The economic feasibility of large cargo-carrying catamarans

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L a b . V . S c h e e p s b o u v ^ l u U ! ^

T e c h n i s c h e A R G H I E H

j AUA Paper

No. 69-394

THE ECONOMIC FEASIBILITY OF LARGE C A R G O - C A R R Y I N G C A T A M A R A N S

by

JAMES H . ROBINSON

General Dynamics Corporation

Quincy, Massadiitaètts

V O O R

AIAA

2nd Advanced Marine Vfihicies

and Propulsion Meeiing

SEATTLE, WASHINGTON/MAY 21-23, 1969

nm pvUicetien righfi raiarvsd by American Inititut« of Aarenaullct (md Ailranoutici. 1390 Aviriv« öf Rm Aoisricot, New York, N. t. IQOW.

**Abilrecl* may b* pybllihad wilhaul ptrraiiilon if cradit it B<y*? 'o author and le AIAA. (Pricei AIAA Membar %\S0. Nonmember $US}**

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T H E E C O N O M I C F E A S I B I L I T Y O F L A R G E G À R G O - C A R R Y I N G C A T A M A R A N S * J a m e s H . R o b i n s o n , C h i e f N a v a l A r c h i t e c t , A d v a n c e E n g i n e è r i n g G e n e r a i D y r i a m i c s / Q u i n c y D i v i s i i ä i ( ^ i n c y , M a s s a c h u s e t t s A b s t r a c t r _{T h e e c o n o m i c potential o f c a t a m a r a n s v s . '} conventional h u l l s i s presented f o r L O / L O and R O / R O ç o n i i g u r a t L o n s c o v e r i n g deadweights £ r o m

10,000 t o 2 5 , 0 0 0 t o n s , route lengths f r o m 2 , 0 0 0 to 7,000 m i l e s , a n d speeds £com 18 to 28 knots. M a t h e m a t i c a l l y r e l a t e d s e r i e s of s h i p s axe d e f i n e d , and a c q u i s i t i o n costs estimated. O p e r a t -ing costs and revenues a r e e s t i m a t e d , depend-ing on a s s u m e d operating p r o f i l e s . E c o n o m i c f i g u r e s of m e r i t a r e c o m p a r e d t o show quantitatively how the types c o m p a r e , l l x e c a t a m a r a n s a r e shown to be about 13 to 44 percent l e s s p r o f i t a b l e than the equivalent conventional h u l l s , and, in g e n e r a l , f o r both types, l a r g e r s i z e s and longer routes a r e the most p r o f i t a b l e . T h e speed trends a r e opposite f o r the two t y p e s , w i t h slow speeds m o r e d e s i r -^ a b l e f b r the c a t a m a r a n s a a d h i g h e r speeds b e t t e r / ^ j j o T the conventional h u l l s . [ Introduction T h e p a r a m e t r i c studies r e p o r t e d in t h i s b r i e f p a p e r a r e a i m e d at a s s e s s i n g the economic f e a s i b U i i ^ o f l a r g e c a r g o - c a r r y i n g c a t a m a r ^ i s , w i t h s p e c i f i c r e f e r e n c e t ô l i f t - ( m / l i f t - o f f container-s h i p container-s , and r o l l - o n / r o i l - o f f t r a i l e r container-s h ^ container-s . One ä i j e c t l v e i s to show w h e r e i n the s p e c t r u m of a s s u m e d deadweights, « i d a r a n c e & and s p e e d s , the c a t a m a r a n shows the most p r o m i s e . T h i s i s done b y d i s c u s s i n g how catamarans c o m p a r e e c o n o m i c a l l y with conventional s h i p s , o v e r a range of c a r g o deadweights f r o m 10,000 to 2 5 , 0 0 0 t o n s , a range of endurances f r o m 2 , 0 0 0 to 7,000 n a u t i c a l m i l e s , and a range of speeds ùrom 18 to 28 knots.

T h e w o r k r e p o r t e d h e r e r e p r e s e n t s p a r t of the W r e s u l t s o f a m o r e es^enslve study made under

contract with the M a r i t i m e A d m i n i s t r a t i o n . T h e l a r g e r study included a r e v i e w of c a t a m a r a n technology, an a n a l y s i s of c a r g o handling methods, and e x p e r i m e n t a l and t h e o r e t i c a l ctHiclusions of p o w e r i n g and motions i n w a v e s .

G e n e r a l A p p r o a c h Methodology

In p r i n c i p l e , the methodology employed in t h i s study i s r e l a t i v e l y s i m p l e and s t r a i g h t f o r w a r d . It i s m a i n l y a questicm of d e t e r m i n i n g the b a s i c design p a r a m e t e r s of a s e r i e s of catamaran h u l l s and equivalent conventional s h i p s - - f o r the types to be c o n s i d e r e d — and d e t e r m i n i n g t h e i r a c q u i s i -tion and o p e r a t i n g cpsts together with e a r n i n g

c a p a b i l i t i e s . T h e s e l a t t e r t h r e e f a c t o r s a r e t h a i c o m b i n e d i n v a r i o u s w a y s to f o r m e c o n o m i c f i g u r e s of m e r i t w h i c h a r e then plotted to show t r e n d s w i t h deadweight, endurance, speed and other s e c o n d a r y f a c t o r s .

In d e f i n i n g the s e r i e s qf s h i p s , c o n s i d e r a t i o n . has been g l v e a to h i s t o r i c a l data c o n c e m i n g h u l l p r o p o r t i o n s , and the extrapolation of c u r r e n t d e s i g n concepts into v e r y U r g e s i z e s . F o r e s t i -m a t i n g ship design p a r a -m e t e r s f o r Ôie c a t a -m a r a n s e r i e s , h o w e v e r , h i s t o r i c a l data has not been a v a i l a b l e f o r the t y p e s and s i z e s of ships e n -v i s i o n e d , and c o n s i d e r a b l e design de-velopment — w i t h s p e c i a l em^diasls on s t r u c t u r a l weights — has been r e q u i r e d . E v e n f o r the coiivehtlonal s h i p s , tbe s i z e s at the h l g ^ ^ d of the s p e c t r u m a r e w e l l above c u r r m t p r a c t i c e .

Once h a v i i i g d e f i n e d the s e r i e s o f s h i p s to be c p m p a r e d , the hext t a s k i s to estlmsUe the

a c q u i s i t i o n cos t s of the d i f f e r e n t candidates. H i e a p p r o a c h h e r e i s to u s e e x i s t i n g and accepted b a s i c design c r i t e r i a , e. g . , t h é r e l a t i o n s h i p of s t e e l weight t o cubic n u m b e r , m a c h i n e r y weight v s . h o r s e p o w e r , and c o st s of e r e c t i n g s t e e l and i n s t a l l i n g m a c h i n e r y and o u t f i t t i n g equipment a s c u r r e n t ^ a v a i l a b l e .

T h e next t a s k Is to estimate the pperating c o s t s o f t h e candidates o v e r ü i e i r l i f e t i m e s , w h i c h has -been a s s u m e d to b e ^ t w a i t y - f i v e y e a r s , w i t h np s c r a p value at the end of ûat p e r i o d . The { d e r a t -ing c osts have been n o r m a l i z e d to an equal amount each y e a r o v e r the l i f e t i m e o f the ship f o r both c a t a m a r a n and conventional s h i p , and, i n g n i e r a l , insurance r a t e s , p o r t c o s t s , c r e w wages and o ü i e r f a c t o r s of o p e r a t i n g c c s t s a r e c o n s i d e r e d tp be a s s e s s e d on the s a m e bases f p r the twp types

of s h i p s .

The t h i r d U s k i s to d e t e r m i n e the g r o s s r e v e -nue, and t h i s has been estimated a s im annual r e t u m based oa the n u m b e r o f tpns c a r r i e d between p o r t s , the distance between those p o r t s , an a s s u m e d f r e l e ^ t r a t e , and tiie n u n ü r e r of t r i p s p e r y e a r .

F i n a l l y , i n p r d e r to c c m p l e t e the p i c t u r e on methpdplpgy, the v a r i o u s f a c t o r s a r e combined i n s e v e r a l economic f i g u r e s of m e r i t w h i c h w i l l be d i s c u s s e d In sui>sequent p a r a g r a p h s . T h e s e p e r -m i t c o -m p a r i s o n s between types f o r a g i v ^ s e r v i c e and w i t h i n type f o r d i f f e r e n t v a r i a t i o n s — s u c h ä s speed. • W o r k suppprted by M A R A D Cpntract M A 4318

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7 - ; L . , : ^ 7 - ' * * r . - V Ä

Scope of A n a l y s i s

^ The types Pf s M p s considered r e s u l t e d f r o m thé requirement that Übe study c o n s i d e r s u n i t i z e d c a r g o s y s t e m s , and the types chosen s i m p l y r e p -resent c u r r e n t and f u t u r e t r e n d s in ü i i s c a t e g o r y .

The c a t a m a r a n ' s i n h e r e n ü y l a r g e s t a b i l i t y a l l o w s a complete load of c o n t a ü i e r s to be stacked on d e c k , 'but P o l y f o r the L O / L O c o n f i g u r a t i o n . F o r the r o l l - O D / r o l l - P 0 c p n f i g u r a t i o n , separate decks a r e needed f o r each l a y e r of v e h i c l e s , and c o n -s i d e r a b l y m o r e -s u p e r -s t r u c t u r e and h u l l weight i -s Ü i e r e f o r e r e q u i r e d . A general approach to e c c n p m l c a n a l y s i s m u s t a l s c be v e r y s p e c i f i c In c e r t a i n b a s i c a r e a s . One s u c h a r e a c o n c e m s s y s t e m d e f i n i t i o n . C o n s i d e r a -t i o n pf a l l aspec-ts of -the -t r a n s p c r -t a -t l p n s y s -t e m f r p m consignee tp consignor i s obviously beyond the scope p f t h i s Investigation, s i n c e the study i s tp a c c e s s the m e r i t s of a catamaran not a t r u c k o r barge s y s t e m . In a m p l i f i c a t i o n of the f o r e g o i n g , c e r t a i n c o s t s , c o m m o n to either ^ ^ c a t a m a r û o r cpnventtpnal h u l l s y s t e m s , Iiave ^ ^ b e « i e l i m i n a t e d . F o r e x a m p l e , ownership pf

the t e r m i n a l s Is d i s r e g a r d e d , and an a p p r c ^ r i a t e charge made tp the ship f o r loading p r ù n i p a d î n g c a r g p . O w n e r s h i p o f c m t a i n e r s p r t r a i l e r s i s e l i m i n a t e d f r p m the study and a l s o no charges a r e made tP the ship p p e r a t p r f p r c o n s c l l d a t l h g l e s s than & d l c o n t r e r l o a d s . T h e accent lias been on e x p r e s s o p e r a t i o n , and a r a t i o n a l e i n d i c a t i n g the e f f e c t s o f m u l t i p q r t pperaUon w a s develpped. E s s e n t i a l l y , addittonal port ctuurges and t i m e i ^ e n t i n i n t e r p o r t p a s s a g e s , w h i c h do not c o n t r i b -ute to a d d i t i o n a l r e v e n u e , c a n only degrade tiie

e c o n o m i c a l p e r f o r m a n c e f r o m the e x p r e s s b a s e -l i n e .

Economic- C r i t e r i a

T h r e e d i f f e r e n t f i g u r e s of m e r i t have been c o n -s i d e r e d in thi-s an-sily-sl-s; a l l have -s o m e -standing, but a l l have t h e i r î l m i t a t l p n s . It Is f e l t , h o w e v e r ,

that t h e i r u s e w i l l s i f t out the r e l a t i v e m e r i t s pf the d i f t e r e n t types of ships w h i c h a r e compared In this study. T h e r a m i f i c a t i o n s of f i n a n c i n g a r e considered beyond the scppe o f this study and a s t r a i g h t f p r w a r d assumption that the shipowner i n ' v e s t h i s own money i s made. A l s o , 'the ship l i f e

-t i m e Is -taken a-t -t w e n -t y - f i v e y e a r s and s -t r a l g h -t l i n e d e p r e c i a t i o n a s s u m e d wtUi n p s c r a p v a l u e at ü i e end of l i f e . T ^ e s a r e reckcmed at 52^J~an<^r f o r the r e q u i r e d f r e i ^ i t rate and net p r e s e n t value f a c t p r s , a 12% r e t u m o r intgivegtlcate. i s a s s u m e d .

One o f the f a c t o r s considered i s c a p i t a l r e -c o v e r y f a -c t o r ( C R F ) the u s e of w i i i -c h i s made p o s s i b l e by the assumption that revenues a r e p r e d i c t a b l e , w h i c h f o l l o w s f r o m the assumption of û-eight rate and l o a d f a c t o r in these analyses. The c o i t a l r e c o v e r y f a c t o r used i s that.applying to the a f t e r t a x c a s e , and i s denoted by C R F ' . O s e p f the advantages of the C R F approach i s that an interest r a t e does not have to be a s s u m e d , b e -cause i n f a c t the c a l c u l a t i o n l e a d s to the internal r a t e o f r e t u r n , and the percent r e t u r n Is

inde-pendent o f the n u m b e r of s h i p s w h i c h have to b e bpiight tp m a i u t a i n a s p e c i f i e d s e r v i c e .

R e q u i r e d f r e i g h t r a t e ( R F R ) Is another c r i t e r i o n . u s e d , and i n this a n a l y s i s the r e q u i r e d f r e i g h t

r a t e computed Is that r a t e w h i c h w o u l d r e s u l t i n a 1 2 ^ r e t u m on the investment a f t e r taxes.

F i n a l l y , net p r e s e n t value ( N P V ) has been i n -cluded i n these c p m p a r i s o n s and i t i s s e n s i t i v e tp the number p f ships r e q u i r e d to m a i n t a i n a c e r t a ù i

s e r v i c e . In the c a s e p r e s e n t e d , it i s the n u m b e r r e q u i r e d to m a i n t a i n w e e k l y s a i l h i g s . In t h i s a n a l y s t s , the a f t e r tax c a s e i s t a k e n , w h i c h means that N P V i s net annual r e t u m a f t e r tax, a l l o w i n g c r e d i t f o r d e p r e c i a t i o n , d i v i d e d by an a f t e r tax c a p i t a l r e c o v e r y f a c t o r , a l l m i n u s the a c q u i s i t i o n cost. In spme c a s e s , t h i s v a l u e c o m e s put z e r p , w h i c h s i m p l y means the a s s u m e d i n t e r e s t r a t e i s the a c t u a l r a t e of r e t u r n . Development of C a t a m a r a n S e r i e s G e n e r a l A p p r p a c h T h e c a t a m a r a n s e r i e s developed f o r these a n a l y s e s a r e iKised on p a i r s of s y m m e t r i c a l h u l l s , whose p r o p o r t i o n s and f o r m c p e a i c i e n t s a r e r e

-lated to length and speed. They a r e not e x t r e m e i n any w a y , but Uie length to b e a m r a t i o s a r e ahput t w i c e what the equivalent conventional m o n o -h u l l would -have. T -h e p a r a m e t e r s v a r y s m o p t b l y o v e r the r ^ g e s of deadweights, speeds and &i-d u r a n c e s c o n s i &i-d e r e &i-d . W i t h i n Üie l i m i t s of &i-d e c k

a r e a and yolume r e q u i r e d for the p a y l o a d , the ^ h u l l s p a c i n g . i s a c o m p r o m i s e t o a v p i d e x c e s s i v e f added r e s i s t a n c e (with h u l i s tpo c l P s e together)

and e x c e s s i v e s t m c t u r a l weight (with h u l l s tcp f a r 1 apart).

T y p i c a l Designs

T h e L O / L O container catamaran i s c o n i p l e t e l y , d e c k - l o a d e d and containers need be stacked

a c t u a l l y no m o r e than about 4 h i g h , w h i c h would be the c a s e f o r the l a r g e s t s h i p w i t h the lowest speed, whereas a s t a c k height of 2 would s u f f i c e f o r the s m a l l e s t ship w i t h the highest speed. L a y -outs w e r e made to c o n f i r m that the deck a r e a s would be s u f f i c i e n t f o r the c a r g o , o r the c o n t a i n e r s .

F o r the R O / R O t r a i l e r s b i p , s u p e r s t r u c t u r e d e c k s a r e n e c e s s a r y to accommodate the v e h i c l e s w h i c h a r e r o l l e d on at each l e v e l , with no need f o r r a m p s w i t h i n the s h i p . A g a i n , layouts w e r e made tp d e t e r m i n e that the payload could be c a r r i e d .

F i g u r e s i and 2 show t y p i c a l arrangements f o r the twp types pf catamarans d i s c u s s e d i n t h i s paper.

Development of Conventional S e r i e s Genieral A p p r o a c h

A s i n the c a s e pf the c a t a m a r a n s e r i e s , the cpnventional s h i p s e r i e s w e r e devielpped having reasonable proportions i n accordance with p r e s e n t day p r a c t i c e . A s i d e f r o m r e l a t i n g proportions and c o e f f i c i e n t s to length and speed, b e a m b e c a m e another v a r i a b l e because of i t s r e l a t i o n s h i p to

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m

21

DECK LOADED

LO/LO CONTAINER CATAMARAN

TYPICAL ARRANGEMENT

F i g u r e 1 { W T - 1 7 . 5 0 0 T O N S « O ' C O N T A H E R S . (F 3 HIOH = 8 0 4 IF 4 HIGH = 8 » 30 M 90 UB P U U I A T 6 2 - L E V E L

RO/RO CATAMARAN

TYPICAL ARRANGEMENT

857-40' TRAILER SPACES

F i g u r e 2 ï r a n s v e r s e s t a b i l i t y , â n d a unk[ue s o l u t i o n had to be develpped f p r e a c h s h i p d e s i g n . A c o n s i d e r a -tion of the r e q u i r e m e n t s f o r the oonven-tional m o n o h u l l s e r i e s leads to the c o n c l u s i o n that the stiips tend to foe vplume l i m i t e d , and p r i s m a t i c c p e f f i c i e n t s a r e t h e r e f p r e Ipwer l i i a n might n p r m a l l y be expected f p r the deadweights and s p e e d -l e n g ü i r a t i p s invo-lved. The L O / L O s h i p s a r e designed s o that no b a l l a s t i s r e q u i r e d i n the f u l l load condition, but t h i s i s r e l a x e d f o r the R O / R O c p n f i g u r a t i o n .

T y p i c a l D e s i ^

I t i e c ö n f a l h é r s h i p i s f a i r l y t y p i c a l of e x i s t i n g conventional designs althpugh t h è a s s u m e d s e r i e s go f a r beyond the s i z e s of e x i s t i n g s h i p s . The

u s u a l c e l l u l a r s t r u c t u r e to accommodate c o n t a i n

-so -so W IZO

e r s below decks i n s t a ^ s , p l u s containers stacked e v e r hatches a r e a s s u m e d . F p r the R O / R O t r a i l e r s h i p no cargp i s a s s u m e d to be stowed b e -low the -lowest continuous deck (second deck) and a l l Uie mactiinery i s below that deck. The c a r g o decks a r e t h e r e f o r e c o m p l e t e l y open f r o m one end to the other to f a c i l i t a t e the leading and unloading of the s h i p . A s i n the case f o r the catamarans, layouts w e r e made to j u s t i f y the s p a c e r e q u i r e d f o r the pay l o a d s . F i g u r e s 3 and 4 show t y p i c a l

designs f o r the L O / L O c o n t a i n e r s h i p without c r a i i e s and the R O / R O t r a i l e r e ^ i p .

D e f i n i t i o n of C o m p a r i s p n M a t r i x

In the complete p a r a n i e t r i c analyses made a s p a r t of the o v e r a l l s t u t ^ , some 200 d i f f e r e n t s h i p

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- - " r - a - » , . . . ff... ••-•.'••i^"-,- ri-'^^'''^;; „'>f f .

L O / L O GONTAINERSHIP

TYPICAL ARRANGEMENT

FOR 17,500 T DWT

F i g u r e 3 0 25 so TS 100

fMtnU. UPPER DECK

RO/RO TRAILERSHIP

TYPICÄL ARRANGEMENT

FOR 17,500 T DWT

F i g u r e 4 t m LOAOIIIC P/S IS so TS too designs a n d / o r p p e m t i P n a l c p n s t r a i n t s w e r e cpnsidered f r o m the s h i p c o n f i g u r a ü p n and economic p e r f o r m a n c e standpoints. The i n v e s t i -E^tion of b a s i c v a r i a t i o n s i n t y j w , s i z e , speed, and range was supplemented by studying the e f f e c t s <A c r a n e s p n o r o f f the s M p s , d i f f e r e n t h u l l s p a c -i n g s , d -i f f e r e n t load f a c t o r s and d e l a y s , and the use of a l u m i n u m s h i p s t r u c t u r e s . T h i s paper w i l l be concerned p r i m a r i l y with the b a s i c c o m p a r i -sons of s t e e l L p / L O and R Q / R Q c a t a m a r a n s and conventipnal m p n p h u l l s .

B a s i c D e s i g n Inputs

T p generate s u f f i c i e n t i n f p r m a t i p n on both the c a t a m a r a n s and ccnventicmal s h i p s f o r c p m p a r a -t l v e p u r p o s e s , -twp separa-te compu-ter p r o e m s have b e f f l developed; F p r a given set pf design r e q u i r e m e n t s each p f these cpmputer p r p g r a m s

pne f o r the c a t a m a r a n and the other f o r the c o n -ventional s h i p - evaluates and p r i n t s out the r e q u i r e d v e s s e l ' s c h a r a c t e r i s t i c s , weights and estimated a c q u i s i t i o n costs. In addition, annual operating costs and g r o s s revenues on e:q)ress and m u l t l p o r t routings a r e determined, and used along w i t h other f a c t o r s to f h i d capital r e c o v e r y f a c t o r s , r e q u i r e d f r e i g h t r a t e s and net present v a l u e s .

R e s u l t s of Ship Generation

B r i e f p a r t i c u l a r s of the catamarans and c o n ventional ships developed to s a t i s f y the c o m p a r i -sons d i s c u s s e d i n t h i s paper a r e g i v o i i n T a b l e s 1 through 4. O n l y the s m a l l e s t , the l a r g e s t ahd the m e d i u m s i z e s h i p a r e c o n s i d e r e d f o r the L O / L O (without c r a n e s ) and R O / R O catamarans and conventional s h i p s . It should be npted that

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T a b l e s

T a b l e 4

the qupted d i s p l a c e m e n t s and d e a d w e l ^ t s r e f e r tp the f u U - l c a d cpndition, but the o p e r a t i n g c o s t s and g r o s s revenues r e f e r t o a 70% l o a d f a c t o r , e s ç p r e s s s e r v i c e o p e r a t i o n , w i t h an a s s u m e d h e i g h t r a t e A m i l l s p e r measuremrait ton n a u t i c a l m i l e . ;

R e s u l t s pf E c p n p m l c C p m p a r i s o n F i g u r e ^ 5 through 16, j t r e s e n t e d i n t h i s b r i e f p a p e r , c o n d u i s e some of the m a j o r r e s u l t s into clxarts w h e r e c p n ^ a r i s c m s between types can be r e a d i l y ^ a w n . T h r e e f i g u r e s give the c a p i t a l r e -c p v e r y f a -c t o r a f t e r t a x e s , three give îQie r e q u i r e d f r e i g h t r a t e , tp e a r n 12% a f t e r ta:£es, three give the net p r e s e n t value a f t e r taxes f o r a f l e e t of . s h i p s r e q u i r e d to m a i n t a i n w e e k l y s a i l i n g s , and t h r e e g i v e a c q u i s i t i o n c o s t s f o r t h i s s a m e ü e e t . H i e s m a l l e s t , l a r g e s t , and m e d i u m s i z e ships i n each case a r e p l o t t e d , but f o r s e v e r a l speeds S P ü i a t the e f f e c t pf speed can be a c c e s s e d r e a d i l y & p m the f i g u r e s . W h e r e only a s m a l l segment of a c u r v e appears , additiohal sppts a r e npt a v a i l -able but the t r e n d s p a r a l l e l the » I j a c e n t c u r v e s f c r s i m i l a r types.

D i s c u s s i o n o f R e s u l t s

A s a p r e l u d e to this s e c t i o n It should be noted that the w o r d optimum does not ^ p e a r and no c l a i m s axe made that the ship s e r i e s developed could not be made better w i t h s u c c e s s i v e design , i t e r a t i o n s . L i k e w i s e , the choice of economic p a r a m e t e r s could be debated.

Ships G e n e r a l

T h e ship s i z e s f o r the c a t a m a r a n a r e l a r g e , being P v e r 1,000 feet in length f p r the l a r g e s t deadwelght/endurance/speed combination, and being only s l i g h t l y below 600 feet f o r tile s m ^ l e s t .

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defined by a Rabe* c o e f f i c i e n t , and f a l l s within the range of . 07 to . 15.

It was noted p r e v i o u s l y that each conventional L O / L O s h i p achieved a balance between weight and v o l u m e , s o that i n d i v i d u a l s h i p designs r e -sulted f p r e a c h set pf r e q u i r e m e n t s . It may be npted a l s o tha.t hi the l a r g e s i z e s the conventipnal s h i p s a r e equally a s long as the c a t a m a r a n , but d i s p l a c e m e n t and p o w e r s a r e c o n s i d e r a b l y l e s s . T h e R O / R O conventional ship e s s e n t i a l l y r e s u l t s In t h r e e b a s i c h u l l s , since they a r e volume l i m i t e d , but w i t h v a r y i n g power p l a n t s , f u e l capiaci t capiaci e s , and b a l l a s t c a p a c capiaci t capiaci e s to p r o v capiaci d e the r e q u capiaci r -ed s o l u t i o n s . T h e s h i p s a r e a p p r e c i a b l y l a r g e r than the containerships and they a r e a l s o m o r e conventional a s f a r a s Iraigth to b e a m r a t i p s a r e c p n c e m e d .

E c o n o m i c C o m p a r i s o n

T h é r e s u l t s of the c o m p a r i s o n s of the b a s i c s h i p types o v e r the ranges of deadweights, e n d u r a n c e s , and speeds c o n s i d e r e d , s e e m ^ l r l y s e l f -evident f r p m the s e c t i o n on r e s u l t s . It may be pointed out, h o w e v e r , that f o r t h e c o n t a l n e r a h ^ L O / L O c o n f i g u r a t i o n , the cpnventional s h i p Is m a r k e d l y s u p e r i o r tP the c a t a m a r a n , whereas f p r the t r a i l e r s h i p R O / R O c o n f i g u r a t i o n the gap i s n a r r o w e d a p p r e c i a b l y . T h i s i s due m a i n l y to the f a c t that the conyentionaL s h i p i s degraded

p e r c ë i t a g e - w i s e m u c h m p r e than the c a t a m a r a n . In both c a s e s , h o w e v e r , the R O / R O s h i p i s i n f e r -i o r to Its L O / L O counterpart. The gap between the catamaran and conventional s h i p i s n a r r o w e s t f o r the s m a l l e s t , ahprteat r a n g e , s l o w e s t c o m -bination. T h e c a p i t a l r e c o v e r y H c t p r I C K J " ) and r e q u i r e d f r e i s t r a t e ( R F R ) c p m p a r l s p n s shPw exactly the s a m e t r e n d s , a s should be the c a s e . The net present value ( N P V ) c u r v e s r e p r e s e n t v a l u e s d e r i v e d f o r the n u m b e r s o f s h i p s r e q u i r e d to maintain w e e k l y s a i l i n g s . T h e a c q u i s i t i o n co s ts c u r v e s a l s o r e p r e s e n t the total Investment n e c e s s a r y f o r the f l e e t of s h i p s needed to m e e t w e e k l y s a i l i n g s . T h e n u m b e r s pf s h i p s can be d e t e r m i n e d by c p m p a r i n g f l e e t cpsts w i t h p e r s h i p a c q u i s i t i o n cpsts given p r e v l p u s l y hi T a b l e s 1 through 4. T^ie r e s u l t s i n t h i s s u m m a r y a r e f o r e x p r e s s s e r v i c e ; m u l t l p o r t . s e r v l c e ' a l w a y s has the .effect of degrading tJie operation. The ma.in

r e a s o n Is that m p r e t i m e i s spent entering porto and b e i n g d e l a y e d , w h i l e revenue i s generated based on a m i l e a g e l e s s than the t o t a l t r i p length.

E f f e c t of Deadweight. M o s t of the r e s u l t s had p r e v i o u s l y been plotted on a deadweight b a s i s , but i n a l l c a s e s the trends w e r e i n c r e a s i n g p r o f i t a -b i l i t y w i t h i n c r e a s i n g deadweight. T h i s i s a s would be expected - the economy of s i z e i s h a r d to beat. À l a r g e c a t a m a r a n could be m o r e p r o f i t -able than a s m a l l cpnventlpnal s h i p but that i s npt a v a l i d c p m p a r i s p n .

E f f e c t of E n d u r a n c e , la most c a s e s the l o n g e r the endurance - w h i c h i n t h i s a n a l y s i s i s tanta-mount to;.speoifying m o r e t i m e

spei^

e a r n i n g r e v -enue - the g r e a t e r the p r o f i t a b i l i t y . The 2000 m i l e c a s e s w e r e always Uie l e a s t p r o f i t a b l e , but f o r the io/lX> conventional s h i p the 7000 m i l e case showed s l i g h t l y l e s s {nvf Itabillty

than

the 4500 m i l e c a s e , fhe explanation f o r t h i s i s not r e a d U y apparent, but i n a z ^ event i t i s v e r y s n m U . T h e e x t r a t i m e spent e a r n i o g revenue ap-. p a r e n t l y dpes nbt o f f s e t the e x t r a expense of pp-e r a t i n g a s l i g h t l y l a r g pp-e r s h i p .

ECfect pf Speed. The graphs presented a r e plptted on the b a s i s of speed, so that the trends a r e r e a d i l y apparent. A s w i t h other trends, the slopes a r e not d r a m a t i c , ahd i n f a c t speeds,

Pther

than what appear to be o p t i m u m , could w e l l be j u s t i f i e d f p r o ü i e r r e a s p n s .

The r e s i s t a n c e penalty taken b y the c a t a m a r a n shows i n the c u r v e s , because the c a t a m a r a n should always be d r i v e n at l e s s speed than i t s conventional counterpart i n o r d e r to m i n i m i z e the p r o f i t a b i l i t y gap. À s would be expected i t pays to d r i v e the l a r g e r s h i p somewhat & s t e r .

S e n s i t i v i t y A n a l y s i s

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w h i c h afiTect coats p r revenue p n î y w i ü i o u t a f -f e c t i n g s h i p i s s i z e p r t r ^ i s per y e a r - m a y be stodied d i r e c t l y threugh t h e i r i m p a c t p n the C R F f p r m u l a t i p n . E x a m p l e s would b e : s t e e l c o s t p e r ppund, c r e w wages, f u e l c o s t p e r b a r r e l , p o r t c h a r g e s ànâ f r e i g h t r a t e s .

O t h e r cpsto a f f e c t p r p f l i a b i l i t y b y a f f e c t i n g tte-pperation of a ship, i n t e r m s of cargo c a r r i e d o r t r i p s p e r y e a r . These a r e most r e a d i l y a s s e s s e d through r e r u n n i n g o f the s h i p d e s i g n p r o g r a m -but w i t h s h i p c h a r a c t e r i a t i c s a l r e a d y known, hence a g r e a t savings i n t i m e . E x a m p l e s would be: load f a c t o r , c a r g o handling t i m e and delay i n p o r t .

T h e n there a r e f a c t o r s w h i c h a f f e c t s h i p design, ahd t h e r e f o r e a c q u i s i t i o n cost, and operating cost and probably g r o s s revenue. These must be a s s e s s e d through running of the s h i p design p r o -g r a m - but i t i n v o l v e s r e d e s i -g n pf the b a s i c s h i p , a t i m e cpnsumlng prpcediure. E x a m p l e s wpuld b e : s t e e l weight f a c t o r , h u l l spacing (catamaran), and a l u m i n u m c o n s t r u c t i o n .

A s an example of the second type of s e n s i t i v i t y a n a l y s i s , c o n s i d e r the effect of load f a c t o r . F i g

-ure 17 shows the e:^ect of v a r y i n g t t ù s t>elpw and above the 0.7 value a s s u m e d f p r the t>asic p a r a -m e t r i c r e s u l t s . Ä s -might be expected, a f a i r l y l a r g e i m p a c t c n c a p i t a l r e c P v e r y f a c t o r i s noted. T h i s should be expected, s i n c e the g r o s s revenue

* T h e Rabe c p e f f i c i e n t i s the rattP pf c l e a r space between h u l l s to the length on the w a t e r l i n e .

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f p r the s h i p i s d i r e c t l y r e l a t e d to the percent pf f u l l load c a r r i e d . The d e f i n i t i o n of load f a c t p r i s that percentage of toe f u l l l o a d c a p a b i l i t y f o r which revenue i s c o l l e c t e d . T h i s means that f o r toe cpntainershlp, f o r e x a m p l e , e m p t i e s might s t i l l be c a r r i e d i n toe v a r i o u s s l p t s , but they wpuld not be producing revenue. O t h e r w i s e i t might m e a n that l e s s than a f u l l load of c o n t a i n e r s i s c a r r i e d . I b i s s i g n i f i c a n t p a r t pf the g r a p h i s the s l p p e p f the c u r v e s and i t i s expected that c u r v e s f o r other s i z e s of o t o e r s h i p s i n the m a t -r i x would e ^ i i b i t p -r e t t y m u c h toe same s l o p e .

trrtCT OP LOAD PACTo» wa/mo CATAHARAB CTRMLaMmPi

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V

lata PACTOR H g u r e 17

A s a n example pf the t h i r d typie pf s e n s i t i v i t y a n a l y s i s , c o n s i d e r F i g u r e 18, w h i c h shews the e f f e c t qf s t e e l weight f a c t p r pn toe R Ö / R O c a t a -m a r a n t r a i l e r s h i p . l h e s t i -m a t i n g the s t r u c t u r a l weights f p r the s h i p s , e s p e c i a l l y f p r the c a t a m a -ran, aiid f p r l a r g e s i z e s of cpnventional h u l l s as w e l l , s o m e r o o m f o r e r r o r ^ s t s . T h i s f i g u r e

EPFECT OP antEl WBQHT PACTOR M)/RD CATAHARAM r n u t L E U U P t

It"—

Shows how C R F ' would v a r y i f toe weight of s t r u c

t u r e w e r e more o r l e s s than that w h i c h was a s s u m e d . . T h e g r a p h shows that toe e f f e c t i s s p m e -what l i n é à r , toe slppe b e m g p r a c t i c a l l y the s a m e f p r d i f f e r e n t points to the m a t r i x . The magnitude of the change o n C R F * i s noticeable, but the p e r -cent e r r o r introduced b y reaspnable e r r p r s m weight e s t i m a t i p n a r e npt g r e a t . C u r v e s of p r a c -tically the same

slope

c a n be developed f o r toe a l u m i n u m weight f a c t o r v a r i a t i o n .

S i n c e h u l l s p a c i n g i s a f a c t o r w h i c h i s settled uppn somewhat a r b i t r a r i l y to the develppment pf s e r i e s pf catamarans, i t i s d e s i r e a b l e to show the e f f e c t pf v a r y i n g t M s . it should be noted that.if s p a c i n g i s d e c r e a s e d siq>erstructure m u s t be toc r e a s e d to p r d e r to atoctocommpdate toe same n u m -b e r of v e h i c l e s , so one change cannot -be made without toe other. T h i s tends to o f f s e t toe i m p a c t and F i g u r e 19 shpws what the e f f e c t i s pn the s t e e l R O / R O c a t a m a r a n . T h e r e i s a g e n e r a l t e n -dency to s u r e s t toat n a r r p w e r spacings be used, bid; unfortunately toe m p d e l test r é s u l t e dp not a l l o w extrapplatipn toto t h i s a r e a w i t o any degree pf a s s u r a n c e as to

what

wpuld happen a s f a r a s r e s i s t a n c e penalty i s c p n c è r n e d .

• n r c T O P HULL sPAaHG ON r r a n . KI/KDCATAMAUW r n u i L c n n P ) .

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H g u r e 19 C o n c l u s i o n s

ITEU. «KICHT rACTOR

F i g u r e 18

O v e r tlyj ranges of v a r i a b l e s c p n s i d e r e d , and subject tp the stoted assumptions, this p a r a m e t r i c a n a l y s i s shows that the c a t a m a r a n i s , i n a l l c a s e s , i n f e r i p r to toe c c m p a r a b l e cpnventional s h i p . Bpto types have been d é s i g n e d tp dp toe same j o b s , and t h e r e f p r e t h e i r revenue generatmg c a p a c i t i e s a r e e s s e n t i a l l y toe s a m e . The a c q u i s i t i p n cpsto a r e , hpwever, a p p r e c i a b l y g r e a t e r f o r toe c a t o m a r a n p r i m a r i t y because ttmt type r e q u i r e s m o r e s t r u c -t u r e and h o r s e p o w e r . The resul-tan-t l a r g e r , c p s t l i e r s h i p Is a l s P m p r e expensive to pperate stoce matotehance c o s t s , insurance p r e m i u m s , ' p o r t charges, and f u e l b i l l s w i l l be g r e a t e r . So,

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toe r e s u l t i s no sur^nrise f r o m a q u a l i t a t i v e s t a n d -DPint. The p r i m a r y value pf toe a n a i y s i s i s ite.

.uantitative a s p e c t . B y and l a r g e , ppwer and

"Structural weight r e q u i r e m e n t s f o r toe c a t a m a

r a n pose s e v e r e pehalUes w h i c h cannot be o v e r -come to c o m m e r c i a l applicattons where cargp pf reaspnable densities m u s t be c a r r i e d .

A n o t h e r f a c t o r to c o n s i d e r i s that certato f e a -t u r e s pf -toe c a -t a m a r a n , w h i c h migh-t w e l l -tocrease i t s a c q u i s i t i o n and operation costs o v e r those pf the cpnventipnal h u l l , w e r e npt taken mto a c c p ü h t .

F o r e x a m p l e ; the c o s t p e r pound pf s t e e l e r e c t e d cpuld be g r e a t e r because of toe a w k w a r d and l a r g -e r s i z -e s and to-e f a c t that two h u l l s might hav-e to b e b u i l t separately and iîien jplned together a f t e r launching. In addition, toe p r o b l e m s o f d r y d o c k -i n g s u c h beamy v e s s e l s would c a l l f o r s p e c -i a l schemes o r . f a c i l i t i e s , and m a i œ u v e r a b i l i t y might be s u c h a s to c a l l f o r m o r e tugs.

The way to make a c a t a m a r a n c o m m e r c i a l s h i p appear i n toe t>est l i g h t i s to c o m p a r e i t under

c i r c u m s t a n c e s unfavorable to the conventional ^ s h ^ . T h e r e s u l t s show that these would be f p r III

the s m a l l - s i z e , s h o r t - r a n g e , s l o w - s p e e d R O / R O | l s e r v i c e . H e r e , the c a t a m a r a n i s s t i l l scmewhat R l e s s p r o f i t a b l e than the cpnventtonal ship, but t h e ^ d i f f e r e n c e I s a m i n i m u m . A s e n s i t i v i t y a n a l y s i s (not r e p o r t e d here) f o r a R O / R O c a t a m a r a n shpws that, i f a l u m t o u m c o n -s t r u c t i o n i -s u-sed, even t h o i ^ h a c q u i -s i t i o n c o -s t i -s m c r e a s e d , toe p r o f i t a b i l i t y a s e x p r e s s e d b y C R F * i s i n c r e a s e d s l i g h t i y . S w i Ü , hpwever, s t i l l b e below the s t e e l conventicuial s h i p . It should b e noted too toat a. combination c a t a m a r a n , althpugh admittedly having s p m e degree pf f l e x i b i l i t y g r e a t -e r than to-e lO/XO or R O / R O typ-es, do-es n-et show m c r e a s e d p r p f i t a b i l i t y under any c p m b i n -atipn pf loadtogs.

to c p m p a r i n g the twb s e r i e s pf s h i p s , np a t -tempt has been made tp p p t i m i z e either Pf the designs. E x p e r i e n c e has shown, hpwever, that f s h i p p e r f o r m a n c e c u r y e s a r e f a i r l y f l a t - and

reasonable v a r i a t i p n s to p r o i » r t i o n s f ö r a given h u l l would not have g r e a t e f f e c t o o n C R F . These e f f e c t s l o s e s i g n i f i c a n c e when c o n s i d e r i n g that, i n most c a s e s , toe r e s u l t e f p r the c a t a m a r a n and toe cpnventional s h i p a r e f a r a p a r t .

The c a t a m a r a n i s seen to be a weight l i m i t e d

type

of s h i p , aiid toèrèfôre c a r r y t o g e x t r a weighte of c a r g o handling equipment, s u c h a s heavy c r a n e s - which wpuld be r e q u i r e d w i t o a barge c a r r i e r a>ncept - appears dpomed f r o m

tlie

s t a r t . A c o m p a r i s p n between L O / I X ) c a t a m a r a n s w i t o and without cranes s u j ^ r t e t h i s cpncluston.

One f u r t o e r peint to r e m ë m b e r abput this c o m

-parison i s that, althpugh the cp nt a iner ships at the

Ipw end ef toe s c a l e a r e not e x c e s s i v e l y l a r g e , the t r a l l e r s h i p s a r e l a r g e by today's standards. It ^might be that extrapolation below the 10,000 tons

deadweight would be to o r d e r f o r c o m p a r i n g t r a i l -e r s h i p s . H alumtoum qonstructlpn i s c p n s i d -e r -e d i t p n l y makes sense to want to t r y i t on a s m a l l e r s h i p f i r s t . '

W i t o r e s p e c t to speed, i t was toought a t toe beginning pf t h i s stiufy that the s l e n d e r h u l l s of the c a t a m a r a n might be m e r e e a s i l y d r i v e n than the cpnventional s h i p . F o r toe payldads c o n s i d e r e d m t h i s study, hpwever, toe c a t o m a r a n i s weight lixóited and r e q u i r e s a p p r e c i a b l e d i s p l a c e m o i t to the h u l l s . E x t r e m e s l e n d e r n e s s cannot be a c h i e v -ed, and the two h u l l s r e s u l t to a h i g h penalty pn wetted s u r f a c e , S P that l l i e r e s u l t a n t hprsepow-ers . f p r c a t a m a r a n s a r e m u c h g r e a t e r than ^pr c o m - ^ p a r a b l e cpnventional:ships, w h i c h a r e a l s P seen to be l i g h t e r .

.ID. s u m m a r y , t h i s study has f a i l e d to shpw toe c a t o m a r a n to advantage o v e r comparable c o n v e n -t i p n a l s h i p s . These c o n d u s i c n s a r e pnly v a l i d w i t h i n the r a n g e s o f the v a r i a b l e s studied, and p p s s i b l y c a r r y i n g v e r y l o w density cargp to s m a l l -e r B p / R p s h i p s Pf a l u m t o u m m l ^ giv-e a n advan--tage to the c a t a m a r a n .

Recommendations f p r F u r t h e r R e s e a r c h A r e v i e w c f c u r r e n t c a t a m a r a n l i t e r a t u r e f ô i n t s up toe heed f o r m e r e d e f i n i t i v e date pn w h i c h to base f u t u r e d e s i g n s . The cpnceptual w p r k done f p r the s e r i e s p f s h i p s , s^dijected to ecpnpmic a n -a l y s e s to t h i s study, w-as fr-alùght w i t h d i f f i c u U i e s because of t h i s l a c k of dato.

Tlie R O / R O cpncept a p p e a r s tp be toe m o s t p r o m i s i n g of ttu)se studied, and there i s r o p m f o r develppment of t h i s concept, e s p e c i a l l y f o r the I P W density cargpes and pn s m a l l e r s h i p s .

L i k e w i s e toe use o f alumtoum s e e m s to p f f e r spme advantage to pOsetting toe tocrease to s t r u c t u r a l weight. A c c e p t a b l e design c r i t e r i a and cpnstructlpn c c s t s a r e s t i l l d e t e r m ^ t s t c toe MSe of a l u m t o u m , and w o r k needs to be dpne to p v e r -come toem.

M o d e l teste and m o t i o n a n a l y s e s , while not d i s c o u r a g i n g the use of catamarans,, do potot up toe need f o r reftoement of the technlques>

It s e e m s c l e a r that the negative r e l a t i y e r e -sults found i n tois ecpnpmic study stem d i r e c t l y f r p m toe f r a m e of r e f e r e n c e . They can be toought pf i n a p o s i t i v e way, howeVer, since a b r o a d a r e a of p o s s i b l e use f o r the c a t a m a r a n has heen i n v e s -tigated and found u n p r o f i t o b l e . T h e r e i s m> need to c o v e r t h i s ground a g a i n . T h e r e Is r e a l l y no need to pursue p r e l i m i n a r y designs f p r the rnpst l i k e l y candidates of toose c o n s i d e r e d .

Two b a s i c p r e m i s e s s e e m tenable, namety: (1) toe c a t o m a r a n concept w l U p r e v a i l , albeit f b r s p e c i a l s e r v i c e s f o r w h i c h t h e i r attributes pf l a r g e deck a r e a s , high s t a b i l i t y , and p p s s i b l y 10

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h i g h speed pptential under light l o a d s , make toem r e a d i l y adaptable; and (2) t e c h n i c a l design f a c t o r s concerning hydrodynanxlcs, s t r u c t u r a l strengto, and p r o p u l s i o n plant, as w e l l a s c p n s t r u c t i p n and pperating p r p b l e m s w i l l r e q u i r e a n a p p r e c i a b l e amount o f f u r t o e r s t o d y . A n y r e c o m m e n d a t i o n f o r f u r t o e r r e s e a r c h and development would s e e m to have to s t a r t f r o m toese p r e m i s e s . B y w a y o f e x a m p l e , a s s u m e that d e s i g n r e -quiremente s p e c i f y a 4000 ton, 400 f p p t , 40 knot s h i p , 1. e. one w i t o f a i r l y I P W dlsplacement-Iengto r a t i p , but quite high speed-length r a t t o . A b r i e f a n a l y s i s w i l l show that f i t t i n g the abPve toto two h u l l s r a t h e r than one could w e l l r e s i ü t i n a n a p p r e c i a b l e savings to total S H P . A l s o , t h i s a p -p l i c a t i o n highlights the machtoery c o s t and f u e l b i l l aspecte to toe potot ^ e r e toe c a t a m a r a n might be toe b e à e r c h o i c e . B u t Just what toe h u l l f p r m ahould be, and h P w to design the cpnnectton s t r u c t u r e leaves r p P m f o r m u c h s p e c u l a t i o n .

What a p p e a r s , now, to be toe most u s e f u l approach to f u t u r e w p r k pn catamarans i s a f i v e -pronged attack o n the f o l l o w i n g :

H y d r o d y n a m i c s aspecte - speed and jpower, seakeeping, contro l i a b i l i t y : T h i s could e m b r a c e m e t h o d i c a l s é r i e s of m p d e l teste a s w e l l a s cpmputer studtes. S t r u c t u r a l aspects - longitudinal r a c k i n g and toter-hull connection: T h i s c o u l d a l s p e m -b r a c e m o d e l testily a s w e l l a s computer s t u d i e s .

P r o p u l s i o n plant aspecte - s i z e , weigUt> and a r r a n g e m e n t : H i e mato challenge here i s tp get l a r g e amounte o f power toto s m a l l packages, and of c o u r s e c o n v e r t i n g thte to tiarust.

C b n s t r u c t i p n aspecte - s i z e l i m i t a t i o n f o r coBstri»:tion ä s a unit, a l t e r n a t i v e s f o r c o n s t r u c t i n g hulls s e p a r a t e l y and Joining a f t e r launching: M o s t of the e f f p r t here wpuld p r o b a b l y be a i m e d a t c o n s t r u c t i o n concepte.

O p é r i a t i ó n a l aspecte - n a v i g a t i o n a l p r o b l e m s , support f a c i U t i e s , m a r -keting; Elxistlng m a r k e t i n g analyste might be adapted, f o r the case pf high speed s b p r t h a u l s e r v i c e , f c r e x a m p l e . The f o r m u l a t i o n of a reaspnable p r p g r a m to a c c p m p l i s h toe f p r e g o i n g to not easy. T h e "brute f p r c e " a p p r p a c h i s npt w a r r a n t e d because pf the

high cpst of m p d e l studtes a n d ccmputer t i m e , and toe U m i t e d appUcatton pf the r e s u l t e . S t U l , p r p g r e s s must be made, and e x p l o r a t o r y w o r k to the a r e a pf m u c h s m a l l e r , s h p r t e r range, higher speed ooncepte n i a y be the p l a c e to s t a r t . H i g ^ p e r f p r m a n c e i s the k e y note - but not to toe extent f o r w h i c h h y d r o f o i l s and s u r f a c e e&ect s h i p s a r e b e m g c o n s i d e r e d .