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The United States has traditionally designed new weapons to operate from the types of hulls developed previously for older, proven systems. These warships have been basically long, slim monohulls because that shape is fast and fuel-efficient. The monohull was used by early man well before the age of sail and may date back to the caveman using a log to float downriver. Later, Roman galleys had catapults and rams with which to attack an enemy ship. The age of steam stimulated significant progress in propulsion. However, there has been little basic change in the geometry or speed of destroyers since World War I, even with the advent of nuclear and gas turbine propulsion. Moreover, the proliferation of antennas for radio, electronic countermeasures (ECM), radar, navigation, fire control, and now satellite communications has complicated topside arrangement, because they are basically “add-ons” to existing concepts of superstructure design. The change to missiles and rapid-fire guns with guided projectiles further perplexes topside antenna arrangements.
Given the characteristics of modem communications, sensors, and weapons, we probably have not given much thought to returning to the basic geometries of the “defense in depth” concept and applied it to warship design because of the tradition and success of the monohull shape. Perhaps such an inquiry is in order in light of the changes from flaghoist, eyeball, and guns to radio, radar, and missiles. We should consider future naval operations and seek the surface ship design that will best accomplish the Navy’s mission in light of current and projected technology. Answers to “What if?” and “Why not?” will downplay tradition.
Background: Two basic geometrical shapes occur naturally in the world’s oceans: cylinders and hemispheres. Cylindrical sharks and barracudas use their keen sensors and speed to find and attack prey quickly with their “forward battery.” Hemispheric sea urchins, jellyfish, and octopi are equipped by nature to defend every inch of their hemisphere. The naval ship, however, must be able to operate both offensively and defensively. Thus, we might consider a combination of nature’s two basic shapes for ships.
The naval surface ship must have sensors and weapons that operate underwater and in the atmosphere. Yet ship motion initiated by the sea surface must be minimized to achieve human efficiency and weapons and sensor effectiveness. Existing permanently on the surface of the world’s oceans is not natural. Whales surface for air, and flying fish briefly skim the tops of the waves. Seagulls leave the air to swim temporarily on the ocean’s surface. Ducks leave the surface to dive, but fly to land or protected water during a storm. Not many aquatic creatures live permanently on the ocean’s surface, immersed partially in water and partially in air. Yet, with surface ships, man has attempted to do just what nature has found difficult. These ships sometimes do not operate effectively during a tempest. They must be made as safe and stable as possible in high seas so that their equipment and crews can achieve 100% operational effectiveness.
Although the approximate true bearing of a target or threat may be known, the relative bearing of the incoming threat or target will vary as a result of own-ship maneuvers. In addition, the threat or target can come from above, below, or along the air/water interface. Therefore, ideally, a ship’s weapons and sensors should be equally effective around 360° relative.
Consider an aircraft passing near a ship, where the target position vector in a series of vertical planes through the relative bearing to the aircraft starts below the horizon as the aircraft approaches from a great distance. Then, the vector elevates until the aircraft reaches the closest point of approach, at which time it recedes slowly below the horizon again. The probability of the aircraft passing directly overhead is small; therefore, the position probability density vector for all aircraft at the zenith is smaller than those vectors near the horizon. Similar situations exist for surface ships, submarines, mines, etc. Thus, the ship can be threatened from any point on a distorted ellipsoid shape, as illustrated in Figure 1, where the outer ellipsoid represents the vertical plane and the inner ellipsoid an oblique view of a circle in the horizontal plane. Direct incoming threats such as missiles, projectiles, and torpedoes would not have random tracks with respect to the ship (unless the enemy had poor aim), but nevertheless we could develop a similar threat probability surface.
This ellipsoid, or “saucer,” locates the most probable positions of a number of “things” which the surface ship may want to communicate with, sense, avoid, or attack- Therefore, it is useful to consider this same ellipsoid as a shape on which to distribute antennas, sensors, and defensive and offensive weapons to obtain the most effective hemispheric clear view. Certain modem equipment has a number of blind spots. There may not be time to turn the ship to unmask a sensor or weapon so that she can defeat an incoming sea-skimming missile.
The ellipsoid has geometrical shape characteristics similar to the radiation pattern of a vertical dipole antenna. I*1 general, electromagnetic radiation in the atmosphere spreads spherically unless it is trapped at a particular frequency by the ionosphere and reflected by the ocean’s surface. In this case, the spreading is cylindrical about a vertical axis. Therefore, we may want to consider the ellipsoid for ship design, because of the physics of electromagnetic radiation as well as the threat and target probability surface mentioned earlier. Phased-array radars, communications, and sensors can be located on the ellip' soidal surface to good advantage. Also, we must consider the observables or signatures the ship emits by which she may be detected by an enemy (see Figure 2).
From the standpoint of radio communications, a single central multifrequency tunable antenna could be located topside at the center of a smooth ellipsoid, providing a11 omnidirectional beam pattern. In contrast, the field of antennas placed in compromise locations on board conventional monohulls suffers distorted beam patterns. For instance, four AN/SSR-1 receive antennas are required 0° most monohulls to get 360° coverage for satellite communications.1 Furthermore, the superstructure’s irregular geometry contributes to electromagnetic interference-
^s°, survivability is questionable for the many antennas Mattered around the superstructure.3
However, phased-array radar, ECM, and communica- '°n antennas placed around the periphery of an ellipsoid aad/or conical superstructure would be more ideally located geometrically for omnidirectional and beam steering c aracteristics. Furthermore, they could be designed to be !tl0re survivable and to exhibit graceful degradation. Per- faPs because of increasing computer power availability complex designs as well as for signal processing, con. rrr|a] antenna arrays are more frequently appearing on '’’craft.4 Also, dish antennas using the top of a smaller bpsoid comprising the bridge as a radome could provide ecUre communications between the ship and a geostation-
^ satellite.
Although the ellipsoid may be efficient electromagneti- ■ ai‘y, one can easily surmise that it would not be a particu- ar*y swift ship. There is rather interesting historical precedent, though of mixed success, for a round ship.
In 1875, Russian Vice Admiral Popoff designed and built a round battleship. Her 121-foot diameter provided a seagoing citadel for twin 11-inch guns. According to Chief Engineer J. W. King, U. S. Navy, the Admiral Popoff was a steady gun platform with little draft and a speed of 8.5 knots. A minimum amount of armor was needed to protect the greatest buoyancy because of the circular shape.5 The round battleship was considered successful enough that a second one, the Novgorod, was built. In addition, Czar Nicholas II, who suffered from seasickness, had the 3,900-ton royal yacht Livadia built using this round concept. The Livadia served for 46 years before being broken up in 1926. The round design, apparently successful in inshore and coastal waters, had difficulty generating the propulsive power needed to make a given speed, and she had difficulties in heavy seas.6
A surface ship with the most efficient shape both offensively and defensively is desired. Perhaps the best way to achieve this is to combine nature’s offensive cylindrical shark form with a defensive circular pincushion shape. One way to achieve the desired end is to combine the small water-plane area twin hull (SWATH) concept with an ellipsoid using a truncated pyramidal framework to connect the underwater and airborne portions.
The SWATH concept may prove to be the most useful of the advanced ships because of its less complex buoyant lift vice dynamic and powered static lift for hydrofoils, air cushion vehicles (ACVs), and surface effect ships (SESs). Currently, however, there are only a few SWATH ships in the world; in contrast, there are more than 1,300 hydrofoils, ACVs, and SESs. In addition, of the total number of advanced ships worldwide, the Soviet Union has 52%, the United States 2%, and the rest of the world 46%.7
The SSP Kaimalino, the first SWATH, designed by Dr. Tom G. Lang, has been operating successfully in Hawaiian waters for a number of years. Seakeeping and control tests conducted in January 1979 showed that this 220-ton vessel in a Sea State 5 caused no difficulties or discomfort for the crew.8 More recently in the United States, SEACO, Inc., built and tested the Swave Lino, reporting much reduced motions in a seaway and increased operating efficiency.9 In a presentation about the SD-60 SWATH demonstrator boat, RMI, Inc., compared a 60- long ton SWATH with a 100-long ton conventional cutter. At flank speed in five-foot wave height seas, the SWATH had one-tenth the accelerations of the cutter.10
In the turbulent North Sea, the SWATH design was considered in a recent study to be the only practical sea transportation for carrying personnel to offshore oil platforms.11 The resulting 2,000-ton ship, which could carry 200 passengers with sleeping accommodations, is about half the size of a frigate that might have to operate near the Iceland-Faeroes Gap during wartime. Further, the U. S. Coast Guard is designing a SWATH with a 131.8-foot length, 57-foot beam, and a displacement of 465 long tons.12 Finally, the Japanese are reportedly building a 3,500-long ton diving support vessel.13
The SWATH concept, then, is maturing after a number of demonstrations and seakeeping tests. Although the
U. S. Navy has no SWATH in the budget, it has recommended such a design for the T-AGOS to wed-array sonar ships, and two recent reports from the Naval Studies Board at the National Academy of Sciences recommend SWATH. One panel, chaired by Dr. Robert A. Frosch, recommended the SWATH as an air-capable missile ship also useful as an ASW sensor operating element for the battle group.14 A second panel recommended the SWATH as a mine countermeasures craft.15 Yet another Naval Studies Board panel, led by Dr. David Potter, reported its findings on SWATH to the Chief of Naval Operations.
Not only does the SWATH decouple itself from the motion of the seas, but the shape of the upper body can be decoupled from the hydrodynamic shape considerations. That is, the SWATH upper body can be designed with more flexibility than can the superstructure of a monohull, whose base is more or less constrained to the shape of the main deck. Dr. Frosch, in a speech at the Naval Advanced Marine Vehicles Symposium in 1972 at the U. S. Naval Academy, said:
“The very geometries of these vessels will also change our views of what is possible to do with a ship. Instead of being all volume, some of them tend to have extensive flat areas, just from the nature of the design, and this suggests other possibilities and other capabilities.”16
Therefore, we can readily visualize a rectangular upper body on a SWATH launching and recovering helicopters. Also, the rectangular geometry is amenable to modular SEAMOD (currently Ships Systems Engineering Standards) concepts. This rectangular geometry is also compatible with flat plate phased-array radars such as the Aegis SPY-1 radar, which was designed to fit orthogonal bridge superstructures. Phased-array radars designed to a curvilinear conformal geometry are also within the state of the art for ships.
Now, because of the flexibility of upper body design we have with the SWATH, let us consider an alternative to the rectangular box: a saucer shape.
The SWATH-Saucer Concept: The SWATH-Saucer concept attempts to combine the swift underwater cylinder with the airborne ellipsoid to minimize induced motions and provide adequate structural strength. In this case, a truncated pyramidal framework connects the underwater and airborne shapes (see Figure 3). This design leads to angled struts, which in turn improve the hydrodynamic characteristics.
One problem in the past with catamaran, trimaran, and SWATH designs has been the strength of the linkage between the separate hulls. In particular, the Navy’s auxil- liary submarine rescue catamaran ships Hayes (T-AGOR- 16) and Pigeon (ASR-21) experienced cracking in the plating in the cross-structure between the twin hulls.17 However, these problems are well understood now, and solutions are known. A unique system of triangles forming a pyramidal structure and a tetrapod mast can significantly increase the strength and unity of this design as shown by the straight lines in Figure 3. The twin hulls and the two foils connecting the twin hulls form the base of a pyramid •. and create a combination SWATH and hydrofoil similar in concept but different in foil arrangement. Of course, the foils will increase the drag, but they can be useful f°r control of pitch and for a passive sonar array, as will be described.
The truncated pyramidal shape was chosen initially from geometrical and truss design considerations. The curved surface shell also offers more strength than does a flat surface. These curved surfaces, because they follow the simple mathematics of the ellipsoid and cylinder, are amenable to numerical machine fabrication, automatic welding, or composite material construction similar to “spinning” a fiberglass missile case. If the structural framework is made of pipe, then power and data lines can be protected within the pipes from battle fragmentation damage, electromagnetic pulse, electromagnetic detection, and electromagnetic interference. Thus, a pyramidal structure around which a combination SWATH-Saucer hull is formed is a new possible shape for ships of the future.
A saucer-shaped exoskeleton of radar-absorbing composite materials over a steel pyramidal framework could make the SWATH-Saucer more difficult to detect. Another natural fallout of the pyramidal framework is that of angled struts. Heretofore, SWATHs have been constructed with vertical struts. Minimum damping forces in this mode, however, result in relative instability in pitch without any automatic control. The angled-strut SWATH should alleviate much of this pitch instability and provide a strong truncated pyramidal framework. The pitch motion is dampened both by the flare of the struts and by their inclination. The flare provides a greater rate of change of buoyancy once the SWATH is disturbed. As the boW pitches down, a water mass is accelerated inboard and downward. Simultaneously, the stem pitches upward- accelerating a mass of water outboard and upward. The inward and outward reaction forces cancel, but the resulting forces up in the bow and down at the stem dampen the pitch of the SWATH. On the negative side, the flare and angle will induce more motion in a seaway than straight struts, and some compromise must be reached.
The performance characteristics of a SWATH with vertical struts were compared to a SWATH with 20° angled stmts. The thickness of the angled stmt was adjusted s° that the water-plane areas of both SWATHs were the same. Preliminary results using the SWATH Seakeeping Evaluation Program (SSEP) indicated that the angled-strut SWATH had lower resonance frequencies than the verti' cal-stmt SWATH. Pitch and heave were also lower at 20' and 28-knot speeds for the angled-stmt SWATH. At zero speed, however, the angled stmt SWATH exhibited slightly larger pitch and heave near the resonant fre' quency.18 Whereas these results were quite preliminary and no further work has been done to date, they do ind*' cate an area of research that may be fmitful in the future-
Whereas the circular shape has been used before as submersible, a hovercraft, and even the aforementioned battleship in czarist Russia, what is believed to be a ne^j combination is that of a SWATH-Saucer. The SWATH
design decouples the platform from surface wave action to a significant extent and allows relatively high speed in a high sea state compared to a monohull because of reduced pitching and rolling motion. This allows the two cylindrical hulls to operate completely submerged, and the upper hull to be completely airborne, supported by the struts that connect the two shapes. The small water-plane area of the struts is the feature that allows minimum transfer of wave energy to the platform.
The variable cross section of the struts is designed as a compromise (rather than constant cross section struts) to assist in damping pitch motion once it has begun and to reduce slamming in higher sea states. The design water line is at the narrowest cross section of the struts. A ballasting system in the ship can keep the design water line the same for various loadings and “tune” the ship for the best ride on a given heading in a seaway. The draft can be reduced by deballasting for entering port.
To complete the base of the pyramidal framework for some SWATHs, foils forward and aft could connect the twin cylindrical hulls to prevent them from flexing. These foils, if fixed, will further assist in reducing pitch because they will resist movement perpendicular to their larger cross section. If the foils are movable (especially the forward foil), then the pitch motion of the SWATH-Saucer can be dynamically controlled. The forward foil could be a movable fairing around a cross-hull circular connection through which various electrical cable, small pipe lines, and controls could be used to cross-connect machinery in the twin hulls.
A number of options should be considered for propulsion and ship’s electrical power. The decision would largely be dependent upon the mission and size of the SWATH-Saucer. Small surveillance platforms or towed decoys could have battery power from lead-acid batteries placed in the underwater hulls. Supplementary power could come from fuel cells, photovoltaic cells, a Darrieus windmill, internal combustion engines, or external combustion Stirling cycle engines. Because the twin struts act like twin keels, the SWATH-Saucer, even in smaller sizes, has good directional stability, making it amenable to auxiliary powering by sail when considering fuel economy.
Larger vessels could have gas turbine engines located in the twin hulls with a colinear shaft arrangement through a planetary gear to the screw. The drawback to this design is that a large volume of air and exhaust would have to pass through the thin struts. Also, for sonar applications of the SWATH, a significant noise-quieting effort would have to be made to reduce the hullbome noise.
Another option for quiet underwater hull-mounted sonar applications would be to have the gas turbines located in the ellipsoid, powering airborne propellers or ducted fans. Yet another obvious combination would be for the topside gas turbines to drive propellers located aft on the twin hulls either mechanically or electrically.19 Another remote possibility is to enhance thrust by using the gas turbine exhaust in the nozzlelike passage formed by the struts on the sides, by the ellipsoid on the top, and by the ocean on the bottom. The jet exhausts could yield an effect like the enhanced thrust from a high-bypass fanjet.
Location of the gas turbines in the upper hull also offers interesting possibilities. First, they could be located vertically within the ellipsoid and exhaust downward and aft. The infrared (IR) signature of the ship could be reduced by this arrangement. However, current marine gas turbines such as the LM2500 would have to be redesigned for the lubrication and bearing systems to operate properly. Starting a new design with this requirement is certainly within the state of the art; a number of aircraft jet engines are designed to operate with the aircraft in a vertical climb. Such a vertical arrangement would permit a very rapid modular replacement of the gas turbine propulsion system.
Existing marine gas turbines operating horizontally can be located within the area where the struts join the ellipsoid to conform with the linear geometry of the struts. The exhaust can still be ducted between the struts and directed aft to reduce the IR signature.
For the larger ships, a nuclear reactor in the underwater hulls might be specified. In contrast to surfaced nuclear submarines, where a portion of the reactor compartment and engine room are above water, a SWATH-Saucer’s reactor would always be beneath the surface except when the ship is in drydock. This might permit reduced shielding requirements. Another advantage is that since the entire propulsion system would be located below the waterline, it would be relatively invulnerable to direct damage from a cruise missile.
The SWATH-Saucer described will have more skin frictional drag than a monohull, which is important for low speeds. Partially offsetting this is the higher propulsion coefficient resulting from the propeller location. Also, the wave drag will be less than that of a monohull, making the SWATH more fuel efficient at high speeds where wave drag predominates. The bottom line is certainly that SWATH will not be as fast as a monohull of the same size and power at cruising speeds except in a high sea state. As a displacement ship, the SWATH cannot match the speed of a hydrofoil or surface effect ship. However, the advantages of the SWATH-Saucer might well outweigh the disadvantages, especially in high sea states. Too, the reduced wake could reduce the detectability of the SWATH-Saucer from aircraft and satellites.
The sonar arrangement on any SWATH can offer significant advantages, even when the propulsion machinery is located underwater. With a target on the starboard side, ship propulsion could be by port shaft only, thus reducing the own-ship self-noise factor. Also, the directional stability offered by the twin struts limiting yaw makes the SWATH a good candidate for a towed array.
An arrangement similar to the four flat faces of the Aegis AN/SPY-1 radar can be structured underwater on the SWATH-Saucer. Using the rectangular base composed of the twin hulls and the foils/hull cross-braces, four linear wide-aperture arrays (WAAs) can be established. This arrangement even permits a ship to look astern; traditionally, a baffle area precluded detecting targets in this area. The optimum arrangement of hydrophones for the WAA is precisely linear, thereby simplifying the mathematical solution of the target range and bearing. The SWATH-Saucer provides four linear arrays at right angles, thereby providing 360° passive ranging capability.
Finally, one of the most important sonar characteristics of the SWATH-Saucer is that the twin hulls remain submerged even during high sea states. In a monohull, the sonar dome can come out of the water when the sea state is high. A Proceedings article entitled “Seakeeping” indicated that an all-up sonar on a 400-foot ship can have as little as 30% availability at 60° latitude in the North Atlantic during the winter because of weather alone (September 1983, pp. 63-67). With hulls deeply immersed below the turbulent surface, a SWATH could be a significantly better sonar platform than a monohull from this point alone-
Concerning topside electromagnetic radiation, a more symmetrical unobstructed beam pattern is physically compatible with antenna arrangements around the ellipsoid, neck, and bridge as indicated in Figure 4. A phased-array air-search radar similar in concept to the Aegis AN/SPY-1 radar but with a greater number of smaller faces evenly distributed over a larger area could be located around the ellipsoidal upper hull. Similarly, a phased-array surface- search radar could be located around the ellipsoidal bridge. Communications antennas and IR and ECM sensors could be arranged around the conical neck of the superstructure at a point at which the diameter is compatible with the antenna size for frequency of the radiation in question. The SWATH-Saucer could securely communicate with satellites by microwave dish antennas located in the bridge ellipsoid where the top of the ellipsoid is a radome.
The Navy’s shipboard electromagnetic compatibility analysis (SEMCA) could be used to evaluate the perfot' mance of such a system. The zero to 90 degree elevation and hemispherical optical coverage for various systems designed for the symmetrical saucer superstructure would be significantly greater than is currently possible (espe' daily since the saucer would have no stacks because the gas turbines would exhaust downward).
SWATH-Saucer Applications: At the present state of development, the SWATH-Saucer could take the form of n small craft such as an experimental unmanned surveillance platform. The size could be from 20 to 30 feet in length so that it could be handled by a destroyer as is a ship’s liberty launch or captain’s gig. The uses could be severalfold and depend on the modular payloads placed on board, such as surveillance, deception, decoying, or remote weapons equipment. It could be sent in way of an enemy or ia waters where a warship should not be risked.
In the 18 April 1983 Aviation Week and Space Techno/' °gy, Richard D. DeLauer, Undersecretary of Defense f°r Research and Engineering, wrote about the “nth” genera' tion computer seen for use in “autonomous systems, able to receive general instructions, navigate to the field °f action, carry out a military mission and return for further instructions.” The unmanned surveillance platform could use such a computer for its operational reprogrammable brain.
The U. S. Naval Academy built an angled-stru1 SWATH under the sponsorship of Naval Sea Systems Command (NavSea) 05R. Although that SWATH was
^u'lt partially for pedagogic as well as research purposes, 11 illustrates what can be done with low-power, light- 'Ve'ght electronics controlled by a computer and remote Eimunications. Energy stored in about 800 pounds of Series in the extended Mk-37 torpedo hulls is supplemented by approximately 80 square feet of solar cells. This SWATH, as an unmanned surveillance platform, can e remotely controlled and sent to gather data.
The small SWATH could also be used as a missile and torpedo decoy towed behind a surface ship. At higher sPeeds, foils would lift the SWATH-Saucer higher out of . e Water to reduce the skin frictional drag but at the same JjE lessen the submergence desired for sonar application. E decoy could have radar, IR, jamming, sonar, and c°rnmunications to distract heat-seeking, home-on-jam, Eradiation, and radar-homing missiles as well as smart torPedoes from a ship.
Another application of a small SWATH-Saucer shape is '^Ustrated in Figure 5. Inspection of underwater pipeline or cables could be accomplished more easily by straddling the work, for light and television could reach both sides and the top of the pipe or cable. Repair work on the pipe or cable could then be performed best by bottoming over the work. Such a shape is also amenable to carrying a swimmer delivery vehicle, mine, or torpedo between the twin hulls. (This is similar to a concept I previously espoused as an at-sea SWATH support ship for a sub that would be nestled between the twin hulls for replenishment or crew change.)20 One attribute of such a submersible design would be enhanced surface stability. If the weight and ballast permitted, the vessel could operate as a SWATH on the surface and avoid being swamped by heavy seas.
A missile patrol boat or missile/torpedo patrol boat is the next-size application for the SWATH-Saucer (see Figure 6). If the truncated pyramidal framework of the boat is made of pipe, the four sloping edges of the pyramid structure provide natural, almost vertical, launch tubes for missiles. The missiles are also ballistically protected from possible battle damage. Because this vessel is small, the SWATH configuration would provide a more stable platform than a monohull of the same displacement. The boat could also carry torpedos, which could roll into the water for launch. The small radar and visual cross section of this craft could permit it to get closer to an enemy task force without detection than is currently possible with other craft.
A special mission/rescue ship of about 500-1,000 tons could be the mother ship to a helicopter, submersible, and air cushion vehicle. Therefore, more intensive operations can be performed in the air, under the surface, or on the surface as appropriate. As a benchmark, the Navy’s SSP Kaimalino at 220 tons has launched and recovered helicopters in a Sea State 4.21 A small ship of this design would be useful in a search and rescue role, interdiction of drug runners, protection of off-shore oil rigs, and special mission work.
The decrease in the thickness of the ellipsoid as the design proceeds radially outward horizontally could provide a geometrically compatible arrangement for the next- generation vertical launch system. As illustrated in Figure 4, a family of various length and diameter tubes, which exhaust downward without a complex gas management system, fits neatly in the ellipsoid. Therefore, ballistic, cruise, surface-to-surface, surface-to-air, and surface-to- underwater missiles, as well as decoys, can be accommodated in the proper-size launch tube. These same tubes can be used to drop torpedos, mines, or sonobuoys.
Figure 4 shows a missile ship concept with a more extensive family of missiles than a destroyer contains. Sophisticated phased-array surface and air-search radar, communication, and ECM antennas yield an integrated and effective electromagnetic suite.
An advanced-weapon air defense ship is depicted in Figure 7. One likely candidate for the particle beam weapon is a betatron accelerator. Such a device fits conveniently around the periphery of the ellipsoid. Another advantage to the truncated pyramidal framework SWATH is that it is stiff and will not hog and sag in a seaway as will a monohull. This feature will be important for a particle beam weapon where a near-optical test bench rigidity is needed for accurate beam formation and transmission.
Because a chemical laser can have a very toxic exhaust, such as hydrogen or deuterium fluoride, the laser cavity can be arranged vertically as shown in Figure 7. In this example, the chemical mixture would flow from forward aft and then exhaust downward and aft between the hulls, while the laser beam streams upward to the pointer tracker. Actual weaponization will not occur until the current technology program is successfully completed for the gas dynamics laser, electric discharge laser, as well as the chemical laser. Also, the free electronic laser shows promise for high average power and efficiency. The SWATH-Saucer could provide a geometry amenable to weaponization of the high-energy laser as well as particle beam weapons.
A conceptual sketch of a large seacraft/aircraft mother ship appears in Figure 8. The same elevator which lifts helicopters and V/STOL aircraft topside, lowers surface craft and submersibles into the water between the twin hulls. One advantage of a centrally located elevator is that the craft only have to be moved radially in and out to and from the central elevator. In contrast, on a conventional aircraft carrier, aircraft are shuffled about considerably on the hangar deck in order to use outboard elevators.
A SWATH-Saucer passive sonar system could give a conformal 360° passive sonar capability to a surface ship. The fiber optic sensor system, with a diameter of about one inch, could be located in the thin foils connecting the twin hulls as well as along the hulls. Because of the deep submergence of the SWATH hulls and the reduced pitching and motion in a sea state, the sensitivity of such a system is higher than that of a conformal array on a monohull. To reduce self-noise, the propulsion system in the underwater hull on the same side as the target can be shut down temporarily.
Departing from the saucer geometry, a SWATH aircraft carrier is shown in Figure 9 with a more conventional shape. Given short notice of impending attack by an enemy, an aircraft carrier would have to be able to augment a combat air patrol and launch a counterstrike immediately. Figure 9 shows six catapults, port and starboard runways, and an elevator/translator system. A plate to which the aircraft are attached can move up and down the elevator shafts as well as translate port, starboard, forward, and aft from any shaft on the hangar and flight deck. This would allow a faster preparation and launch rate even in high sea states, for the aircraft could be positively fixed to the plate during fueling, arming, elevating, and translating to a position for catapulting. Additional “assembly line” techniques could be instituted by using the after elevator for up only and the forward elevator for down in a vertical carousel arrangement. Dual runways provide redundancy as well as the ability to simultaneously launch from one side and recover on the other. Also, the skipper can keep an eye on the deck operations and the navigation situation more easily with the after bridge arrangement.
Recommendations: No one individual can master the many operational and engineering disciplines involved in the design of the modem naval ship, i.e., hydrodynamics, naval architecture, marine engineering, weapons, communications, structure, materials, electrical, mechanical, etc. Hence, some of the proposed solutions to such diverse problems as seakeeping, detectability, sonar performance, electromagnetic compatibility, antenna placement, survivability, structural efficiency, and integration of advanced technology should be debated, corrected, and improved by the specialists. Then, the trade-offs and compromises must be made. The SWATH-Saucer and the equipment arrangements suggested are an attempt to synthesize a compromise solution to some of the problems facing the Navy now and in the future.
Immediate work should be done in a number of areas, if the recommended SWATH-Saucer concept is thought worthy of further investigation. First, the Navy should provide support to investigate more thoroughly the seakeeping ability of an angled-strut SWATH. After computer studies are completed, some tests could be performed using the U. S. Naval Academy SWATH until a model with variable angle struts can be fabricated. Also, variable cross section struts need to be studied to determine the optimum variation.
Second, an operational analysis study of the possible roles and missions of SWATH-Saucers of various sizes should be commissioned. A conventional ship of similar tonnage and mission could be used for comparison, and measure-of-effectiveness computer programs could be used to evaluate the pros and cons of the two ships.
Third, structural design of a SWATH-Saucer should be investigated to check the feasibility and efficiency of such a design. Fourth, a topside antenna, sensor, and weapon arrangement should be generated from a computer program, which then designs the topside geometry to best fd the optimum arrangement. An integrated composite of ellipsoids, cones, and hemispheres may be the result.
Finally, after these and other required studies are performed, a prototype unmanned surveillance platform, towed decoy, or missile patrol boat should be built f°r actual experience with such a novel shape. With these small craft, there are no large dollar or political obstacles involved. Therefore, a prototype might be possible in a short time from which extrapolated data might be useful for larger ship design estimations.
Conclusions: The SWATH-Saucer concept holds promise for a more effective integration of modern weapon, sensor, communication, and propulsion systems into the hull. The hull form itself may be better able to perform ds mission, for its geometry is more in tune with the immutable laws of physics governing hydrodynamics, the propagation of underwater sound, electromagnetic radiation, and the operational requirements of a ship. The motion the ship in a seaway may be reduced even over that of a conventional SWATH as a result of the angled struts. ^ summary of these advantages and others follows:
- Lower induced motions
- Better underwater coupling
- Vertical launch compatibility
- Better advanced weapons platform
- Geometrically compatible electromagnetic radiation
- Lower visual/radar/IR cross section
- Amenable to composite construction
- Enhanced chemical-biological-radiological defense
- Weapons, sensors, antennas visually hidden
- Best compromise for naval architecture, weapons, electronics, and sensor engineering
- More survivable
But the SWATH-Saucer concept is not without its disadvantages, a summary of which follows:
- Doesn’t look traditional
- Curvatures more complex
- Deeper draft
- More wetted surface
The SWATH offers greatly reduced motion because of a simple displacement geometry. With SWATHs, we can have much smaller ships with acceptable motions. With smaller ships, we can afford larger numbers of them in the defense budget. More ships dispersed over greater areas may be the key in the next war, for even a swift ship cannot be in two places at once. Considering this, should we not be doing more with SWATH?
‘Preston E. Law, Jr., Comments on “The Unimast Concept—A Major Departure in Shipboard Radar Antenna Installation Philosophy,” Naval Engineers Journal, June 1981.
2Preston E. Law, Jr., “Accommodating Antenna Systems in the Ship Design Process,” Naval Engineers Journal, February 1979, pp. 65-75.
3Julian S. Lake, “On Bringing Back the Battleships,” Defense Electronics, March 1982, pp. 21-22.
4R. C. Hansen, “A Decade of Conformal Antenna Array R&D,” Microwave Journal, April 1982.
5J. W. King, The War-Ships and Navies of the World (Annapolis, MD: Naval Institute Press, 1880).
6Peter Kemp, History of Ships (London: Orbis Publishing Co., 1978).
7F. H. Michaelis, keynote address, 7th Marine Systems Conference Symposium, New Orleans, LA, 23-25 February 1983.
8James A. Fein, “Seakeeping and Motion Control Trials of SSP Kaimalino in Sea States 4 and 5,” David W. Taylor Naval Research and Development Center report DTNSRDC-81/015, February 1981.
“Scott E. Drummond, “SWATH Ships—Calming Seas for Operating Efficiency,” SEA Technology, August 1983, pp. 33-34.
‘“George Luedeke, Jr., “A New SWATH for U. S. Maritime Service,” AIAA/ SNAME/ASNE 7th Marine Systems Conference, New Orleans. LA, 23-25 February 1983.
“R. D. Gaul, A. C. McClure, and G. O. Joseph, “Semi-Ship Favored as Crew Transporter,” Offshore, 5 October 1981.
12J. E. Rodrigues, Chief Shipbuilding Branch, U. S. Coast Guard Headquarters, telephone conversation with author, 26 October 1983; R. G. Allen and R. S. Holcomb, “Coastal SWATH Ship Design and Experience,” presented at OCEANS ’83, 30 August 1983.
13Naval Studies Board, “Report of the Mine Warfare Study Group (U), vol. VUI. The SWATH as an MCM Platform,” National Academy of Sciences, Washington, D C., September 1982.
14Naval Studies Board, “The Implications of Advancing Technology for Naval Aviation,” National Research Council, Washington, D.C., 1982.
15Naval Studies Board, “Report on the Mine Warfare Study Group. . . .
16S. E. Veazey, “SEAMOD Combat Systems for Advanced Platforms,” Naval Engineers Journal, February 1978, pp. 53-60.
"Naval Studies Board, “Report on the Mine Warfare Study Group. ...”
18R. Stall, “Inclined Strut SWATH Seakeeping Preliminary Analysis,” unpublished example, DTNSRDC, April 1983.
‘““Electric Propulsion with High Fuel Economy,” Maritime Defense, July 1980. 20Veazey, pp. 53-60.
21Naval Studies Board, "Report on the Mine Warfare Study Group. ..."
Captain Veazey received a BS in electrical engineering from the U. S. Naval Academy and a PhD in physics from Duke University. He has served in three submarines and has had a number of billets as engineering duty officer. Captain Veazey was offtcer-in-charge of White Oak Laboratory and then the chairman of the Naval Systems Engineering Department at the Naval Academy. Captain Veazey was an executive scientist at OR1, Inc., and is currently Division Director, Systems Engineering Division, Automated Science Group, Inc.