Marine Technology, Vol. 28, No. 3, May 1991, pp. 129-141

Preliminary Design of a High-Speed SWATH Passenger/Car Ferry A. P a p a n i k o l a o u , 1 G. Z a r a p h o n i t i s , 1 and M. A n d r o u l a k a k i s 1

The paper summarizes results of a recent research project of the National Technical University of Athens on the preliminary design and computer-aided optimization of a high-speed small waterplane area, twin hull (SWATH) passenger/car ferry. The projected vessel would be employed as a link in a rapid marine transit system connecting the Greek mainland (port of Piraeus) with the island of Crete (port of Heraklion). Alternative routes, leading to different vessel sizes and speeds, can be studied by the same developed design methodology and are currently under consideration for the local Greek or further Mediterranean market. Following a three-stage, techno-economical optimization to estimate the main dimensions and the hull form of the projected vessel, the preliminary design of a prototype SWATH vessel has been completed at NTUA, comprising all main steps of the well-known design spiral. Because the developed vessel is a prototype, it was essential to develop the proper analytical and numerical, computer-aided design tools to enable the necessary repetition of the various steps in the framework of a converging design. Theoretical predictions of the vessel's hydrodynamic behavior (powering and seakeeping) have been accompanied by a series of towing tank model experiments. The economic and operational advantages of the proposed concept are explained.

Introduction

FIRST, the objectives of the research project at the National Technical University of Athens (NTUA) should be explained: • Develop a new concept for a rapid marine transit system connecting the Greek mainland with the many islands in the Aegean and Ionean Seas. • Develop computer-aided design tools for the systematic analysis and preliminary design, including cost evaluation, of small waterplane area, twin hull (SWATH) vessels. • Develop a methodology for the hydrodynamic/economic optimization of SWATH vessels. • Perform model experiments to validate theoretical results on horsepower requirements and seakeeping behavior. • Estimate construction costs on the basis of data of Greek shipyards and German diesel engine manufacturers. • Complete a parametric economic evaluation for a vessel on the Piraeus/Heraklion (Crete) route in terms of required freight rate (RFR) and net present value (NPV) criteria. • Complete a feasibility study/preliminary design for the same vessel. The pros of a high-speed SWATH passenger/car ferry against a conventional monohull with the same payload capacity but approximately half the speed are as follows:

Physical/hydrodynamic criteria (SWATH pros against monohull): --low horsepower requirement for high speeds, --superior seakeeping, --ample stability, and --good maneuverability.

--increased number of round trips per year, --superior seaworthiness/riding comfort, --shorter embarkation/disembarkation time, --large deck area, --good passenger conveniences aboard for daytime trip, --low noise/vibration level, --attractiveness for passengers/tourists results in high utilization year round, --promising high-technology vessel for investors and shipyards--substantial state support (Greece), and --high revenues expected. The high-speed SWATH passenger/car ferry concept can even be compared with competing aircraft transport. The pros in favor of SWATH are:

Operational/economic criteria (SWATH pros against aircraft): --fares significantly lower, --trip time for door-to-door transport not much longer (range up to 200 miles), --private cars and heavy baggage aboard, ---quality of ride, service, etc., and safety. The cons of a high-speed SWATH passenger/car ferry as compared with a conventional monohull are:

Physical/Hydrodynamic Criteria (SWATH cons against monohull): --large wetted surface---increased frictional resistance (Important for low speeds only), --sensitive to weight changes--draft/trim control required, and --pitch instabilities/fins required.

against

Operational/economic criteria (SWATH cons against monohull):

1National Technical Universityof Athens, Department of Naval Architecture and Marine Engineering, Athens, Greece. Manuscript received at SNAMEheadquarters June 25, 1990.

- - n e w technology vessel--risk for investors/shipyards, --low payload level--excludes heavy truck transports --unique structural problems relating to structure or material used, --advanced ballast and fin control systems required, and --higher construction costs expected.

Operational/economic monohull):

criteria

(SWATH pros

--trip time can be cut by half,

MAY 1991

0025-3316/9112803-0129500.51/0

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129

Investment/operational costs Based on the aforementioned criteria, the high-speed SWATH passenger/car ferry has been considered a promising alternative solution for linking the main islands of the Aegean Sea (Crete, Rhodos, Samos, Lesbos) with the port of Piraeus or an alternative port in the Athens area. The aforementioned islands are all approximately 160 to 220 nautical miles (nmi) off Piraeus. Based on a preliminary economic analysis of the existing monohull fleet now servicing these islands, it has been found that a vessel carrying approximately 800 passengers and 80 cars and running approximately twice the speed of the existing vessels, that is, at approximately 30 knots, can be attractive to shipowners. Therefore, a vessel of such capacity was the starting point for a new, refined investigation into the technical and economic viability of the SWATH concept. Similar work was done previously for the main routes connecting mainland Italy with the island of Sardinia [1].2 As the center of manifold economic activities in Crete, Heraklion was chosen here as candidate trade route; it is about 180 nmi from Piraeus. In this paper the methodology of optimization of the main dimensions and the hull form of the vessel with respect to the least horsepower requirement in calm water and acceptable seakeeping behavior in characteristic southwest Aegean seaways is briefly described. Previous studies restricted the optimization to the wave resistance only [2,3]. However, because of the substantial frictional resistance of twin-hull vessels due to the larger wetted surface, when compared with monohulls of equal displacement, it was considered essential to optimize for the total resistance. Additionally, the seakeeping behavior at roll/pitch/heave resonances, mainly influenced by the waterplane area and its moments as well by the hydrodynamics of the wetted hull form, together with the constraint to install the required diesel machinery in the lower hulls, led to a complicated multiparametric nonlinear optimization problem with constraints. This problem has been solved in two stages in the framework of a global and local hydrodynamic optimization, as explained briefly below and in more detail in references [4,5]. Further, a systematic economic evaluation of the proposed system, in terms of economic criteria, such as NPV and RFR, showed that the concept could be quite attractive to shipowners. Based on these results, the preliminary design of a prototype SWATH vessel has been completed at NTUA, comprising the following main steps: ----determination of the main dimensions and form coefficients; ----estimation of weights of hull structure, machinery and outfitting; --computer-aided hull form optimization and ship lines drawings through standard and newly developed computer software; --hydrostatic analysis, intact and damaged stability, dynamic stability in waves, design of stabilizing antipitching fins; --hydrodynamic analysis, theoretical prediction of powering, selection of machinery and propellers, theoretical prediction of seakeeping; ----design of midship section and longitudinal structural plan (computer-aided drawings); --general arrangements of all main spaces, including machinery room (computer-aided drawings); --load-line calculation and tonnage measurements; and --preliminary estimation of construction cost, according to 2Numbers in brackets designate References at end of paper. 130

MAY 1991

figures of Greek shipyards and international manufacturers. The aforementioned steps have been accompanied by resistance and seakeeping tests of a 1:17 model of the developed prototype SWATH Aegean Queen. These experiments were performed at the NTUA towing tank in June and November 1989 and confirmed the theoretical predictions to the extent possible.

Optimization procedure The starting point for the optimization procedure, to follow, was the projected high-speed SWATH passenger/car ferry Aegean Princess [6], the main characteristics of which are summarized in Table 1. The optimization was conducted by the following three-stage procedure (see Fig. 1). First, a parametric economic study on the influences of size, transport capacity and speed was performed using economic criteria such as NPV and RFR. It should be mentioned that

Table 1 Main characteristics of high-speed passenger/car ferry Aegean Princess [6]

Box length, m Box beam, m Strut length, m Strut beam, m Lower hull length, m Lower hull beam, m Lower hull draft (overall), m Depth to car deck, m Displacement, t Dwt Passenger capacity Car capacity Speed (service), knots Main engines (in the lower hulls) Horsepower at service speed

....

56.20 28.70 42.775 2.185 53.50 4.88 4.714 8.914 1275.00 311.50 800 72 30.00 4 Pielstick 18 PA6 V280 mcr: 7200 hp each at 1000 rpm 24 360 hp

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CRITERIA

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FOR GIVEN MAIN OIMENSIONS

Fig. 1 SWATH vessel: three-stage optimization flow chart

MARINE TECHNOLOGY

the initial prototype vessel, namely, the Aegean Princess, was originally "manually" optimized for least resistance by systematic variation of its hull form, but without applying a formal optimization algorithm [7]. Second, for any given size, capacity and speed resulting from the first-stage economic evaluation, a global hydrodynamic optimization problem was solved to give the main proportions and form parameters of a SWATH with standardized lower hulls and struts. This optimization minimized the total resistance or shaft horsepower requirement for the desired underwater SWATH configuration. Third, a local form variation or refinement of the wetted hull form was performed, again minimizing the required horsepower. The resulting complex mathematical optimization problems, with constraints, were all of a nonlinear programing (NLP) type and could be solved numerically by developed computer software or standard optimization routines. The details of this three-stage procedure are given in the following.

Table 2 Main economic characteristics of high-speed passenger/car ferry Aegean Duchess

Number of passengers Number of cars Ratio passengers/car Speed (service) knots Range, naut. mi Round trips/day Operating days/year Crew size Tax rate, % Desired interest rate before tax, % Economic life, years Fuel cost, $US/t Building cost Eng~ine cost Actual freight rates for one way trip, $US/passenger Actual freight rates for one way trip, SUS/car Capacity utilization, %

700 88 7.95 30.0 360 1 330 20 50 15 15 170 current level in Greece current level in Germany 12.90 56.30 80 (annual average)

Parametric economic evaluation The economic comparisons and first-stage optimization studies were performed for a multitude of SWATH concepts and were based on the economic criteria of required freight rate and net present value, t h a t is, the net present value index (NPVI). Both criteria are based on investment and operating costs and are, hence, suitable to be used as a shipowner's criteria. To evaluate these measures of merit, a complete cost estimation model was developed for the SWATH design. Shipbuilding cost was subdivided into estimates for labor and material costs for the categories of hull and superstructure (steel and aluminum, respectively), machinery and outfitting systems. Operating expenses included fuel, crew, maintenance, insurance and miscellaneous other costs. To estimate these costs, the studies had to rely on basic cost information graciously provided by various manufacturers and suppliers of equipment. Because of the uncertainty of certain costs with respect to their actual and future validity, extensive sensitivity studies have been performed, including systematic variations of specific cost data in a specified range. However, by far the greatest economic influence in a highspeed SWATH design stems from hydrodynamic performance, engine horsepower and fuel consumption. In this study, an average of 50 percent of the building costs and 75 percent of the operating costs were derived from the installed machinery horsepower requirement. Therefore, the hydrodynamic characteristics of a SWATH design deserve prime attention. The aforementioned parametric economic evaluation of the proposed system was performed in collaboration with a team from the Technical University of Berlin under the lead of Professor H. Nowacki and in the framework of a bilateral exchange program between Greece and Germany. Details of this specific research are given in [3] and [5] and are omitted here for the sake of brevity. The main economic data and results of the performed parametric economic evaluation leading to a second prototype design (Aegean Duchess) are given in Tables 2 and 3. These results suggest that, under the assumptions made, the prototype design promises to be of definite economic attractiveness to the shipowner. F u r t h e r sensitivity studies were undertaken to substantiate these evaluations and to explore the effects of the main design parameters, as reported in more detail elsewhere [3,5].

Hydrodynamic modeling In all the economic parametric studies, the underwater configuration of the SWATH was optimized with regard to MAY 1991

Table 3 Main techno-economic results of high-speed passenger/car ferry Aegean Duchess

1048 165 132 20 173 15.9 3.85 7.48 660 75.4 11.5 50.1 3.4 0.216

Displacement, t Payload available, t Payload used (80%), t Horsepower, service speed Investment cost, M $US Operating cost, M $US/year Revenue, M $US/year Annual number of trips Required freight rate, $US/t Required freight rate, $US/passenger Required freight rate, $US/car Net present value, M $US NPVI

total resistance, based on certain assumptions relating the main dimensions of the vessel to a standardized hull form. This so-called global hydrodynamic optimization was followed by the local form optimization in the final stage of the design procedure. The hydrodynamic modeling of the resistance problem of the SWATH ship was based on the assumptions of slenderness for the hull form and of high speed for the vessel [8]. The wave resistance itself is calculated according to the thin-ship theory of Michell, as modified by Lin and Day (1974) for SWATH ships. This method is computationally quite fast and proved to be an essential tool for performing the global hydrodynamic optimization. Alternatively, an approach has been programmed based on Strettensky's theory on the wave resistance of a ship moving in a canal. This method was applied first to twin-hull vessels by Eggers and later on by Chapman. In an extension of this method, the ship can be assumed approximated by a finite number of t r i a n g u l a r or quadrilateral facets, the slope of which can be optimized to lead to least wave resistance [6]. This second method has been employed in the last-stage local form optimization procedure. The frictional resistance of the ship can be easily estimated based on the International Towing Tank Conference (ITTC) '57 correlation line. Alternatively, in the local form optimization model, the frictional resistance has been approached by surface integration of local coefficients for skin friction according to P r a n d t l ' s formula for plates in turbulent flow [6]. The pressure-viscous resistance of the vessel has been approximated using well-known formulas for axisymmetric shapes and foils according to Hoerner. For details, see [8]. MARINE TECHNOLOGY

131

The aforementioned h y d r o d y n a m i c modeling for the resistance e s t i m a t i o n of S W A T H hull forms and t h e r e l a t e d comp u t e r p r o g r a m have been tested for a v a r i e t y of S W A T H hull forms for which e x p e r i m e n t a l d a t a a r e available. In most tested cases, t h e a g r e e m e n t between t h e o r y and e x p e r i m e n t h a s been within t h e 5 percent limit. It should be r e m e m b e r e d t h a t t h e F r o u d e n u m b e r of t h e tested vessels, which a r e all slender, is well above 0.30; thus, the wave resistance theories a n d t h e r e l a t e d c o m p u t e r p r o g r a m s used seem to be more t h a n sufficient for the purpose for which t h e y have been developed. Global

hydrodynamic

optimization

The first stage, g l o b a l h y d r o d y n a m i c optimization, concerns t h e d e t e r m i n a t i o n of o p t i m a l m a i n dimensions a n d form p a r a m e t e r s of t h e lower hull and s t r u t s for least t o t a l resistance. It is hence a s s u m e d t h a t the vessel has a s t a n d a r d form with the following characteristics: 1. Lower hulls a r e of circular cross section. 2. Lower hulls consist of ellipsoidal nose, p a r a l l e l midbody a n d parabolic tail, whose lengths can be varied. 3. Lower hull axes a r e horizontal, p a r a l l e l a n d s y m m e t r i c to t h e centerplane. 4. S t r u t s lie in vertical planes, single s t r u t per hull concept. 5. S t r u t profiles have parabolic nose, p a r a l l e l midbody and parabolic tail. The lengths of nose and tail p a r t a r e equal. On t h e basis of these geometrical characteristics t h e wetted p a r t of t h e S W A T H hull can be described in t e r m s of t h e following ten p a r a m e t e r s (see Fig. 2): = lower hull length = lower hull nose length = lower hull tail length = lower hull d i a m e t e r = lower hull draft = distance between lower hull -- s t r u t length = s t r u t beam S L N (SLT) = s t r u t nose (tail) length LCF = c e n t e r of floatation LH LN LT BH TH SP LS BS

The lower hull d i a m e t e r B H is t r e a t e d as a d e p e n d e n t variable and is d e t e r m i n e d from t h e d i s p l a c e m e n t condition. The

r e m a i n i n g nine p a r a m e t e r s a r e considered as free variables and a r e optimized within t h e i r feasible limits by a n o n l i n e a r p r o g r a m m i n g method, namely, t h e T a n g e n t Search Method of H i l l e a r y [9]. A s e a k e e p i n g constraint, t h a t is, t h e avoidance of resonances in r o l l / p i t c h / h e a v e for typical seaways of t h e southwest A e g e a n Sea, is applied. The g e n e r a l conclusions from t h e global h y d r o d y n a m i c optimization studies are: 1. F o r a service speed of 30 knots (Froude n u m b e r 0.7), L H tends to t h e g r e a t e s t possible, and L N , L T and, generally, L S to the s m a l l e s t permissible values. This results in long and slender lower hulls with long p a r a l l e l parts. 2. The o p t i m u m LCF m a y be off a m i d s h i p s e i t h e r forward or aft. In practice, LCF is chosen considering t h e p l a c e m e n t of t h e s t r u t s for s t r u c t u r a l i n t e g r i t y (box support and r u d d e r location). 3. A t t h e speeds considered, a n increase in S P tends to reduce resistance, t h o u g h only g r a d u a l l y . The choice of S P is also influenced by t h e roll period constraint. 4. The required horsepower does not d i m i n i s h monotonically with an increase in TH. In fact, t h e frictional resistance does a n d t h e wave resistance m a y sometimes increase with an increase in draft. The best d r a f t can be found by t h e optimization procedure. 5. The s m a l l e s t s t r u t b e a m B S would r e s u l t in t h e least horsepower. In practice, t h e required value of B S is governed by t h e roll period c o n s t r a i n t and, in p a r t i c u l a r , by t h e clearance width required to install and access the engines in t h e lower hull. A local s t r u t b e a m of 2.6 m was finally used in this study for this reason. A reduction in this value and subsequent power savings is conceivable. 6. The dimensions of t h e deck box obviously impose cons t r a i n t s on t h e lower hull s e p a r a t i o n (SP), strut, a n d lower hull lengths. The box contains t h e c a r deck so t h a t its dimensions v a r y in integer m u l t i p l e s of car spaces. This h a s a cert a i n influence on the optimization process when the underwater hull is being a d a p t e d to a given box of fixed size. As a r e s u l t of the first-stage formal h y d r o d y n a m i c optimization, the horsepower r e q u i r e m e n t of t h e initial " m a n u a l l y " optimized prototype design, n a m e l y t h a t of t h e A e g e a n P r i n cess, could be lowered by more t h a n 17 percent. The m a i n characteristics of this second prototype design, also described in the techno-economical p a r t of this p a p e r u n d e r t h e n a m e A e g e a n Duchess, a r e given in Table 4.

\ /

Local

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form optimization

The second stage, h y d r o d y n a m i c optimization, which is a local form optimization for given m a i n c h a r a c t e r i s t i c s of t h e

lower hull and struts, relies on L a g r a n g e ' s m u l t i p l i e r method and consists of the following m a i n steps [6]: ~--,

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Main characteristics of high-speed passenger/car ferry Aegean

Duchess

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Box length, m Box beam, m Strut length, m Strut beam, m Lower hull length, m Lower hull beam, m Lower hull draft (overall), m Depth to car deck, m Displacement, t Dwt, t Passenger capacity Car capacity Speed (service), knots Main engines

7 Fig. 2 Standardized SWATH geometry sketch

132

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Horsepower at service speed

51.15 31.70 33.15 1.60 48.1 3.63 4.92 9.12 1048.0 221.5 700 88 30 4 MTU 16V 1163 TB63 mcr: 5000 hp each at 1100 rev/min 20 173

MARINE TECHNOLOGY

1. Discretization of t h e globally optimized hull form into a mesh of p l a n a r t r i a n g u l a r or q u a d r i l a t e r a l panels (see Fig. 3 as an example). 2. E v a l u a t i o n of t h e wave resistance for the discretized hull form according to S t r e t t e n s k y ' s i n t e g r a l method. Surface integrals a r e replaced by sums of e l e m e n t a l i n t e g r a l s over t h e surface of t h e panels, w h e r e a s e l e m e n t a l i n t e g r a l s over t h e panel's surface a r e e v a l u a t e d a n a l y t i c a l l y a n d depend only on t h e vertical p l a n e coordinates of t h e p a n e l ' s corner points a n d t h e velocity of t h e ship. 3. E v a l u a t i o n of t h e frictional resistance t h r o u g h surface i n t e g r a t i o n of local shear-friction stresses. The surface integral is a g a i n replaced by a sum of e l e m e n t a l i n t e g r a l s over t h e panels, t h e surface of which is expressed as a function of the vertical p l a n e coordinates of t h e panels' corner points. 4. Following 2 and 3, t h e total resistance of t h e vessel can be expressed a n a l y t i c a l l y as a function of the vertical p l a n e coordinates of t h e p a n e l s ' corner points a n d the slope of t h e panels a g a i n s t t h e vertical plane. Besides geometry, of course, t h e ship's velocity and t h e p r o p e r t i e s of t h e fluid a r e f u r t h e r p a r a m e t e r s of t h e resistance formula. 5. F o r m u l a t i o n of t h e y-derivative, t h a t is, to t h e r a t e of change of t h e c o n s t i t u e n t s of t h e resistance formula, t h a t is, to t h e wave a n d frictional resistance, in t h e transverse direction. As a result, we obtain an expression d e p e n d i n g only on the i n i t i a l form of t h e discretized ship and t h e transverse coordinates of t h e panels' nodes. 6. F o r m u l a t i o n of L a g r a n g e ' s functional with t h e following m a i n constraints: given displacement, l o n g i t u d i n a l c e n t e r of buoyancy a n d c e n t e r of floatation, least b e a m of t h e struts, a n d closed-body constraints. F u r t h e r constraints on t h e hull form can be added to t h e optimization procedure. 7. S e t t i n g up of L a g r a n g e ' s system a n d d e t e r m i n a t i o n of L a g r a n g e ' s m u l t i p l i e r s a n d t h e values of t h e t r a n s v e r s e coordinates of t h e nodes of t h e optimized vessel. F i g u r e 4 shows a locally optimized S W A T H hull form for F r o u d e n u m b e r 0.7, corresponding to a service speed of 30 knots in full scale a n d a payload c a p a c i t y equal to t h a t of the Aegean Duchess. F o r this vessel, t h e s t r u t and t h e lower hull have been locally constrained for t h e m a c h i n e r y to fit into the lower hulls. The m a i n c h a r a c t e r i s t i c s of this vessel, n a m e d Aegean Queen, a r e given in Table 5. These c h a r a c t e r i s t i c s have been modified slightly in t h e final design to account for inaccuracies in the i n i t i a l design steps. The second-stage local h y d r o d y n a m i c optimization resulted in a gain, in t e r m s of horsepower savings, of m o r e t h a n 11 percent. I t seems feasible to reduce the horsepower requirem e n t to values of less t h a n 17 000 hp, however, only if the least b e a m c o n s t r a i n t of t h e s t r u t has been removed.

Fig. 4

SWATH locally optimized hull form for Fn = 0.7, partially constrained

strutand lower hull

Table 5 Main characteristics of locally optimized high-speed passenger/ car ferry Aegean Queen

Box length, m Box beam, m Strut length, m Strut beam (max locally), m Lower hull length, m Lower hull beam (max diameter), m Lower hull draft (overall), m Depth to car deck, m Displacement, t Dwt, t Passenger capacity Car capacity Speed (service), knots Main engines

51.15 31.70 35.80 2.600 50.00 3.80 5.00 9.20 1050.00 22O.O0 750 88 30 4 MTU 16 V 1163 TB 63 mcr: 5000 hp each, 1100 rev/min

Preliminary design Main characteristics The m a i n characteristics of the projected S W A T H passeng e r / c a r ferry Aegean Queen on t h e P i r a e u s to H e r a k l i o n Crete route a r e given in Table 6. These d a t a a r e slightly different from those in Table 5 for certain practical reasons. General arrangement The g e n e r a l a r r a n g e m e n t of t h e Aegean Queen is shown in Figs. 5 and 6, which a r e c h a r a c t e r i s t i c a l l y d r a w n by m e a n s of AUTOCAD in t h e f r a m e w o r k of a computer-aided ship design procedure [10]. The ship lines of t h e Aegean Queen, d r a w n and faired by AUTOCAD [10], a r e shown in Fig. 7. The p a s s e n g e r / c a r ferry Aegean Queen provides on h e r m a i n deck a n a r e a of 51.5 by 31.7 m (1632.55 m 2) for 2 × 376 passengers a n d 80 ( a l t e r n a t i v e l y 84) p r i v a t e cars. E m p h a s i s has been placed on high comfort for the passengers (fully air-conditioned spaces, low v i b r a t i o n / n o i s e level, easy chairs, bars, lavatories, baggage room, easy e m b a r k i n g / d i s e m b a r k i n g ) - - i n a n y case, in t e r m s of comfort a n d safety, m u c h b e t t e r t h a n on a i r c r a f t or tourist class by conventional ship. Table 6 Aegean Queen principal characteristics

Box length, m Box breadth, m Strut length, m Strut breadth, m (locally) Lower hull length, m Lower hull diameter, m (locally) Draft, m Side depth to main deck, m Displacement, t Dwt, t Number of passengers (one class) Number of cars (one deck) Speed, knots Main machinery power (MCR)

Fig. 3 SWATH globally optimized hull form (SWATH--NTUA 1; initial ship)

MAY 1991

Gross tonnage (intern.) Net gross tonnage (intern.)

51.5 31.7 37.6 2.60 50.0 3.80 5.00 9.46 1060 226 752 8O (+ 4) 30.0 MTU 16V 1163 TB 63 mcr 5000 PS each 1100 rev/ min 2544 grt 763 nrt

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133

NTIIA A T H E N S

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Side profile of passenger/car ferry Aegean Queen

MAY 1991

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Passenger/car deck of high-speed SWATH Aegean Queen

MARINE TECHNOLOGY

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Fig. 7 Lines of Aegean Queendrawn and faired by AUTOCAD [10]

The cars can easily embark/disembark through a stern ramp and the drivers can enter the passenger spaces through side doors. During loading/discharging the vessel will be ballasted, so that the trim and draft are acceptable as required by the specific port conditions. In case of emergency, the passengers can move to the upper deck through two sets of stairways, one located in the center of the passenger spaces and the second one astern. Alternatively, emergency exits on the ship's sides can be arranged. In the upper deck (Fig. 8), there is located the bridge, rescue equipment and simple accommodation for 25 crew members. An alternative design, not shown here, provides space for additional passengers on the upper deck without significant changes in the overall characteristics of the projected vessel. The safety and equipment standards of the ship comply with the regulations of relevant Greek authorities, considering exceptions given for unconventional twin-hull vessels of the catamaran type, as to the size of anchoring equipment and other items. Propulsion

system

and machinery

The selected propulsion system consists of four diesel engines of type MTU 16 V 1163 TB 63, each developing a maximum continuous rating power of 5000 hp at 1100 rpm. The engines are installed in line, one pair per hull, and drive, through a Renk reduction gear, two 5-bladed controllablepitch Escher-Wyss propellers, of diameter 3.42 m and working at 250 rpm. The machinery arrangement of Aegean Queen is sketched in Fig. 9. The hull is sized so that removal of the engines through the strut is possible when required for service, though, according to the engine manufacturer, this is

Fig. 8 Upper deck arrangement

MAY 1991

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~

Machinery arrangement

likely to happen only three times during lifetime of the ship (15 years). The machinery room is longitudinally subdivided by a watertight bulkhead to fulfill the damaged stability criteria. Machinery personnel can communicate through a watertight door between the two compartments. It is clear that, since there are 2 × 2 engine compartments, the auxiliaries of each engine-pair can be designed so that they can serve either room in case of damage or flooding. Electric power is supplied by two MTU 6V 396 TB33 electric power units, providing an electric power of 440 kW each (one is reserve), that is, sufficient to support all auxiliary systems of the vessel (cooling of engines, ballast, etc.), including the full air-conditioning of the ship. These units are arranged, one in each lower hull, in the compartment astern of the forepeak of the vessel. The machinery rooms are equipped with remote control for all equipment located in the lower hulls. In addition, the main machines and auxiliaries should be remotely controlled from the bridge. The vessel should have a relevant class for fully automated ships with 24 hr unattended machinery room. Estimation

of weights

The weights of the projected ship have been estimated, to the extent possible, according to detailed data for the structure, machinery and outfitting. As for the structural part, the weights of the scantlings and plates used are taken according to the midship sectional plan, shown in Fig. 10. Note that the hull material of lower bodies, struts, sponsons and box, up to the main deck, is higher tensile steel (HY 80), whereas the superstructure is aluminum alloy (A1 5O86). The machinery equipment weights could be determined quite exactly through the given data of a collaborating diesel engine manufacturer, whereas the outfitting weights stem from detailed analysis of the outfitting of the projected vessel [11]. Finally, the estimated deadweight of the vessel includes 55 t of fuel and 15 t of provisions, whereas the payload (passengers/cars) is about 145 t. The vessel has a reserve of about 35 t for packed cargo or water ballast. Table 7 gives the main weight groups of the Aegean Queen. It should be stressed that a careful weight analysis of a SWATH-type ship is essential for her design, because of the small waterplane area and the corresponding low values of TPI and MCT (see hydrostatics).

Fig. 10 Midshipsection

MARINE TECHNOLOGY

135

Table 7

Aegean Queen weight groups

12.0

--

Weight Group

Weight, t

Structure Machinery equipment Outfitting Dwt Total

LCG, m

KG, m

517 000 212 000 105 000 226 000

25.740 16.110 30.106 32.321

7.829 2.330 10.346 9.418

1 060 000

25.650

7.317

LIGHT

Hydrostatic analysis of the present vessel has been performed by use of Archimedes software [12]. Typical righting arms of the projected ship are shown in Fig. 12. Characteristically, the metacentric height of the Aegean Queen is at the departure condition, GM = 12.206 m, and the range of stability is about 78 deg. The vessel can be proven to fulfill the Safety of Life at Sea (SOLAS) criteria for passenger ships as to intact and damaged stability [12]. Especially, as to the damaged stability, it can be simply shown t h a t the watertight box has sufficient buoyancy to carry the whole superstructure, in case of need. The ship complies with the rules for "two-compartment ships," with the worst case being the simultaneous flooding of the two-compartment machinery room, causing a significant heel and trim of the ship by the

Lhull = 2 . 9 4 1 m L..... 2.211 m

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