GB2027396A

GB2027396A - Submersible twin-hull watercraft

Info

Publication number: GB2027396A
Application number: GB7910052A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-03-23
Filing date: 1979-03-22
Publication date: 1980-02-20
Also published as: JPS6114995B2; GB2027396B; FR2420477B1; JPS54126387A; FR2420477A1

Abstract

A submersible watercraft designed for stability in varying degrees of submergence has first and second hulls 1, 2 constructed as submarines containing a propulsion unit, and ballast tanks adapted to be flooded and blown for varying the buoyancy of the watercraft. A buoyant pilot's cab 4 is disposed generally above the two hulls approximately in a longitudinal symmetry plane defined between the first and second hulls. A plurality of tubular members 3 rigidly interconnect the pilot's cab and the first and second hulls, and each has at least a section which is pressure resistant and weighs less than the volume of water displaced by the section when it is submerged. <IMAGE>

Description

SPECIFICATION Submersible twin-hull watercraft TECHNICAL FIELD The present invention relates to submersible watercraft; in particular, to a submersible watercraft having two hulls disposed generally parallel to and spaced apart from each other. A pilot's cab having a pressure vessel with viewing ports and a steering stand for the watercraft is disposed generally above the hulls approximately .in a longitudinal symmetry plane. The two hulls and the pilot's cab are rigidly interconnected by tubular strut. The two hulls contain propulsion and control mechanisms and are adapted to accommodate between them a submersible craft, a diver work chamber, pipeline repair gear or other operating equipment.

BACKGROUND ART Experience with oil and natural-gas exploration, production and transmission in the North Sea has shown that, because of the frequent bad weather, surface vessels can be deployed in such work only on a limited scale. The time spent coming and going from and to the nearest port to avoid storms represents a major loss of working time for surface vessels engaged in the North Sea project.

Underwater craft suited for undersea work usually are relatively small and can be employed only in conjunction with a mother ship on the surface. When the mother ship has to leave the area because of impending bad weather, it is forced to take the dependent submersible craft along, even though the submersible craft could in principal avoid the heavy sea conditions by submerging below a relatively shallow depth.

Submersible craft with a surface buoy serving as power-supply unit are similarly affected by bad weather.

German Offenlegungsschrift 23 56 537 of one of the present inventors discloses a catamaran surface vessel having a submersible gondola located between the two hulls of the catamaran.

The catamaran remains afloat when the gondola is lowered for underwater travel. The submersible gondola has a torpedo-like shape widely used for self-propelled underwater craft because of its low resistance to motion for the volume of water displaced, relative to other shapes. Although the catamaran, by virtue of the form stability provided by its two spaced-apart hulls, has a high resistance to capsizing, it is nonetheless susceptible to bad weather and rough seas as are other surface vessels.

United States patent No. 1,757,174 to Douglas discloses a seagoing vessel having five pontoons: a cabin pontoon, two waterline pontoons, and two power pontoons. The two waterline pontoons are disposed below and to either side of the cabin pontoon. A power pontoon is disposed below each watertine pontoon. The vessel of the '1 74 patent is a surface vessel. Only the power pontoons, located beneath the waterline pontoons, are submerged when the vessel is under way.

Consequently, the vessel is also unaffected by heavy seas.

DISCLOSURE OF THE INVENTION The present invention has as its object to provide a watercraft which may be employed as floating and submersible operating equipment which may be deployed under a wide variety of weather conditions. Moreover, it is intended to be suited for use as a supply and communications base for a fully or partly autonomous submersible craft up to great depths.

Broadly, the watercraft of the present invention includes a first submersible hull and a second submersible hull disposed generally parallel to and spaced apart from one another. The two submersible hulls are constructed in the manner of submarines, having watertight pressure housings and ballast tanks which may be flooded and blown. The submersible hulls also include propulsion units for motive power and steering mechanisms for control of the craft The watercraft further includes a submersible pilot's cab disposed generally above the hulls approximately in a longitudinal symmetry plane defined between the two hulls. The pilot's cab includes a watertight pressure vessel and can function as a buoyancy body in that its weight is less than the weight of water it displaces by the pressure vessel when submerged.The pilot's cab has pressure-resistant view ports and contains a steering stand to permit a pilot to maneuver the craft. The watercraft further includes tubular struts rigidly interconnecting the first hull, the second hull, and the pilot's cab. The tubular struts have at least sections which are constructed as pressureresistant bodies which have a net buoyancy, in that the weight of such a section is less than the weight of volume of water it displaces when submerged.

A feature of the watercraft of the present invention is that when surfaced it has the seaworthy qualities of a catamaran. Moreover, the watercraft is weight stable both in a completely submerged condition and in a partially submerged condition, when the pilot's cab is completely or partly above the mean waterline. A partially submerged condition can be achieved by not flooding the ballast tanks completely or by flooding only a fraction of the tanks. Consequently, the craft can be used and is operational both as a form-stable surface-bound catamaran and as a weight-stable submersible craft or semisubmersible craft.

The watercraft in accordance with the invention is well suited both for subsea work to be performed or supervised from the surface and for subsea work to be performed or supervised from a fully or partly submerged position.

In the surfaced condition; in other words, as a surface craft; it is particularly suited for fairweather use. The craft then displays the high stability of form of a catamaran.

When the water becomes rougher, some of the ballast tanks of the hulls can be flooded so that the two hulls are substantially completely below the surface, but with the pilot's cab above the water surface. Work can be carried out in this semisubmerged condition so long as the difference in height between wave crests and troughs is not greater than the edge-to-edge spacing between the hulls and the pilot's cab, because the change in buoyancy due to submergence to different depths of the connecting members and of the pressure-resistant buoyancy bodies is small relative to the mass of the hulls.

This is why the attitude of the craft will be quite stable even in a moderately rough sea, whereas a surface-bound catamaran in the same sea would be listing a great deal.

In a still heavier sea, such as is encountered even in the North Sea on not more than about 10 to 20% of the days of the year, the craft thereby can submerge completely, thereby avoiding bad weather without having to return to port.

Thus the watercraft in accordance with the invention is ideally suited for use as a working platform in fair weather and as a base vessel for a small submersible craft in any kind of weather. A special advantage is that a small submersible craft can be picked up safely by the watercraft even in a heavy sea, or a storm, because the picking up can be accomplished at a depth sufficient to avoid the effects of the turbulance on the surface. With prior-art systems, picking up a submersible craft is ordinarily possible only in a relatively calm sea.

Moreover, when appropriately outfitted, the watercraft in accordance with the invention can be deployed directly, for example, as a working craft to perform underwater work such as repair and welding operations on drilling islands and subsea pipelines, for jetting pipelines in and out, as an exploration and salvage unit, as an underwater base for a submersible vessel designed for greater depths for soil-mechanics measurements, and for drilling work. Thus the watercraft in accordance with the invention lends itself not only to allweather use but has broad uses in virtually any kind of underwater work.

In addition, a preferred watercraft of the invention, in contrast to many special-purpose underwater apparatuses, is a relatively high-speed craft, both when submerged and when surfaced, because its hulls are naturally streamlined and the pilot's cab pressure vessel and the connecting members are also preferably faired. A slight motive power inefficiency when submerged occasioned by the use of two hulls and a pilot's cab relative to that of a single optimally streamlined submarine of equal net displacement is more than offset by the stability and usefulness of the configuration of present invention floating on the surface of the sea and resting on the sea floor.

Thus, a further advantage in subsea operations is that the craft rests firmly on the floor with its two hulls and leaves a sheltered working space between them. The craft can therefore be positioned to straddle a line on which work is to be done.

One or both of the hulls of the watercraft may be equipped with a pressure chamber with egress to the outside for divers. In preferred embodiments of the invention the pilot's cab pressure vessel comprises, in addition to a pilot's compartment, which is preferably maintained under atmospheric pressure by a first pressure controller, a diver exit chamber adapted to be placed under ambient pressure by a second pressure controller. This diver exit chamber is provided with at least one diver exit, disposed on the underside and closable by a hatch. Locating a diver exit chamber in the pilot's cab pressure vessel disposed above the two hulls has the advantage that divers have at all times free access to the diver exit chamber that is unimpeded by projecting seabed obstructions or the like.In addition to or in place of the diver-exit chamber provided in the pilot's cab pressure vessel, a second diver exit may disposed in one of the struts connecting one of the hulls with the upper pressure vessel. The diver exit chamber then is preferably provided with at least one diver exit shaft disposed on the underside and closable by a hatch.

In preferred embodiments of the invention, a hoist is accommodated in the diver exit chamber and a shaft with closable hatches is disposed below the hoist. In a particularly preferred embodiment, however, there is disposed between the diver-exit chamber and the pilot's compartment a third compartment with a closable hatch which can be placed under ambient pressure by a suitable pressure controller and in which a hoist and/or lines for a working medium (electric current, compressed gas or pressurized liquid) can be accommodated. If desired, this third compartment may be adapted to be connected through pressure-resistant doors with the diver exit chamber and/or the pilot's compartment. By separating the diver hatch and the hoist hatch, the danger that divers may get with their supply lines caught in work lines or in the hoist is minimized.

The pressure resistant doors can provide access to the diver exit chamber or the pilot's compartment.

This will prove advantageous when a repair is to be made in the third compartment while the watercraft is submerged and the repair is not to be carried out by divers because their time is too expensive. The third compartment then can also serve as an air lock permitting passage from the pilot's compartment to the diver exit chamber or vice versa in the submerged condition. In addition, the third compartment may be made accessible from one hull or from both hulls through a strut.

This makes the watercraft in accordance with the invention very versatile in use and provides a high level of safety in the event of unforeseen incidents, since appropriate action may be taken both by divers and by personnel remaining under atmospheric pressure.

While work on the ocean floor, at depths permissible for divers, may be carried out both with the prior-art systems and with the embodiment of the invention described above, the work radius of a diver is limited by an umbilical cord connected between the diver and the submerged vessel, or by the diver's ability to find his way back to the diver exit chamber if he is untethered. Of course, such a limitation in the horizontal is less onerous because it can be overcome by proper location or by changing the location of the submersible. However, it is not readily possible to reach work sites located much above the ocean floor.

It is also known to lower diver chambers constructed as autonomous pressure bodies, such as diving bells, from surface vessels to the depth at which the work site is located. However, such operations are highly dependent on the weather and are generally uneconomical, especially in reaches of the sea where the weather frequently is bad, as in the North Sea, for example, since they can be usefully employed only for a short time in relation to the time spent coming and going.

The work to be done at different levels between the sea-bottom and the sea surface frequently consists of repair and maintenance work on exploration and production platforms which are located on or above the water surface and which rest on piling or have other structural members extending far downward, and often all the way to the seabottom. It is notpossible for a submersible to dock at the underwater part of such structures because of the hazards to the structure and to the submersible which this would entail because of changing currents, for example. Thus it is contemplated to construct a submersible craft of the type described above in such a way that divers may be employed to carry out work at any desired level above the seabottom or below the water surface.In a particularly preferred embodiment of the invention, the diver exit chamber to this end is constructed, in a manner not novel as such, as a separate diver-exit pressure vessel which is detachably secured to the watercraft and, after detachment, linked to the watercraft through hauling means.

In this arrangement in accordance with the invention, when the watercraft rests on the ocean floor, the diver-exit pressure vessel can be detached from the submerged craft and allowed to ascend, while continuing to be linked to the craft through hauling means such as ropes or chains.

Once the diver-exit pressure vessel has reached a desired level, paying out of the hauling means is halted and the divers are able to leave the pressure vessel at the approximate level of their work site and to perform the work while the submerged craft stably rests on the seabottom and the diver exit pressure vessel is suspended, much like a captive balloon, relatively undisturbed below the zone influenced by the state of the surface of the sea. After the divers have returned to the pressure vessel, the latter can be hauled in and docked at the craft.Before or after docking, the divers can reach the interior of the craft, and specifically a decompression chamber, through an air lock accessible after docking or through another diver exit port of the craft In this operating mode, it is advantageous that diver work sites at any desired subsea level can be reached by divers surely and safely, and that neither the submersible watercraft nor the structure on which work is to be done will be endangered, since the watercraft need not dock at the structure. On the other hand, the underwater mission is virtually unaffected by the weather conditions prevailing on the surface. The divers may make use of the installations and facilities aboard the submerged craft and return to it after having completed their mission.In operations of longer duration, an additional shuttle capsule may be used as a link between diver-exit pressure vessel and the submerged watercraft to transport divers from the watercraft to the dive-exit pressure vessel and back. A further advantage is that diving missions may be carried out in areas where the depth of the sea is greater than the permissible depth for a diver. The permissible sea depth then is determined solely by the permissible diving depth of the watercraft, since pressures less than ambient pressure may be maintained within the diver-exit pressure vessel while it is at a depth greater than the depth limit for an untethered diver. In this case, however, the transfer from submerged watercraft to diver exit chamber and back must be made through an air lock enterable after the. diver-exit pressure vessel has docked with the watercraft.

On the other hand, when the use of the system described is limited to reaches not deeper than the depth limit for untethered divers, there will be no need to provide means for docking the diver-exit pressure vessel with the craft The transfer from the diver exit pressure vessel to the craft then can take place through the water and appropriate exit port of the watercraft. However, embodiments are preferred wherein the diver exit pressure vessel is adapted to dock by its exit port with the craft A closable docking port then is preferably disposed at the top of the watercraft, which makes it readily possible to bring the exit port, ordinarily disposed on the underside of the diver exit pressure vessel, into alignment with the docking port, thus providing for passage between submersible craft and diver exit pressure vessel. However, it is also possible, and in preferred embodiments of the invention contemplated, to locate the docking port on the side of the watercraft In this case, the diver exit pressure vessel is either swung around prior to docking, with the transfer again taking place through the exit port of the diver-exit pressure vessel, or the diver exit pressure vessel is provided with an additional closable side opening which is used for docking and is opened after docking. It is not absolutely necessary that an air lock be provided next to the docking port in the submersible watercraft since the diver exit pressure vessel may be constructed in such a way that it is completely closed or closable after docking, with the pressure in the diver exit chamber then being adjusted to the pressure in the craft, following which the divers can make the transfer.Generally, however, the arrangement will be such that the docking port gives direct access to a decompression chamber, which can then be placed under any desired pressure and, specifically, under ambient pressure to protect the divers from decompression accidents. The required decompression can then be accomplished in the decompression chamber.

The diver exit pressure vessel is preferably constructed so that in the operating condition it will be buoyant. In this case, it will suffice to attach a hauling means such as a rope or chain to the diver-exit pressure vessel and to pay out this hauling means gradually in order to position the diver exit pressure vessels at the desired working level. Alternatively, the arrangement may be such that while the diver-exit pressure vessel itself has no buoyancy, a buoyancy body is attached to the hauling means or to the pressure vessel.

In preferred embodiments of the invention, at least two hauling means in the form of ropes are provided which are run through eyes attached to the largest horizontal periphery of the diver exit pressure vessel. The hauling means may be fastened to these eyes or simply run through them, in which case they serve solely as guiding means. In the latter case, the hauling means preferably extend upwardly from the diver exit pressure vessel and are kept taut by buoyancy bodies fastened to their ends. Brakes are then mounted on the outside of the diver exit pressure vessel which are adapted to be released and to be actuated from the inside, and which permit the diver-exit pressure vessel to be fixed at the desired level.The vertical motion of the diver exit pressure vessel may be produced by means of tanks in said chamber adapted to be flooded and blown out, and which generate positive or negative buoyancy, depending on the degree to which they are filled.

Alternatively, the diver exit pressure vessel may have positive buoyancy at all times and may be moved in the vertical direction by an additional hauling means through a winch which pays it out or hauls it in.

In a preferred embodiment of the invention, at least one propulsion unit is rigidly or pivotably mounted on the pilot's cab pressure vessel for improved maneuverability of the craft. This propulsion unit can be supplied through the connecting members between the hulls and the pilot's cab pressure body.

In preferred embodiments of the invention, at least one of the members connecting each hull with the pilot's cab pressure vessel is constructed as an enterable passageway in the form of a strut At least one of these passageways leads to the pilot's compartment, and at least one of the remaining passageways leads to the diver exit chamber or to the third compartment of the pilot's cab pressure vessel. The number of connecting members between the hulls and the pilot's cab pressure vessel may be selected at will on the basis of the strength requirements of the overall structure. Preferably two tubular connecting members (three if there are three compartments) are provided between each hull and the pilot's cab, and additional buoyancy bodies, which may be faired, are disposed in the space between the connecting members or struts.The buoyancy bodies are compartmentalized in respect of their horizontal cross-sectional areas to prevent the water from sloshing back and forth when the bodies are partly flooded. These buoyancy bodies will increase the stability of the craft in surfacing and submerging. The passageways provide great versatility in the uses of the craft since all compartments of the pilot's cab pressure vessel communicate with the hulls through enterable passageways.

The difference in height between the hulls and the' pilot's cab is preferably equal to the difference in height between wave crest and wave trough in average sea conditions in the area where the craft is to be deployed. This spacing determines the range over which the craft in accordance with the invention can be deployed as a semisubmersible when the pilot's cab pressure vessel still is completely or partly above the average waterline, since satisfactory operating behavior is secured when the hulls are still submerged in the wave trough while the pilot's cab pressure vessel still is not completely submerged in the wave crest The edge-to-edge spacing between the hulls and the pilot's cab pressure vessel, may range from 5 to 6 m, for example. This will permit the craft to be used on about 70 to 90% of the days under the unfavorable weather conditions prevailing in the North Sea.

In a preferred embodiment of the invention, at least one of the two hulls contains a supply of compressed gas for blowing ballast tanks for supplying divers and decompression chambers, and for the diver exit chamber. An electric motor serving as a power supply when the craft is submerged is preferably housed in the engine room accommodating the internal-combustion engine. The electric batteries required to power the motor are carried as ballast in the bilge area of the two hulls. In other embodiments of the invention, the batteries are disposed as ballast beneath the hulls in separate pressure vessels parallel to the hulls. Carrying the batteries in the bilge area or in separate pressure vessels, helps to improve the weight stability of the craft.

Moreover, at least one of the connecting members or struts between one of the hulls and the pilot's cab pressure vessel is provided with a closable exit which in surface operation may also serve as an air intake or as egress to the deck.

In preferred embodiments of the invention, the hulls are constructed in the manner of autonomous craft and are provided with pressureresistant viewports in the work areas.

To broaden the uses of the craft in accordance with the invention still further, there is mounted on each of the two hulls, in accordance with a preferred embodiment, half of a swinging bridge which serves as a working bridge and, if desired, as carrier for a smaller submersible craft, especially when the craft is in the surfaced condition. To increase the stability, the two halves of the swinging bridge can be joined together, and in addition fixed or removable connecting struts can be provided between the hulls to reduce stresses in the area between the struts and the pilot's cab pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS Further details and variants of the present invention will become apparent from the following description, in conjunction with the claims, of an embodiment illustrated in the simplified, diagrammatic drawing, where Fig. 1 shows, partly in side elevation and partly in section, a twin-hull watercraft with a pilot's cab disposed above the hulls; Fig. 2 is a top plan view of the craft according to Fig. 1; Fig. 3 is a front elevation (left half) and a view of the stern (right half) of the craft according to Figs. 1 and 2; Fig. 4 shows the craft, partly in front elevation and partly in section, in working position on the seafloor; and Fig. 5 is a perspective view of a submersible with a detachable diver-exit chamber.

BEST MODE FOR CARRYING OUT THE INVENTION The watercraft shown has a first hull 1 and a second hull 2, each of which is rigidly connected to a pilot's cab 4, disposed above the two hulls 1 and 2, by means of two struts 3 and 3' which are inclined towards a vertical longitudinal symmetry plane defined between the two hulls and also inclined towards a vertical transverse plane passing through the hulls and which approach each other toward the top. The two hulls 1 and 2 have outwardly the same shape, and each consists of an elongated, essentially cylindrical hull pressure vessel 5 whose after end tapers to a propulsion unit 6 and whose forward end is formed by a generally hemispherical section 7.

The hulls 1 and 2 are constructed as submarines.

The hull pressure vessel 5 is surrounded by a fairing 8 which determines the outer shape of the hulls 1 and 2 and which at the bow end, near the deck, is provided with a side thruster 9. The struts 3 are constructed as pressure-resistant tubes which are joined at one end to a hull pressure vessel 5 and at the other end to the pilot's cab, 4, the joints at both ends being watertight. The pilot's cab 4 has a pressure vessel comprising a cylindrical, elongate body 10 whose ends are provided with forward and aft hemispherical sections 11 and 12, respectively. Approximately at its center the elongate body 10 is partitioned by a dished, pressure resistant bulkhead 13 into a diver-exit chamber 1 5 and a control and work room 14 serving as a pilot's compartment.

Passage from the pilot's compartment 14 to the diver-exit chamber 15 and vice versa is possible through a closable hatch 16 provided in the bulkhead 13.

The arrangement is such that the two forward struts 3 terminate in the pilot's compartment 14, and the two after struts 3' in the diver exit chamber 1 5. The elongate body 10 is provided in the area of the pilot's compartment 14 with viewports 16 and with an exit hatch 17. The pilot's compartment 14 contains a steering stand (not shown) for piloting the vessel. In the diver exit chamber 1 5 a hoist 1 8 is disposed whereby loads may be hauled in or lowered through a tubular, vertical utility shaft 19 which terminates in the floor of the diver exit chamber 15 and is closable at both ends by means of hatches. Afairing 21 at whose end is mounted a propulsion unit 22 with a propeller adjoins the after end of the pressure body 10.

The struts 3 and 3' are provided with the tube stubs 23 and 23' respectively disposed approximately radially to their longitudinal extension, and closable by means of hatches.

Passage from the pilot's cab pressure vessel 4 to the hulls 1 and 2 and vice versa is possible through the struts 3 and 3', which are constructed as passageways. The forward struts 3 terminate in areas of the hull pressure vessel 5 which are under atmospheric pressure, while at least a first of the aft struts 3' does not terminate in a corresponding compartment, it being closed off by a pressureresistant hatch. Built onto one of the struts 3' is a diver exit 23'. The relatively small cornpartnient 24, which is bounded by two pressure-resistant bulkheads 25, adjoins at both ends a decompression chamber 26.

Compressed-gas tanks 27 are accommodated in an after area of the hull 1, while an internalcombustion engine 28 driving an electric generator which supplies the craft with power is housed, in a space closed off by bulkheads, in an after area of the hull 2. In addition to or in place of the electric generator 29, a hydraulic pump may be provided to supply corresponding systems with a working medium. In surface operation, the necessary air for combustion is supplied to the internal-combustion engine through an air intake 30, while in the semisubmerged condition the engine is connected through a line (not shown) to a snorkel 31 disposed at the top of the upper pressure body 4. In place of or in addition to this snorkel, a floating snorkel may be used. In submerged operation, energy from batteries 32 disposed in the bilge area of one hull or both hulls 1 and 2 is used to power a drive motor 33 which drives a suitable hydraulic pump. This hydraulic pump also feeds the propulsion units 6, 6' and 22.

Alternatively, electric motors powered directly from the batteries can be used for the propulsion units 6 and 22. Power to the propulsion units 6 and 6' on the first and the second hulls 1 and 2 respectively can be varied independently to turn the vessel in response to control signals from the steering stand. The side thruster 9 assists in controlling the direction of the motion of the watercraft when submerged. In addition to the snorkel, antennas, lights and the like are mounted on the pilot's cab 4.

Fig. 3 shows the craft in the surfaced condition, one half of the figure being a view of the bow, and the other half a view of the stern, of the craft.

Mounted on each of the two hulls 1 and 2 is a half bridge 35, adapted to be swung out of the way by means of actuating members 36. The pivots of the half bridge 35 are inside the fairing 8. In operating position, the half bridges 35 provide work space specifically, they may carry an autonomous or semiautonomous submersible craft of known design. In the surfaced condition, maintenance and service work may readily be performed on the submersible craft 37. When the submersible craft 37 is to leave the base watercraft or is to be picked up by it in a smooth sea, the semisubmerged operating condition is brought about and the half bridges 35 are swung out of the way, whereupon the submersible craft 37, which may still be suspended from the hoist 18, is lowered.The submersible craft 37 is picked up in reverse order, with the base watercraft semisubmerged or, in a choppy sea, submerged.

The watercraft disclosed lends itself particularly well to use as a base vessel for a submersible craft 37 designed for greater depths as it permits the submersible to be deployed largely independently of the weather since the submersible craft 37 can be picked up in the submerged condition, and hence unaffected by surface motion of the sea.

However, a submerged base watercraft offers the further advantage of permitting much better communication with the submersible craft 37 located at greater depth since the base watercraft then is located below boundary layers which often adversely affect communications.

The underwater watercraft disclosed is suited not only for use as a base craft for a submersible craft, but also for use as an underwater work station, for work on pipelines, for example. To this end, it may be provided, as shown in Fig. 4, with grips 39 for laying or aligning pipe sections 38, said grips being adapted to be operated by actuating members 40 and 41 and to be raised or lowered by a hoist 42. In addition suitable dredge buckets, drills or means for jetting trench 43 may be provided.

To be able to shift the transition of the craft from the form-stabilized condition (surface operation) to the weight-stabilized condition (submerged operation) into a desired range of the semisubmerged condition, additional buoyancy bodies (not shown) adapted to be flooded and blown are preferably disposed between the struts 3 and surrounded by suitable fairing to reduce to water resistance in the submerged and semisubmerged condition. Struts 3 and 3' are also preferably enclosed by suitable fairing. Such fairing is conventional and need not be described.

To increase the mechanical stability, the two hulls 1 and 2 are preferably interconnected by cross struts in the forward and after areas, discussed below in connection with Fig. 5.

The underwater craft shown in Fig. 5 also has two hulls 1 and 2, each of which is rigidly joined by means of three struts 3a-c which are inclined to a longitudinal symmetry plane defined between the two hulls 1 and 2. The three struts 3ac thus approach corresponding struts on the other hull at the top when the craft is in a horizontal rest position. Three cross struts 50a-c connect corresponding pairs of inclined struts 3. A pi[ot's cab 4 is mounted on the front cross strut 50a.

Disposed in the middle of the center cross strut 50b is a chamber 51 which has a top docking port 52 and a side docking port 53. A diver exit pressure vessel 11 5 which contains a diver exit chamber can be connected to one of these two docking ports, which when so connected is joined to it in a rigid and pressure-resistant manner. On its underside, the spherical diver exit pressure vessel has a diver exit shaft 1 20 at whose lower end appropriate flanges, sealing and mounting means are disposed. The diver exit pressure vessel 11 5 is provided with lateral guide eyes 54 through each of which a hauling means 55 is run.Fastened to the ends (not shown) of the hauling means 55 extending upwardly from the diver exit chamber 11 5 are buoyancy bodies (also not shown), which maintain the hauling means 55 in approximately vertical position. Through appropriate flooding and blowing means, the diver-exit pressure vessel 11 5 can be balanced so that it has virtually no buoyancy, or has positive or negative buoyancy.

Moreover, it is provided with clamping means for making fast to the hauling means 55, said clamping means being constructed as brakes which may be actuated, released and applied from the inside.

Normally the diver-exit pressure vessel 115 is firmly attached to one of the two docking ports 52 or 53. When the craft has submerged and rests on the seabottom, the diver-exit pressure vessel 115, which has been entered by the working divers, is released and blown to give it positive buoyancy so that it is able to ascend along the hauling means 55, which have first been paid out, to the level on which the work site for the divers is located. A diver 56, connected to the diver exit chamber through an umbilical cord 57, is able to leave said chamber, through the diver exit shaft 120, after it has been placed under ambient pressure.On completion of the work, the diver 56 returns to the diver exit chamber 11 5, and the braking means can then be released, after the diver exit shaft 120 has been closed, if desired, with the diver exit chamber 11 5 then beginning its descent after the desired negative buoyancy has been brought about by flooding. Once the diver exit chamber 11 5 has reached the vicinity of the chamber 51, it can start to dock at the docking port 52 or 53. After docking, the diver or divers can leave the diver exit chamber within the diver exit pressure vessel 11 5 and reach the decompression chamber 26 through the center cross strut 50b, the strut 3b, and the compartment 24.

Instead of the described design of the diver exit pressure vessel 11 5, in which it is provided with flooding and blowing means and with a releasable brake for making fast to the hauling means 55, the diver exit pressure vessel 11 5 may also be constructed so that under water it always has buoyancy. In this case, the hauling means are fastened directly to the guide eyes 54 and the diver exit chamber 11 5 is caused to ascend by paying out the hauling means 55, and caused to descend by hauling them in. To this end, there is mounted on the center cross strut 50b a suitable winch which pays out or hauls in the hauling means (preferably two), constructed as steel cable.

To increase the mechanical stability of the interconnection between the two hulls, additional cross struts 58 are preferably provided which increase the stability of form of the system or reduce the stresses, respectively.

The submersible water craft of the present invention is provided with suitable power-supply units and other conventional requisite equipment.

The engineering details of such equipment are not necessary for an understanding of the present invention and, for consciousness will not be described.

It is not intended to limit the present invention to the specific embodiments described above. It is recognized that changes may be made in the apparatus specifically described herein without departing from the scope and teachings of the instant invention, and it is intended to encompass all other embodiments, alternatives and modifications consistent with the present invention.

Claims

1. A submersible watercraft, comprising: (a) a first hull and a second hull, the two hulls being disposed generally parallel to and spaced apart from each other, the hulls being constructed as submarines and containing a propulsion unit and a direction control mechanism for maneuvering the watercraft, each hull having: (a.1) water-tight walls defining a submersible pressure hull, and (a.2) ballast tanks adapted to be flooded and blown for varying the buoyancy of the watercraft; (b) a submersible pilot's cab disposed generally above the two hulls approximately in a longitudinal symmetry plane defined between the first and the second hulls, the pilot's cab having:: (b.1) a pilot's cab pressure vessel having pressure-resistant viewports and a hatch for admitting a pilot to the interior of the pressure vessel, and (b.2) å steering stand for piloting the watercraft, the pilot's cab weighing less than the volume of water it displaces when submerged, thereby serving as a buoyancy body; and (c) a plurality of tubular members for rigidly interconnecting the pilot's cab and the first and the second hull, each of the tubular members extending between the pilot's cab and a hull and having at least a section which is pressure resistant and weighs less than the volume of water displaced by the section when it is submerged, so that the watercraft has the stability of a catamaran when surfaced and is weight stable when completely submerged and when partially submerged with the two hulls substantially completely below the mean waterline, and the pilot's cab at least partly above the mean waterline.

2. The submersible watercraft according to claim 1, in which the pilot's cab includes: (b.3) a first enclosure defining a pilot's compartment, the steering stand being located in the pilot's compartment, (b.4) first pressure controlling means for maintaining the pilot's compartment under approximately atmospheric pressure, (b.5) a second enclosure defining a diver-exit chamber for accommodating a diver, and (b.6) second pressure controlling means for placing the diver exit chamber under an ambient pressure.

3. The submersible watercraft according to claim 2 in which the second enclosure of the pilot's cab has a diver-exit opening in the enclosure and a tubular diver-exit shaft having a sealable hatch at one end joined to the opening and projecting outward from the pilot's cab providing a passageway for divers to pass between the water and the diver-exit chamber.

4. The submersible watercraft according to claim 3 in which the second enclosure of the pilot's cab has a utility opening in the enclosure and a tubular utility shaft joined to the opening and projecting outward from the pilot's cab for permitting supplies, lines and the like to pass from the diver-exit chamber to the outside of the pilot's cab, the utility shaft having a first sealable hatch and a second sealable hatch mounted respectively at the two ends of the utility shaft.

5. The submersible watercraft according to claim 4 in which the utility opening is located in the floor of the diver-exit chamber and the tubular utility shaft extends linearly in a generally vertical direction when the watercraft is in a horizontal rest position, the watercraft further including a utility hoist located at the diver-exit chamber and capable of being positioned directly over the utility opening for hoisting articles-through the utility shaft.

6. The submersible watercraft according to claim 3 in which the pilot's cab includes a third enclosure defining a third compartment, the third enclosure being located between the diver exit chamber and the pilot's compartment, the third enclosure having a first opening for access to the third compartment, the first opening having a closable hatch mounted thereon, the pilot's cab further including third pressure-controlling means for maintaining the third compartment under atmospheric pressure.

7. The submersible watercraft according to claim 6 further including a hoist mounted in the third compartment.

8. The submersible watercraft according to claim 6 in which the third enclosure includes a second opening, the first opening providing passage between the third compartment and the pilot's compartment and the second opening providing passage between the third compartmenl and the diver-exit chamber, the first and the second openings being fitted with pressureresistant doors.

9. The submersible watercraft according to claim 1 in which a diver-exit hatch is located in one of the tubular members.

10. The submersible watercraft according to claim 1 further comprising: (d) a diver-exit vessel detachably connectable to the watercraft, the diver-exit vessel being constructed as a pressure vessel adapted to accommodate a diver; and (e) hauling means for linking the diver-exit vessel to the watercraft.

11. The submersible watercraft according to claim 10 further comprising: (f) a sealable docking port mounted in the watercraft adapted to permit a diver to pass into an interior of the watercraft, and in which the pressure vessel of the diver-exit vessel has a diverexit opening therein, the diver-exit vessel including: (d. 1) a sealable hatch for closing the diverexit opening; and (d.2) docking means for sealably detachably joining the pressure vessel to the docking port of the water craft for enabling a diver to transfer between the watercraft and the diver-exit vessel underwater.

12. The submersible watercraft according to claim 11 in which the docking port is mounted on a side wall of the watercraft.

13. The submersible watercraft according to claim 12 in which the pressure vessel of the diver exit vessel has a second diver-exit opening therein, the second diver exit opening being located on a side, and the diver-exit vessel further includes: (d.3) a second sealable hatch for closing the second diver-exit opening.

14. The submersible watercraft according to claim 10 in-which the hauling means comprise a first rope and a second rope, each rope being attached at one end to the watercraft, and in which the diver-exit vessel is fitted with a first eye and second eye, the two eyes bei'ng located' respectively at opposite points on a largest horizontal periphery of the diver-exit vessel, the first and the second ropes passing respectively through the first and the second eyes.

15. The submersible watercraft according to claim 14 further comprising a first buoyancy body and a second buoyancy body, the two buoyancy bodies being attached to the first and the second ropes respectively for maintaining the two ropes taut in operation.

1 6. The submersible watercraft according to claims 1 5 in which the diver-exit vessel further includes a first brake and a second brake, the two brakes being releasable and actuable from inside the diver-exit vessel, the first brake and the second brake acting upon the first and the second ropes, respectively.

1 7. The submersible watercraft according to claim 1 5 in which the diver-exit vessel weighs less than the volume of water it displaces when submerged, and in which the watercraft further comprises winch means attached to the first and the second ropes for paying out and hauling in the first and the second ropes.

17. The submersible watercraft according to claim 1 further comprising an internalcombustion-engine power plant located in one of the hulls.

1 8. The submersible watercraft according to claim 1, in which the pilot's cab further includes a periscope mounted on the cab for observation during semisubmerged operation.

19. The submersible watercraft according to claim 1 in which the pilot's cab further includes a propulsion unit mounted on the cab.

20. The submersible watercraft according to claim 1 in which at least one of the tubular members serves as a strut and has a passageway extending therethrough.

21. The submersible watercraft according to claim 20 in which the passageway extends between one of the two hulls and the pilot's cab.

22. The submersible watercraft according to claim 20 in which there are at least four tubular members interconnecting the pilot's cab and the first and the second hull, at least two tubular members serving as struts extending between the pilot's cab and the first hull, and at least two tubular members serving as struts extending between the pilot's cab and the second hull.

23. The submersible watercraft according to claim 22 further comprising supplemental buoyancy bodies located between the struts for increased stability in surfacing and submerging.

24. The submersible watercraft according to claim 1 in which the pilot's cab is disposed at least about 5 meters above the two hulls.

25. The submersible watercraft according to claim 1 further comprising a compressed gas supply located in one of the two hulls.

26. The submersible watercraft according to claim 1 further comprising a plurality of electric storage batteries located in bilge areas of the two hulls, the batteries thereby serving as ballast for two hulls.

27. The submersible watercraft according to claim 1 further comprising a plurality of generally elongated storage pressure vessels adapted to contain electric storage batteries, each storage pressure vessel being attached to one of the two hulls and extending generally parallel to the hull.

28. The submersible watercraft according to claim 1 in which one of the tubular members is provided with a closable exit port.

29. The submersible watercraft according to claim 1 in which one of the hulls further includes a pressure resistant viewport for observing a work area.

30. The submersible watercraft according to claim 1 further comprising a swinging bridge located between the two hulls, the swinging bridge comprising a first and a second half-bridge section, the first and the second half-bridge sections being pivotably attached to the first and second hulls to permit the swinging bridge to be swung out of an area between the two hulls.