US3063397A

US3063397A - Sub-surface craft

Info

Publication number: US3063397A
Application number: US836556A
Authority: US
Inventors: Jr Harold Boericke
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-08-27
Filing date: 1959-08-27
Publication date: 1962-11-13
Anticipated expiration: 1979-11-13

Description

Nov. 13, 1962 H. BoER1cKE,JR

SUB-SURFACE CRAFT Filed Aug. 27, 1959 6 Sheets-Sheet l ATTORNEYS Nov. 13, 1962 H. BoER1cKE,JR

SUB-SURFACE CRAFT 6 Sheets-Sheet 2 Filed Aug. 27, 1959 N INVENTOR 1' HAROLD BOERICKE,JR.

ATTORNEYS Tis Nov', 13, 1962 6 Sheets-Sheet S Filed Aug. 27, 1959 DoA m m mv w c N` @E wm m m om N n@ .n m @Si 3 m R QQ m H mm N V wm om im N N m No No Nm u No om N1 om Q Q Q U Q Q wm wm om in, E wm B .Is mm m @E m Nm S NQ Nm E No N1 Nv om HMTE n? H m wm wm wm i. Nom M Q wm wm @.V Pm w 1H.. HH .|:S N.. mm .I+ mm |l mm m ...Q .w`n` H l i ...El

ATTORNEYS SUB-SURFACE CRAFT Filed Aug. 27, 1959 6 Sheets-Sheet 4 ATTORNEYS Nov. 13, 1962 H. BOERICKE, JR

SUB-SURFACE CRAFT Filed Aug. 27, 1959 6 Sheets-Sheet 5 INVENTOR HAROLD BOERICKE, JR.

ATTORNEYS H. BOERICKE, J R

SUB-SURFACE CRAFT Nov.- 13, 1962 6 Sheets-Sheet 6 Filed Aug. 27, 1959 INVENTOR fa .zhn17dl4 ATTORNEYS HARoLb BoER1cKE,JR.

3,063,397 SUB-SURFACE CRAFT lilarold Boericke, Jr., 1122 16th St. NW., Washington, D.C. Filed Aug. 27, 1959, Ser. No. 836,556 Claims. (Cl. 114-57) (Grmted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

The present invention relates to sub-surface craft combining the high top speed and ygood propulsive qualities of a submerged submarine with the structural and operational simplicity of a surface ship.

It is well known in naval architecture that the speed of a surface ship is greatly limited by wave formation and resistance resulting from thesewaves. As the speed o-f a ship is increased its Fronde number increases, this number lbeing a relationship `dependen-t upon ships speed. At Froude numbers of 0.3 and greater, wave resistance increases at a very fast rate. This phenomenon limits the speed of conventional full bodied surface vessels to a maximum Froude number of about 0.5.

It is also 'well known that such surface ships must .slow down greatly in heavy weather and that in gales, surface ships Imust usually stop or drift with the waves merely to survive. It is also well known that the eflfects of rough seas vary both the velocities -and the direction of water flow into the propellers. Another effect encountered in the operation of a conventional ship in rough seas in the slamming of the ships bottom on the waves. The ship tends to dive and leap in a Seaway causing water on the deck, and high pressures from the slamming on the ships bottom, which tend to cause great structural strains on the shi-ps hull.

It is also well known in naval architecture that a submarine, operating at a depth below the surface of 3 times the `diameter of the hull or greater, experiences a negligibly small wave resistance; nearly all of its resistance being frictional and eddy making resistance. Operation at depths of more than 3 diameters eliminates a crucially important limitation to the speed experienced by all of the conventional surface ships since the frictional 'and eddy making resistance of a submarine increases Iwith speed ,at a very much slower rate. Therefore the top speed of a submerged submarine is potentially much higher than that of the conventional full bodied surface ship of the same length and immersed volume.

It is further well known in naval architecture that only a negligibly small motion caused by ocean waves is experienced by a submerged submarine operating at a depth below the water surface of 3 diameters or greater. Operation at these depths avoids the critically important limitation to speed of conventional surface ships yoperating in rough seas. The allweathercapability of the submarine therefore is absolute, compared with the severely limited capability of surface ships.

The submarine operating near the surface, however, begins to be effected by waves depending on its nearness to the surface. An important feature of this operation is the mode of response to the waves. When a ysubmarine operating near the surface enters an oncoming train of waves, and as the wave crest passes over the bow, the additional weight of the water in the wavecrest causes a downward force on the bow. This force on the submarine operating near the surface is opposite in sense to that of the wave surface, that is when the surface is up, the force is down. Thus, the wave force acting on a submarine operating when near the surface is 3,053,397 Patented Nov. i3., 1962 opposite in sense to the force acting on the surface ship of the same length heading into the same waves at the same speed. This distinction is important. Y Y

It must tbe realized that the submarine has complications which make it the most expensive type of vessel to build Iand the most complicated type to operate. The conventional submarine has a pressure hull, ballast tanks, trim tanks, negative tanks, diving planes, and must have a system of propulsion which will enable it to stay below 0 the surface for an extended period of time.

Consider 4a surface ship attached to the top of a submarine operating in head seas. The wave forces on the two would be opposite in sense, and tend to cancel each other out. The present invention is essentially a surface ship attached to the top of the submarine. Theoretically by varying the proportionate sizes of the two it would 'be possible to get a combination having a zero pitching motion. A conventional surface ship operating in ywaves longer than its own length will heave at an amplitude about equal to the wave height. In waves shorter than its own length it will heave less, depending on the relative length of ship and wave. Because most of its buoyancy is concentrated near the surface, the conventional surface ship is excited by the orbital motion of the wave at its maximum amplitude; that is, near the surface; it will heave a maximum amount. This applies particularly to heaving in seas of lengths of l to 5 tim-es the ships length.

The submarine operating near the surface, will heave an amount depending lhow near it is `to the surface. A s the orbital motion of the lwave decreases rapidly with depth, the heaving motion Iwill also become less to the same degree.

-A sub-surface ship, being configured much like a submarine operating near the surface, will have .similar heaving characteristics. It will heave much less than a surface ship of the same length operating through the same sea-way at the same speed.

Seakeeping qualities are one of the main reasons for many surface vessels being as large as they are and speed considerations have also been a `factor in lengthening many surface vessels. This invention makes size a less compelling reason fo-r speed and seaworthiness. The subsurface ship of this invention provides a means of meeting mounting performance requirements lwith smaller and cheaper ships.

It is therefore an object of the present invention to provide a vessel having better sea-keeping qualities than conventional craft.

Another object is to provide a vessel which will reach a top speed in smooth water which is considerably higher than conventionally shaped full bodied surface ships of the same length and immersed volume.

A further object of the present invention is to provide a craft which will exhibit pitching and heaving motion an order of magnitude lower than `existing displacement type surface vessels ofthe same length.

Still another object is the provision of the craft ,on which the propeller axis is suiciently far below the water surface so -as to experience a minimum disturbing effect from the excitation of waves.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification related to the annexed drawings in which:

FIG. 1 is a side elevational View of a preferred ernbodiment of this invention;

FIG. 2 is a partial stern view of the vessel of FIG. l;

FIG. 3 is a partial bow View of the vessel of FIG. l;

FIG. 4 is a series of vertical cross sections of the embodiment shown in FIG. l;

FIG. 5 is a series of horizontal cross-sections of the embodiment shown in FIG. 1;

FIG. 6 is a side elevational view of another embodiment of this invention;

FIG. 7 is a partial stern view of the embodiment shown in FIG. 6;

FIG. 8 is a partial bow view of the embodiment shown in FIG. 6;

FIG. 9 is a series of vertical cross-sections of the embodiment Yshown in FIG. 6;

FIG.l l0 isa series of horizontal cross-sections of the embodiment shown in FIG. 6;

FIG. 11 is a side elevational view of another embodiment in this invention;

- FIG.l 12 i s a partial stern View of the embodiment shown in FIG. 11;

, FIG. 1,3 is a partial bow View of the embodiment shown in FIG. 11;

, FIG. 14 is a series of vertical cross-sections of the embodiment shown in FIG. 11;

FIG. 15 is a series of horizontal cross-sections of the embodiment shown in FIG. 11;

FIG. 16 is a side elevational view of still another embodiment of this invention;

FIG. 17 is a partial stern view of the embodiment shown in FIG. 16;

FIG. 18 is a partial bow view of the embodiment shown in FIG. 16;

FIG. 19 is a top View of the embodiment shown in FIG. 16;

FIG. 20 is a series of vertical cross-sections of the embodiment shown in FIG. 16;

FIG. 21 is a side elevational View of a fifth embodiment of this invention;

FIG. 22 is a partial stern view of the embodiment shown in FIG. 21;

FIG. 23 is a partial bow View of the embodiment shown in FIG. 21;

FIG. 24 is a series of vertical cross-sections of the embodiment shown in FIG. 2l;

FIG. 25 is a series of horizontal cross-sections of the embodiment shown in FIG. 21;

FIG. 26 is a side elevational View of still another embodiment of this invention;

FIG. 27 is a partial stern view of the embodiment shown in FIG. 26;

FIG. 28 is a partial bow view of the embodiment shown in FIG. 26;

FIG. 29 shows a series of vertical cross-sections of the embodiment shown in FIG. 26; and

FIG. 30 shows a series of horizontal cross-sections of the embodiment shown in FIG. 26.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several Views there is shown in FIG. l which illustrates a preferred embodiment, an underwater hull 41, to which is connected an island 44. Hull 41 is a body which is essentially an elongated streamlined body of revolution of circular cross-sections as shown in A-H in FIG. 4.

The island 44 is, in general, almost as narrow near the waterline as where it joins the body41, in order to minimize wave resistance. Rudder 43 is an extension of island 44. Propeller 42 is located at the stern end of the body 41, thereby causing a substantially circumferentially uniform wake distribution which results in a high propulsive eiiiciency. The circular cross-sections of the hull combined with the vertical sides of the island represent a form of nearly minimum wetted surface consistent with the features of form which are proportioned to reduce wave drag. Above the water line W.L., the island 44 flares outwardly from the vertical axis and also extends in a forward direction resulting in a center of volume of the reserve buoyancy 45 which is forward of 4 the center of volume of the body 47 and the center of volume of the underwater protion of the island 46.

In a ship of this type, its machinery, fuel and payload are enclosed in body 41; crews accomodations and access to the island, and control and communications in the small superstructure 48.

FIGS. 6-10 show a modified type of subsurface craft having certain features of form which improve its motion and seakeeping properties as well as provide certain practical features. Sections B through J', FIG. 9, show body 51 which is elliptical in cross-sections with its major axis located horizontally. By this shape more immersed volume can be concentrated further away from the water surface at a given draft than with a hull whose body has a substantially circular cross-section as shown in FIGS. 1-5.

The single island is wider at the water line than it is at the junction of the body as shown in sections B through F in FIG. 9. This is combined with a reserve buoyancy having much flare, which is shaped broad on deck and which projects forward and forms a bow overhang as can be seen in FIG. 6 and FIG. 9A'. In addition, the reserve buoyancy has a longitudinal ridge 53, termed a chine, located above the waterline to control and suppress the bow wave and provide ample reserve buoyancy near the deck. The flaring shape of the island and of the reserve buoyancy forward provides a shape which prevents diving in a following sea, suppresses which would otherwise be a very high bow wave, and keeps decks reasonably dry in a head sea. In addition the forward projection of the bow provides a hoisting point for the anchor chain to swing anchors clear of the obstructing underwater portions of the hull. A feature which will reduce the motion is the actuated anti-rolling fin 55 which counteracts roll. The rudder 43 is all movable, for maximum effectiveness, and is located on the afterpart of the body, forward of the propeller 42, and is positioned far enough astern of the island to receive nearly unobstructed water for effective turning. Also notable on this embodiment are stern planes 54 which give an additional measure of pitching control.

FIGS. 11 through 13 show another type of sub-surface craft in accordance with this invention having

twin islands

57 and 58. The twin islands have a smaller crossu section at the water line than the single island of FIGS.

1 or 6, therefore the wave making resistance is smaller and the excitation from waves is less. This results in a higher speed and less motion than is possible for a single island craft. The body or underwater hull of this embodiment is elliptical in cross-section, again placing a maximum amount of immersed volume as far away from the surface as possible for a given draft. The two is- -lands are located as far apart as practical in order to provide as much longitudinal stability as possible with the minimum water plane area dictated by this type of design. As can be seen from the cross-sections A2, B2, and H2 in FIG. 14 the

islands

57 and 58 have a carefully tapered junction with body 50 for maximum strength and a minimum waterline area for minimum wave resistance.

Islands

57 and 58 both have longitudinal chines 53 which are utilized to inhibit spouting of waterupward along the island and to provide suicient width for a suitable amount of reserve buoyancy. In order to maximize reserve buoyancy, it has been found expedient to blunt the trailing edges as shown in FIG. 15 sections I, on both islands into a tiat end which is commonly called a transom. The forward island has a larger volume both above and below the water line than the after island, causing the resultant centers of volume of the

islands

46 and 45 below the water line W.L. and above it respectively, to be forward of the center of volume 47 of the body, which results in a favorable type of pitching response.

Auxiliary planes

54 and 56, at the stern and bow respectively give a measure of added control under severe conditions.

The rudder 43 is attached to the after island 57 and faired in with it for a minimum of drag. Propeller 42 is mounted on the aftermost portion of body Sli. A ship of this form has its machinery, fuel, payload, and principal living quarters located in body Si); control, communications, and access located in the forward island 53; and machinery air supply and access enclosed in after island 57.

FlGS. 16-20 describe a three island sub-surface craft with island 6l located on the center line aft, and

islands

62 and 63 located side-by-side forward and emerging at substantially right angles from an elliptical shaped underwater hull 65. The transverse separation of the forward islands provides suliicient transverse statical stability so that the center of gravity of the craft can be higher than in a twin island craft and in addition carry movable surfaces 59 behind each bow island which assist in main taining an exact draft under rough sea conditions, somewhat analagous to the bow diving planes of a submarine. The shape of the islands is characterized by the same features as those of the twin island craft.

The two islands are located as far apart as practicable in order to provide as much longitudinal metacentric stability as possible with the minimum water plane dictated by the design. The forward islands connect with the body at right angles with the surface of the body thereby minimizing interference drag. The islands then bend into a straight upward direction piercing the surface and at a considerable distance above the surface are joined together by a horizontal platform 6e. if desired, the platform '64 could be extended and join the tops of all three islands. The after island is shaped the same as its counterpart in the twin island sub-surface craft described above.

ln this configuration machinery, payload and fuel are included in body `65; control, communications, and living quarters are in platform tid; access is provided by forward islands 6l and 63, and the air supply and access for the machinery by the after island 6l.

Chines 53 are again provided in this embodiment for the purposes described in connection with the other embodiments. Also included in this embodiment are auxiliary movable stabilizing planes at the stern 54 for added longitudinal stability control.

The embodiments described thus far have a relatively deep draft at all times, which due to harbor depth restrictions, currently about feet, limit their use to ships of relatively small size, approximately 7000 displacement tons and less.

FlGS. 2l through 25 show a type of vessel in which the draft may be varied between large limits. The letters WL. denote the normal operating waterline of the ship, while the letters W.L.D. denote the water line used when the ship is in shallow water or being docked. The draft may be varied to -any point between these limits according to speed, water depth, and wave conditions encountered. The deeper of the two drafts is used at high speeds in smooth or rough seas in deep water.

Underwater hull d6 is elliptical in cross-section but, as can be seen in FIG. 25, has a slightly constricted longitudinal cross-section, a shape which hydrodynamics research indicates to have a minimum wave resistance at shallow submergences of the body.

A propeller 4Z is located on the stern and a rudder 43 is formed by an extension of the island 67.

Waterline at the shallow submergency WLB. is as wide as the waterline of a `conventional ship, and its initial metacentric stability is also comparable. The vertical positions of the center of gravity of the machinery, fuel oil and cargo, however, are low, all being located in the underwater `body de of the vessel as near to the inner bottom as possible. A low resultant center of gravity of the ship is also facilitated by filling all empty innerbottom tanks '7l with sea water as the oil is depleted. A low resultant center of gravity is necessary to insure the positive -stability at all immersions.

CII

The island 67 extends for nearly the full length of the craft and has a water plane of sufficient length to provide pitching control in the waves without the need for external tins. This island contains living quarters and consumable stores. A small raised superstructure 43 maintains control and communications spaces.

Displacement changes from one draft to the other are accomplished by variable

water ballast tanks

68 and 69 located in the ends of the ship as seen in FIGS. 2l and 25. When these tanks are empty the ship floats higi in the water in the shallow draft condition, but as water is pumped into the

ballast tanks

63 and 69 by pumps 72 the ship sinks to a new deeper waterline. Alternatively to increase the immersion more quickly, the water may be allowed to gush into the tanks by means of flood holes 73 and vent valves 74.

Another embodiment of the varia-ble draft ship is shown in FIGS. 2630. As contrasted with the previous figures, it has a single island '76 with minimum size for the purpose of minimizing motion at the greater draft, a minimum displacement change when changing draft, and a maximum top speed at the deep immersion. The body 75 has a spindle shaped hull slightly flattened on top to provide a water plane sufficiently wide to give adequate metacentric stability at the minimum immersion. The island 76 is of relatively short length and of great neness ratio for minimum wave resistance and is located as far forward as possible for the reasons outlined above.

Pitching control is achieved mainly by changing buoyancy of the island 76, therefore the size of

water planes

54 and 56 is reduced to a minimum. The buoyancy change of island '76 is, in eifect, an apparatus which senses the height of oncoming waves to maintain pitching control. Auxiliary control planes 56, located at the bow, and control planes 54, at the stern, assist in providing longitudinal trim control.

Ballast tanks such as were provided in the previous embodiment are used to vary the displacement. Because of the volume of the hull between the largest and the smallest immersions is smaller than that of the previous embodiment shown in FlGS. 21-25, the sizes of the

necessary ballast tanks

63 and 69 are correspondingly smaller, providing more usable space in the ship.

Also, the island '7d is smaller than the previous embodiment; a lower wave resistance at maximum immersion will be experienced resulting in a higher top speed for the same power. ln this craft the prime mover, the payload, fuel, and most of the crew accommodations are in the body 75 and the control and communication spaces are located in the flared portion at the top of the island.

The rudder of this embodiment is secured to the small cross-section of the hull at the stern and is divided into two sections 43 and 1l-3a to give adequate steering. Propeller A4t2 is placed rearward of the rudders a sufficient distance to provide a nearly circumferentially uniform flow of water into the propeller, a condition favorable for maximum propulsive eiiciency.

Thus it is seen that the shapes described in this invention dier from those in a conventional surface ship in that the buoyancy is placed at the greatest practicable depth below the water surface compatible with operation as a surface ship.

The various embodiments have in common certain other features of form. Each has a streamline elongated form located at the lowest point of the hull, the vertical center of which is located at from one-half to two and one-half body diameters below the water surface. A tower or towers connect the body with the surface and the above water portions of the towers form the reserve buoyancy. Although embodiments having one, two or three islands have been shown, the number may vary from l to 5 or more without departing from the spirit of this invention. Each embodiment has a rudder and a propeller or propellers mounted on the stern of the craft.

All embodiments also have a center of volume 45 of the reserve buoyancy and a center of volume 46 of the underwater portion of the island or islands both forward of the center of volume 47 of the body. This important feature is new and useful in this invention and is mainly relied upon to insure effective hydrodynamic control of the pitching motion.

Removing most of the immersed volume of a surface ship to the greatest practicable depth as accomplished by this invention allows the resistance and the speed characteristics approach those of a high speed submarine. This is done by making the portions of the hull in the immediate vicinity of the water surface, that is the wavemaking portions, as small as possible consistent with retaining the simplicity of surface ship control and providing sufficient internal volume.

Removing most of the volume of the surface ship to the greatest practicable depth as in the present invention causes a reduction in heaving and pitching motion to a small percentage of that of a conventional surface ship. Rolling amplitudes are of the same order of magnitude as that of a conventional ship but are subject to being drastically reduced by means of mechanical devices such as anti-rolling fins. Thus, a hull form all of whose major motions are either inherently small or subject to being greatly minimized, can now approach for the first time the goal of the surface ship having zero motion in a sea- Way. This has obvious operational advantages.

The propulsive efficiency of the ship depends upon the propeller efliciency, and also upon the hull-controlled and sea-controlled flow conditions under which the propeller operates. Significant improvements to the ilow environment of the propeller are made by this invention. These improvements relate to nearer approaches to steady state ow conditions in both smooth water and rough seas. By placing the propeller 42 low at the same volume of the bulk of the immersed volume, the effects of a rough sea varying both velocity and direction. of the water flow into the propellers is greatly minimized over that of the conventional surface ship. Thus the propulsive efficiency in rough water is maximized.

In addition, the circular or near-circular hull shape in a region forward of the propellers in this invention gives a nearly circumferentially uniform flow distribution into the propellers. Thus, if each propeller blade element is adapted to the velocity and direction of flow it experiences at its particular radius, the fow condition will remain nearly constant as the blade element sweeps around its circumference. This flow condition contrasted with the actual unsymmetrical flow condition of a conventional surface ship, produces increased propulsive efciency.

Pitching angles are limited and the draft of the forms of this invention is so deep that slamming is eliminated. Also the position of the centers of buoyancies of the reserve buoyancy 45 and the immersed portion of the island 46 are placed forward of the center of buoyancy of the body 47 for reasons of seaworthiness and pitching control. A consequence of this relation of ehapes is drydecks in a head sea. Another more important result is a positive type of pitching response to waves, that is, when a wave crest is encountered, the bow goes up; if a wave trough is encountered the bow goes down. This response prevents uncontrollable diving or leaping in a sea-way. An uncontrollable diving condition has proven to be an insuperable disadvantage in previous craft of this type.

ln the condition of slower speeds and following seas, which has proven to be the most uncontrollable in previous craft, the water particles in the wave crest travel in the same direction as the ship. For this reason, dynamic forces for pitch and depth control such as stern planes or bow planes, are relatively ineffective. Reserve buoyancy has to be mostly relied upon to insure a level pitching attitude. This buoyancy must be forward to provide the necessary forward moment arm for vertical buoyancy restoring forces, and to Isense changes in the height of waves. Buoyancy arranged in this way gives inherent pitching control. It has been relied upon to provide all of the pitching control in all of the embodiments of this invention except in the configurations shown in FIGS. 6 through 20 and 26 thru 30, wherein auxiliary stern planes 54 and bow planes S6 give an additional amount of pitching control.

T he statical stability of subsurface craft is a consideration which greatly influences the choice of form. The two main types of stability are defined as follows:

Metacentric or surface ship stability is created by immersion and emersion of wedges of volume at the water plane of a floating body as it is being heeled. Metacentric stability is maximized for a given volume by the largest and broadest water-plane in the direction of heeling. Pendulum stability, on the other hand, is created by the ships weight acting through its center of gravity, which is below -the center of buoyancy. Pendulum stability is maximized for a given volume by the greatest possible distance between the center of gravity and the center of buoyancy (analogous to the length of a pendulum). As can be seen the metacentric .type of statical buoyancy is possessed by surface vessels and the pendulum type of submarines. Because the sub-surface craft of this invention processes some of the characteristics of both types its statical stability also takes on some of the characteristics of both types. The transverse statical stability of certain types of sub-surface craft whose islands are located on the center line of the underwater hull is almost entirely of the pendulum type. In each case the water plane is very narrow transversely. The immersed and emersed wedges of buoyancy as the vessel heels about the longitudinal axis, are so small in relation to the immersed volume, that these craft have a negligible transverse metacentric stability. Thus, the center of gravity of such vessels must be so low as to be below the center of buoyancy thus forming a pendulum stability.

The embodiment of FIGS. 16-20 however, has a considerable metacentric component because the forward two islands are spaced widely apart in a transverse direction. As a result, the wedges of change in buoyancy while heeling have a larger transverse moment arm, giving an appreciable metacentric stability. Because of this feature, the center of gravity does not need .to be as low as for craft of the preceding type in order to provide for an adequate transverse stability. Pendulum stability is Still present but is proportionately not as large as in previous craft in making up the total transverse stability, which is always the algebraic sum of the metacentric and pendulum stability.

The longitudinal static stability of subsurface craft is mostly of the metacentric type. The long slim shape of waterplane whether it be of the single island or twin island configuration, makes for a considerable wedge volume in the act of pitching; that is, when the hull is rotated about a transverse axis. For this reason metacentric stability is predominant. A small amount of pendulum stability is still present, however, because the center of gravity must be low enough to satisfy the requirements for transverse stability.

The embodiments showing variable draft ships vary their immersion to suit the speed, water depth, and wave conditions encountered. The shallower of the two drafts is used when at low speeds, while entering harbor, and whenever accurate maneuvering needs to be done next to a dock or pier. The deeper of the two drafts is used at high lspeeds on rough seas wherever a large depth of water is available. Displacement changes from one depth to another are accomplished vby the variable

water ballast tanks

68 and 69 shown in FIG. 2l. When these tanks are empty, the ship floats high in the water; when water is pumped into the tanks the ship sinks to the new deeper water line.

Operation at high speeds in rough water is optimized by two criteria: (l) A large displacement-length ratio (short heavy ships), and (2) A long pitching period. The addition of water into the tanks of the ship increases 9 the former criteria by increasing the displacement, and lengthens the natural pitching period of the hull by increasing the longitudinal radius of gyration, and thus the longitudinal mass moment of inertia, by reducing the water plane size, and also by increasing the displacement of the vessel.

The longer pitching period decreases the response the ship experiences from a head sea condition by avoiding resonance.

To increase the transverse stability of the ship while it is changing from one waterline to another, any empty intenbottom tanks 71 are filled with seawater vthus. maintaining a low center of gravity. Normally these tanks, bounded by the outer bottom and the interbottom of the ship are filled with :fuel oil, except when some of the oil has been consumed by the engines.

Thus there have been described several embodiments of a sub-surface craft combining the advantages of a surface vessel and a submarine without the inherent disadvantages of each. The vessel of this invention inherently combines controlled pitching motion in rough seas, deck dryness, high top speeds, and a maximum propulsive eciency from the propeller-hu1l combination.

=It should be understood of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention disclosed herein which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A ship comprising a spindle shaped underwater hull to which are attached a plurality of islands, a portion of said islands being submerged, the total cross-sectional area of said islands in the plane of the water line being small as compared with the longitudinal cross-sectional area of said underwater hull; yand means including the physical dimensions of said hull and said islands whereby the elliptical center of said underwater hull lies between one-half and two and one-half hull diameters below the waterline surface; two of said plurality of islands being attached in side-by-side relationship perpendicularly to the surface of the forward portion of said underwater hull and :a platform connecting at least two of said plurality of islands above the waterline.

2. The invention as dened in claim 1, |wherein the stern portion of said spindle-shaped underwater hull iS l0 substantially circular in vertical cross-section with a propeller rotatably mounted at the tip thereof, and the vertical cross-section of the remaining portion of said underwater hull is substantially elliptical with a horizontal major axis.

3. A ship comprising a spindle shaped underwater hull having a mid section which is constricted transversely, said underwater hull having at least one island attached thereto at the constricted portion thereof, a portion of said inland being submerged `and having a small crosssectional area at the plane of the water line as compared to the longitudinal cross-sectional area of said underwater hull; and means including the physical dimensions of said hull and said island whereby the vertical center of said underwater hull lies between `one-half and two and onehalf hull diameters below the water line surface.

4. The invention as defined in claim 3, wherein the stern portion of said spindle shaped underwater hull is substantially circular in vertical cross-section with a propeller rotatably mounted at the tip thereof, and the vertical cross-section of the remaining portion of said underwater hull is substantially elliptical with a horizontal major axis.

5. The invention as defined in claim 4, wherein the center of buoyancy of the portion of the ship above water andthe center of Ibuoyancy of said submerged portion of said island are both forward of the center of buoyancy of the body of the ship.

References Cited in the tile of this patent i UNITED STATES PATENTS 234,794 Lundborg Nov. 23, 1880 525,179 Baker Aug. 28, 1894 1,373,329 Hoar Mar. 29, 1921 1,436,902 Perley Nov. 28, 1922 1,753,399 Blair Apr. 8, 1930 2,101,613 Engelman Dec. 7, 1937 2,887,977 Piry May 26, 1959 FOREIGN PATENTS 588,351 France Jan. 30, 1925 564,382 Germany Nov. 18, 1932 590,270 Germany Jan. 4, 1934 402,450 Italy Mar. 9, 1943