US3430597A

US3430597A - One-point mooring system for loading or unloading fluids into or from a ship

Info

Publication number: US3430597A
Authority: US
Inventors: Henricus J Zunderdorp
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1966-05-06
Filing date: 1967-07-31
Publication date: 1969-03-04
Anticipated expiration: 1986-03-04
Also published as: DE1531026A1; ES340150A1; FR1522666A; JPS5128918B1; GB1177926A; DE1531026B2; NL6706105A; US3515182A

Description

March 1969 H. J.ZUNDERDORP I 3,430,597

ONE-POINT MOORING SYSTEM FOR LOADING OR UNLOADING FLUIDS INTO OR FROM A SHIP Filed July 51, 1967 INVENTOR:

HENRICUS J. ZUNDERDORP .Hmmaz fins AGENT United States Patent 42,252/ 66 U.S. Cl. 114-230 Int. Cl. B63b 21/00, 21/52, 51/02 9 Claims ABSTRACT OF THE DISCLOSURE A one-point mooring system for ships including fixed and rotatable mooring parts on the floor of a body of water, a spring buoy positioned over the mooring parts and a mooring cable extending between the buoy and the rotatable parts and having a free end connectable to a ship. The other end of the cable is secured to the buoy or the rotatable part. Suitable pulleys on the rotatable part and buoy cooperate with the cable so that mooring forces from the ship are translated to the buoy which is pulled under water thereby absorbing energy and relieving the strain on the mooring parts.

Background of the invention The invention relates to a one-point mooring system for loading or unloading fluids into or from a ship. More specifically, it relates to the type of mooring system described in U.S. patent application No. 636,466, filed May 5, 1967 which discloses a mooring system comprising a first part and a second part rotatable relative to the first part, the second part being provided with a mooring device for securing a mooring cable of a ship thereto, a first fluid line secured to the first part, and a second fluid line rotatably connected to the first fluid line; said system being arranged below the water surface and being secured to the bottom of a body of water and the first fluid line(s) being connected to (a) fluid discharge or supply line(s), arranged in or adjacent to the bottom of the body of water.

When the above-mentioned mooring system is used for mooring large ships, for example, crude carriers of 200,000 or 300,000 d.w.t., it is possible that the mooring forces reach very high values.

The mooring forces should of course be kept below an acceptable value and it is an objective of the invention to provide for this purpose means suitable for use in the above-mentioned mooring system.

Summary Therefore, according to the invention, a spring buoy is connected to the second part of the above-mentioned mooring system in such a way that, after mooring a ship to the second part by means of a mooring cable, the mooring load will be able to pull the spring buoy vertically downward.

By using this arrangement large quantities of mooring energy can be safely absorbed. An important advantage of the proposed arrangement is that the cross-section of the spring buoy and its height above the water surface can be designed in such a way that almost every spring characteristic can be obtained.

Description of the drawings The invention may be carried into practice in various ways but one specific embodiment will now be described by way of example with reference to the accompanying drawings in which:

3,430,597 Patented Mar. 4, 1969 FIGURE 1 is a diagrammatic representation in side elevation of one possible embodiment according to the invention; and,

FIGURE 2 is a graph showing some spring characteristics obtainable with the arrangement according to the invention.

Description of the preferred embodiments In FIGURE 1, a first part 200 is secured to a pile 203 driven into the bottom 201 of a body of water 202. On the first part 200 a second part 204 is so arranged that it is rotatable around a vertical axis relative to the first part 200. A first fluid line 205 is secured to the first part 200. A second fluid line 206 is rotatably connected to the first fluid line 205 by a pipe swivel 207. It will be appreciated that this arrangement is located below the water surface 208 of the body of water 202. The first fluid line 205 is connected to a fluid supply or discharge line 209 arranged in or adjacent to the bottom 201. The line 209 is, for example, connected to the line 205 by a flexible coupling 210. The second part 204 is provided with a mooring device 211 for securing, directly or indirectly, a mooring cable of a ship thereto.

Above the system as described a spring buoy 212 is floating. This spring buoy 212 is provided with a pulley 213 which is so secured that it is rotatable around a horizontal axis 214.

The pulley 213 is so secured to the buoy 212 by means of a swivel 215 that the pulley is moreover rotatable around a vertical axis. On the rotatable part 204 a pulley 216 is so secured that it is rotatable around a horizontal axis. An end of a cable 217 is secured to the mooring device 211 of the rotatable part 204. This cable 217 is led over the pulley 213 and from there over the pulley 216 as shown. The cable 217 is adapted to be secured, directly or indirectly, to a ship, for example, by a cable 218, which is secured to a ship 219. Thus, it will be seen that

pulleys

213 and 216 and the cable 217 collectively comprise a form of tackle for operatively interconnecting the spring buoy 212 and the rotatable part 204. The tackle may include any number of cable runs as will be described later.

The buoy 212 comprises a cylindrical lower part 220 and a cylindrical upper part 221, the lower part 220 having a larger diameter than the upper part 221. Attention is drawn to the fact that the invention is not restricted to this particular shape of the buoy 212.

The buoy arrangement as shown can be suitably used in all the embodiments of the mooring system as described in the U.S. patent application No. 636,466, filed May 5, 1967.

The use of the system according to the invention will now be described.

Assume that a ship 219 arrives at the mooring system, then the ship will pick up a mooring cable and a hose arranged in the manner as described in said earlier patent application. The mooring cable, which is in FIGURE 1 the cable 218, will be secured to the ship 219. Then the hose (not shown), of which one end is permanently secured to the second fluid line 206, will, after its free end has been hoisted onto the ship 219, be secured with said free end to the loading or unloading lines of the ship 219. Now loading or unloading of the ship 219 can take place. During loading of the ship, for example, fluid will flow through the line 209, the coupling 210, the line 205, the pipe swivel 207, the line 206, the hose or flowline 222 extending to the ship 219 and through the loading lines (not shown) of the ship 219 into the tanks of the ship 219. During unloading of the ship 219 the fluid will flow in the opposite direction.

Before, after and during loading or unloading, the ship 219 will be free to swing around the mooring system,

3 pointing its bow to the mooring system. This is possible since the part 204, the swivel 207 arid the pulley 213 are rotatable around vertical axes. So far the operation of the mouring system is basically the same as the system as described in said earlier patent application.

Let it be assumed that because of the waves, currents or winds the ship 219 is pulling heavily at the cable 218, then the ship 219 pulls through the cable 218 and the cable 217 at the buoy 212. This causes the buoy 212 to move vertically downward against the buoyancy force, resulting in a large energy absorption.

The graph according to FIGURE 2 shows along its ordinate the mooring force M, and along its abcissa the displacement D of the buoy vertically downward. When the mooring force M is zero the vertical displacement of the spring buoy 212 is zero, which means that the spring buoy 212 is in the initial position as shown in FIGURE 1. When the mooring force M is raised the spring buoy 212 will be pulled deeper into the water 202 and, since the upper part 221 has a constant cross-section, the displacement D will be proportional to the mooring force M. In other words, the characteristic will be a straight line I. When the buoy 212 has been pulled completely under the water surface 208 (see point A), the buoyancy force remains constant and the relationship between M and D will be a straight line parallel to the abcissa, said straight line being indicated by II. Vertical downward displacement of the spring buoy 212 can now continue until the spring buoy 212 reaches the bottom 201. In order to prevent the spring buoy 212 from being damaged by contact with the bottom 201 or with the mooring system on the bottom, it is possible to provide the bottom side of the spring buoy 212 with suitable stops, for example, in the shape of legs (not shown), so constructed that the legs contact the bottom 201 when the spring buoy 212 is in its lowest position so as to prevent contact between the spring buoy 212 and the mooring system. Alternatively, it is possible to provide the mooring system on the bottom 201 and the lower side of the spring buoy 212 with cooperating stops or buffers (not shown) so that the mooring system at the bottom 201 can stop the spring buoy 212 when it reaches its lowest position. When the spring buoy 212 is in its lowest position point B, as shown in the graph, has been reached.

In the graph according to FIGURE 2, the cross-hatched area indicates the energy absorption of the system. This energy absorption capacity can be raised to very high values by increasing the number of cable runs of the cable 217 between the second part 204 and the spring buoy 212. In the embodiment according to FIGURE 1 there are shown two runs of cable cooperating with one pulley 216 on the second part 204 and one pulley 213 on the spring buoy 212. Instead it is possible to use four runs of cable cooperating with two pulleys on the spring buoy 21.2 and two pulleys on the second part 204, or to use six runs of cable cooperating with three pulleys on the spring buoy 212 and three pulleys on the second part 204. Instead it is possible to use one cable run cooperating with one pulley on the second part 204 or to use three cable runs cooperating .with one pulley on the buoy and two pulleys on the second part 204, five cable runs cooperating with two pulleys on the buoy and three pulleys on the second part 204. If the number of cable runs is even one end of the cable 217 has to be secured to the second part 204, if said number is uneven said end of cable 217 has to be secured to the buoy. In short, the number of cable runs can be raised at will, if necessary.

An important advantage of the system as described is that the cross-section of the spring buoy 212 and its height above the water surface 208 can be designed in many different ways so that almost every desired spring characteristic can be obtained. The design of the buoy determines the maximum mooring line force M since, after the moment the spring buoy 212 has completely submerged, the mooring cable force will remain at a constant value,

As explained above, the spring characteristic of the spring buoy 212 as shown in FIGURE 1 is indicated by the full lines I and II. If instead a spring buoy is used having a conical shape with its apex pointing upwardly and with a height which is smaller than the height of the spring buoy previously discussed, a characteristic will be obtained as indicated by dotted lines III and IV. If the said cone is pointing with its apex downwardly a characteristic is obtained as indicated by the dotted lines V and IV.

The slope of the first part of the line 0A (line I) is determined by the cross-sectional area of the buoy and the number of cable runs pulling on the buoy, whereas the level of the horizontal line AB (line II) depends, for a given cross-section, on the initial height of the buoy above the water surface. This horizontal line determines the maximum force in the mooring line.

When no mooring force acts on the buoy 212, it extends into the water to a certain initial depth. This initial depth can be varied, if desired, if an embodiment of the buoy is used which allows pumping of some water into or removing some water from the buoy.

In order to prevent the buoy 212, when no ship is moored to the mooring system, floating away from its location, special devices can be used. It is, for example, possible to secure a stop device on cable 218 or on one of the cable runs 217. Instead it is possible to secure a connecting cable between the buoy 212 and the bottom 201 or one of the

parts

207, 204 or 200.

Attention is drawn to the fact that instead of cables, chains or ropes can be used, if desired.

I claim as my invention:

1. An underwater one-point mooring system for ships, said system comprising:

a first mooring part secured to the floor of a body of water and positioned beneath the surface of said body of water;

a second mooring part rotatably carried underwater by said first part for rotation about a substantially vertical axis;

first fluid conduit means carried by said first mooring part;

second fluid conduit means rotatably connected to said first fluid conduit means and carried by said second mooring part, said second conduit means including a fiowline extendable to a ship floating on said body of water;

buoyant means positioned above said mooring parts;

and

tackle means interconnecting said buoy means and said second mooring part including mooring cable means making at least one run between said buoy means and said second mooring part and having a free end connectable to said ship floating on said body of water whereby movement of said ship away from said mooring parts will cause said buoyant means to submerge when said mooring cable means is connected to said ship.

2. A mooring system as defined in claim 1 wherein said buoyant means comprises a buoy carried by said body of water.

3. A mooring system as defined in claim 1 wherein said tackle means includes first pulley means carried by said second mooring part and cooperable with said cable means.

4. A mooring system as defined in claim 3 wherein said tackle means further includes second pulley means carried by said buoy means and cooperable with said cable nieans.

5. A mooring system as defined in claim 4 wherein said first and second pulley means each comprise at least one pulley.

6. A mooring system as defined in claim 2 wherein said buoy means comprises a substantially cylindrical buoy.

7. A mooring system as defined in claim 6 wherein said buoy comprises a cylindrical lower portion and a cylindrical upper portion, said lower portion having a larger diameter than said upper portion.

-8. An underwater one-point mooring system for ships,

said system comprising:

first fluid conduit means carried by said first mooring part;

second fluid conduit means rotatably connected to said first fluid conduit means and carried by said second mooring part, said second conduit means including a flowline extendable to a ship floating on said body of water;

buoy means positioned above said mooring parts; and,

mooring cable means operatively connected to said buoy means and extending downwardly to said second part, at least a portion of said cable means being operatively connected in sliding contact with said second part and extending upwardly to a free end adapted to be secured to said ship whereby movement of said ship away from said mooring parts will cause said buoyant means to submerge when said mooring cable means is connected to said ship.

9. A mooring system as defined in claim 8 wherein said cable is operatively connected in sliding contact with said buoy means and extends downwardly to said second part in two runs, one run being secured to said rotatable part and the other run having a portion operatively connected in sliding contact with said second part and extending upwardly to a free end adapted to be secured to said ship.

References Cited UNITED STATES PATENTS 2,478,217 8/1949 Walters et al 114230 2,894,268 7/ 1959 Gl'iebe 98 3,151,594 10/1964 Collipp 114230X TRYGVE M. BLIX, Primary Examiner.

US. Cl. X.R. 98