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The CGBL – a Product Improved Version of the CG 52 Philip Sims ABSTRACT There are indications that the next cruiser design will be a large ship, both in dimensions and displacement. It will inevitably be compared to the existing cruisers of the CG 47 class. The CG 47 class was a mod-repeat of the DD 963 class and carried over many “big destroyer” legacies such as an aluminum superstructure and a compensated fuel system. The mod-repeat ships had extremely limited service life reserves. In the mid-1980s, the Navy desired to evaluate future technologies for future ships but using the CG 47 as a starting point invoked that ship’s inherent features which often confused the evaluation. For example, fitting a composite superstructure showed little change over an aluminum superstructure ship although the Navy policy was not to use aluminum but steel in the future. A composite superstructure would show weight savings over a steel superstructure ship. A modern features CG was needed to evaluate future technologies so a 1986 study created the CG Base Line (CGBL). It was a “product improved” version of the VLS variants of the CG 47 class (CG 52 onward) with full design margins, full service life reserves, clean ballast fuel system and all electric auxiliaries. Military mission improvements included radar cross section reduction, a steel superstructure with increased fragment protection, and a Collective Protection System. The changes increased the dimensions of the ship to a waterline length of 620 feet, a beam of 69 feet and a full load displacement of 13,675 tons. Since the combat system (over half the
cost of the ship) and the main machinery was unchanged, the cost increase was much less than the size increase would indicate. The major increase in displacement was due to a low-cost-perton steel superstructure and features that could reduce cost such as combat system modularity and generous internal volume easing construction. The resulting ship was more survivable, faster, had much better seakeeping and could accept a major mid-life modernization. The paper describes the ship impact of each of the changed features. The size of the DDG 1000 and the CG(X) alternatives are easier to explain if compared to the CGBL rather than the CG 52. INTRODUCTION In order to conduct a Congressionally requested Alternative Propulsion Study, a series of baseline future ships were created. One concept was a Medium Surface Combatant whose study baseline (Medium size, Fossil fuel, Mechanical drive = MFM-1) had a 721 foot length on the waterline, an 82 ft beam and it displaced 21,260 long tons [Reference 1]. The illustrations in Ref 1 show a flush deck hull and a twin tower superstructure configuration [Figure 1].
Figure 1: MFM-1 – a nominal future surface combatant.
The ship study was fitted with a very high powered radar, 157 large missile 1
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cells and a 155 mm Advanced Gun System along with substantial ASW, aviation and light gun armament. While not specifically a CG(X) alternative, the 2006 MFM-1 represents a “peek ahead” at the large combat system ships which the CG(X) Analysis of Alternatives would have to evaluate. The MFM-1’s 21,260 tons displacement often draws the comment from people who see it for the first time that it is “twice as big as CG 52”. Other variants of that ship in Reference 1 are even larger in displacement. In comparing ships by ratioing their displacements, you have a numerator and a denominator. This paper is about whether the denominator which first comes to mind, the 9,500 ton CG 52, is the right ship to compare to a future large surface combatant. REPLACEMENT OF THE OFFENSIVE SURFACE COMBATANT BY THE CARRIER The date of the replacement of surface combatants by aircraft carriers as the dominant naval weapon has been claimed by different writers as having occurred at one of several events. Some credit the sinking of the Repulse and Prince of Wales. Others point to the Battle of Santa Cruise where neither surface fleet saw the other, while some think the inflection point was the pivotal battle of Midway. However, there were brutal surface combatant battles at night off Guadalcanal where airplanes played only a supporting role before or after. No aircraft were involved in the December 1944 Duke of York’s sinking of the Gneisenau in 1944 in an Artic gale. The final displacement of the surface combatant as a Navy important fighting force did not occur until the large
Midway class carriers with radar equipped aircraft arrived after WWII. The very large ship meant that operations in bad weather’s high sea states was possible. Fitting carrier aircraft with radar meant the ability to attack the enemy ships in bad weather and at night (and finding one own ship upon return) was now possible. The surface combatant had lost even its primary fighting role in night and bad weather. The mission of the surface combatant was now as a carrier escort. THE EARLY SUPER CARRIER ESCORTS Muir [Reference 2] describes the effect on the surface force of becoming dedicated to the escort mission, Some classes, the DD 930s and DDG 2s, found a role of escorting the still numerous Essex class carriers but the future of the Navy escort force was seen as centered on the super carriers of the Forrestal class onward. The all-weather nuclearbomber-armed super carriers needed escorts that could keep up with them. The DLG 9 class was found to be a bit small to keep up with long and heavy big carriers. The first large class of super carrier escorts, the DLG 16 class Destroyer Leaders shown in Figure 2, set the pattern for the ship type – around 500 feet long, an 80,000 horsepower propulsion plant and a displacement of at least 7,000 tons. Those features allowed an escort to keep up with a super carrier. Being a dedicated escort drove a certain kind of design logic since there was no such thing as a wounded escort – a damaged ship was a hole in the screen and it was better that the ship drop out and the screen reform with intact ships. Thus it was acceptable to have relatively unarmored ship with the survivability 2
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emphasis being on saving the crew and the hull. Retention of partial combat capability was not a priority because it had little value for a pure escort. The US Navy evolved the “big destroyer” through the DLG 26 class and several nuclear alternatives.
what the DD 963 would have been if it had been upgraded to its intended DDG configuration.
Figure 3: The as-delivered ASW destroyer DD 963 (NS).
Figure 2: The DLG 16 class was designed as a super carrier escort (NS).
While current design emphasizes reducing signatures, it should be remembered that an artifact of the “save the carrier” escort era was the installation of some ships of the ULQ-5 S-band blip-enhancer which was intended to have escort give radar returns resembling that of a carrier to confuse enemy targeting. [ Reference 3]. THE DIRECT ANCESTORS OF THE CG 47 CLASS Friedman [Reference 4] and Potter [Reference 5] provided extensive material on the creation of the DD 963 class. The as-delivered ASW destroyers, Figure 3, were intended to be modernized and converted to antiaircraft guided missile armed ships. Except that they were not fitted with a lightweight 8 inch gun forward, the DD 993 class, Figure 4, were essentially
Figure 4: The intended upgrade of the ASW destroyer to an anti-air DDG would have resembled the DD 993 class (NS).
THE CG 47 CLASS The ships that became known as the CG 47 class went through their design and, in the case of the lead ship, keel 3
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laying as DDGs [Figure 5]. The rather convoluted relationship between DD, DDG and CG hull numbers and designators is described in Appendix A.
Figure 5: All of the design documents for the CG 47 describe her as the DDG 47
Staiman [Reference 6] provides a history of the process of fitting Aegis to the DD 963 hull and then fitting the Vertical Launching System (VLS) to CG 52 onward. A relevant question is if, during the design phase, it was ever considered to make the hull larger. After the CG 47 came in heavier than expected, the use of a forty foot “plugand-slide” hull lengthening was considered to get back buoyancy and hull volume. The concept of plug-andslide is an attempt to reconcile the desire
to reuse engineering drawings with the fact that the best place to change the lines and the best place to add volume do not coincide. Another complication is the USN length based damage criteria which a simple plug places the bulkheads in the wrong location for an assumed longer damaged area. As shown in Figure 6, the proposed plug-and-slide hull change resulted in three major groupings of the ship hull compartments. Ends of the ship were the existing lines and the existing compartments making for a high drawing reuse. The middle of the ship had a section of old compartments and the new lines where the plug was to be inserted and forward of that where existing lines were pushed ahead. The overall compartment drawings were to be retained but the drawings of anything connected to the shell had to be changed. The area of greatest change was the new volume within the old lines. Since length drives bending moment, all the midships structural scantling drawings would have had to be changed. The decision was made not to add buoyancy but to remove weight in the follow ships with the Take Off Tons Sensibly (TOTS) program described by Staiman.
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Figure 6: A 40 foot lengthening of later CG 47s, using the plug-and-slide approach, was considered.
signature, carrier the value of signature control became greatly increased. The CG 52 onward had a revolutionary combat system but, as mod-repeat ships, the basic nature of the hull was not changed to match that combat system.
THE TRANSFORMATIONAL CRUISER The fitting of VLS to the CG 52 made that ship into what would later become fashionable to call a ‘transformational” weapons system. The Russians had installed a limited number of large cruise missiles on their ship earlier but the miniaturized jet engine and folding wings of a Tomahawk missile allowed fitting an extremely large number in a compact launching system. The surface combatant had acquired an ability it never had before of conducting a far inland strike or to attack other ships at a range of 100s of miles away. Capability of independent action changes a surface combatant’s basic design logic. There is such thing as a wounded cruise missile ship. It may have lost a mission area or speed but, due to the missiles’ selfguiding after launch nature, the wounded ship can still play an important role over 100s of miles. For such a ship, changing the design to be able to “fight hurt” becomes very useful. No longer operating in consort with the large dimension, hence large
THE TECHNOLOGY ASSESSMENT PROCESS A person develops a new idea – it can be a technology or an improved design standard - to resolve a chronic fleet problem. The obvious questions are 1) what does it cost? and 2) what are the benefits? If the new concept is large enough in volume, manning, weight or center of gravity to affect the size of the ship (either up or down), a major part of the cost question is resizing the ship. If the performance benefits are altered depending on where the baseline system is located on ship, future and not just existing locations have to be addressed. The process is to define the new idea and analyze it when applied to the baseline ship in a ship synthesis model such as the Navy’s Advanced Ship System Evaluation Tool 5
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(ASSET) which can resize the ship. It is helpful in explaining the results to people familiar with ships but outside the design community to use a familiar baseline ship to eliminate time in defining the baseline. In the mid-1980s the DDG 51 was still a paper ship and the CG 52 was considered the exemplar of a modern surface combatant. It was also a large surface combatant class which would have to be replaced far enough in the future for technologies to successfully go through the long development process.
fair to assess stabilizing device technology on such a baseline which would reward fins (provide a lot of motions relief with small size system) and punish Frahm tanks system (basically unacceptable due its free surface)? A more typical moderate value metacentric height ship would be a fairer baseline to assess motions control systems. As part of the mod-repeat philosophy, the lines of DD 963 class were retained even though the following classes were much heavier. Seawater responds not to lines but the hole in the water. The nearly 10,000 ton hole in the water for the CG 52 is much different than the designed 7,800 ton DD 963 hole in the water although the lines of both ships are identical. Pushing the lines deeper in the water resulted in the shift of the centers of buoyancy and water plane farther aft. If one looks carefully at pictures of the CGs released by the Navy [Figure 8], one notices a very slight nose down attitude due to that shift. It could only be partially compensated by locating the needed lead ballast aft. Having a bit of a nose down trim does not harm the operations of the ship, but raises the question of its suitability as a starting point to compare to proposed future alternative lines.
PROBLEMS WITH THE CG 52 AS A BASELINE The CG 52 has several significant problems when asked to serve as a technology analysis baseline some of which came from her large carrier escort pedigree. If one wanted to assess the value of a composite superstructure, the replacement of the CG’s lightweight aluminum superstructure would show little change. However, the policy at the time was not to use aluminum superstructures for the larger surface combatants. Thus, to show any possible benefits of a composite superstructure, it would be necessary to compare it to a steel superstructure which would be otherwise fitted to a future cruiser. If an advocate wished to propose new armor for the Combat Information Center, it would make a difference if it were in the traditional carrier escort above-the-weatherdeck location or in the hull as in the DDG 51 class. Other ship specific features come from the CG 52’s mod-repeat design history. The class has a small metacentric height (GM) but a long righting arm to achieve satisfactory stability. This means the ship takes on a considerable roll in a high speed turn, as if Figure 7. If any weights are off center, a low GM ship has a tendency to take on a noticeable calm water list. Would it be
Figure 7: CG 53 rolls in a high-speed turn. (N)
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Figure 8: CG 61 shows the very slightly nose down inclination of her weather deck edge. (N)
by 20 men to match the Ship Manning Document. The CG 52 80,000 horsepower propulsion plant and electrical generators supplying steam from waste heat were replaced by a plant modeled on that of the DDG 51. The new machinery provided 100,000 horsepower for propulsion and had 4 generators, without waste heat recovery, to make it an all electric ship. The fuel storage system was changed from a compensated ballast system to a noncompensated fuel system with clean ballast tanks. The deckhouse material was changed from aluminum to steel. It featured substantial anti-fragment armor and increased nuclear blast resistance.
THE CGBL UPGRADES Starting with a CG 52 match run in ASSET, it was changed into a new design ship by adding full design and construction margins plus service life reserves. They were applied to weight, center of gravity (KG), electric load, hull powering and accommodations as described in Table 1. If the modeled ship had been actually intended for construction with an existing (hence low risk) combat system, the margins would have been much lower. Since it was intended to evaluate technology as if it were being fitted onto a totally new design, totally new ship margins were used. This being before the Smart Ship program, the ship’s manning was increased 7
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Table 1: Generic Margins and Service Life Reserves
Design Margin 10 percent 8 Percent
Light ship Weight Light ship Center of Gravity rise Full Load Displacement Full load Center of Gravity rise Electric Load Air Conditioning Load Internal Arrangement Area Accommodations Drag in Speed-Power Calculation Hull Girder Stress
20 percent 20 percent 5 percent
Service Life Reserves
10 percent 1 ft 20 percent 20 percent 10 percent
8 percent 1 ton per square inch
The topside was shaped like that of the DDG 51 [Figure 9] to reduce Radar Cross Section. Another added survivability features was a Collective Protection System. A possible future cruiser feature, not found on the DDG, was installation of a small secondary Combat Information Center and a small communications space aft to ensure Tomahawk launch capability even if the main rooms were damaged. Berthing for a DESRON flag space was fitted to the ship Although the combat system was the same as the CG 52, several components were to be installed in modules. The two guns were in modules and so was the helicopter hangar. This would allow construction and testing outside the shipyard and, in the future, facilitate their replacement by newer weapons. The CGBL bow gun is located further aft than on the CG 52 in order to fit the width of the modular box within the converging bow lines. The aft gun is located further forward to fit the depth of the modular box within the rising keel line. To improve speed and seakeeping, the hull was lengthened and the hull coefficients optimized. The hull was of a
flush deck configuration in order to increase reserve buoyancy aft and eliminate the inherent structural weak point of a sudden hull depth change.
Figure 9; The not-yet-built but under design DDG 51 was the source of many features used by the CGBL.(N)
The overall result was a strike capable cruiser designed to DDG 51 standards and technology or better. Adding these features increased the weight and dimensions of the ship as described in Table 2. Figure 10 shows an outboard profile of the CGBL.
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Table 2: Displacement and Dimension Growth due to Various Features
Start is CG 52 Match Changes: SMD Ship New Design Margins and Service Life Reserves New Uprated Machinery Modular Combat Systems Steel SS Non-Comp Increase Survivability Speed and Seakeeping Sum:- - - - - - - - - - - - - - - - Result is the CGBL:
LBP, ft 529
Beam, ft 55.4
-+31 ---+60 -----620
-0.2 +0.5 +1.9 +5.7 +0.5 -2.2 -----69.0
Disp Full Load, LT 9,420 +65 +1,240 +50 +605 +535 +375 +685 +700 -------------13,675
Speed, kts 29.7 -.1 -1.4 +1.8 +0.5 -0.3 -0.4 -0.3 +1.0 -------30.5
Figure 10: CGBL profile part of a pair created at the same time with the sister painting being that of the Mission Essential Unit (MEU) concept of a hybrid cruiser-carrier. In the pre-computer graphics era, painting a portrait is how two dimensional engineering drawings were converted into a three dimensional view of the new concept. Incidentally, the mid-
THE CBGL PAINTING The head of the NAVSEA Preliminary Design division, George Kerr, desired to highlight the division’s ability to produce new concepts, so noted marine and aviation artist Richard Allison was paid to create an oil painting of the CGBL [Figure 11]. It is 9
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1980s date of the painting is revealed by the DDG 51 in the background having a nearly vertical lattice mast instead of the final design’s inclined tripod.
Figure 11: The CGBL painting unchanged, except for the addition of the secondary CIC, regardless of hull changes In fact, the modular installation of the guns and aviation facilities was intended to reduce combat system construction and installation cost although increasing ship weight due to module boundaries. A steel superstructure weighs twice as much as an aluminum but the metal is half the cost and easier to weld. It is a weight increase without a cost increase. Also as part of the “steel is cheap” philosophy, generous deck heights were used to ease assembly.
THE CGBL EVALUATED The CGBL showed a major increase in displacement but the combat system had remained the same as the CG 52 and, as shown in Figure 12, from reference 7, the combat system is at least 50% of the cost of the ship. Figure 12 shows that, while the platform part of the ship has a learning curve over time, the payload part of the ship had a countervailing improvement curve. The ships with the Block IV version of the combat system had 60% of the ship in payload and 40% was platform. Thus for a CGBL using a CG combat system, 50-60% of the cost from the CG remained 10
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growth assigned to various modern features added onto the existing ship.
Figure 12: CG payload and platform cost percentages.
Figure 13: The DDG 1000 is a very large destroyer. How can its size be explained to the public?
Many features such armor, the Collective Protection System, hull and superstructure shaping increase ship’s cost but have direct military value. The long length adds weight but with the improved hull coefficients, the ship is faster, and a much better seakeeper.
If a modern features CG 52 is nearly 14,000 tons, the DDG 1000 and CG(X) are not as great of a growth as it appears when compared to the actual big-destroyer-legacy and mod-repeat CG 52.
THE CGBL COMPARED TO CURRENT CONCEPTS
The obvious question is what is the value of a paper about a mid-1980s math model of a cruiser to today’s shipbuilding effort? The DDG 1000, Figure 13, has a 14,600 ton displacement making much larger than any previous DDG and larger than the CG 52. How can the Navy explain the size of the DDG 1000 and the upcoming CG(X) to the public? One can ‘build down’ by starting with the new ship design and remove feature by feature to make it smaller but that process involves divulging a great deal of design information about those new ships. The alternative is to “build up” by starting with a well known ship, in this case the CG 52, and add features to explore which ones are making the ship larger. This paper presents such a build up approach with weight
The 1986 CG Base Line (CGBL) was a mathematical model of a cruiser with modern features needed to evaluate future technologies. One reason for the need of a new baseline was many of the features of the CG 47 class can be traced back to her “big destroyer” heritage. In fact, the lead ship was called the DDG 47 all the way through the keel laying of the first ship. The big destroyer legacies included an aluminum superstructure, CIC above the weather deck and a compensated fuel system. The CG 47 was designed with the philosophy of the ship being a mid-life modernization at delivery which meant the ships had extremely limited service life reserves. The VLS versions of the class, the CG 52 onward, were loaded up with additional weapons. Using a match run mathematical 11
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model of the CG 52 as a starting point for technology studies invoked that ship’s inherent features and mod-repeat design choices. These legacies often confused results of the evaluation of technologies for future cruisers. The CGBL was a “product improved” version of the CG 52 created with the ASSET ship synthesis model. It had full design margins, full service life reserves, clean ballast fuel system and all-electric auxiliaries. Military mission improvements included radar cross section reduction, a steel superstructure with increased fragment protection, and a Collective Protection System which increased the displacement considerably. The math model of the ship was used for several years to conduct technology evaluations such as composite superstructures and new machinery. As the DDG 51 class became the most well known ship in the fleet, that class became the preferred baseline for technology studies and the use of the CGBL declined. The CGBL is of historical interest now as a “missing generation” of a transitional type that could have been built in between the CG 52 class and the DDG 1000 and the CG(X). It has been noted that those two ships are predicted to be much larger than the in-service cruisers. However, the CGBL had dimensions of a waterline length of 620 feet, a beam of 69 feet and a full load displacement of 13,675 tons. The size of the DDG 1000 and the CG(X) alternatives are easier to explain if compared to the CGBL rather than the CG 52.
Conference and Expo, November, 2007. Fort Lauderdale, FL 2) Muir, Malcom, Jr., Black Shoes and Blue Water: Surface Warfare in the United States Navy 1945-1975, (Naval Historical Center, Washington, DC 1996). 3) Friedman, Norman, World Naval Weapons System 1991/92, (Naval Institute Press, Annapolis, Maryland 1991), pg 533. 4) Friedman, Norman, U.S. Destroyers; An Illustrated Design History, (Naval Institute Press, Annapolis, Maryland 1982), pg 298. 5) Potter, Capt. Michael C., Electronic Greyhounds: The Spruance-Class Destroyers, (Naval Institute Press, Annapolis, Maryland 1995), pg 49. 6) Staiman, Robert C., “Aegis Cruiser Weight Reduction and Control”, Naval Engineers Journal, May 1987, pg 190. 7) Johnston, John and Mathai, Cathy, “Where The SCN $ Go: An Affordability Focus”, Association of Scientist and Engineers, 28th Annual Technical Symposium, 1991. pg 6. Photo Credits: N = US Navy NS = Navsource Web Page Philip Sims graduated from Webb Institute in 1971 and went to work for the Naval Ship Engineering Center. He was part of the FFG 7 design team in 1972. From 1973 to 1975, he performed aircraft carrier design studies for the Sea Based Air Study and CVV design. He received a master’s degree from MIT in 1976. The 1977-80 period was spent conducting design studies for the CGN 42, the reserve FFX, and the DDX (later DDG 51) projects. From 1981-83, he was the naval architect on the BB
References 1) Webster, James S., Fireman, Howard, Allen, Dillon A., MacKenna, Adrian, and Hootman, John C., “Alternative Propulsion Methods for Surface Combatants and Amphibious Warfare Ships,” presented at the 2007 SNAME Maritime Technology 12
ASNE Day 2008 62 reactivation and Ship Design Manager for the BB 61 and CA 134. He was member of the NATO Staff Requirements Working Group for the NATO Frigate Replacement for the 1990s (NFR 90). The early 1990s were spent on CGN, DDG 993 and CG 47 modernization studies. He prepared destroyer/frigate studies as part of the Force Architecture phase of SC 21. In 1999, he started conducting the first pre-milestone A studies of JCC(X) and stayed with the program until the cancellation in 2003. He performed the DDG 51 conversion and mod-repeat studies for the CG(X) Analysis of Alternatives. He is currently conducting Comparative Naval Architecture and LCC(R) studies.
hull number instead of taking the next AGF hull number. An example of a name change of an in-service ship was the change of the DDG 5 from being the Biddle to being the Claude V. Ricketts in 1964. When the CG 47 carried her DDG hull number into the CG list, it left a gap in cruiser numbering system. It has claimed by outside observers that CG 43-46 hull numbers were reserved for follow-on hulls of the cancelled CGN 42 but that is not the case. When the USN builds ships as part of the Foreign Military Sales process, they are given USN hull numbers during the construction process. For example, the DDG 25 was the USN building hull number for the ship that became the Australian Navy’s D-38 HMAS Perth. The four ships built for the pre-revolutionary Iranian Navy were assigned US DD designators and hull numbers during construction. When purchased by the USN, they should have been redesignated as DDGs because of their long range AAW missile armament. The Navy had intended them to be DDG 47-50 so it reserved that block of numbers for the four ships. Once again, the administrative pain of the massive documentation changes required if a hull number was revised made that undesirable so they ended up with a DDG designators but retained their destroyer hull numbers. When a new design DDG class came along, those reservations made the DDG 51 the next available hull number. This convoluted history is why so many of the CG 47 and DDG 51 hull numbers overlap.
APPENDIX A: THE RELATIONSHIP BETWEEN DD, DDG AND CG HULL NUMBERS AND DESIGNATORS The ten ships of the DLG 9 class were reclassified as the DDG 37 class instead of joining the larger DLGs as being redesignated as CGs. The last of those ships was the former DLG 15, the Preble, which became the DDG 46. Thus the next available DDG number was 47. The ships that became known as the CG 47 class went through their design and, in the case of the lead ship, the keel laying as DDGs. When it was decided to redesignate the lead ship as a CG, it was too difficult to change all the documents to the next available cruiser hull number which was CG 43. In many ways, the hull number is more of a ship’s permanent identifier rather than its type designator or even its name, both of which have been changed on USN ships while leaving the number the same. An example of a retained hull number is the command ship conversion of the AGF 11, the Coronado, which kept its original LPD