NL2004529C2

NL2004529C2 - Vessel and method for raising a load under water using the vessel.

Info

Publication number: NL2004529C2
Application number: NL2004529A
Authority: NL
Inventors: Hubrecht Servaas Dijke
Original assignee: Uab Laivu Projektai
Priority date: 2010-04-09
Filing date: 2010-04-09
Publication date: 2011-10-11

Description

Vessel and method for raising a load under water using the vessel

The invention relates to a vessel, such as an Anchor Handling Supply Vessel (AHSV), comprising, a hull having a longitudinal midplane defining a starboard and a port side of 5 the hull, a cable for picking up tensile forces, a winch connected to the hull for taking up the first cable and driving means for driving the winch in rotation. The invention also relates to a method for raising a load under water using such a vessel.

Floating platforms at sea, such as Floating Production, Storage and Offloading (FPSO) 10 platforms for processing and storage of oil and gas, are positioned nearby drilling platforms and anchored to the sea bottom by multiple anchor lines. Water depths at such locations can be as high as 1.500 meter. Pullout forces for lifting the anchors used for positioning FPSO’s are unpredictable and can exceed 1.000 metric ton. For lifting such anchors and anchor lines use is made of Anchor Handling Supply Vessels of the above 15 mentioned type. Thereto a cable is connected to the anchor line and/or to the anchor. By driving the winch in rotation a pullout force will be exerted on the anchor. However, during operation at sea there is a risk of significant heeling which even may lead to capsizing of the vessel due to the forces and the moment exerted by the cable on the vessel. This even more holds in case of rough sea conditions, wherein wind and waves 20 increase the risk of heeling of the vessel.

The invention has for its object to provide a vessel, which at least partially obviates the above stated drawbacks.

25 According to the invention a vessel, such as an Anchor Handling Supply Vessel, is provided for this purpose, which comprises a hull having a longitudinal midplane defining a starboard and a port side of the hull, a first cable for picking up tensile forces, a first winch connected to the hull for taking up the first cable, driving means for driving the first winch in rotation, wherein the hull is provided with a passage for 30 passing the first cable, wherein a first end of the passage extends through the hull substantially at the midplane of the hull and below the water line of the hull. A given force exerted by the cable on the vessel results in a decreased moment, due to the decreased distance between the force line exerted on the vessel and the midplane of the vessel. The force exerted by the cable on the vessel is a stabilizing force, which tends to 2 prevent heeling of the vessel and substantially exerts a downward force. As a result, there is a decreased risk of significant heeling or capsizing of the vessel. Also, higher pullout forces can be applied or lighter vessels can be used. In this context by cable is also meant rope, wire, chain etc. The vessel may also be a pontoon, ship or boat. The 5 midplane can be a plane of symmetry of the hull, depending on the design of the hull.

The corresponding method for raising a load under water using a vessel according to the invention comprises moving the vessel to a first position near the load, passing at least a part of the first cable through the passage, connecting the second end of the first cable to 10 the load and raising the load by driving the first winch.

The location along the midplane at which the passage extends through the hull is in principle free to choose. Although it is not excluded that the passage may extend through the hull at or near the bow or stem of the vessel, preferably the vessel has a 15 centre of gravity, wherein the passage extends through the hull substantially below the centre of gravity of the vessel. During operation, this results in decreased pitching of the vessel for a given force exerted by the cable on the vessel.

To further decrease the risk of heeling or even capsizing of the vessel, the vessel 20 comprises a keel, wherein the midplane extends through the keel.

The second end of the passage may end below water level within the hull. A subsequent passage may be connected to this passage in a watertight fashion, wherein the subsequent passage ends above water level. In a preferred embodiment, a second end of 25 the passage extends above the water line of the hull.

To improve the handling of the first cable at sea, the first cable is connectable to the winch at a first end of the first cable and a floating body is connectable to the first cable at a distance from the first end, wherein the floating body is arranged to pass through 30 the passage. In this way, the floating body will exert a pull force on the first cable, towards the water surface. The location of the floating body and as a result also of the first cable is visualised from the vessel and can easily be grabbed if it is desired to haul the first cable aboard. This is especially advantageous in case of rough sea conditions.

3

In a corresponding embodiment of the method according to the invention, the method comprises connecting a floating body to the first cable at or nearby the second end of the first cable before passing the first cable through the passage, passing a length of the first cable through the passage such that the weight of the first cable pulls the floating 5 body substantially through the first end of the passage, lifting the first cable by driving the winch such that the floating body raises to water level outside the passage and hauling the floating body and at least a part of the first cable aboard.

In a further embodiment the vessel further comprises a second cable for picking up 10 tensile forces, at a second end thereof provided with connecting means for connecting the second cable to the first cable, a second winch connected to the hull for taking up the second cable and driving means for driving the second winch in rotation. A second cable can be used for assisting the first cable in raising a load from the bottom under water. The second cable can be connected to the first cable outside the hull, which 15 simplifies hauling the load aboard. This even more holds in case of loads, which do not fit through the passage in the hull.

The corresponding method comprises connecting the second end of the second cable to the second end of the first cable after passing at least a part of the first cable through the 20 passage to form a loop around the passage and the hull. A referred embodiment according to the invention comprises moving the vessel before hauling the floating body and at least a part of the first cable aboard. Moving the vessel results in increased predictability of the location of the first cable or the floating body and cab therefore within a shorter period of time be hauled aboard. This even more holds in case of rough 25 sea conditions, as in such conditions it is difficult to visualise the floating body and/or the first cable.

The break loads of the first and/or second cable can be freely chosen. In a preferred embodiment the break load of the first cable is higher than the break load of the second 30 cable. As a result the second cable can be designed with a smaller diameter and/or the second cable can be manufactured from a lighter material. This results in a second cable, which has improved handling characteristics and is cheaper.

4

In another embodiment the break load of the first cable is at least 750 metric ton, preferably at least 850 metric ton and most preferably at least 950 metric ton. First cables having such high strength allow the first cable to raise heavy loads and it is these heavy loads for which the vessel according to the invention can be put into practice 5 advantageously. The given strength allows the vessel according to the invention to raise anchor lines of, among others, floating platforms at sea or other heavy loads.

In a corresponding method the load which is raised from a bottom is an anchor line of a moving platform at sea, which anchor line comprises an anchor fixed into the bottom.

10

The cables can be made of various materials. Preferably the first and/or second cable comprises at least one material selected from the group consisting of: metal, ultra-high-molecular weight polyethylene, aramids. Such materials combine high strength with low weight and low costs.

15

In yet another embodiment connecting means are connected to the second end of the first cable. This allows for easy connecting the first cable to the load. Preferably, the connecting means comprise a shackle. A shackle is reliable and strong. Furthermore, a shackle can easily be attached to the first cable, e.g. to a splice of a rope or a link of a 20 cable.

Preferably, also the break load of the connecting means is at least 750 metric ton, preferably at least 850 metric ton and most preferably at least 950 metric ton to allow the cables to raise heavy loads corresponding to the strength of the first cable.

25

The invention will now be further elucidated on the basis of the following detailed description of a preferred embodiment, which is given solely by way of example and must not therefore be deemed limitative. In the figures: 30 figure 1 shows a longitudinal section of a vessel according to the invention, prior to raising an anchor line of a platform at sea; figure 2 shows a longitudinal section of the vessel of figure 1, wherein a part of the first cable is passed through the passage; 5 figure 3 shows a longitudinal section of the vessel according to figure 2, wherein the vessel has been moved and wherein the first cable has been partly raised; figure 4 shows a longitudinal section of the vessel according to figure 3, wherein the first cable has been has been hauled aboard and connected to the second 5 cable; figure 5 shows a longitudinal section of the vessel according to figure 4, wherein a shackle has been connected to the second end of the first cable and to the anchor line; figure 6 shows a schematic view of the vessel according to figure 5, wherein the 10 shackle is moved towards the anchor at the bottom; figure 7 shows a schematic view of the vessel according to figure 6, wherein the anchor and the anchor line have been partly raised by raising the first cable; and figure 8 shows a cross section of the vessel through the line A-A of figure 1.

15 An Anchor Handling Supply Vessel (AHSV) 1 according to the invention is shown with reference to figure 1. The vessel 1 is used for raising an anchor line 50 with an anchor 51 of a floating platform 52 at sea (see also figures 5 and 6). The vessel 1 floats at sea, having a water level 2. In the shown embodiment the vessel comprises a hull 3, having a longitudinal midplane 4 defining a starboard (4a) and a port side (4b) of the hull 3 (see 20 figure 8). A first winch 5 is connected to the hull 3 for taking up a first cable 6 for picking up tensile forces. The first winch 5 comprises an electro motor and a control (not shown) for driving the first winch 5 in rotation about an axis 7. The hull 3 is provided with a passage 8 for passing the first cable 6. The passage 8 extends through the bottom 3a of the hull 3, wherein a first end 8a of the passage 8 extends through the 25 hull substantially at the midplane 4 of the hull 3 and below the water line 3b of the hull 3, which water line 3b corresponds to the water level 2. The vessel 1 comprises a keel 9, fixed to the bottom hull 3, wherein the midplane 4 extends through the keel 9. A second end 8b of the passage 8 extends above the water line 3b of the hull 3. The first cable 6 is connected to the winch 5 at a first end 6a (not shown) of the first cable 6. A buoy 10, 30 having a buoyancy of approximately 1.3 metric ton is connected to the first cable 6 at the second end 6b of the first cable 6, wherein the dimensions of the buoylO are relatively small compared the passage 8, to allow the buoy 10 to pass through the passage 8. A second winch 11 is connected to the hull 3 for taking up a second cable 12 for picking up tensile forces. The second winch 11 comprises also an electro motor and 6 a control (not shown) for driving the second winch 11 in rotation about an axis 13. At a second end 12a the second cable 12 comprises a shackle 14 for connecting the second cable 12 to the first cable 6. At the second end 6b of the first cable 6a a shackle 15 is connected, for connecting the first cable 6 to an anchor line 50 of a platform 52 (see 5 figure 5). The first cable 6 and second cable 12 are manufactured from steel wires and have a break load of 1.000 metric ton and 400 metric ton, respectively.

The method for raising the anchor line 50 and anchor 51 fixed to the anchor line 50 will be elucidated here below with reference to figures 2-7.

10

The vessel 1 is positioned nearby the platform 52. The first cable 6 is lowered through the passage 8 by driving the winch 5 in counter clockwise direction corresponding arrow 16 (see figure 2). The first cable 6 is guided about a pulley 17. After unrolling approximately 80 meter of the first cable 6 from the winch 5, the buoy 10 is positioned 15 in the passage 8 where it will float at water level. After unrolling approximately 93 meter of the first cable 6 from the winch 5, the weight of the cable 6 pulls the buoy 10 down below water level 2, such that the buoy 10 is sufficiently below the bottom of the hull 3 a not to damage neither the vessel 1 nor itself. The vessel 1 makes a forward speed of about 10 kilometre per hour, wherein the first cable 6 and the buoy 10 are positioned 20 in backward direction with respect to the vessel 1 (see figure 3).

The buoy 10 should now be visible from the vessel 1. Optionally a few metres of the first cable 6 can be hauled aboard by driving the winch 5 in clockwise direction, opposite to arrow 16, such that the buoy 10 raises to or close to water level 2.

25

At the stem side la of the vessel 1, the buoy 10 is grasped and brought aboard, where after the buoy 10 is loosened from the first cable 6 and a second end 12b of the second cable 12 is attached to the first cable 6 (see figure 4). Further, a first end of a chain 18 is connected to the shackle 14 of the first cable 6 and to the other end of the chain 18 a 30 triplate 19 is fixed. Both the chain 18 and the triplate 19 have a break load of 1.000 metric ton. The triplate 19 allows for easy connecting the first cable 6 to the anchor line 50 and to the anchor 51.

7

The vessel 1 is then positioned close to the platform 52, such that the triplate 19 can be connected to the anchor line 50 (see figure 5).

Subsequently, the first cable 6 and second cable 12 are hauled and lowered respectively, 5 such that the first cable 6 picks up any forces from the anchor line 50. The vessel 1 makes forward speed away from the platform 52 into the direction of the anchor 51, wherein during sailing both the first cable 6 and second cable 12 are lowered in relation to the speed of the vessel 1. This is shown in figure 6, wherein arrow 20 corresponds to the direction of the vessel 1 towards the anchor 51. As the triplate 19 comes into contact 10 with the anchor 51 (the most right position in figure 6), an additional 20 meters of the first cable 6 and second cable 12 is lowered for safety. Also in this condition, the first cable 6 picks up any forces from the anchor line 50, wherein as much as 1.000 meter of the first cable is unrolled from the winch 5. Now, the vessel 1 is ready to pull the anchor 51 out of the bottom 53. Driving the winches 5 and 13 in clockwise direction opposite 15 arrow 16, wherein the first cable 6 and second cable 12 are raised with equal speed, does this (see figure 7). Raising the cables 6,12 with equal speed prevents the second cable 12 from picking up any load from the anchor line 50 and from entangling with the anchor 51. The pull out force can be as high as 900 metric ton.

20 From figure 7 it is clear that the first cable 6 extends through the passage 8, wherein the force of the first cable 6 on the winch results in only a small moment on the vessel 1. During hauling of the anchor line 51, the vessel is moved backwards towards the platform 52, opposite to arrows 20 of figure 6. At a predetermined distance from the platform 52 the anchor 51 is hauled aboard, at the stem side of the vessel la. The anchor 25 51 is loosened from the anchor line 50, where after the anchor line 50 is hauled aboard of the platform 52.

The above mentioned steps may be repeated for the total number of anchor lines 50 and anchors 51, by which the platform 52 is connected to the bottom 53.

30

Figure 8 shows a cross section of the vessel 1 through the passage 8. From this figure it is clear that the force exerted on the vessel 1 by the cable 6 results in a small moment about the midplane 4 of the vessel 1. As a result the risk of excessive heeling or even capsizing of the vessel 1 during operation is minimized or at least decreased.

Claims

1. Vaartuig, zoals een vaartuig voor het liften van een anker, omvattende: 5. een romp met een middenvlak in de langsrichting van het schip, die een stuurboordzijde en een bakboordzijde van de romp definieert; een eerste kabel voor het opnemen van trekkrachten; een eerste met de romp verbonden lier voor het opnemen van de eerste kabel; aandrijfiniddelen voor het in rotatie aandrijven van de eerste lier; 10 waarbij de romp is voorzien van een passage voor het doorvoeren van de eerste kabel, waarbij een eerste einde van de passage zich hoofdzakelijke in het middenvlak en onder de waterlijn van de romp door de romp uitstrekt.A vessel, such as an anchor lifting vessel, comprising: 5. a hull with a center plane in the longitudinal direction of the ship, defining a starboard side and a port side of the hull; a first cable for taking up tensile forces; a first winch connected to the hull for receiving the first cable; drive means for driving the first winch in rotation; 10 wherein the hull is provided with a passage for passing through the first cable, wherein a first end of the passage mainly extends through the hull in the central plane and below the waterline of the hull.

2. Vaartuig volgens conclusie 1, met het kenmerk dat het vaartuig een zwaartepunt heeft en dat de passage zich in hoofdzaak onder het zwaartepunt door de romp uitstrekt.Vessel according to claim 1, characterized in that the vessel has a center of gravity and that the passage extends through the hull substantially below the center of gravity.

3. Vaartuig volgens conclusie 1 of 2, met het kenmerk dat het vaartuig een kiel 20 omvat, waarbij het middenvlak zich door de keel uitstrekt.3. Vessel as claimed in claim 1 or 2, characterized in that the vessel comprises a keel, wherein the central surface extends through the throat.

4. Vaartuig volgens een der voorgaande conclusies, met het kenmerk dat een tweede einde van de passage zich door het vaartuig uitstrekt tot boven de waterlijn.Vessel according to one of the preceding claims, characterized in that a second end of the passage extends through the vessel above the water line.

5. Vaartuig volgens een der voorgaande conclusies, met het kenmerk dat de eerste kabel aan een eerste einde met de lier verbindbaar is en dat een drijvend lichaam op afstand van het eerste eind met de eerste kabel verbindbaar is, waarbij het drijvend lichaam is aangepast zodat het door de passage past.5. Vessel as claimed in any of the foregoing claims, characterized in that the first cable can be connected to the winch at a first end and that a floating body can be connected to the first cable at a distance from the first end, the floating body being adapted such that it fits through the passage.

6. Vaartuig volgens een der voorgaande conclusies, met het kenmerk dat het vaartuig verder omvat: een tweede kabel voor het opnemen van trekkrachten, die aan een tweede einde ervan is voorzien van verbindingsmiddelen voor het met de eerste kabel verbinden van de tweede kabel; een tweede met de romp verbonden lier voor het opnemen van de tweede kabel; 5 en aandrijfmiddelen voor het in rotatie aandrijven van de tweede lier.6. Vessel as claimed in any of the foregoing claims, characterized in that the vessel further comprises: a second cable for absorbing tensile forces, which is provided at a second end thereof with connecting means for connecting the second cable to the first cable; a second winch connected to the hull for receiving the second cable; 5 and drive means for driving the second winch in rotation.

7. Vaartuig volgens conclusie 5 of 6, met het kenmerk dat de breeksterkte van de eerste kabel groter is dan de breeksterkte van de tweede kabel. 10Vessel according to claim 5 or 6, characterized in that the breaking strength of the first cable is greater than the breaking strength of the second cable. 10

8. Vaartuig volgens een der conclusies 5-7, met het kenmerk dat de breeksterkte van de eerste kabel ten minste 750 ton, met voorkeur ten minste 850 ton en met de meeste voorkeur ten minste 950 ton is.A vessel according to any one of claims 5-7, characterized in that the breaking strength of the first cable is at least 750 tons, preferably at least 850 tons and most preferably at least 950 tons.

9. Vaartuig volgens een der voorgaande conclusies, met het kenmerk dat de eerste en/of de tweede kabel een materiaal omvat dat is geselecteerd uit de groep bestaande uit: metaal, ultra-hoog-moleculair gewicht polyethyleen, aramide.Vessel according to one of the preceding claims, characterized in that the first and / or the second cable comprises a material selected from the group consisting of: metal, ultra-high-molecular-weight polyethylene, aramid.

10. Vaartuig volgens een der voorgaande conclusies, met het kenmerk dat met het 20 tweede eind van de eerste kabel verbindingsmiddelen zijn verbonden.10. Vessel according to any one of the preceding claims, characterized in that connecting means are connected to the second end of the first cable.

11. Vaartuig volgens conclusie 10, met het kenmerk dat de breeksterkte van de verbindingsmiddelen ten minste 750 ton, met voorkeur ten minste 850 ton en met de meeste voorkeur ten minste 950 ton is. 25Vessel according to claim 10, characterized in that the breaking strength of the connecting means is at least 750 tons, preferably at least 850 tons and most preferably at least 950 tons. 25

12. Werkwijze voor het onder water liften van een gewicht met gebruikmaking van een vaartuig volgens van de conclusies 1-11, omvattende: het naar een eerste positie nabij het gewicht bewegen van het vaartuig; 30. het door de passage voeren van ten minste een deel van de eerste kabel; het met het gewicht verbinden van het tweede eind van de eerste kabel; en het door het aandrijven van de lier liften van het gewicht.A method for lifting a weight under water using a vessel according to any of claims 1-11, comprising: moving the vessel to a first position near the weight; 30. passing at least a portion of the first cable through the passage; connecting the second end of the first cable to the weight; and lifting the weight by driving the winch.

13. Werkwijze volgens conclusie 12, gekenmerkt door het met het tweede einde van de eerste kabel verbinden van het tweede eind van de tweede kabel na het door de passage voeren van ten minste een deel van de eerste kabel voor het vormen van een lus rond de romp. 5A method according to claim 12, characterized by connecting the second end of the second cable to the second end of the first cable after passing at least a portion of the first cable through the passage to form a loop around the trunk. 5

14. Werkwijze volgens conclusie 13, met het kenmerk dat de werkwijze verder omvat: het aan of nabij het tweede einde van de eerste kabel verbinden van een drijvend 10 lichaam voorafgaande aan het door de passage voeren van de eerste kabel; het door de passage voeren van een lengte van de eerste kabel zodat het gewicht van de eerste kabel het drijvend lichaam in hoofdzaak door het eerste einde van de passage trekt; het liften van de eerste kabel door het aandrijven van de eerste lier, zodat het 15 drijvend lichaam buiten de passage stijgt tot het watemiveau; en het aan boord halen van het drijvend lichaam en ten minste een deel van de eerste kabel.14. A method according to claim 13, characterized in that the method further comprises: connecting a floating body at or near the second end of the first cable prior to passing the first cable through the passage; passing a length of the first cable through the passage so that the weight of the first cable pulls the floating body substantially through the first end of the passage; lifting the first cable by driving the first winch so that the floating body rises outside the passage to the water level; and bringing on board the floating body and at least a portion of the first cable.

15. Werkwijze volgens conclusie 14, met het kenmerk dat de werkwijze omvat het 20 bewegen van het vaartuig voorafgaande aan het aan boord halen van het drijvend lichaam en ten minste een deel van de eerste kabel.15. Method as claimed in claim 14, characterized in that the method comprises of moving the vessel prior to bringing the floating body on board and at least a part of the first cable.

16. Werkwijze volgens een der conclusies 12 - 15, met het kenmerk dat het gewicht een ankerlijn is van een bewegend platform op zee, waarbij de ankerlijn een 25 anker omvat dat in de bodem is gefixeerd.16. Method as claimed in any of the claims 12-15, characterized in that the weight is an anchor line of a moving platform at sea, wherein the anchor line comprises an anchor that is fixed in the bottom.