US3557742A

US3557742A - Cargo vessels

Info

Publication number: US3557742A
Application number: US771431A
Authority: US
Inventors: Reuben Murphy Gainsley
Original assignee: Vickers Ltd
Current assignee: Vickers Ltd
Priority date: 1967-11-21
Filing date: 1968-11-20
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26

Abstract

A vessel made up of interlockable sections, the aftermost one being a propulsion unit housing machinery, crew accommodation, the bridge and other offices and being independently navigable. A cargo-carrying section can be removably attached to the forward end of the propulsion unit and when attached mating surfaces of tapered shoulders and recesses are locked in wedged together positions. Power operated devices are provided for drawing the propulsion unit and the cargo-carrying section together and locking them in position. The forward end of the cargo-carrying section can be shaped similarly to the forward end of the propulsion unit so that further similar cargo-carrying sections can be attached end-to-end forward of the propulsion unit.

Description

United States Patent 1 1 3,557,742

[72] Inventor Reuben Murphy Gainsley [56] ReferencesCited London, England UNITED STATES PATENTS [211 P 7771431 3,398,716 8/1968 Neilson 114 235 [221 Fled 3417721 12/1968 v' 114235x 451 Patented Jan.26 1971 l l 1 3,446,173 5/1969 011011061211. 114/235 [73] Assignees Vickers Limited London, England a British company; Reuben Murphy Gainsley, known as Reuben Murphy G. London, England [32] Priority Nov. 21, 1967, Jan. 18, 1968 [33] Great Britain [31] 52,862 and 52,319

[54] CARGO VESSELS 17 Claims, 16 Drawing Figs.

[52] US. Cl 114/235, 1 14/77 [51] Int. Cl B63b 21/00, B63b 3/02 [50] Field ofSearch 1 14/235, 77

OTHER REFERENCES German Printed Application No. 1,202,675 10-1965 114- 235; 2 pages spec, 2 shts,Dwg.

Primary Examiner-Trygve M. Blix Attorney-Pennie, Edmonds, Morton, Taylor and Adams ABSTRACT: A vessel made up of interlockable sections, the aftermost one being a propulsion unit housing machinery, crew accommodation, the bridge and other offices and being independently navigable. A cargo-carrying section can be removably attached to the forward end of the propulsion unit and when attached mating surfaces of tapered shoulders and recesses are locked in wedged together positions. Power operated devices are provided for drawing the propulsion unit and the cargo-carrying section together and locking them in position. The forward end of the cargo-carrying section can be shaped similarly to the forward end of the propulsion unit so that further similar cargo-carrying sections can be attached end-to-end forward of the propulsion unit.

PATENTEU JANZBISYI I saw 1 BF 6 mama] M26 19?:

., SHEET 2 BF 6 FIGS.

PATENTEU JAN 2 6 I97! SHEET 3 BF 6 PATENTEDJANPTSISYI SHEU' u 0F 6 3.557.742

FIGS.

cxnoo VESSELS The present invention relates to cargo vessels and comprises an oceangoing vessel incorporating a cargo-carrying hull with a detachable propulsion unit provided at the after end thereof.

According to the present invention there is provided a cargo vessel comprising in combination a cargo-carrying hull and a propulsion unit attached or attachable to the after end of the hull, the forward end of the propulsion unit and the after end of the hull having tapered shoulders and cooperating seatings therefor located at each side and on the centerline of the vessel to provide aligned engagement between said hull and said unit and to transmit thrust and shear forces therebetween, there being means for locking the tapered shoulders in the cooperating seatings.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. I is a longitudinal section through a cargo vessel in accordance with one embodiment of the invention;

FIG. 2 is a plan view of the embodiment shown in FIG. 1; FIG. 3 is an enlarged section along the line III-III of FIG. 2; FIG. 4 is an enlarged section along the line IV-IV of FIG. 2; FIG. 5 is an enlarged schematic elevation of a detail of FIG.

FIG. 6 is a plan view of the detail shown in FIG. 5;

FIG. 7 is an enlarged section along the line VII-VII indicated in FIGS. I and 8;

FIG. 8 is an enlarged view of a detail of FIG. 1;

FIG. 9 is an enlarged schematic-elevation of the after end of a cargo vessel of the invention;

FIG. 10 is a part section taken along the line X-X of FIG. 9;

FIG. 11 is a section along the lie line XI-XI indicated in FIGS. 9 and 10;

FIG. 12 shows, on an enlarged scale, a detail of FIG. 9;

FIG. 13 is a plan view of the detail shown in FIG. I2;

FIG. 14 is a view similar to FIG. 12 showing a modification of a detail of FIG. 9;

FIG. 15 is a view similar to FIG. 12 showing a further modification of a detail of FIG. 9; and

FIG. 16 shows a modification of a detail of FIG. 15.

Referring now to the drawings, FIGS. I and 2 show a cargo vessel in the form of an oceangoing barge comprising a cargocarrying hull l with a propulsion unit 2 detachably secured to the after end thereof. The cargo-carrying hull extends aft from the vessel's bows 3 and, as shown in the drawings, defines a plurality of holds 4 having access hatches 5 and loading derricks 6. The propulsion unit 2, which in FIGS. I and 2 is shown attached to (or plugged-in" to) the after end of the hull I, is shown in greater detail in FIGS. 5 and 6. This propulsion unit 2 contains the propulsion machinery (not shown) for the vessel and is provided with a bridge 7 incorporating a wheel house 8, crew's quarters 9, steering gear 10 and all the sundry radio and navigation equipment normally provided in a seagoing vessel. Moreover, since the propulsion unit is capable of making short passages alone, some fuel tanks (not shown) will be incorporated in the unit. However, the main fuel tanks (not shown) of the vessel are provided at convenient locations in the hull I.

As stated hereinbefore, the propulsion unit 2 is attached or pluggedin to the after end of the hull 1. For this purpose, the forward end 11 of the unit 2 is tapered symmetrically each side of the vessels centerline as shown in FIGS. 2 and 6, tapering inwardly and forwardly in vertical planes and, as shown in FIGS. 1 and 5, it also inclines upwardly and forwardly from the bottom in a swimhead. The after end 12 of the hull l terminates in a mating substantially V-shaped cavity providing a seating 13. The after end 12 of the hull I has port and starboard tongues 12' and 12" extending aft to flank the seating 13 with their inboard surfaces in vertical planes and with under surfaces sloping aft and upwardly. The sides of the propulsion unit 2 have corresponding cavities providing seatings for the tongues, the starboard seating being indicated by I7 in FIG. 5. Three tapered shoulders 14, I5 and 16 project from the tongues I2 and I2 and from the forward end 11 respectively and mating V-shaped recesses are provided in the cavities to receive them. The shoulders and recesses also have surfaces inclined to the horizontal so that when the hull I and the propulsion unit 2 are locked together there are extensive areas spread over a substantial distance longitudinally of the vessel that are wedged together to resist hogging and sagging. It will be seen from FIG. I that the elevational profile of the forward end 11 and its shoulder 16 is similar, though not identical, to that of the tongues 12' and 12" and their shoulders l4 and 15. The inward taper of the forward end I l is continued by the sides of the shoulder 16 and the central recess 18 in the seating 13 which receives that shoulder is correspondingly shaped. There are power-operated means for drawing the shoulders in to the cooperating seatings and for locking these shoulders in position. These will be described in more detail later.

In order to avoid direct contact between steel plates, which could give rise to dangerous chafe, to prevent distortion of the surfaces in contact by providing some compressibility, to make for an easy wedging action and to enable a rigid interlock to be achieved when the hull I and propulsion unit 2 are drawn together by power-operated means, the hull I and/or the propulsion unit 2 have linings or facings of a suitable material on each said mating surface. As shown in FIGS. 7 and 8, a plurality of baulks=of greenheart timber 19 or rubber fen-. ders, for example, are secured by bolts or like means (not shown) in longitudinal aligned relationship on each surface of the hull which mates with a cooperating surface of the propulsion unit 2. As shown in FIG. 7, each said cooperating surface of the hull l is channeled with greenheart baulks secured on the ridges or crests between adjacent channels. In this manner longitudinal gaps or channels 20 are defined at each mating surface and the dimensions of these gaps are such that a skin diver may pass therethrough to determine that no driftwood or other debris interferes with the mating propulsion unit and hull surfaces before said propulsion unit and hull are locked together. The channels also provide means for access to the bearing surfaces to facilitate initial shaping and fit during construction, and similarly when replacing baulks 19 after damage or wear. It will be understood that in an alternative arrangement it is the propulsion unit 2 that is provided with the channels 20 and the greenheart baulks 19.

As diagrammatically shown in FIG, 8, a locking device 21 is located at the centerline of the vessel for locking said propulsion unit and hull together and in the remaining FIGS. these locking devicesare shown in more detail. Each device also serves to draw the tapered shoulders into the mating seatings therefor. Each tapered shoulder is extended by a pin or bolt- Iike element such as is shown in FIGS. 9 and 12 in which the shoulder 14 has a pin 22 welded or otherwise secured thereto. This pin 22 projects through an aperture 23 defined in the base of the V-shaped seating 17 for accommodating the shoulder 14 and has a slot 24 therein dimensioned to receive a heavy tightening and locking wedge 25. Two earns 26 controllable by hydraulic piston and cylinder assemblies 27 are pivotally mounted within the propulsion unit to control downward tightening and locking movement of the wedge 25 and further piston and cylinder assemblies 28 are similarly carried by the propulsion unit and are arranged one on each side of the wedge 25 in such manner that the pistons thereof engage laterally projecting flanges 29 which are integral with said wedge. These piston and cylinder assemblies 28 are operable to releasethe locked cooperating shoulders and seatings when it is desired to separate the propulsion unit 2 from the hull I. For this purpose it is merely sufficient to retract the pistons of the piston and cylinder assemblies 27 to permit free pivotal movement of the cams 26 and to actuate the piston and cylinder assemblies 28 to cause the pistons thereof to move upwardly and raise the wedge 25 out of the slot 24. When the wedge is clear of this slot to permit longitudinal displacement of the pin 22, a further hydraulically controlled piston and cylinder assembly 30 carried by the propulsion unit is actuated to eject the pin 22 therefrom and hence displace the tapered

shoulders

14 and 15 outwardly from mating engagement in the cooperating seatings.

With the above-described tightening and locking arrangement, when it is desired to attach the propulsion unit 2 to the after end of the hull 1, said propulsion unit is aligned with the V-shaped recess 13, and is moved slowly in toward the assembled operative position. When the unit 2 and hull 1 are correctly aligned and any interposed undesirable driftwood or debris has been removed by sending a skin diver down the channels 20, the wedges are dropped into the slots 24 in the .pins 22. As stated hereinbefore, each of the tapered

shoulders

14 and 15 is provided with a wedge controlled locking device and, if desired, the tapered shoulder 16 may also be provided with a similar locking device incorporating a pin carried by the propulsion unit 2 to cooperate with wedges and hydraulic control piston and cylinder assemblies mounted within and carried by the hull 1.

Referring now specifically to FIG. 12, which shows the locking device associated with the shoulder 14, the piston and cylinder assemblies 27 are then actuated to displace the pistons outwardly forcibly to rotate the cams 26 and urge the wedge 25 downwards into the slot 24. This, in turn, will draw the shoulder into the cooperating seating until the desired optimum position is attained. By maintaining pressure in the piston and cylinder assemblies 27, the earns 26 are firmly held in position and the wedge 25 is thus locked with the drawn-in propulsion unit and hull in the operative oceangoing position. The locking devices associated with the other shoulders are simultaneously similarly operated.

When it is desired to separate the propulsion unit from the hull 1, it is simply necessary to'relieve the pressure from the piston and cylinder assemblies 27 of each locking device, to actuate the piston and cylinder assemblies 28 until the wedges 25 are lifted clear of the slots 24in the pins 22, and then to actuate the piston and cylinder assemblies 30 to eject said pins 22 in the manner described hereinabove. It is always necessary forcibly to eject the tapered shoulders from the seatings therefor since after a long sea voyage, during which the vessel has probably travelled several thousand miles, said shoulders are jammed and firmly wedged in the seatings.

FIG. 14 shows an alternative device for drawing the tapered shoulder 16 in to the seating 18 therefor and for locking this shoulder in the desired operative position. Similar alternative devices may also be arranged to draw and lock the

shoulders

14 and 15 in the respective associated seatings. In FIG. 14, a screw-threaded shaft 31 is longitudinally displaceable within the shoulder and projects through an'aperture in the leading end thereof. This shaft 31 is guidedly carried by a bearing in the form of a trolley 32 displaceable by rollers 33 along rails 34 carried by support means 35 within the shoulder 16. The end of the shaft 31 remote from the trolley 32 has a slot 36 extending therethrough to receive a cotter pin 37 and the shaft is slidably supported intermediate the ends thereof in bearings mounted in the leading end wall of the shoulder.

When this alternative device is employed to draw the shoulder 16 into the seating 18 therefor, the propulsion unit 2 is maneuvered into position astem of the hull 1 and advances to enter the shoulder into the seating. On advance of this shoulder into the seating the slotted end of the shaft 31 projects through an aperture in the bottom of the seating 18 and the cotter pin 37 is dropped into the slot 36 behind the seating bottom. A stop 38 is proved provided to prevent movement of said cotter pin right through the slot 36 and fixed surfaces 38a are provided for the cotter pin 37 to bear against during the separating of the propulsion unit and hull, as described in more detail below. Thereafter, aligned clamping of the shoulder within the seating is effected by moving the shaft 31 rearwardly to draw the retained cotter pin into locking engagement with the underside of the seating bottom. This rearward movement of the shaft 31 is effected by rotating a nut 39 which is screw-threadedly mounted thereon and for this purpose a driving pinion 41 meshes with said nut 39. During rearward movement of the shaft 31 as aforesaid, the nut 39 bears against the leading endwall of the shoulder and remains bearing against this end wall to lock the shoulder in the seating. In

FIG. 14 a gap has been left between the nut and end wall for clarity. During forward movement of the shaft 31, the nut bears against an annular bearing surface 41a rigidly supported within the shoulder 16.

When it is desired to separate the propulsion unit from the hull l the pinion 41 is simply rotated in the opposite direction, which causes the nut 39 to'move a very short distance along the shaft 31, still meshing with the pinion 41, until it meets the annular bearing surface 410. Continued rotation of the pinion 41 in this opposite direction will move the pin 31 further out of from the leading end wall of the shoulder until the cotter pin 37 bears against the fixed surfaces 38a, and still further rotation will cause the shoulder 16 to be forced away from the seating 18. Instead of having fixed surfaces 38a for the cotter pin 37 to bear against, the end of the shaft 31 itself could bear on a fixed surface below the seating 18.

In the devices described with reference to FIGS. 9 to 14, the or each wedge 25 and cotter pin 37 are necessarily both large and very heavy. It is therefore necessary to provide a block and tackle arrangement and/or hydraulically operated means for initially raising and lowering the or each said wedge and cotter pin into and out of aligned engagement with the slots therefor.

FIG. 15 shows a further device for drawing the tapered shoulder 16 into the seating 18 and, like the arrangement shown in FIG. 14, incorporates a screw-threaded shaft. In the device shown in FIG. 15, however, a shaft 42 is journaled in a bearing 47 and is additionally supported by spring-loaded bearings 49. This shaft 42, which hasa screw-threaded portion 43 at one end thereof and a splined portion 44 at the opposite end, is rotatable a by a pinion 45 keyed on said splined portion 44 and meshing with a worm 46. The splined portion 44 of the shaft 42 permits longitudinal displacement of said shaft whilst still retaining the pinion in mesh with the worm 46.

As shown in FIG. 15, the screw-threaded portion 43 of the shaft 42 engages in a nonrotatable spherical seating 50 which is held against longitudinal movement in a bearing 48. With this arrangement rotation of the shaft 42 will displace the bearing 47, which accommodates said shaft 42 through the intermediary of a part-spherical collar 51 secured thereto, either towards or away from the bearing 48 depending upon the direction of rotation of said shaft 42. For this purpose, the bearing 47 is slidably mounted on rails 52 and can be clamped thereto to prevent relative displacement therebetween at any desired location and, with the bearing 47 clamped in this manner to said rails 52 (which rails are, in turn, rigidly supported within the shoulder 16), rotation of the shaft 42 will move the shoulder 16 into or out of a locked position within the seating 18. Thus, in order to attach the propulsion unit to the hull part the shoulder 16 is introduced into the seating 18 with the shaft 42 withdrawn completely within said shoulder 16 and supported at one end by the bearing 47 and at the other end by the bearing 49. The shaft is then advanced towards the threaded set seating 50 by moving the bearing 47 to the right along the rails 52. During this advance, the righthand end of the shaft 42 will align itself with the seating 50 by virtue of the conical end of said shaft 42 locating within seating 50, the spring loading of the bearings 49 and the spherical housing within the bearing 47 permitting the necessary degree of lateral movement. Thereafter, the shaft 42 is rotated a few turns by means of the worm and pinion gearing 45, 46 to engage the screw-threaded portion 43 within the seating 50, whereupon the bearing 47 is clamped to the rails 52 and further rotation of the shaft 42 pulls the tapered shoulder 16 into firmly bedded contact with seating 18.

Finally, FIG. 16 shows a modification of a detail of FIG. 15 in which the shaft 42 is freely rotatable within the collar 51. In this modification, the bearing 47 is firmly held within the shoulder 16 and rails for this bearing are unnecessary.

Furthermore the collar 5! can' be clamped by means (not shown) to the shaft 42 when it is desired to draw the shoulder [6 into the seating 18 therefor by rotation of said shaft 42.

In the device illustrated in FIGS. and 16, the assembly incorporating the bearing 47, rails 52 (where appropriate) and driving pinion 45 is advantageously immersed in an oil bath to facilitate operation thereof. Moreover, these devices could equally well be employed to draw the tapered

shoulders

14 and 15 into their respective seatings.

If the the cargo vessel hull l and propulsion unit 2 are of standard dimensions, one such propulsion unit may be used in conjunction with any number of correspondingly dimensioned hull units. Thus, ideally, whilst one hull unit is being loaded in a first port, a second similar hull unit can be being unloaded in a second port whilst the propulsion unit is ferrying a third hull unit either loaded or unloaded between the two ports. This considerably reduces the tum-round time of a loaded vessel since, for example, the propulsion unit on arriving at the second port with a loaded hull can, either before or during unloading of said hull, relatively quickly be detached therefrom and attached to an already unloaded hull immediately to ferry this unloaded hull back to the first port. For this purpose the propulsion unit can, as stated hereinbefore, make short passages without a hull between docks in order that having been detached from one hull it may travel to a further dock to be attached to another.

The shoulders 14, I5 and 16 are tapered not only to facilitate introduction into the respective seatings but also to transmit both thrust and shear forces between an attached hull and propulsion unit.

Although a cargo vessel of the invention is primarily intended for transporting bulk cargo and aims at reducing the tum-round time of such a vessel in port, it may, of course, be used to transport liquid cargo in which case the holds 4 are replaced by liquid-carrying tanks.

It will be understood that instead of a single cargo-carrying hull there could be a number ofhull'sections interlockable end-to-end with only the foremost hull section formed with a normally shaped bow. The other sections would be formed with shoulders and seatings as described above. Thus on arrival at a port the vessel could unplug one or more sections to be loaded or unloaded at that port, be replugged together as necessary with or without the addition of new hull sections from that port, and continue to a further port.

it will also be understood that although the specification refers to cargo vessels throughout, it is intended to embrace exclusively passenger or mixed passenger and cargo carrying vessels, for example car ferries.

lclaim:

l. A cargo vessel comprising in combination a cargo-carrying hull and a propulsion unit engageable with the after end of the hull, the forward end of the propulsion unit having a central forwardly projecting wedge portion and the after end of the hull having a corresponding tapered recess to receive said wedge portion, the wedging action being both lateral and vertical, and means for locking the hull and propulsion unit together when said portion is wedged in said recess, wherein the improvement comprises an after end hull structure having a rearwardly extending wedging portion on each side of said recess, the sides of the propulsion unit having corresponding tapered recesses to receive said wedging portions, the principal tapering of said portions and recesses being towards the horizontal.

2. A cargo vessel as claimed in claim 1, wherein the mating surfaces of the propulsion unit and the cargo carrying hull have nonresilient ribs providing access channels therebetween.

3. A cargo vessel as claimed in claim 2, wherein the ribs include baulks of greenheart timber.

4. A cargo vessel as claimed in claim 1, wherein the central wedge portion has two planar parts, of which the forward higher part is more nearly horizontal than the more rearward,

lower part.

5. A cargo vessel as claimed in claim 1, wherein there are cooperating means at the extremities of corresponding wedge portions and recesses for drawing and mechanically locking the hull and propulsion unit together.

6. A cargo vessel as claimed in claim 5, wherein said drawing and locking means includes a pin with a slot near its free end secured'to and projecting from the associated extremity, the bottom of the corresponding recess having an aperture for receiving the pin, a wedge arranged beyond the aperture, means for forcing the wedge into said slot when the propulsion unit is mated with the hull, the wedging action of said wedge being adapted to draw said unit and said hull tightly together, and means for locking the wedge in position in the slot.

7. A cargo vessel as claimed in claim 6, wherein the locking means includes hydraulically operated cam means for cooperating with said wedge.

8. A cargo vessel as claimed in claim 6, wherein hydraulic means are provided for acting on the end of said pin to assist separating the hull and propulsion unit when the drawing and locking means are disengaged.

9. A cargo vessel as claimed in claim 5, wherein said drawing and locking means include a pin movably mounted in the associated extremity to project a controlled amount, the bottom of the corresponding recess having an aperture for receiving said pin and means for holding the free end of said pin, means for moving the pin outwardly to project through the associated aperture when the propulsion unit is mated with the hull and inwardly to withdraw the pin and hence draw the propulsion unit and the hull tightly together when the end of the pin is held.

10. A cargo vessel as claimed in claim 9, wherein the pin is provided with a screw threaded portion and the means for moving the pin includes a nut mounted on said screw threaded portion, means for rotating the nut, and stops for preventing axial movement of the nut.

11. A cargo vessel as claimed in claim 9, wherein the holding means includes a cotter pin engageable in a slot near the end of the movable pin.

12. A cargo vessel as claimed in claim 5, wherein said drawing and locking means include a shaft movably mounted in the associated extremity to project a controlled amount, there being a screw-threaded portion on the free end of said shaft, the bottom of the corresponding recess having a screwthreaded aperture for receiving said screw-threaded portion, there being means for holding said shaft in an axially stationary position projecting from said extremity, and means for rotating the shaft in this position, when the propulsion unit is mated with the hull and with the screw-threaded portions engaged to draw the propulsion unit and the hull tightly together.

13. A cargo vessel as claimed in claim 12, wherein an axially movable and lockable bearing provides said holding means.

14. A cargo vessel as claimed in claim 12, wherein said holding means comprises a collar lockable on said shaft and a fixed bearing rotatably mounting said collar.

15. A cargo vessel as claimed in claim 12, wherein the rotating means includes a gear mounted on splines on said shaft to permit axial movement of the latter with respect to the gear.

16. A cargo vessel as claimed in claim 1, wherein the forward end of the hull is formed in the same manner as the forward end of the propulsion unit, whereby further similar hulls can be interlocked end-to-end forward of the propulsion unit.

17. A cargo vessel as claimed in claim 16, wherein there is a plurality of'interlockable hulls, the foremost one being formed with a conventional bow.

Claims

1. A cargo vessel comprising in combination a cargo-carrying hull and a propulsion unit engageable with the after end of the hull, the forward end of the propulsion unit having a central forwardly projecting wedge portion and the after end of the hull having a corresponding tapered recess to receive said wedge portion, the wedging action being both lateral and vertical, and means for locking the hull and propulsion unit together when said portion is wedged in said recess, wherein the improvement comprises an after end hull structure having a rearwardly extending wedging portion on each side of said recess, the sides of the propulsion unit having corresponding tapered recesses to receive said wedging portions, the principal tapering of said portions and recesses being towards the horizontal.

4. A cargo vessel as claimed in claim 1, wherein the central wedge portion has two planar parts, of which the forward higher part is more nearly horizontal than the more rearward, lower part.

6. A cargo vessel as claimed in claim 5, wherein said drawing and locking means includes a pin with a slot near its free end secured to and projecting from the associated extremity, the bottom of the corresponding recess having an aperture for receiving the pin, a wedge arranged beyond the aperture, means for forcing the wedge into said slot when the propulsion unit is mated with the hull, the wedging action of said wedge being adapted to draw said unit and said hull tightly together, and means for locking the wedge in position in the slot.

12. A cargo vessel as claimed in claim 5, wherein said drawing and locking means include a shaft movably mounted in the associated extremity to project a controlled amount, there being a screw-threaded portion on the free end of said shaft, the bottom of the corresponding recess having a screw-threaded aperture for receiving said screw-threaded portion, there being means for holding said shaft in an axially stationary position projecting from said extremity, and means for rotating the shaft in this position, when the propulsion unit is mated with the hull and with the screw-threaded portions engaged to draw the propulsion unit and the hull tightly together.

17. A cargo vessel as claimed in claim 16, wherein there is a plurality of interlockable hulls, the foremost one being formed with a conventional bow.