US3595191A

US3595191A - Ships and boats

Info

Publication number: US3595191A
Application number: US766715A
Authority: US
Inventors: John Wakelam Grundy
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-10-11
Filing date: 1968-10-11
Publication date: 1971-07-27
Anticipated expiration: 1988-07-27

Abstract

The hull of a ship of the kind which is driven by submerged propellers is provided with a downwardly facing recess divided by longitudinal and transverse partitions into separate pockets for containing air. The pockets preferably extend over substantially the whole of the bottom of the hull and are arranged in rows extending substantially from the bow to the stern of the vessel. An air duct is provided extending between the frontmost and rearmost pocket in each row.

Description

United States Patent [72] Inventor John Wakelarn Grundy 3,48l,296 l2/l969 Stephens 1 14/67 63,Cleveland Road, North Shields, 3,455,267 7/1969 Tucker 1 14/67 Nonbmberhnd England Primary Examiner-Andrew H. Farrell [2| Appl. No. 766,715 Aimmey-Wenderoth, Lind & Ponack [22] Filed 0ct.ll, 1968 [45} Patented July 27, I971 [54] SHIPS AND BOATS n Clams 9 0mm"; ABSTRACT: The hull of a ship of the kind which is driven by r v 114/67 submerged propellers is provided with a downwardly facing Illl- B63b 1/3 recess divided by longitudinal and transverse partitions into [50] Field of Search ll4/67.l separate k t f r ontaining air. The pockets preferably extend over substantially the whole of the bottom of the hull [56) Rem-wees (mad and are arranged in rows extending substantially from the bow UNITED STATES PATENTS to the stern of the vessel. An air duct is provided extending 1,621,625 3/ 1927 Casey l l4/67 between the frontmost and rearrnost pocket in each row.

PATENTEUJULZYIQ'II I 3,595,191

sum. 1 0r 2 JOI-LN WAKELAM GRUNDY, Inventor Attorneys PATENTFD JUL 2 7 IBM SHEET 2 [IF 2 JOHN WAKELAM GRUNDY, Inventor mama. d

Attorneys SHIPS AND BOATS This invention relates to ships and boats and has a particularly important but not exclusive application in relation to the largest oceangoing ships, such as oil tankers and ore carriers.

According to this invention there is provided a ship having a hull which is driven by at least onesubmerged propeller and which has on its bottom a peripheral downwardly facing recess, at least one longitudinally. extending partition and at least one transversely extending partition disposed within the recess, the bottom edges of which partitions are immersed in the water so that the partitions divide the recess into a plurality of separate forward and rearward pockets, the bottom edge of the skirt being at a greater depth than the bottom edges of the longitudinal partition, compressor means for charging the pockets with air, and an air duct extending between at least one of the front pockets and at least one of the rear pockets which air duct bypasses the compressor means.

The air is self-circulating through the air duct or ducts owing to the forward motion of the vessel and the resulting differential pressures which are built-up between the front and rear pockets. If desired, however, means such as a fan, blower, flow control valve or orifice may be provided in the or each air duct for controlling the forward flow of air therethrough.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGS. 1 to 4 illustrate respectively elevation, plan, end elevation and enlarged part-sectional end elevation of an oil tanker having air pockets on its bottom,

FIG. 5 illustrates the transfer ducts provided by the invention,

FIGS. 6 and 7 show respective cross-sectional forms of the partitions, and Q FIGS. 8 and 9 illustrate in inverted plan respective modifications of the shape of the partitions.

Referring now to FIGS. 1 to 4, an oil tanker of say 200,000 tons deadweight is shown. Such a vessel may be l,l feet in overall length, I63 feet in beam, and have a maximum draught of 58 feet and a freeboard of 18 feet. The vessel is driven by submerged propellers 30 and the hull has a member of downwardly opening air pockets I9 which together extend over substantially the whole area of the bottom of the hull. The pockets 19 are arranged in four rowswhich are disposed two rows on each side of the fore and aft extending centerline of the vessel. To define a recess for division to form the pockets, the vessel has extending round its bottom edge a rigid but hollow skirt structure 21 projecting 8 feet below the bottom wall 22 of the huIL'Wall 22 is a double wall. The outer wall 23 of the skirt is curved as shown. The disposition of the skirt at the forward and stem ends of the vessel is such as to enable the air pockets to extend over the maximum length of the hull consistent with the skirt having its full depth. The space bounded by the skirt is subdivided by three

vertical partition walls

24, 25, 26 of which wall 24 extends along the centerline of the vessel and

walls

25 and 26 are disposed on opposite sides of and extend parallel to wall 24. These walls extend 6feet below the bottom of the hull.

Walls

25 and 26 and/or the skirt 21 are made sufficiently strong to enable the vessel to be supported by these members on bilge blocks if it becomes necessary for the vessel to be drydocked.

In addition to the lengthwise extending partition walls 24 to 26, four fixed partitions 27 of the same height as partition walls 24 to 26 extend across the bottom of the vessel and have their ends sealed with respect to the skirt 21. In addition, a seal is fonned where each partition crosses each of the partition walls 24 to 26. Thus 20 air pockets 19 are formed, each pocket being sealed from its neighbors. The partitions 27 may be in the form of simple vertical parallel sided walls, but in this particular instance in order to reduce the resistance offered by these partitions to the forward movement of the vessel owing to the presence of a depth of water below the air in the compartments, the partitions have their front faces 28 inclined forwardly and downwardly as indicated in FIGS. 6 and 10. The partitions may alternatively be vertical walls having bulbous lowermost portions 28a projecting forwardly as shown in FIG. I l.

The vessel has a bulbous bow 29 and has submerged propellers 30.

Compressors are provided on the vessel for supplying air under pressure into each pocket. In operation, air is pumped into the pockets until there is no water or only a small depth of water in the pockets. When the vessel gets under way, some of the air may escape from the pockets as the vessel pitches and rolls. The water level in each pocket tends to reach a generally steady level, and thereafter air need only be pumped into the pocket for making-up purposes. The air in the pockets reduces the wetted area of the bottom of the hull substantially and thus reduces the resistance of the hull to forward motion. The dividing partition walls 24 to 26 and partitions 27 between the 7 pockets substantially increases the capacity of the vessel to withstand rolling and pitching without losing an undue quantity of the air from the pockets. In addition, the partition walls and partitions contribute a substantial degree of stability to the vessel by suppressing or preventing free-surface effects of the water.

According to this invention air ducts 38 extend respectively between the front pockets 39 and the respective rear pockets 40, and each duct 38 contains a fan, blower or flow control valve or orifice 41 for regulating flow through the duct.

Air which escapes from the forward pockets tends to collect in the rear pockets 40, and the ducts 38 permit this air to be transferred to the front pockets 39. The fan, blower, or flow control valve or orifice 41 enables this flow to be controlled if desired.

Compressors are provided on the vessel for supplying air under pressure into each pocket.

Each pocket has therein a detector B (see FIG. 6) for sensing when the water level in the pocket exceeds a predetermined average depth, say 2 feet. The detector is isolated from any effects of pitching and rolling, for example, by mounting it in a self-draining cavity 14 which only contains sufficient water to operate the detector when there is a steady influx of water due to excess head within the air pocket. The detector is adapted when actuated, to transmit a signal for initiating the supply of further air under pressure to the pocket until the water level returns to a predetermined satisfactory level, which in the present instance is 2 feet. This depth of water in the pockets permits a maximum roll angle of the order of 5 and a maximum pitch angle of the order of 1.

The best shape, size and number of the pockets and the best height and cross-sectional shape of the walls of the pockets will normally be determined for a particular vessel by model testing in a tank. In comparison with a conventional vessel therefore a higher speed of the vessel may be obtained for a given power output or, alternatively for driving the vessel at a given speed smaller engines may be employed.

Except in very severe conditions, the depth of water in the pockets will not normally exceed 2 feet and the detection system is set to maintain the water level at substantially this value.

It will be understood that in rolling motion of the ship, the air pressure in each pocket will rise and fall, and this effect can be employed to control an antiroll device. For example, where ballast tanks are provided on opposite sides of the vessel the pressure difference between two pockets symmetrically disposed with respect to each other about the centerline of the vessel may be employed to control the movement of water between the ballast tanks on opposite sides of the centerline in a sense to counteract the rolling action. Similarly this pressure difference may be employed to the control vane-type stabilizers.

It will be understood that stationary and moving waves will occur in the pockets corresponding to but of smaller amplitude than the waves which occur on the surface. It is there fore necessary for the height of the walls of the pockets to be sufficient to prevent the occurrence of these waves from permitting the escape of air from the pockets. It may be necessary or desirable in some cases to provide a deeper pocket opposite a position just behind the stationary bow wave of the ship, and in any construction the heights of the transverse walls may differ from each other along the length of the vessel. As an example of average sea conditions, it has been shown from statistics based on observations over several years that in the severe sea conditions of the North Atlantic Ocean, 95 percent of the waves are below feet in height, and a pocket height of 6 feet will normally be adequate to contend with these conditions. An efficient design of bulbous bow can however do much to reduce the number of transverse partitions 27.

In the construction shown in FIGS. 1 to 4 the transverse walls 27 extend at right angles to the fore and aft direction and this is preferred, but these walls may in other arrangements be inclined to the said direction as shown in FIG. 8 and may also be curved along their length as shown in H0. 9. In such arrangement the transverse walls will be symmetrical about the central foreand aft-extending plane of the vessel.

if the pockets are permitted to become full of water, very high drag forces are exerted on the vessel, by reason of the increase of wetted area, viscous friction, and the resistance created by the transverse partitions, and advantage of this can be taken by providing in each pocket a valve or valves 15 (shown for reasons of clarity in FIG. 4 only) which can be operated in an emergency to allow the air to escape from the pockets so that the pockets become filled with water. This will provide a very substantial braking effect on forward or rearward movement of the vessel.

In the event of the vessel running aground, additional air canbe pumped into the pockets to raise the vessel by, sag l8 inches to 2 feet, to assist in floating the vessel off. Also, if the vessel becomes icebound, the air supplied to the pockets may be heated to assist in freeing the vessel.

If desired, the space within the skirt 2] may be used to provide tanks, for example for ballast or fuel.

It will be understood that existing vessels can readily be modified to incorporate the present invention.

Referring now to FIG. 5, a substantially modified construction is shown in which transverse partitions 35 are provided which are hinged by their upper ends to the bottom of the hull. The partitions are buoyant so that their free edges float on the water in the pockets. One or more air ducts 36 are provided in the hull for each intermediate pocket 37 and extend between the front and rear ends of the airspace within the pocket. As before air ducts 38 extend respectively between the front pockets 39 and the respective rear pockets 40, and each duct 38 contains a fan, blower or flow control valve or orifice 41 for regulating flow through the duct. Each partition 35 is sealed at its ends with respect to the longitudinal walls.

Moving waves within the pockets sometimes touch the bottom of the vessel and thus entrap air, and the duct or ducts 36 tend to prevent this air from being pumped out of the pocket by permitting it to escape forwardly past the wave. Air which escapes from the forward pockets and collects in the rear pockets 40, is transferred to the front pockets 39 by ducts 38. The fan, blower, or flow control valve or orifice 4! enables this flow to be controlled if desired.

The hinging of the partitions 35 enables their lower edges to follow the contour of the waves so as to reduce or prevent air leakage under pitching, and also reduces the resistance of the partitions to forward motion of the vessel.

An important advantage of the constructions described is that the heat loss from the vessel through the bull to the water is reduced by the presence of the air pockets. A tanker carrying, say, crude oil has heating coils for heating the oil to maintain the oil at a sufficiently low viscosity to enable it to be pumped, and the costs of such heating can therefore be reduced. Other vessels transport cargoes, such as liquified petroleum or natural gas, and the capacity and/or the operating costs of the necessary refrigerating equipment and the capacity of the insulating material may in such cases be reduced.

lclaim:

l. A ship having a hill which is driven by at least one submerged propeller and which has on its bottom a peripheral downwardly extending skirt defining a downwardly facing recess, at least one longitudinally extending partition and at least one transversely extending partition disposed within the recess, the bottom edges of which partitions are immersed in the water so that the partitions divide the recess into a plurality of separate forward and rearward pockets, the bottom edge of the skirt being at a greater depth than the bottom edges of the longitudinal partition, compressor means for charging the pockets with air, and an air duct extending between at least one of the front pockets and at least one of the rear pockets which air duct bypasses the compressor means.

2. A ship as claimed in claim 1, wherein a plurality of longitudinally extending partitions and a plurality of transversely extending partitions are provided which divide the recess into foreand aft extending rows of pockets, said longitudinally extending partitions extending over the full length of the recess, and wherein an air duct is provided for each of said rows of pockets which extends from a rear pocket of the row to a front pocket of the row and bypasses the compressor means.

3. A ship as claimed in claim 1, wherein the pockets are disposed in rows extending longitudinally of the hull, and an air duct is provided extending between the frontmost pocket and rearmost pocket in each row and bypassing said compressor means for enabling air to flow forward from the rear pocket to the front pocket.

4. A ship as claimed in claim 1, wherein a valve is disposed in the air duct for controlling the forward flow of air through the air duct.

S. A ship as claimed in claim 1, wherein a control orifice is provided in the air duct for controlling the forward flow of air through the air duct.

6. A ship as claimed in claim I, wherein a fan or blower is disposed in the air duct for controlling the forward flow of air through the air duct.

7. A ship as claimed in claim 1, wherein each transverse partition extends at right angles to the length of the vessel.

8. A ship as claimed in claim 1, wherein each transverse partition is straight and is inclined to the length of the vessel.

9. A ship as claimed in claim 1, wherein each transverse partition is arcuate and is generally inclined to the length of the vessel.

10. A ship as claimed in claim 1, wherein each transverse partition is hingedly mounted by its upper edge on the underside of the vessel and is adapted so that its free lower edge floats on the water in the pockets, the ends of the partition being sealed with respect to the tops and sidewalls of the pockets.

II. A ship as claimed in claim I, wherein valve means is provided which is operable to release the air trapped in each pocket.

Claims

1. A ship having a hill which is driven by at least one submerged propeller and which has on its bottom a peripheral downwardly extending skirt defining a downwardly facing recess, at least one longitudinally extending partition and at least one transversely extending partition disposed within the recess, the bottom edges of which partitions are immersed in the water so that the partitions divide the recess into a plurality of separate forward and rearward pockets, the bottom edge of the skirt being at a greater depth than the bottom edges of the longitudinal partition, compressor means for charging the pockets with air, and an air duct extending between at least one of the front pockets and at least one of the rear pockets which air duct bypasses the compressor means.

2. A ship as claimed in claim 1, wherein a plurality of longitudinally extending partitions and a plurality of transversely extending partitions are provided which divide the recess into fore- and aft-extending rows of pockets, said longitudinally extending partitions extending over the full length of the recess, and wherein an air duct is provided for each of said rows of pockets which extends from a rear pocket of the row to a front pocket of the row and bypasses the compressor means.

5. A ship as claimed in claim 1, wherein a control orifice is provided in the air duct for controlling the forward flow of air through the air duct.

6. A ship as claimed in claim 1, wherein a fan or blower is disposed in the air duct for controlling the forward flow of air through the air duct.

11. A ship as claimed in claim 1, wherein valve means is provided which is operable to release the air trapped in each pocket.