US3864924A

US3864924A - Diving bell for wellhead placing and maintenance in shallow water

Info

Publication number: US3864924A
Application number: US407392A
Authority: US
Inventors: Maurice Joseph Piotin
Original assignee: SUBSEA EQUIPMENT ASS Ltd
Current assignee: Total Compagnie Francaise des Petroles SA
Priority date: 1972-10-17
Filing date: 1973-10-17
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: JPS49125201A; GB1427418A; AU6083973A; IT995917B; NO146191B; NO146191C; JPS5529237B2; CA1002875A; FR2155706A5; DE2351889A1; NL153137B; NL7306946A; DE2351889B2; DE2351889C3

Abstract

A diving bell having three parts, a control chamber at the top center, a work chamber beneath the control chamber, and an annular ballast chamber surrounding the control chamber. Outlets are provided at the top and bottom of the annular ballast chamber to connect the inside thereof with the outside medium. A pump is provided to transfer water back and forth between the work chamber and the ballast chamber in order to retain a buoyancy reserve and to facilitate control of the connection and watertightness of the diving bell on an underwater base platform.

Description

United States Patent n 1 Piotin [111 3,864,924 Feb. 11, 1975 DIVING BELL FOR WELLI-IEAD PLACING AND MAINTENANCE IN S I-IALLOW WATER [75] Inventor: Maurice Joseph Piotin, Boulogne,

France [73] Assignee: Subsea Equipment Associates Ltd.,

Hamilton, Bermuda [22] Filed: Oct. 17, 1973 [21] Appl. No.: 407,392

[30] Foreign Application Priority Data Oct. 17, 1972 France 72.36677 [52] US. Cl 61/69 R [51] Int. Cl. B63c 11/44 [58] Field of Search 6l/46.5, 69 R, 69 A; 166/.5

[56] References Cited UNITED STATES PATENTS 530,398 12/1894 Cooper 61/69 R 1,803,526 5/1931 Finn 6l/69 A 2,519,453 8/1950 Goodman 61/69 R 6/1971 Lowd et al 6l/46.5

3,589,133 3,609,981 10/1971 Cook 61/69 R 3,626,703 12/1971 Richhurg 61/69 R FOREIGN PATENTS OR APPLICATIONS 148.022 12/1954 Sweden 61/69 R Primary E.\'aminer-Paul R. Gilliam Assistant Examiner-D. H. Corbin Attorney, Agent, or Firm-Sughrue, Rothwell, Mion. Zinn & Macpeak [57] ABSTRACT A diving bell having three parts, a control chamber at the top center, a work chamber beneath the control chamber, and an annular ballast chamber surrounding the control chamber. Outlets are provided at the top and bottom of the annular ballast chamber to connect the inside thereof with the outside medium. A pump is provided to transfer water back and forth between the work chamber and the ballast chamber in order to retain a buoyancy reserve and to facilitate control of the connection and watertightness of the diving bell on an underwater base platform.

16 Claims, 7 Drawing Figures PATENI FEB! 1 1915 sum '1 0? 4 DIVING BELL FOR WELLHEAD PLACING AND MAINTENANCE IN SHALLOW WATER The invention concerns a diving bell for carrying out the installation ofa wellhead for performing any checking or maintenance operation on a wellhead at atmospheric or near atmospheric pressure.

Known diving bells for operational use are either too improvised for carrying out inspection work in complete safety or needlessly complicated when the working depth is several tens of metres. In the first intance,

the operational diving bell is composed of a straightforward bell divided by a horizontal bulkhead fitted with a watertight door as in the case of the James U.S. Pat. No. 3,5l2,583, having an upper chamber for carrying the technicians and a lower chamber capping the wellhead by resting vertically on a horizontal platform integral with the wellhead and resting laterally and in watertight fashion against a cylindrical surface surrounding the wellhead and integral with the said platform. With such a system, it is not possible to void either the jolting which occurs when the bell is lowered into the water due to the apparent variation in weight induced by the swell or the risk of accidents which might occur in the bells lower chamber without it being possible to intervene from the upper chamber.

In the second instance, the need for personnel working at atmospheric pressure to be safe requiresthe use of several rings which must be lowered separately, extreme precision being required for the joints between .them as they have to withstand dangerously high hydrostatic pressure. Such apparatus requires many checking, sealing and safety measures, thus reducing the viability of the assembly.

The main purpose of this invention is a diving bell capable of carrying personnel at atmospheric pressure directly to the wellheadwithout jolting during-the descent or during the return to the surface. The apparatus disclosed comprises a central control chamber arranged in the upper part connected to the lower open part of the bell by a watertight door, and an annular ballast chamber, the said annular chamber having at least one outlet for connecting the said ballast chamber to the external medium on both its upper and lower sections. Thus, it sufficies to open these outlets during immersion for the weight of the bell to increase rapidly and to a large extent prevent the action of the swell on account of the intercommunication provided between the upper and lower parts of the ballast chamber, particularly when the level of the water lies between the upper and lower outlets.

Another purpose of the invention is a bell of this type, the lower part of which has a flooding door in its top section leading directly outside the bell. Thus, not only can the filling speed of the lower part of the bell be increased during immersion by opening the flooding door, but safety is further increased because the flooding door makes an immediate exit of the bell possible without the need to use the upper central chamber.

Another purpose of the invention is a bell of this type having, in addition to control valves for closing the said upper and lower outlets in the said ballast chamber as well as means for progressively pumping out the water that it contains with the object of changing its buoyancy state from negative buoyancy to a buoyancy of practically nil, means of hauling for ensuring the support of the bell during its state of negative buoyancy and means of independent propulsion enabling it to state of practically nil. Thus, the bell in its heavy state is able at one and the same time to move along just below the surface of the water without risk and at a relatively high speed of descent due to the means of hauling, then reduce speed to the value required for the purpose of adopting its buoyancy of practically nil and to approach the wellhead very slowly by means of the propulsion medium.

Another purpose of the invention is a bell of this type in which the volume of the lower part of the bell, demarcated by its bearing surface on the base platform by the compartments inner walls and by the ballast chamber, is more or less equal to or less than the volume of the ballast chamber.

When the bell is resting on its base platform, it can be seen that the transfer of water at a lower pressure than ambient pressure from the lower part of the bell to the ballast chamber not only helps to ensure the watertight sealing of the bell due to the pressure on the sea bed being exerted on the outside of the bell but also ensures thatthe bells'buoyancy reserve is retained. Thus the inverse operation, that is to say the return of the water from the ballast chamber to the inside of the bell followed by opening the channel for it to the ambient medium, enables the bell to return immediately to the surface. Furthermore, when the lower part of the bell is once again at atmospheric pressure, no severe impact will be able to have any effect whatsoever on the bell.

Other advantage and characteristics will be apparent from the following description, set out in relation to the attached drawing which shows, by virtue of being a non-limitative example, one method of application of this invention.

On the drawing:

FIG. 1 is a diagrammatic representation of the ball in partial axial section shown resting on its base platform.

FIG. 2 the view in axial section of a detail of the seal on the lower part of the bell,

FIG. 3 the diagrammatic view of the blocks lockingon system,

FIG. 4 the diagrammatic view of a variant of the bell shown in FIG. 1,

FIG. 5 a digrammatic view of the bell in the process of immersion,

FIG. 6 a diagrammatic view of the bell at the moment of its contact with the base platform,

FIG. 7 the diagrammatic view of the bell while work is being carried out on the wellhead.

If reference is made to FIG. 1, where the bell 1 has been drawn in a general way in a position where it is already resting on the peripheral portion of a base platform 3 integral with the drilling head 9 by means of its centre part 2, it can be seen that the bell 1 is fundamentally divided into three parts: a top centre part or control chamber 4, an annular or ballast chamber 5, and a bottom part 6 open at the base. The top centre part or work chamber 4 serves, on the one hand, to carry the personnel and, on the other hand, as an inspection and control chamber. For this purpose, it is watertight and communicates with the outside by means of the door 7 and with the bottom part 6 by means of the door 8. This bottom part, which in fact consists of the bell proper, acts at atmospheric pressure as the working chamber when it rests in watertight fashion on the platform 3, which insulates perfectly the upper and lower zones of which it forms the limit.

The base platform 3 is attached beforehand to the drilling head 9 by any known method and in watertight manner. For example, the centre part 2 can be welded beforehand to the drilling head 9. When such'an operation has not been carried out, the centre part 2 can be manufactured in two parts that can be welded round drilling head 9. The centre part 2 can also be fitted with suitable joints, the part being introduced with the help of cone 2a. With regard to base platform 3, it may have a profile enabling it to rest in collar 2b through the intermediary of any suitable joint, also brackets 3a may be provided to help to strengthen the convex base platform 3. In this way, base platform 3 may be provided with assorted equipment, including particularly four guide pillars 10. It is designed and built to resist hydrostatic pressure when, with bell 1 resting on base platform 3, the working chamber 6 is emptied of the water it contains. In order to illustrate the part played by the base platform 3 as a support and in an intermediate role, dotted line 12 shows diagrammatically the piping leading to the flow line through the intermediary of the coupling 38', the blow-out preventer 13 preventing fluid returning from the flow lines into work chamber 6. In the same way, other piping has been illustrated at 14 for connecting up to another flow line through the intermediary of connector 38a, the blow-out preventer 39 preventing fluid returning to work chamber. 6. These pipe layouts have only been drawn in to act as a reminder of conventional wellhead installation operations.

The work chamber 6 is fitted with a flooding door 15 leading directly outside so that in an emergency it is always possible to leave work chamber 6 without first having to pass through the control chamber 4. In addition to thissafety function, flooding door 15, enables work chamber 6 to be rapidly filled or emptied during the immersion or raising of the bell 1.

An emptying pump 16 enables water acting as ballast in work chamber 6 to be passed into the annular chamber 5. The transfer circuit has been drawn diagrammatically 17a and 17b, and it is controlled from circuits (not shown) in the control chamber. In addition, the work chamber 6 comprises electrical control connections 43 and hydraulic control connections 42 coupled respectively on the one hand to the electrical display and distribution panel 44 and, on the other hand, to the hydraulic distribution panel 40.

A connection 45 enables the balance of pressures between chambers 4 and 5 by means of control valves 46 and 47 respectively on the one hand and control valve 48 on the other hand to be maintained.

An assembly 22 contains all the regenerating and atmospheric control equipment enabling life to be supported in a confined space. This assembly is connected to the electric display and distribution panel 44 by connection 23.

Television, handling, and safety equipment, complete the installation. This equipment which may be of any sort, has not been drawn in for the sake of a clearer drawing.

The control chamber 4 includes all the opening and shutting controls for doors 7 and 8, flooding door 15, and

outlets

20 and 21 located in the top and bottom parts of the annular chamber 5, which acts as a ballast tank.

Control chamber 4 also includes all the safety and control equipment necessary and, in particular, the controls for transmitting information concerning buoyancy regulation and the controls of the independent means of propulsion 27 located on the outside walls 51 of bell l and preferably directly below ballast chamber 5.

The electrical display and distribution panel 44 is permanently connected to the electrical services support cable 32 by means of connection 24. The sending of messages to the surface is carried out by the system 49 which is connected to the transmission cables inside sleeve 34. This sleeve also contains the air intake piping and connects control chamber 4 to the surface so that air can be supplied to the diving bell when required, irrespective of how long it is immersed.

The hydraulic distribution panel 40 is connected to the hydraulic power supply 18 by means of circuit 41.

The means of propulsion 27 are fitted in a tube and free to swivel round axis 27a, FIG. 4. They may be of conventional type and preferably comprise electric motors 30 driving propellers 29.

An attachment or fastening device 31, drawn in greater detail in FIG. 5, enables the bell I to couple up, on the one hand, to the electrical services support cable 32 connected on the surface to a winch 35 and, on the other hand, to a suspension cable 32a connected on the surface to a second winch 35a, its bottom end fitted with a block 33. This block has some recesses 33a, visible in FIG. 3, in which locking latches 3317 move. When the attachment 31 enters the block, locking latches 33b, pushed by springs, lock attachment 31 by locating in the slots 31a. Unlocking is carried out by simple hydraulic control directly from control chamber 4 or from a control station 37 on the surface receiving information from control chamber 4 through the me dium of cables contained in sleeve 34.

In addition the bell is fitted with conventional equipment such as the kentledge 71 for the compressed air bottles 72.

Also it will be noticed that the shape of the lower edge of outside walls 51 prevents the seal 50, FIG. 2, becoming crushed. In fact the extreme peripheral part 51b is higher than zone 51c resting on base platform 3, thus the portion of the seal 50 proud of the location 51a is not crushed. The position of the seal before the bell is lowered into position is shown in dotted line. Furthermore, as the seal lip thickness is less than the difference between the height of peripheral part 51b in relation to the height of zone 51c, the surroudning water exerts a pressure at location 51a equal to ambient hydrostatic pressure, thus pressing the bottom face of the seal 50 down onto the base platform 3 with a force proportional to such pressure.

For the approach and locating operations on the base platform, the bell is fitted with a sonar device 65, FIG. 4, connected to the display cabinet 63 by connection 64. The sonar device 65, preferably located on the centreline of the bell 1, produces signals by the sending out of two sonic beams .69 and from

emitters

66 and 67 with the help of echo reflectors 68 and the reflection of the drilling head 9 these reflections are read on the display cabinet 63 in control chamber 4 and possibly retransmitted to the surface. At the end of the operation, the sonar device 65 is restowed on walls 51 by any appropriate means, shown diagrammetically by 74.

When the bell described is required for operational use, it is suspended from block 33 after the personnel have enetered the control chamber 4 and closed doors I 7 and 8, after which the immersion phase proper commences. Movement across the water surface is carried out just as rapidly as the block allows. Outlets 20 and2l, FIG. 5, being open as well as flooding door 15, it can be seen that the effects of the swell are for the most part avoided, the water level inside work chamber 6 and ballastchamber 5 freely following the variations in the swell.

After this first phase and when the bell has reached a depth of about ten metres, thereby avoiding the influence of the swell, the descent is stopped.

Outlets

20 and 21 are closed, and the water in ballast chamber 5 is partly expelled up to the point where the apparent weight of the bell reaches a determined reduced weight, for example of 5 tons. AT the end of this second phase, this lightening then enables block 33 to be disconnected from attachment 3], afterwhich bell 1 is only supported by the electrical services support cable 32. Flooding door 15 is closed, then the water in ballast chamber 5 is expelled sufficiently so that the negative buoyancy state becomes one of practically nil buoyancy.

Approach operations towards the base platform are then begun, employing the means of locating and propulsion just described, until the bell contacts the base platform 3 at practically zero speed, the guide pillars ensuring the exact position of the bell 1 on the base platform 3.

During a latter phase, FIG. 6, the emplacement of bell l on base platform 3 is completed by connecting up ballastchamber 5 and work chamber 6, which has the effect of inducing the bell 1 to sit better on the platform owing to the difference in hydrostatic pressure in the two chambers at the moment of connecting up and to the action of the seal 50 which seals off the interior of the bell 1 from the ambient medium after connecting up has taken place. Then, by means of pump 16, the water in work chamber 6 is transferred to ballast chamber 5, followed by the connecting up of work chamber 6 to the atmospheric pressure lines in the sleeve 34 through the medium of control valves 46, 47 and control chamber 4. It thus becomes possible to open door 8 as shown in FIG. 7. Prior to this opening, the atmosphere in work chamber 6 has been regulated by assembly 22 so that it becomes possible to carry out the work required on the wellhead or drilling head 9.

On completion of the work and the return of the personnel into the control chamber 4, it is sufficient to pump the water in ballast chamber 5 back into work chamber 6, then connect work chamber 6 to the outside by channel 170 for a return to the same conditions at the start of the final phase. Raising procedure is then carried out until the bell l is near but below the zone affected by the swell. Raising is then stopped and partial filling of the ballast chamber 5 proceeds in order to tension the electrical services support cable 32. It then suffices to lower block 33 so that the attachment 31, FIG. 4, enters the locking device in block 33 and automatically locks into it.

Then ballast chamber 5 can be completely filled,

outlets

20, 21 and flooding door opened, and the surface of the water crossed to re-embark the bell 1 on board the boat 36.

Although the personnel in control chamber 4 operate the controlling manoeuvres for the independent means of propulsion 27 on their own, it is evident that all the manoeuvres of the pair of blocks 33 and the electrical services support cable 32 might also be directly controlled from control chamber 4. Conversely, the means of propulsion 27 might also be directly controlled from the surface, tele-transmission apparatus enabling operators on the surface to know the precise distance of the bell from base platform 3. It is evident that the means of propulsion may include horizontal and vertical propulsion units whether independent or not and that they could be of the propeller type as shown in FIG. 4 or jet type. Moreover they may be controlled from the service and be free to swivel.

I claim: 7

l. A diving bell adapted to rest on a base platform at the bottom ofa body of water, said diving bell comprisa. a control chamber;

b. a work chamber beneath said control chamber,

said work chamber being open at the bottom; and c. an external ballast chamber, said ballast chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, whereby, if both the upper and lower outlets are opened during immersion of the diving bell, the effect of the swell on the diving bell is largely overcome, particularly when the level of the water lies between the upper and lower outlets.

2. A diving bell as recited in claim 1 wherein said ballast chamber is annular in shape and surrounds said control chamber. I

3. A diving bell as recited in claim 1 and further comprising a door between said control chamber and said work chamber.

4. A diving bell as recited in claim 1 and further comprising a flooding door between said work chamber and the exterior of the diving bell. 5. A diving bell as recited in claim 1 wherein the lower surface of said work chamber has a first, inner surface adapted to rest on a base platform, a second, outer surface located at a higher level than the first surface, and an annular recess located between the first and second surfaces and further comprising a seal located in the annular recess, said seal having a lip extending out over the second surface but being thinner than the difference between the levels of the first and second surfaces.

6. A diving bell as recited in claim 1 and further comprising a. means for controlling the closure of the outlets in said ballast chamber and b. means for progressively expelling water contained in said ballast chamber.

7. A diving bell as recited in claim 1 and further comprising means for lowering and raising the diving bell in the water.

8. A diving bell as recited in claim 7 wherein said means for lowering and raising the diving bell in the water comprise:

a. a fastening device integral with the diving bell;

b. a first cable connecting said fastening device to a first winch located on a surface support;

c. a pair of blocks carrying means for interlocking said blocks with said fastening device when the diving bell, rising under the pull of said first cable, brings said fastening device up against said pair of blocks; and

d. a pair of second cables connecting said pair of blocks to a second winch located on a surface support.

9. A diving bell as recited in claim 1 wherein the volume of said work chamber is approximately equal to the volume of said ballast chamber and further comprising means for transferring water back and forth between said work chamber and said ballast chamber.

10. A diving bell as recited in claim 1 wherein the volume of said work chamber is less than the volume of said ballast chamber and further comprising means for transferring water back and forth between said work chamber and said ballast chamber.

11. A diving bell as recited in claim 1 and further comprising a. propulsion means for moving the diving bell laterally and b. means for ascertaining the position of the diving bell relative to a base platform on which it is intended to locate the diving bell.

12. A diving bell as recited in claim 11 wherein said means for ascertaining the position of the diving bell relative to a base platform comprise a sonar transmitter-rcceiver mounted on the diving bell.

13. A method of lowering a diving bell adapted to rest on a base platform at the bottom of a body of water, said diving bell comprising:

a. a control chamber;

b. a work chamber beneath said control chamber,

said work chamber being open at the bottom; and

c. aneiieiaamiia'si ehanibflsai'd ballast' chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, said method comprising the steps of:

i. lowering the diving bell into the water with both the upper and lower outlets open down to a depth where the effects of the swell are no longer felt; ii. closing the upper and lower outlets; and iii. changing the buoyancy of the diving bell from a state of negative buoyancy to a state of practically nil buoyancy.

14. A method as recited in claim 13 wherein the diving bell is initially lowered at maximum speed to a depth where the effects of the swells is no longer felt, water contained in said ballast chamber is then partially pumped back into the body of water until the buoyancy of the diving bell is changed from a state of negative buoyancy to a state of practically nil buoyancy, and positioning and propulsion means located on the diving bell are controlled until the base platform is reached.

15. A method as recited in claim 13 and further comprising the step of sealing the diving bell onto the base platform by pumping the water out of said work chamber after the diving bell has come to rest on the base platform.

16. A method of raising a diving bell resting on a base platform on the bottom of a body of water, said diving bell comprising:

a. a control chamber,

b. a work chamber beneath said control chamber,

said work chamber being open at the bottom; and

c. an external ballast chamber, said ballast chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, said method comprising the steps of:

i. isolating said work chamber from said control chamber;

ii. transferring the water from said ballast chamber into said work chamber;

iii. connecting the work chamber to the outside medium;

iv. raising the working bell to a depth just below the depth at which the swell is first felt;

v. making the buoyancy slightly negative;

vi. opening both the upper and lower outlets in said ballast chamber; and

vii. raising the diving bell the rest of the way out of the water.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. i 3, 864, 924

DATED February 11, 1975 INVENTOR(S) Maurice Joseph PIOTIN It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION:

C01. 1, Line 2, after "wellhead", insert --or--.

Line 25, delete "bells", insert be1l's-.

Col. 2, Line 24, delete "thatthe", insert --that the--.

Col. 3, Line 15, before "base", insert --the-.

Line 37, after "15'', delete Line 43, after "ically", insert "at".

Patent No. Dated lnvntoflsj Maurice Joseph Piotin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 11 line 52, after "block" insert =5? 5, irze 153, delete "AT", insert At Signed and sealed this 1st day of July 1.975.,

SEAL) fittest T C. I'RTSOII Commissioner of Patents Attestin; @ffiCQl? and Trademarks USCOMM-DC 603764 69 U.S. GOVERNMENT PRINTING OFFICE: 8 9 9 o F ORM PO-IOSO (10-69)

Claims

1. A diving bell adapted to rest on a base platform at the bottom of a body of water, said diving bell comprising: a. a control chamber; b. a work chamber beneath said control chamber, said work chamber being open at the bottom; and c. an external ballast chamber, said ballast chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, whereby, if both the upper and lower outlets are opened during immersion of the diving bell, the effect of the swell on the diving bell is largely overcome, particularly when the level of the water lies between the upper and lower outlets.

2. A diving bell as recited in claim 1 wherein said ballast chamber is annular in shape and surrounds said control chamber.

4. A diving bell as recited in claim 1 and further comprising a flooding door between said work chamber and the exterior of the diving bell.

5. A diving bell as recited in claim 1 wherein the lower surface of said work chamber has a first, inner surface adapted to rest on a base platform, a second, outer surface located at a higher level than the first surface, and an annular recess located between the first and second surfaces and further comprising a seal located in the annular recess, said seal having a lip extending out over the second surface but being thinner than the difference between the levels of the first and second surfaces.

8. A diving bell as recited in claim 7 wherein said means for lowering and raising the diving bell in the water comprise: a. a fastening device integral with the diving bell; b. a first cable connecting said fastening device to a first winch located on a surface support; c. a pair of blocks carrying means for interlocking said blocks with said fastening device when the diving bell, rising under the pull of said first cable, brings said fastening device up against said pair of blocks; and d. a pair of second cables connecting said pair of blocks to a second winch located on a surface support.

12. A diving bell as recited in claim 11 wherein said means for ascertaining the position of the diving bell relative to a base platform comprise a sonar transmitter-receiver mounted on the diving bell.

13. A method of lowering a diving bell adapted to rest on a base platform at the bottom of a body of water, said diving bell comprising: a. a control chamber; b. a work chamber beneath said control chamber, said workchamber being open at the bottom; and c. an external ballast chamber, said ballast chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, said method comprising the steps of: i. lowering the diving bell into the water with both the upper and lower outlets open down to a depth where the effects of the swell are no longer felt; ii. closing the upper and lower outlets; and iii. changing the buoyancy of the diving bell from a state of negative buoyancy to a state of practically nil buoyancy.

16. A method of raising a diving bell resting on a base platform on the bottom of a body of water, said diving bell comprising: a. a control chamber; b. a work chamber beneath said control chamber, said work chamber being open at the bottom; and c. an external ballast chamber, said ballast chamber having at least one outlet at its base and at least one outlet at its top, both of which connect the inside of said ballast chamber with the outside medium, said method comprising the steps of: i. isolating said work chamber from said control chamber; ii. transferring the water from said ballast chamber into said work chamber; iii. connecting the work chamber to the outside medium; iv. raising the working bell to a depth just below the depth at which the swell is first felt; v. making the buoyancy slightly negative; vi. opening both the upper and lower outlets in said ballast chamber; and vii. raising the diving bell the rest of the way out of the water.