preferred over a spherical one. The cylindrical buoy 102 has a lower buoy padeye at the lower portion which is attached with a split-key shackle connected to the eye of a swivel below. The swivel allows the buoy 102 to twist without causing the first section chain 112 to kink. The swivel has a lower opening which is connected to a higher end or proximal end of the first section chain 112 via another split-key shackle. The lower end or distal end of the first section chain 112 is connected to the bouncer 110 via a third split-key shackle. The proximal end of the second section chain 122 is connected to the third split-key shackle at the bouncer 110 via a fourth split-key shackle. The anchor 120 is connected to the distal end of the second section chain 120 via a fifth split-key shackle.

[0042] The anchor 120 is designed to have a holding power capable of resisting the moored ship's drag due to current and tropical storm wind of the design weather condition. The size of the bouncer 110 is determined by a catenary analysis, which will be described in detail below. In specific embodiments, the mooring system 100 for a mid-size ship employs a 5,0008,500 lb concrete block sinker as the bouncer 110 for the designed tropical storm weather condition.

[0043] Two types of mooring weights were investigated for use as the anchor 120 in the single-point mooring system 100: concrete block sinkers and Dor-Mor cast iron anchors for the holding sinker. When choosing an anchor, it is important to ensure that the available asset, such as the buoy tender, can handle the anchors along with any associated tackle. In one example, the available asset is a 175 WLM Buoy Tender, which is capable of handling and deploying the largest of concrete sinkers (20,000 lbs).

[0044] FIG. 2 is a table presenting a summary of the available mooring diameter of an area and an estimated free-swing diameter when a 154 cutter is attached to the mooring buoy 102 according to one example. For illustrative purposes, the present disclosure uses a WPC cutter as an example in the calculations and evaluations of the single point mooring system. The WPC cutter is a Sentinel-class cutter having a vessel LOA (length overall) of 154. The maximum water depth is the sum of MLLW (Minimum Lower Low Water) and the tidal range/fluctuation and the storm surge.

[0045] The design of the mooring system 100 involves the following actions: determining the system design load, designing the chain lengths and the sizes of sinkers, and selecting components of the mooring system 100. It takes into account the available mooring diameter, the depth of the water, the size of the ship, and environmental conditions.

[0046] FIG. 3 is a table presenting environmental design conditions for the single-point mooring system 100 according to one example. The designed condition is for survival through tropical storms at a maximum wind speed of 70 knots combined with water current of 3 knots. This was used in the analysis of the required holding power of the anchor 120. A Mean Lower Low Water depth of 25 ft plus tidal range of 4.18 ft and storm surge of 4.7 ft was used to calculate the required chain length of the first section chain 112. The maximum water depth 140 at the design weather condition is 33.88 ft.

[0047] FIG. 4 shows an example of an anchor holding power calculation methodology used for determining the maximum anchoring/single-point mooring design load. The method takes into account the moored ship's topside area, underwater area, and the pressure applied by the wind and current velocities. It includes the calculation of the required holding power (HP) used for selection of the set sinker or holding sinker 120. The current force Fe takes into account the ship's wetted surface area s (i.e., total wetted surface of the ship's underwater shell). The calculation of the prop force Fp includes a constant c which is the projected propeller area divided by the propeller disk area.

[0048] The seabed is sand in this embodiment. To minimize risk of dragging the holding sinker on the seabed, a factor of safety (FS) of 2.0 per ABS (American Bureau of Shipping) Rules is used for the holding power design operating load. The resulting minimum holding power for selection of the set sinker 120 is 22,984 pounds.

[0049] FIG. 5 shows details for typical concrete block sinkers including (A) a top view, (B) an elevational view, and (C) a table presenting weight and dimension details for typical concrete sinkers. Concrete blocks are low cost and readily available sinkers. The mooring system 100 may employ concrete blocks for both the holding sinker 120 and the bouncing sinker 110 as they are relatively inexpensive and locally available.

[0050] The functional holding power of a 20k concrete sinker on the sand seabed 130 is estimated to be 60% of the block's weight, considering the weight in water and the soil fixity due to its being partly buried in sand on the seabed 130. To be compliant with the holding power stated above, this requires two 20,000-pound concrete blocks for the set sinker 120, totaling 40,000 lbs. with a holding power of 24,000 lbs., in order to have a Factor of Safety of 2. The way to connect the two 20,000 lb concrete blocks in water is up to the buoy tender crew. At $0.05 per pound of concrete and $300 per bail per block, the total cost of two concrete sinkers is about $2,600.

[0051] The bouncing sinker 110 is designed as an 8,500-pound concrete block sinker, which weighs 4,560 lbs. in water and bounces on the seabed 130 around the holding sinker 120 to lower the chain pull angle to it at stormy weather when a WPC/WPB cutter is attached to the buoy 102. The WPC cutter is a Sentinel-class cutter having a vessel LOA (length overall) of 154. The WPB cutter is a Marine-Protector-class patrol boat having a vessel LOA of 87. The catenary analysis is provided in the description below in connection with FIGS. 14-20.

[0052] FIG. 6 shows an example of (A) a Dor-Mor anchor 120 and (B) a table containing details on weight and holding power for typical Dor-Mor anchors. The Dor-Mor anchor is a pyramid shaped, cast iron anchor specifically designed for single-point moorings. It provides significantly higher holding power than a similarly weighted concrete sinker for two reasons: higher density and better shape. The shape of a Dor-Mor anchor allows it to continue to embed itself into the bottom surface of the seabed as the force applied increases. Research has shown that a Dor-Mor anchor provides roughly 7 times its weight in holding power. However, to provide this higher holding power, the Dor-Mor has a significantly higher cost than concrete blocks.

[0053] As shown in FIG. 6, a 4,000-pound Dor-Mor has a holding power of 28,000 pounds. At this holding power, the design factor of safety for the Dor-Mor in this application is 2.44. The highlighted Dor-Mor anchor cost is approximately $10,000. In the embodiment, a Dor-Mor anchor is not selected over the two 20K pound concrete sinkers as the holding anchor 120.

[0054] FIG. 7A shows the buoy 102 selected for the mooring system 100. A cylindrical buoy 102 for the single-point mooring system 100 may be preferred. In the embodiment, the selected buoy 102 was one classified as 1988 Type 2CR with modification to its upper padeye.

[0055] In the embodiment, a 1 chain size for the first section chain 112 is selected as it provides a 3.53 factor of safety on proof load (breaking load is significantly higher). Another aspect for selection of this chain size is to provide extended wear capability for increased service life of the mooring system 100.

[0056] As the water depth at the designated mooring location varies and would affect the chain length in regard to maintaining contact between the bouncer and the seabed, a maximum water depth of 33.88 feet was selected for design purposes. This depth is the max of MLLW (Minimum Lower Low Water) plus the tidal fluctuation and the storm surge. The chain length between the buoy and the bouncer to provide sufficient scope during the maximum weather or most severe weather was determined by a catenary analysis to be discussed below.

[0057] Eighty feet of 1 chain between the buoy 102 and the bouncer 110 will prevent the bouncer 110 from bouncing too high in waves during a tropical storm. A practical ninety feet of 1 chain between the bouncer 110 and the set sinker 120 is determined to allow a buoy vessel (e.g., CGC BARBARA MABRITY) to place the bouncer 110 onboard without pulling the heavy set sinker 120, at a normal operational weather condition.

[0058] Because the ninety feet chain between the bouncer 110 and the set sinker 120 is taut, it greatly reduces the risk of chain knotting with itself in the bouncer and set sinker configuration in the single-point mooring system 100. Compared to the 240 chain of a conventional single sinker mooring for this case, the double-sinker configuration saves 70 chain.

[0059] FIG. 7B shows an example of a coupling mechanism between the buoy 102 and the proximal end of the first section chain 112 in the mooring system 100. The coupling mechanism includes a swivel 810 with eye up which has an upper portion connected via an upper split key shackle 820 to a ring at the lower portion of the buoy 102 and which has a lower portion connected via a lower split key shackle 830 to the proximal end of the first section chain 112. A rivet pin shackle 840 may be used for splicing sections of the chain 112 together.

[0060] FIG. 8 shows a swivel including (A) a front view, (B) a side view, and (C) a table presenting weight and dimension details for typical swivels. More specifically, the table presents examples of the swivel 810 with different dimensions, proof loads, break loads, and weights. A single swivel 810 is used for connecting to the mooring chain 112 to allow the buoy 102 to twist without causing the chain 112 to kink. It is connected to the lower padeye of the mooring buoy 102 via the upper split key shackle 820 with the swivel eye up and to the mooring chain 112 via the lower split key shackle 830, as seen in FIG. 7B. In one example, the swivel 800 chosen, 3rd Class, has been sized to match the 1 buoy chain, and has a proof load of 45,000 lb, well in excess of the system's design line load. Swivel dimensions and ratings for a 3rd Class Swivel is shown in the table in view (C) of FIG. 8.

[0061] FIG. 9 shows examples of (A) a split key shackle assembly and (B) a rivet pin shackle assembly, including (C) a front view and (D) a side view of a shackle body, (E) a section view and (F) a side view of a pin, and tables (G), (H), and (I) containing typical details of the components. The tables present examples of the assemblies with different dimensions, proof loads, break loads, and dry and wet weights.

[0062] FIG. 10 shows examples of a split key and a split key pin, including (A) a top view and (B) a side view of the split key and (C) a table containing typical details thereof; and to the split key pin, (D) a top view, (E) the section view of the top view, (F) a side view, (G) the section view of the side view, and (H) a table containing typical details thereof.

[0063] Split key shackles 820, 830 are used to connect the swivel 810 to the buoy 102, the chain 112 to the swivel 810, and the sinkers 110, 120 to the chain 112, 122. As seen in FIGS. 9 and 10, the split key shackle assembly includes a stainless steel split key which is inserted into the pin and bent open to prevent the pin from backing out. Five (5) Class 3 split key shackles are utilized for the single-point mooring system 100. Each Class 3 split key shackle has a proof load of 65,000 lbs., well in excess of the design line load and chain breaking strength. FIGS. 9 and 10 show dimensions and ratings of the Class 3 split key shackles, key, and pin.

[0064] Rivet pin shackles 840 are used for splicing sections of a chain together. They are assembled by heating and hammer forging the end of the pin, and are sometimes referred to as heat and beat shackles. Rivet pin shackles 840 may be used as necessary to join chain lengths, depending on the lengths of chains available.

[0065] FIG. 11 shows an example of a mooring bridle 1200. It is led over the ship deck with the buoy leg 1210 through the ship's closed chock 1214 to connect to the mooring buoy 102. Two bow legs 1220, each 24 ft long, each with a 1-meter eye on the inboard ends, are attached to the port and starboard bitts and to the buoy leg 1210 in a Y-connection using a tow plate 1230. This lets the ship headed on with wind thus minimizing the wind drag. The single buoy leg 1210, 7 ft long, has a 1-meter eye on the inboard leg end, and the outboard 1-meter eye end connected to the buoy upper padeye via a bolt-type shackle. This arrangement would allow the use of the cutter anchor as a back-up mooring system if needed and not foul the mooring bridle.

[0066] The mooring bridle 1200 may use the 3 circumference Double Braided Polyester Rope (Breaking Strength of 64,000 lb) as the towing bridle. The outboard end of the buoy leg connected to the buoy may be provided with a thimble to suit the 1 bolt-type shackle attached to the buoy upper padeye. Previous analysis in a 154 cuter mooring shows that port and starboard mooring bitts at Frame 3 on the cutter are designed to withstand forces greater than the design line load. The evolution to connect the mooring bridle to the mooring buoy may require use of a quick response boat such as the Over-The-Horizontal-IV (OTH-IV) in certain weather conditions. Final operational details of how to connect the 154 cutter to the mooring system will need to be developed with the Fleet Management and the cutter crews using the system, but the 7 feet of the new buoy leg from the tow plate to the buoy will be maintained to avoid submerging the buoy in heavy weather.

[0067] FIG. 12 shows an example of a table of components of the single-point mooring system 100. It utilizes an 8,500 lb bouncer 110 and two 20,000 lb concrete blocks as the holding sinker 120 designed to safely moor a 154 cutter in 70 knots of wind and 3 knots of current on the bow at a designated mooring site. At the design weather condition, the 154 cutter requires a holding power of 11,492 pounds-force to maintain station either at anchor or on a single-point moor. Given the value of the asset and the confined mooring area, a minimum factor of safety of 2.0 per ABS Rules is used. Working (proof) loads for components selected for the system have to be above a load of 22,984 pounds-force to comply with the 2.0 factor of safety. All selected components exceed the minimum factor of safety of 2.0 which provides extended service life and load capability (i.e., winds higher than 70 knots).

[0068] FIG. 13 is a schematic view of a mooring system according to an embodiment illustrating a two-bouncer or double-bouncer configuration (Example 2). The mooring system 200 includes a mooring buoy 202 connected to a ship 204 via a mooring bridle 206 which is attached to an upper portion of the mooring buoy 202. A lower portion of the mooring buoy 202 is connected to a first sinker referred to as a first bouncer 210 via a first section chain 212. The first bouncer 210 is connected to a second bouncer 214 via a second section chain 216. The second bouncer 214 is connected to an anchor 220 via a third section chain 218. The anchor 220 rests on the seabed 230. The second bouncer 214 is configured to rest on the seabed 230 under light to mild weather conditions. The characteristics of the components of the mooring system 200 are designed or selected based on a maximum water depth 240 at a design weather condition (e.g., tropical storm), as well as the size of the ship 204. The second bouncer 214 may have a bouncer weight that is smaller than the anchor weight of the anchor 220. As compared to the single-bouncer embodiment of FIG. 1 described above in detail, this two-bouncer example replaces the bouncer 110 with the first bouncer 210 and second bouncer 214 and replaces the chain 112 with the first section chain 212 and the second section chain 216. The other components may be the same between the single-bouncer example of FIG. 1 and the two-bouncer example of FIG. 13. In this example, the first bouncer 210 may be a 3,000 lb concrete block and the second bouncer 214 may be a 5,000 lb concrete block. The first bouncer chain 212 may be a 50 ft long 1 size chain and the second bouncer chain 216 may be a 45 ft long 1 size chain, with two Class 3 split key shackles at the lower end of each chain (first shackle connecting the two chains 212 to 216 or 216 to 218, then second shackle connecting the bouncer 210 or 214 to the first shackle).

[0069] FIG. 14 is a flow diagram 1400 illustrating an example of a process for determining the length of a first catenary section with a first bouncer just touching the seabed 130. According to a multiple-bouncer embodiment, such as the two-bouncer system 200 shown in FIG. 13, the flow diagram 1400 represents a first group of steps for determining the length of a first catenary section (chain or hawser) for a first bouncer of a 3,000 lb sinker to just touch the seabed at of the maximum weather horizontal resistance and a maximum water depth without storm surge. According to a single-bouncer embodiment, the flow diagram 1400 represents a complete process of all steps for determining the length of the first and only catenary section for the first and only bouncer to just touch the seabed at the full maximum weather horizontal resistance (instead of a fraction as shown in Step 1418) and a maximum water depth with storm surge (as opposed to without storm surge as shown in Step 1424). In this example, the maximum weather horizontal resistance is the required holding power (HP) in FIG. 4 without the factor of safety FS.

[0070] Step 1402 specifies a unit weight of the chain/hawser (chain or hawser) in water, q. Step 1404 specifies a segment length L of the first catenary section (i.e., first section chain or line). A segment is a piece of the chain/hawser that is like a train car in a train connected one by one to make the entire chain/hawser. The segment length L for a chain is the length of a horizontal link plus the next vertical link. The segment length L for a hawser may be 1 m, 2 m, or some other relatively small length. Step 1406 calculates the segment weight as w=q*L. Both the segment length L and the segment weight w are used as input for the iteration process of the first catenary section in the integral box 1410.

[0071] Step 1412 specifies a comfort vertical force F.sub.Vmax provided by the moored facility 104 and the mooring buoy 102. The comfort vertical force refers to a vertical force associated with an acceptable, relatively small longitudinal inclination or trim which would not affect the ship's function. Its calculation depends on the size and type of the moored facility. According to specific embodiments, the comfort vertical force that causes the inclination/trim is determined by the ship's property known as MT1 (moment to trim 1), the amount of the small trim, and the distance from the ship's bow to its center of gravity or floatation.

[0072] Step 1414 specifies the weight in water of the first bouncer W.sub.1 which meets the condition that W.sub.1<F.sub.Vmax. The weight in water must be smaller than the comfort vertical force F.sub.Vmax. In the multiple-bouncer embodiment, W.sub.1 is 1631 lbs, the weight in water of the 3,000 lb concrete sinker. The 3K sinker per FIG. 5 is the thinnest (most plate-like) block among the desirable bouncer candidates (3,0008,500 lb sinkers), so it achieves the most shock absorption to the anchor. The first bouncer should bounce or float to take advance of its shock absorption characteristics.

[0073] Step 1416 specifies a horizontal resistance of the moored facility under the design condition, i.e., the maximum or most severe weather condition. Step 1418 specifies a horizontal force F.sub.H for the first bouncer. In the multiple-bouncer embodiment, the horizontal force is of the maximum weather horizontal resistance F.sub.Hmax. In the single-bouncer embodiment, F.sub.H=F.sub.Hmax.

[0074] Step 1420 calculates the first bouncing bouncer end tangential force T.sub.bouncer based on the weight in water W.sub.1 of the first bouncer from step 1414 and the horizontal force F.sub.H from step 1418. The first bouncer end tangential force is T.sub.bouncer=sqrt (W.sub.1.sup.2+F.sub.H.sup.2).

[0075] Step 1424 specifies a water depth h. In the single-bouncer embodiment, h is the maximum water depth with storm surge. In the multiple-bouncer embodiment, h is the maximum water depth without storm surge.

[0076] Step 1430 calculates the buoy end tangential force T based on the unit weight in water of the chain/hawser q from step 1402, the water depth h from step 1424, and the first bouncer end tangential force T.sub.bouncer from step 1420. The buoy end tangential force T=q*h+T.sub.bouncer.

[0077] Step 1440 calculates the buoy end vertical force F.sub.V0 based on the horizontal force F.sub.H from step 1418 and the buoy end tangential force T from step 1430. The buoy end vertical force F.sub.V0=sqrt (T.sup.2F.sub.H.sup.2).

[0078] The integral box 1410 has inputs of the segment length L from step 1404, the segment weight w from step 1406, the horizontal force F.sub.H from step 1418, the water depth h from step 1424, and the buoy end vertical force F.sub.V0 from step 1440. The integral box 1410 has columns of Segment #, horizontal force F.sub.H, vertical force F.sub.V, angle to horizon , horizontal distance (X dist.) to buoy X.sub.n and water depth Y.sub.n for the n-th iteration, and catenary length L.sub.sum. At the origin (water surface point) of the catenary section, i.e., the beginning of the iteration process of the first catenary section in the integral box 1410, the horizontal force is F.sub.H from step 1418 and remains unchanged in every iteration and the vertical force F.sub.V is the buoy end vertical force F.sub.V0 from step 1440, and the horizontal distance (X dist.) to buoy X.sub.n, water depth Y.sub.n, and catenary length L.sub.sum are all set to zero.

[0079] In the first three iterations (n=1, 2, or 3), calculations for Segment #1, 2, or 3 are performed to show the pattern for each calculation. The n-th chain segment's vertical force F.sub.Vn is calculated by subtracting the segment weight from the previous segment's vertical force F.sub.V(n-1): F.sub.Vn=F.sub.V(n-1)w. The n-th segment's angle to horizon is calculated based on the n-th segment's vertical force and horizontal force: .sub.n=ATAN(F.sub.Vn/F.sub.H). The n-th segment's horizontal distance (X dist.) to the buoy is calculated by adding its horizontal length (L*cos .sub.n) onto the previous segment's X.sub.(n-1): X.sub.n=X.sub.(n-1)+L*cos .sub.n. The n-th segment's water depth is calculated the same way but adding its vertical length (L*sin .sub.n): Y.sub.n=Y.sub.(n-1)+L*sin .sub.n. The catenary length after the n-th segment is calculated by adding the segment length L to the previous catenary length L.sub.sum(n-1): L.sub.sum(n)=L.sub.sum(n-1)+L.

[0080] The iteration process is repeated until the calculated n-th segment's water depth Y.sub.n reaches water depth h. For the single-bouncer embodiment, this h is the maximum water depth with storm surge, which means the chain/hawser is just touching the seabed at the design stormy condition; For the multiple-bouncer embodiment, this h is the maximum water depth without the storm surge, which means it is just touching the seabed at the light weather condition (with of the maximum weather horizontal resistance). For the single-bouncer embodiment, the catenary length after the n-th segment L.sub.sum(n) is the catenary length of the first catenary section with the first and only bouncer just touching the seabed and the catenary analysis process ends. For the multiple-bouncer embodiment, this L.sub.sum(n) is the catenary length of a first catenary section with the 3,000 lb first bouncer connected to the n-th segment, and the process continues in FIG. 15.

[0081] FIG. 15 is a flow diagram illustrating an example of a process for determining the rest catenary sections and the rest bouncers, with the first bounce of 3,000 lb sinker connected to the N-th segment at the first catenary section length L.sub.sum(N) in FIG. 14.

[0082] Step 1502 is the same comfort vertical force F.sub.Vmax in FIG. 14. Step 1504 selects the heaviest 2nd bouncer in the bouncer list in FIG. 16 but less than the (F.sub.VmaxW.sub.1) value for its weight in water W.sub.2. Here W.sub.1 is the weight in water of the first bouncer, i.e., 1631 lbs for the 3,000 lb sinker.

[0083] Step 1506 sets the second catenary section length at a practical value L. The term practical means the winch on the installation/maintenance ship is capable of handling the total weight in water of the first and second bouncers and the chains connected therewith. One shot length of chain of most sizes is 90. The crew usually goes by half shots 45 (i.e., 45,90, 135, etc.). In FIG. 13, one coastal mooring example involving a two-bouncer configuration, L is set to 45. For offshore applications or for hawser cases, L can be determined using other criteria. For simplicity, L can be fixed for subsequent bouncers beyond the first one. Alternatively, L can be adjusted for each subsequent bouncer to obtain the desirable stiffness of the mooring system. Step 1508 is the same q in FIG. 14.

[0084] Step 1510 calculates the extra vertical force F.sub.Vextra of the 2nd bouncer and its catenary section chain/hawser based on the 2nd bouncer weight in water W.sub.2 from step 1504, the 2nd catenary section length L from step 1506, and the unit weight in water q from step 1508: F.sub.Vextra=W.sub.2+q*L.

[0085] Step 1520 is the same buoy end vertical force F.sub.V0 in FIG. 14 (Step 1 of the catenary analysis). Step 1530 calculates the buoy end vertical force for the mooring system based on the buoy end vertical force F.sub.V0 from step 1520 and the extra vertical force F.sub.Vextra from step 1510: F.sub.V0 =F.sub.V0+F.sub.Vextra. Step 1540 is the maximum water depth with storm surge, defined above in Paragraph [0056], h. Step 1550 is the same maximum weather horizontal resistance F.sub.Hmax in FIG. 14 and set it as the horizontal force F.sub.H=F.sub.Hmax.

[0086] Step 1560 involves running the Integral Box 1410 with inputs of the segment length L from step 1404, the segment weight w from step 1406, the horizontal force F.sub.H from step 1550, the maximum water depth with storm surge h from step 1540, and the current buoy end vertical force F.sub.V0 from step 1530. The integral box 1410 has columns of Segment #, horizontal force F.sub.H, vertical force F.sub.V, angle to horizon , horizontal distance (X dist.) to buoy X.sub.n, water depth Y.sub.n, and catenary length L.sub.sum. At the beginning, i.e., the origin or the water surface point of the entire catenary (the first catenary of N segments L.sub.sum(N) length and the second catenary section to be determined), the horizontal force F.sub.H=F.sub.H and the vertical force F.sub.V=F.sub.V0, and the horizontal distance (X dist.) to buoy X.sub.n, water depth Y.sub.n, catenary length L.sub.sum are all set to zero.

[0087] When using an Excel spreadsheet, run the iteration process (as described above in Paragraphs [0078] and [0079]) from the 1.sup.st segment of the first catenary section, through the Segment #(N+1), i.e., the 1.sup.st segment of the second catenary section, till the entire catenary length L.sub.sum reaches (L.sub.sum(N)+L), L is the preset practical length for the second catenary section. Then, on Segment #(N+1) row reduce the F.sub.V value by 1.sup.st bouncer weight in water (W.sub.1, i.e., 1631 lbs). With every iteration since the Segment # (N+1) rerun automatically, check the final water depth Y.sub.n. If Y.sub.nh, the 2.sup.nd bouncer has reached the seabed, resulting in a two-bouncer configuration. The final Segment #N is recorded and the total catenary length L.sub.sum is L.sub.sum(N)+L. Of course, in case of Y.sub.n is much greater than h, it means the 2.sup.nd bouncer picked (W.sub.2) is too heavy, thus select a lighter 2.sup.nd bouncer to rerun the iteration process, or stick to the single-bouncer configuration.

[0088] If Y.sub.n<h, more bouncers are needed to reach the seabed. The last Segment #N is recorded. Adding the third catenary section of another length L and a third bouncer of weight in water W.sub.3, W.sub.3<(F.sub.VmaxW.sub.1W.sub.2), now, for the entire catenary with the third catenary section, the initial buoy end vertical force is F.sub.V=F.sub.V0+W.sub.3+q*L, F.sub.V0 is the initial buoy end vertical force for the entire catenary with the 2.sup.nd catenary section and is shown in the Origin row on the Excel spreadsheet so far iterated to the last row, Row of Segment #N. So, change the initial F.sub.V in the Origin row on the Spreadsheet to (F.sub.V0+W.sub.3+q*L) and keep other inputs same, with every iteration automatically rerun, continue running the same iteration process (as described above in Paragraphs [0078] and [0079]) from the last row till the L.sub.sum reaches L.sub.sum(N)+2*L, then on Segment #(N+1) row reduce the F.sub.V value by 2.sup.nd bouncer weight in water (W.sub.2), and check the final water depth Y.sub.n. If Y.sub.nh, the 3.sup.rd bouncer has reached the seabed, resulting in a three-bouncer configuration. If Y.sub.n<h, keep adding another bouncer and another chain/hawser of L using the logic described in this Paragraph till Y.sub.nh.

[0089] Alternatively, if it is desired to add no more bouncers beyond the i-th bouncer but Y.sub.n<h, the user may increase the length of the i-th catenary section until the i-th bouncer reaches the seabed. The ability to adapt the methodology to different bouncer weights and catenary section lengths and unit weights renders the approach a dynamic process, which allows developing whatever highly non-linear mooring system F.sub.H vs X curve was wanted.

[0090] FIG. 16 shows an example of the values of parameters, properties, and characteristics that may be used in the processes described in the flow diagrams of FIGS. 14 and 15. They include, for instance, the comfortable/acceptable trim, MT1 (moment to trim 1), and bow chock to LCF (Longitudinal Center of Floatation). It includes a list of bouncer concrete block sinkers of different weights from which to choose.

[0091] FIG. 17 shows an example of the values of parameters, properties, and characteristics selected for use in the process in the flow diagram of FIG. 14 according to the two-bouncer embodiment to determine the length of a first catenary section of a two-bouncer mooring system. The first bouncer dry weight is 3000 lbs. The maximum water depth without storm surge is 26.5 ft. The tidal range is 4.18 ft. The storm surge is 4.7 ft. The design condition is a tropical storm of wind speed of 70 knots combined with water current of 3 knots.

[0092] FIG. 18 is a graphical plot of the result of the bouncer catenary chain length for the first bouncer versus the water depth illustrating the bouncer catenary chain shape using the values of FIG. 17 in the calculation. The bouncer catenary chain has a horizontal distance slightly above 40 at a water depth of 26.5 ft. There are 58 segments ending in the final Segment #58.

[0093] FIG. 19 shows an example of the values of additional parameters, properties, and characteristics selected for use in the process in the flow diagrams of FIG. 15 to determine if the second bouncer reaches the seabed for a double-bouncer mooring system. The selected chain length between bouncers is 45 which is half shot of chain. The 5000 lb second bouncer weighs 2720 lbs in water.

[0094] FIG. 20 is a graphical plot of the result of the bouncer catenary chain lengths for the first and second bouncers versus the water depth illustrating the entire double-bouncer catenary chain shape using the values of FIGS. 17 and 19 in the calculation. The first bouncer catenary chain length has a horizontal stretch of about 44 at a water depth of 20. The second bouncer catenary chain has a horizontal stretch of about 44 at a water depth of about 31 (an additional depth of about 11 between the first and second bouncers).

[0095] The plot has 58 segments in the first catenary section ending in Segment #58 for Segment #N and 54 additional segments in the second catenary section from iteration #59 to iteration #112 ending in Segment #112 for Segment #N (L=45 in the case). When the second catenary section is lifted above the seabed, the weight of all the 54 segments of the second catenary section (i.e., 108 steel oval links) needs to be pulled via the first catenary section line to the buoy and the ship. On each segment of the whole chain, the variable vertical force and the constant horizontal force in combination form the resultant force, which is along the axial direction of the segment (presumed straight). The plot for the whole chain is made available on the knowledge of the direction of each straight segment.

[0096] This with-bouncer configuration of single bouncer or multiple bouncers and anchor for the single leg in the single-point mooring buoy system, such as the single-bouncer system 100 of FIG. 1 or the two-bouncer system 200 of FIG. 13, has several advantages. For instance, a conventional single leg SPM buoy is often moved off of its assigned position due to ship traffic dragging it off in an area where the current, tide levels, and external forces are complex. In contrast, because the bouncer 110 lowers the pull angle of the second section chain 122 to the anchor 120, the with-anchor configuration keeps the anchor 120 buried low in the seabed substrate and prevents it from being moved. The first section chain 112 is also a half of a full catenary when shaped from the moored ship's resistance at a much lighter weather condition, and the second section chain 122 is a fixed short length. Therefore, the required minimum total chain length is greatly reduced, compared to the length of a half of the full catenary at the tropical storm weather in the conventional configuration. Because the second section chain 122 is installed taut between the bouncer 110 and the anchor 120, and the first section chain 112 is taut starting at light weather when a ship is moored, the with-anchor configuration significantly minimizes the risk of knotting of the chain 112 or 122 with itself. The bouncer or bouncers when bouncing or floating, especially the plate-like 3,000 lb first bouncer in the multiple-bouncer embodiment, provides the mooring system with significant shock-absorption capacity, thus further prevents the anchor from being moved off.

[0097] The claims define the invention and form part of the specification. Limitations from the written description are not to be read into the claims.

[0098] An interpretation under 35 U.S.C. 112 (f) is desired only where this description and/or the claims use specific terminology historically recognized to invoke the benefit of interpretation, such as means, and the structure corresponding to a recited function, to include the equivalents thereof, as permitted to the fullest extent of the law and this written description, may include the disclosure, the accompanying claims, and the drawings, as they would be understood by one of skill in the art.

[0099] To the extent the subject matter has been described in language specific to structural features and/or methodological steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as example forms of implementing the claimed subject matter. To the extent headings are used, they are provided for the convenience of the reader and are not to be taken as limiting or restricting the systems, techniques, approaches, methods, devices to those appearing in any section. Rather, the teachings and disclosures herein can be combined, rearranged, with other portions of this disclosure and the knowledge of one of ordinary skill in the art. It is the intention of this disclosure to encompass and include such variation.

[0100] The indication of any elements or steps as optional does not indicate that all other or any other elements or steps are mandatory. The claims define the invention and form part of the specification. Limitations from the written description are not to be read into the claims.