Hydrodynamic development of inclined keel hull-propulsion

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O c e a n E n g i n e e r i n g 6 3 ( 2 0 1 3 ) 9 0 - 9 5

ELSEVIER

Contents lists available at S c i V e r s e S c i e n c e D i r e c t

Ocean Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / I o c a t e / o c e a n e n g

Hydrodynamic development of Inclined Keel HuU-propulsion

K.C. Seo-^'* M. Atlar^ D. Wang^'^

' School of Marine Science and Technology, Newcastle University, UK ''Harbin Institute of Technology, China

A R T I C L E I N F O Article history: R e c e i v e d 2 1 O c t o b e r 2 0 1 2 A c c e p t e d 2 6 J a n u a r y 2 0 1 3 A v a i l a b l e o n l i n e 2 1 M a r c h 2 0 1 3 Keywords: I n c l i n e d K e e l H u l l A l a r g e p r o p e l l e r d i a m e t e r E n e r g y s a v i n g G r e e n h o u s e g a s e m i s s i o n A B S T R A C T

The gain in propulsive efficiency using a large propeller diameter w i t h lower shaft rotation is perhaps the simplest and most robust way of improving the fuel economy of a ship. W i t h i n this framework the concept of "Inclined Keel Hull" has attracted much interest in small vessels such as fishing boats and t u g boats to improve their pulling power however there has been no application of this concept to large commercial ships. This is the second of two papers on a hydrodynamic development of an Inclined Keel Hull w i t h a well-designed 3600 TEU container vessel based on the recently completed postgraduate study, (Seo, 2010). In the first paper (Seo et al., 2012) the validation for the bare hull resistance and wake distribution on the propeller plane was conducted by using advanced numerical tools and large scale model' tests as part of an on-going collaborative FP7-EU research project. Streamline (2010). The present paper is the continuation of the validation study for the propulsion analysis of the same vessel by using numerical analysis and large scale self-propulsion tests as part of the same project. The validation study confirmed the worthiness of the Inclined Keel Hull concept by achieving a 4.3% m a x i m u m power saving in the delivered power around design speed.

1. Introduction

A successful s h i p d e s i g n i n t e r m s o f s h i p p o w e r i n g d e m a n d s p r o p u l s i o n devices d e s i g n e d t o give m a x i m u m e f f i c i e n c y a n d t o absorb a l o w s h a f t p o w e r w i t h l o w h u l l pressures, noise, c a v i t a -t i o n e r o s i o n a n d v i b r a -t i o n . I n general i -t is a p l a -t i -t u d e f o r n a v a l a r c h i t e c t s t h a t a large p r o p e l l e r d i a m e t e r i n c o m b i n a t i o n w i t h a l o w r o t a t i o n a l speed leads t o a n a t t r a c t i v e g a i n i n p r o p u l s i v e e f f i c i e n c y d u e t o t h e r e d u c t i o n o f a x i a l losses. A d d i t i o n a l l y , a s l o w t u r n i n g p r o p e l l e r can also have c a v i t a t i o n b e n e f i t s . M a n y a p p l i c a -tions, especially f o r larger t a n k e r s ( h i g h t h r u s t l o a d i n g case) i n w h i c h t h e a x i a l e n e r g y loss d o m i n a t e s , t h e r e f o r e have t a k e n place i n a d a p t i n g large a n d s l o w t u r n i n g p r o p e l l e r s as b e i n g one o f t h e m o r e r o b u s t a n d e f f e c t i v e w a y s o f a c h i e v i n g s i g n i f i c a n t p r o p u l -sive efficiencies (Beek, 2 0 0 4 ; C i p i n g e t al., 1 9 8 9 ) . For t h e same vessel a f u r t h e r increase o f p r o p e l l e r d i a m e t e r w o u l d r e q u i r e t h e d e v e l o p m e n t o f t h e n e w p r o p e l l e r a p e r t u r e . I n o r d e r t o secure a deeper a f t d r a u g h t for a large d i a m e t e r p r o p e l l e r t h e A u t h o r s have i n t r o d u c e d "Inclined Keel Hull" c o n f i g u r a t i o n w h e r e t h e d r a u g h t o f

* C o r r e s p o n d e n c e t o : S c h o o l o f i V I a r i n e S c i e n c e a n d T e c h n o l o g y , A r m s t r o n g B u i l d i n g , N e w c a s t l e U n i v e r s i t y , N E I 7 R U , U n i t e d K i n g d o m . T e l . : + 4 4 0 1 9 1 2 2 2 5 0 6 7 ; f a x : + 4 4 0 1 9 1 2 2 2 5 4 9 1 . E-mail addresses: k w a n g - c h e o l . s e o O n c l . a c . u k , s k c 0 0 7 6 @ h o t m a i l . c o m ( K . C . S e o ) . " F o r m e r l y w o r k e d a t S c h o o l o f M a r i n e S c i e n c e a n d T e c h n o l o g y , U K . 0 0 2 9 - 8 0 1 8 / $ - s e e f r o n t m a t t e r © 2 0 1 3 E l s e v i e r L t d . A l l r i g h t s r e s e r v e d . h t t p : / / d x . d o i . 0 r g / 1 0 . l 0 1 6 / j . o c e a n e n g . 2 0 1 3 . 0 1 . 0 2 6 t h e vessel is g r e a t e r at t h e a f t p e r p e n d i c u l a r t h a n t h a t at t h e fore p e r p e n d i c u l a r w i t h a l i n e a r v a r i a t i o n i n b e t w e e n . N e w c a s t l e U n i v e r s i t y h a v e b e e n e x p l o r i n g t h e d e s i g n a n d o p e r a t i o n a l b e n e f i t s o f t h e I n c l i n e d Keel H u l l c o n c e p t u s i n g a w e l l - d e s i g n e d 3 6 0 0 TEU c o n t a i n e r vessel, w h i c h is d e s i g n a t e d as 'Basis H u l l ( B H ) ' , b y i n c r e a s i n g t h e d i a m e t e r o f its p r o p e l l e r a b o u t 13%. H o w e v e r , i m p r o v i n g t h e o p e r a t i o n a l b e n e f i t s b y t h e increase i n p r o p e l l e r size a n d hence i n p r o p u l s i v e e f f i c i e n c y is n o t a s i m p l e issue as t h e l a t t e r is t h e p r o d u c t o f t h e h u l l , p r o p e l l e r a n d r e l a t i v e -r o t a t i v e efficiencies. The ba-re h u l l -resistance a -r o u n d t h e h u l l a n d i n f l o w v e l o c i t y i n t o t h e p r o p e l l e r p l a n e are i m p o r t a n t h y d r o -d y n a m i c s aspects o f t h e h u l l f o r m -d e v e l o p m e n t . I f t h e increase o f t h e bare h u l l resistance o f I n c l i n e d Keel H u l l ( I K H ) is c o n s i d e r a b l e t h a n t h a t o f BH (Basis H u l l ) t h e e c o n o m i c s o f t h e I K H w i l l n o t w o r k since t h e e x p e c t e d p r o p u l s i v e g a i n f r o m t h e e n l a r g e d d i a m e t e r o f t h e I K H w i l l be l o s t t o t h e p o t e n t i a l increase i n t h e e f f e c t i v e p o w e r o f t h e IKH. U s i n g n u m e r i c a l d e s i g n a n d analysis m e t h o d s s u p p o r t e d by l i m i t e d m o d e l t e s t analysis, Seo ( 2 0 1 0 ) d e m o n s t r a t e d t h a t t h e IKH c o n c e p t m a y p r o v i d e a 4 - 5 % o f p o w e r s a v i n g . I n t h e p r e v i o u s c o m p a n i o n p a p e r (Seo e t a l , 2 0 1 2 ) a b r i e f d e f i n i t i o n o f t h e I K H c o n c e p t a n d its d e v e l o p m e n t f o r t h e 3 6 0 0 TEU c o n t a i n e r vessel w e r e p r e s e n t e d i n c l u d i n g t h e analyses f o r t h e resistance a n d h u l l w a k e b y u s i n g t h e CFD codes. T h e n u m e r i c a l results w e r e v a l i d a t e d f o r t h e bare h u l l resistance a n d w a k e o f t h e B H a n d I K H based o n t h e m o d e l t e s t m e a s u r e -m e n t s . M a i n p a r t i c u l a r s o f t h e BH a n d I K H are g i v e n i n Table 1 .

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The resistance tests w i t h t w o 7.15 m (Lpp) h u i l m o d e l s c o n -f i r m e d t h e success-ful design o -f t h e I K H -f o r m w h i c h r e s u l t e d i n a 1% increase i n t h e e f f e c d v e p o w e r as t h e a u t h o r s had t a r g e t e d i n the I K H d e v e l o p m e n t . I n o r d e r t o d e m o n s t r a t e t h e effectiveness o f the IKH c o n c e p t over t h e B H , t h e p r o p e l l e r m u s t be designed t o operate e f f e c t i v e l y i n a n o n - u n i f o r m a n d u n s t e a d y w a k e f l o w f i e l d b e h i n d t h e h u l l . I n general, t h e m a i n p a r t i c u l a r s o f p r o p e l l e r s are d e t e r m i n e d f o r t h e o p t i m u m c o n d i t i o n b y u s i n g s t a n d a r d ( o r c h a r t ) series m o d e l p r o p e l l e r d a t a a n d t h e basic p a r t i c u l a r s o f t h e p r o p e l l e r is f u r t h e r o p t i m i z e d w i t h respect t o t h e r a d i a l l y v a r y i n g w a k e d i s t r i b u t i o n . A n d f i n a l step o f t h e design a p p r o a c h i n v o l v e s a n analysis o f t h e o p t i m u m p r o p e l l e r i n c i r c u m f e r e n t i a l v a r y i n g three d i m e n s i o n a l w a k e d i s t r i b u t i o n s by using advanced unsteady p r o p e l l e r analysis t o o l s t o f u r t h e r r e f i n e t h e p r o p e l l e r g e o m e t r y f o r b e t t e r c a v i t a t i o n a n d v i b r a t i o n p e r f o r m a n c e .

I n t h i s paper, p r o p e l l e r designs a n d p r o p u l s i o n analyses f o r t h e IKH and BH h u l l s are p r e s e n t e d f o r f u r t h e r v a l i d a t i o n o f t h e r e l a t i v e p r o p u l s i v e p e r f o r m a n c e f o r t h e I n c l i n e d Keel H u l l based T a b l e 1 M a i n p a r t i c u l a r s o f B a s i s H u l l ( B H ) a n d I n c l i n e d K e e l H u l l ( I K H ) . M a i n d i m e n s i o n s B H I K H L p p ( m ) 2 3 2 . 8 2 3 2 . 8 B e a m ( m ) 3 2 . 2 3 2 . 2 D e s i g n D r a f t ( m ) T F 1 1 . 3 1 0 . 5 D e s i g n D r a f t ( m ) T A 1 1 . 3 1 2 . 1 W S A ( m 2 ) 9 2 6 6 9 2 2 0 V o l u m e ( m 3 ) 5 0 8 4 9 5 1 1 3 6 0 . 8 4 0 0 . 8 4 1 o n t h e s e l f - p r o p u l s i o n tests c o n d u c t e d i n t h e SSPA t o w i n g t a n k ( A l l e n s t r o m a n d Riisberg-Jensen, 2 0 1 1 a).

2. Numerical analysis of propulsion

Prior t o t h e design o f a n e f f i c i e n t p r o p e l l e r f o r t h e IKH a n d c o m p a r i s o n o f its p r o p u l s i v e p e r f o r m a n c e w i t h t h a t o f t h e B H a set o f p r e l i m i n a r y s e l f - p r o p u l s i o n tests w e r e c o n d u c t e d w i t h b o t h h u l l m o d e l s .

Based o n t h e p r o p e l l e r h u l l - i n t e r a c t i o n data o b t a i n e d f r o m these early s e l f - p r o p u l s i o n m o d e l tests, w h i c h w e r e o b t a i n e d w i t h s u i t a b l e stock p r o p e l l e r s f o r t h e BH a n d IKH a n d r e p o r t e d i n A l l e n s t r o m a n d Riisberg-Jensen ( 2 0 1 1 a , 2 0 1 1 b ) , t h e p r o p e l l e r designs w e r e carried o u t f o r b o t h BH a n d I K H . B o t h p r o p e l l e r s (i.e. f o r BH a n d I K H ) w e r e d e s i g n e d u s i n g t h e same p r o c e d u r e i n t h r e e stages t h a t are "Basic D e s i g n " , " L i f t i n g Line d e s i g n ( o r W a k e A d a p t a t i o n ) " a n d " B a l a n c e d Design ( o r Design A n a l y s i s ) " . For each o f these stages, t h e d e s i g n s t r a t e g y a n d c r i t e r i a w e r e d i f f e r e n t t o achieve t h e u l t i m a t e d e s i g n o b j e c t i v e , i.e., h i g h e r p r o p u l s i o n e f f i c i e n c y w i t h l o w e r c a v i t a t i o n a n d v i b r a t i o n . Each d e s i g n stage w a s i t e r a t i v e w i t h its o w n o b j e c t i v e t h a t m a d e t h e e n t i r e d e s i g n o p t i m i z a t i o n task m u l t i - o b j e c t i v e a n d i t e r a t i v e as s h o w n b y t h e f l o w c h a r t i n Fig. 1 a n d d e s c r i b e d i n t h e f o l l o w i n g w i t h m o r e d e t a i l s .

I n t h e basic design stage, t h e m a i n design strategy was to m a k e use o f well-established propeller design practices a n d experiences, w h i c h are w e l l presented i n t h e systematic p r o p e l l e r c h a r t series, t o achieve a m o r e reliable basic design and t o a v o i d a n y i n t e r a c t i o n ( a n d hence i t e r a t i o n ) w i t h t h e other t w o design stages. I n t h e basic design stage, t h e m a i n particulars of b o t h propellers ( m a i n l y p i t c h .

S t a r t : D e s i g n S p e c i f i c a t i o n B a s i c D e s i g n : C h a r t s e r i e s D , R P M , A E / A Q, C h o r d , T ^ a x . V B a l a n c e d •

r

e s i g n L i f t i n g L i n e D e s i g n : B a s e d o n W a k e D i s t r i b u t i o n O p t . C i r c u l a t i o n D i s t r i b u t i o n B a l a n c e d D e s i g n

1

U n l o a d T i p L o a d i n g M o d i f y L o a d i n g D i s t r i b u t i o n B a l a n c e d D e s i g n W a k e A n a l y s i s : S e l e c t S k e w D i s t r i b u t i o n O p t . C i r c u l a t i o n D i s t r i b u t i o n L i f t i n g S u r f a c e D e s i g n : C a m b e r & S k e w R e l o c a t e L o a d i n g b e t w e e n C a m b e r & P i t c h U n s t e a d y L i f t i n g S u r f a c e A n a l y s i s : C a v i t a t i o n & H u l l p r e s s u r e s M o d i f y S k e w B a l a n c e d D e s i g n F i g . 1. P r o p e l l e r d e s i g n b l o c k d i a g r a m .

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9 2 K.C. Seo et al. / Ocean Engineering 63 (2013) 90-95

shaft speed and blade area) w e r e selected i n iterative m a n n e r for the o p t i m u m propulsive efficiencies a n d m i n i m u m risk o f cavitation for the m a x i m u m propeller d i a m e t e r for each ship w i t h the same ship speed (i.e. 2 4 knots) by u s i n g B-Series propeller chart (van L a m m e r e n e t al., 1 9 6 9 ) and Burrill's cavitation d i a g r a m ( B u r r i l l and Emerson, 1963). The w a k e fraction and t h r u s t d e d u c t i o n fraction used w e r e based o n the self-propulsion tests w i t h stock propellers.

As s h o w n i n Table 2, a f t e r t h e basic design, t h e o p e n w a t e r e f f i c i e n c y f o r t h e I K H p r o p e l l e r w a s 3.8% h i g h e r t h a n t h a t o f t h e BH d u e t o t h e i n c r e a s e d p r o p e l l e r d i a m e t e r a n d r e s u l t i n g l o w e r p r o p e l l e r s h a f t speed. C o n s e q u e n t l y t h e I K H w a s e x p e c t e d t o achieve a s a v i n g i n s h a f t p o w e r o f 2.7%, d u e t o t h e i m p r o v e m e n t T a b l e 2 C o m p a r i s o n o f b a s i c p r o p u l s i v e p e r f o r m a n c e . S p e e d ( k n ) P / D J / f r I O K Q B H 2 4 1.1 0 . 7 8 4 0 . 2 0 1 0 . 3 7 7 6 I K H 2 4 1.2 0 . 8 9 1 0 . 2 0 3 0 . 4 1 5 0 K T / J ' ' / o N ( r p m ) Q ( k N m ) ' PD ( k W ) B . A . R 0 . 3 2 6 0 . 6 6 7 9 3 . 4 2 9 0 4 2 8 , 3 1 4 0 . 7 2 0 . 2 5 6 0 . 6 9 3 7 3 . 0 3 6 1 7 2 7 , 3 1 1 0 . 6 2 i n t h e o p e n w a t e r e f f i c i e n c y despite t h e 1% increase o f h u l l resistance. I n t h e l i f t i n g l i n e d e s i g n stage, t h e d e s i g n o b j e c t i v e w a s t o a d a p t t h e p r o p e l l e r s , w h i c h w e r e d e s i g n e d f r o m t h e c h a r t series, t o t h e w a k e s o f t h e t a r g e t ships based o n Lerbs' l i f t i n g l i n e m e t h o d (Lerbs, 1 9 5 2 ) . Hence t h e c i r c u l a t i o n d i s t r i b u t i o n s o f b o t h p r o p e l l e r s w e r e o p t i m i z e d t o its i n d i v i d u a l axial w a k e d i s t r i b u -tion, w h i c h w a s o b t a i n e d f r o m t h e m o d e l tests, b y u s i n g a n i n - h o u s e l i f t i n g l i n e code f o r a c h i e v i n g t h e m a x i m u m p r o p e l l e r e f f i c i e n c y w i t h t h e c r i t e n a o f a b s o r b i n g t h e i r r e q u i r e d e n g i n e p o w e r s .

The balanced design stage consisted o f t h r e e sub-stages such as " w a k e analysis", " l i f t i n g surface d e s i g n " a n d " u n s t e a d y l i f t i n g surface analysis". I n t h e w a k e analysis substage the w a k e d i s -t r i b u -t i o n s o f b o -t h s h i p models w e r e c a r e f u l l y analyzed for selec-ting t h e p r o p e l l e r s k e w d i s t r i b u t i o n s i n case t h a t t h e c a v i t a t i o n w a s i n e v i t a b l e . The objective o f t h e l i f t i n g surface design sub-stage was t o f u r t h e r i m p r o v e t h e l i f t i n g line design results i n t e r m s o f t h e blade camber, p r o p e l l e r p i t c h a n d p r o p e l l e r skew. For t h i s p u r p o s e , Greeley a n d K e r w i n ' s l i f t i n g surface design code (Greeley a n d K e r w i n , 1 9 8 2 ) w a s used. The objective o f t h e u n s t e a d y l i f t i n g surface analysis sub-stage w a s t o p r e d i c t the p r o p e l l e r c a v i t a t i o n

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p e r f o r m a n c e a n d v i b r a t i o n . For t h i s p u r p o s e i n - h o u s e u n s t e a d y l i f t i n g surface code IJPCA91 (Szantyr a n d Glover, 1 9 9 0 ) w a s used. As s h o w n i n Fig. 1 i f t h e c a v i t a t i o n e x t e n t a n d s h i p h u l l pressures w e r e acceptable, the c i r c u l a t i o n d i s t r i b u t i o n o p t i m i z e d f r o m t h e l i f t i n g l i n e d e s i g n stage w o u l d be k e p t u n c h a n g e d , a n d t h e d e s i g n i t e r a t i o n w o u l d n o t go back to t h e l i f t i n g l i n e d e s i g n stage. I n t h i s case, t h e l o a d i n g at c e r t a i n r a d i i m a y be r e l o c a t e d l o c a l l y b e t w e e n t h e m a x i m u m c a m b e r a n d p i t c h at t h o s e r a d i i t o i m p r o v e t h e i r c a v i t a t i o n e x t e n t . I n case t h a t t h e c a v i t a t i o n a n d h u l l pressures w e r e excessive, hence n o t acceptable, f i r s t i y t h e s k e w o f p r o p e l l e r w o u l d be increased t o i m p r o v e t h e s i t u a t i o n . I f t h e r e s u l t i n g c a v i t a t i o n a n d h u l l pressures w e r e s t i l l n o t acceptable, t h e r a d i a l d i s t r i b u t i o n o f t h e p r o p e l l e r l o a d i n g h a d t o be m o d i f i e d , u s u a l l y b y u n l o a d i n g t h e blade t o w a r d s t h e t i p . I n t h i s case t h e d e s i g n i t e r a t i o n h a d t o be t a k e n back t o t h e l i f t i n g l i n e d e s i g n stage as s h o w n i n Fig. 1.

The m a i n features a n d sectional d e t a i l s o f each p r o p e l l e r are s h o w n i n Figs. 2 a n d 3 as t h e f i n a l d e s i g n o b t a i n e d f r o m t h e above d e s c r i b e d d e s i g n process w h i l s t t h e basic d i m e n s i o n s o f t h e p r o p e l l e r s are g i v e n i n Table 3 t o g e t h e r w i t h t h e n u m e r i c a l results o f t h e i r p e r f o r m a n c e s based o n t h e u n s t e a d y l i f t i n g surface analysis as d e s c r i b e d above.

As can be seen i n Table 3 t h e BH s h o w e d t h e p o w e r d e l i v e r e d t o t h e p r o p e l l e r at t h i s o p t i m u m o p e r a t i n g c o n d i t i o n w a s P D = 2 7 , 9 6 2 k W . The s i m i l a r analysis f o r t h e I K H p r o p e l l e r i n d i -c a t e d t h a t t h e d e l i v e r e d p o w e r , P D = 2 6 , 8 8 8 k W f o r t h e o p t i m u m o p e r a t i n g c o n d i t i o n . This r e v e a l e d t h a t t h e d e l i v e r e d p o w e r f o r T a b l e 3 C o m p a r i s o n o f b a s i c d i m e n s i o n s a n d n u m e r i c a l p r o p u l s i v e p e r f o r m a n c e o f d e s i g n e d p r o p e l l e r s a t t h e d e s i g n s p e e d ( 2 4 l < n o t s ) . S p e e d ( k n ) B l a d e n o . D i a . ( m ) B.A.R B H 2 4 5 . 7 . 9 1 0 . 7 2 I K H 2 4 5 8 . 9 5 0 . 6 2 P/ D T h r u s t ( k N ) N ( r p m ) Q ( N m ) PD ( k W ) 1 . 0 6 1 9 4 8 9 3 . 4 2 8 5 6 2 7 , 9 6 2 1 . 1 7 1 9 7 5 7 3 . 0 3 4 9 8 2 6 , 8 8 8 1 B a s i s H u l l i I n c l i n e d K e e l H u l l L~-~l

L

2 B R 3 B R 4 B R B l a d e R a t e F r e q u e n c y F i g . 4 . C o m p a r i s o n o f n u m e r i c a l h u l l p r e s s u r e s i n d u c e d b y t h e p r o p e l l e r . T a b l e 4 C o m p a r i s o n o f B H p r o p e l l e r — d e s i g n e d a n d m a n u f a c t u r e d . B H p r o p e l l e r . B l a d e n o . B.A.R B H - d e s i g n e d 5 0 . 7 2 B H - m a n u f a c t u r e d 5 0 . 6 8 I K H p r o p e l l e r w o u l d r e s u l t i n a 3.84% s a v i n g c o m p a r e d t o t h e BH at a 22.6% l o w e r s h a f t speed rate. The h u l l pressure c o m p u t a t i o n s w e r e c a r r i e d o u t at a p o i n t o n t h e h u l l w h e r e t h e pressures w e r e e x p e c t e d t o h a v e t h e p e a k values. These p o s i t i o n s f o r t h e BH a n d I K H w e r e a t 6.2 m a n d 6.83 m a b o v e t h e p r o p e l l e r s h a f t axis i n t h e p r o p e l l e r p l a n e , r e s p e c t i v e l y . I K H h u l l w a s designed t o h a v e a s i m i l a r level o f p r o p e l l e r clearance t o BH h u l l a n d t o r u n a t a d e e p e r d r a u g h t w h i c h has t h e effect o f r e d u c i n g t h e p o t e n t i a l f o r sheet c a v i t y d e v e l o p e d o v e r t h e s u c t i o n side o f t h e p r o p e l l e r , t o g e t h e r w i t h i m p r o v i n g t h e r a d i a t e d h u l l surface pressure. To give a m o r e c o m p r e h e n s i v e c o m p a r i s o n b e t w e e n t h e BH a n d t h e I K H , h a r m o -n i c a -n a l y s i s o f t h e f l u c t u a t i -n g pressure i -n d u c e d b y t h e p r o p e l l e r u p t o f o u r t h b l a d e r a t e are s h o w n i n Fig. 4 . These c o m p a r i s o n results s h o w t h a t t h e I K H w i l l o f f e r b e n e f i t s b y r e d u c i n g t h e h u l l p r e s s u r e f l u c t u a t i o n s at the f i r s t a n d second h a r m o n i c b y a l m o s t 35%.

3. Experimental analysis of propulsion

The m o d e l p r o p e l l e r s w e r e m a n u f a c t u r e d b y SSPA a c c o r d i n g t o t h e d e s i g n data p r o v i d e d b y t h e a u t h o r s t o SSPA. H o w e v e r d u r i n g t h i s process a n u n f o r t u n a t e e r r o r t o o k place r e s u l t i n g i n t h a t t h e m a n u f a c t u r e d BH m o d e l p r o p e l l e r h a d a s m a l l e r BAR t h a n t h e d e s i g n e d one as s h o w n i n Table 4 . The d i f f e r e n c e w a s 5.5% decrease i n t h e BAR due t o t h e h u m a n e r r o r d u r i n g t h e exchange o f i n f o r m a t i o n o n t h e c h o r d l e n g t h s o f t h e blade sections i n t h e excel tables a l t h o u g h t h e d r a w i n g s w e r e c o r r e c t . H o w e v e r t h e r e m a i n i n g data o f t h e BH p r o p e l l e r w e r e t h e same as t h e d e s i g n e d one p r o d u c e d b y t h e a u t h o r s . This u n f o r t u n a t e s i t u a t i o n , i n fact, p u t t h e B H m o d e l p r o p e l l e r i n m o r e e f f i c i e n t a n d hence m o r e c o m p e t i t i v e t h a n t h e i n t e n d e d n u m e r i c a l d e s i g n t h a t m u s t be b o r n i n m i n d i n t h e c o m p a r i s o n s . I n o t h e r w o r d , t h e BH m o d e l p r o p e l l e r w o u l d be o v e r - p e r f o r m i n g d u e t o its l o w e r f r i c t i o n a l loss. H o w e v e r , t h e p r o p e l l e r m a n u f a c t u r e d w i l l be e x p o s e d t o h i g h e r r i s k o f c a v i t a t i o n a n d h u l l pressure t h a n t h e p r o p e l l e r 0 . 8 0 . 4 0 . 2 B H K I - E x p BH IOKq-Exp BH Etao -Exp . IKH Kt-Exp

IKH IOKq -Exp IKH Etao -Exp - « BH Kl-In-house • • • BH IOKq -In -house - • BH Etao-In-house IKH Kt-In-house IKH IOKq-In-house - 0 — • IKH Etao-In-house 0 . 6 O.i A d v a n c e d ratio(J) F i g . 5 . C o m p a r i s o n o f o p e n w a t e r e f f i c i e n c y f r o m m o d e l t e s t a n d i n - h o u s e l i f t i n g s u r f a c e c o d e f o r B a s i s H u l l a n d I n c l i n e d K e e l H u l l ( m o d e l s c a l e ) .

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9 4 K.C. Seo et al. / Ocean Engineering 63 (2013) 90-95

T a b l e 5

C o m p a r i s o n o f p r o p u l s i v e p e r f o r m a n c e a t 2 4 k n o t .

P E( k W ) N ( r p m ) il„ I/H 'IR 'ID PD ( k W )

B H 2 0 , 3 2 3 9 2 . 9 0 . 6 9 8 1 . 0 9 4 0 . 9 9 6 0 . 7 6 0 2 6 , 7 5 1 I K H 2 0 , 5 3 1 7 2 . 8 0 . 7 2 6 1 . 0 9 5 1 . 0 0 5 0 . 7 9 9 2 5 , 6 8 9 p o w e r s a v i n g a r o u n d t h e d e s i g n speed. T h e p o w e r s a v i n g is a p p a r e n t b e t w e e n 18 and 2 6 l<nots w i t h a m a x i m u m o f 4.3% at 2 3 l<nots.

4. Conclusions

4 5 0 0 0 4 0 0 0 0 35000 g 30000 g ° 25000 20000 E f f e c t i v e p o w e r D e l i v e r e d p o w e r - E f f e c t i v e p o w e r - D e l i v e r e d p o w e r • B H • • o - . IKH . . , . . 0 . . . I K H E f f e c t i v e p o w e r D e l i v e r e d p o w e r - E f f e c t i v e p o w e r - D e l i v e r e d p o w e r y -

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1 1 1 1 \ 1 1 1 20 22 24 S t i i p S p e e d ( k n ) F i g . 6 . C o m p a r i s o n o f d e l i v e r e d p o w e r a t f u l l s c a l e . d e s i g n e d a l t h o u g h t h e e a r l i e r p r e s e n t e d h u l l pressure p r e d i c t i o n s w e r e a l l based o n t h e d e s i g n e d , i.e., c o r r e c t p r o p e l l e r .

The e n t i r e p r o p u l s i o n tests w e r e c o n d u c t e d i n SSPA a n d r e p o r t e d b y A l l e n s t r o m and Riisberg-Jensen (2011 a). The c o m p a r i s o n o f the propeller o p e n w a t e r performances f r o m the m o d e l tests a n d in-liouse unsteady l i f t i n g surface code f o r t h e models o f t h e t w o propellers is s h o w n i n Fig. 5. N u m e r i c a l predictions o f t h r u s t and t o r q u e coefficients correspond t o the m o d e l test results w i t h i n 5%. The s e l f - p r o p u l s i o n m o d e l tests w e r e carried o u t at several c r u i s i n g speeds a r o u n d the design ship speed o f 2 4 knots a n d f u l l scale p o w e r p r e d i c t i o n w a s c o n d u c t e d using t h e ITTC 78 p e r f o r m a n c e p r e d i c t i o n m e t h o d .

Table 5 s h o w s t h e c o m p a r a t i v e p r o p u l s i v e e f f i c i e n c y a n d its c o m p o n e n t s as w e l l as t h e f u l l scale d e l i v e r e d p o w e r at t h e d e s i g n speed ( 2 4 k n o t s ) f o r t h e B H a n d I K H . The r e s u l t s o f t h e f i n a l m o d e l test for t h e BH s h o w e d t h a t the o p t i m u m p r o p e l l e r e f f i c i e n c y w a s 0.698 w h i l s t t h e p o w e r d e l i v e r e d t o t h e p r o p e l l e r w a s P D = 2 6 , 5 7 1 k W . T h e s i m i l a r analysis f o r t h e I K H p r o p e l l e r i n d i -cated t h a t t h e o p t i m u m p r o p e l l e r e f f i c i e n c y w a s 0 . 7 2 6 a n d t h e d e l i v e r e d p o w e r w a s P D = 2 5 , 6 8 9 k W . T h i s r e v e a l e d t h a t t h e o p e n w a t e r a n d r e l a t i v e - r o t a t i v e efficiencies o f t h e IKH p r o p e l l e r w e r e 4% a n d 1% h i g h e r t h a n t h a t o f t h e BH a t a 21.5% l o w e r s h a f t speed, r e s p e c t i v e l y . This w o u l d r e s u l t i n a 4% s a v i n g i n t h e d e l i v e r e d p o w e r f o r t h e IKH d e s p i t e t h e fact t h a t t h e I K H p r o d u c e d a 1% h i g h e r e f f e c t i v e p o w e r t h a n t h a t o f t h e BH. A n o t h e r f a c t o r t h a t m u s t be b o r n i n m i n d i n t h i s c o m p a r i s o n is t h a t t h e m a n u f a c t u r e d BH m o d e l p r o p e l l e r w o u l d be o v e r - p e r f o r m i n g t h a n t h e d e s i g n e d one w h i c h w o u l d r e s u l t i n t h e r e d u c e d r e l a t i v e p e r f o r m a n c e g a i n f o r t h e I K H . Fig. 6 s h o w s t h e c o m p a r i s o n o f t h e d e l i v e r e d p o w e r at f u l l scale for b o t h t h e h u l l s w h i c h c l e a r i y p r e s e n t s an average o f 4%

T h i s paper presents t h e f i n a l o u t c o m e o f t h e I K H d e v e l o p m e n t , w h i c h e x p l o r e d t h e p r o p u l s i v e b e n e f i t s o f 13% larger p r o p e l l e r d i a m e t e r t h a n t h e B H , i n t e r m s o f h y d r o d y n a m i c p e r f o r m a n c e w i t h t h e h e l p o f advanced CFD tools a n d l a r g e scale m o d e l tests c o n d u c t e d i n t h e S t r e a m l i n e p r o j e c t S t r e a m l i n e , ( 2 0 1 0 ) . T h e o p t i m u m designs f o r t h e B H a n d IKH p r o p e l l e r s are p r e s e n t e d u s i n g t h e i n - h o u s e s o f t w a r e codes a n d a n assessment o f t h e n u m e r i c a l p r e d i c t i o n s o f p r o p u l s i v e e f f i c i e n c y m a d e against m o d e l test results w a s m a d e . Based o n t h e k n o w l e d g e g a i n e d so far i t w a s f o u n d t h a t t h e success o f t h e ' I n c l i n e d Keel H u l l ' a p p l i c a t i o n i n t o a l a r g e c o m m e r c i a l vessel r e q u i r e s a f i n e balance b e t w e e n t h e m i n i m a l increase i n the bare h u l l resistance a n d a m a x i m u m g a i n i n t h e p r o p u l s i v e e f f i c i e n c y . M o r e s p e c i f i c a l l y t h e f o l l o w i n g c o n c l u s i o n s are r e a c h e d based o n t h e i n v e s t i g a t i o n p r e s e n t e d i n t h i s p a p e r : 1) N u m e r i c a l s t u d y i n d i c a t e d t h a t t h e I K H c a n o f f e r 4% o f p o w e r s a v i n g a n d b e n e f i t s o f r e d u c i n g t h e h u l l p r e s s u r e f l u c t u a t i o n s a p p r o x i m a t e l y b y 35% o v e r t h e BH p r e s s u r e levels at f i r s t t w o h a r m o n i c s f o r t h e d e s i g n speed o f 2 4 k n o t s . 2 ) M o d e l tests r e v e a l e d t h a t t h e o p e n w a t e r a n d r e l a t i v e -r o t a t i v e e f f i c i e n c y o f t h e I K H p -r o p e l l e -r w a s 4% a n d 1% h i g h e -r t h a n t h a t o f t h e BH, r e s p e c t i v e l y , a t a 21.5% l o w e r s h a f t speed. This r e s u l t e d i n a 4.3% m a x i m u m s a v i n g i n t h e d e l i v e r e d p o w e r at 23 k n o t s w h i l s t t h e s a v i n g w a s 4% at t h e d e s i g n speed

3 ) The above findings f a v o r a b l y c o n f i r m t h e n u m e r i c a l p r e d i c t i o n s f o r p o w e r s a v i n g a n d hence s u p p o r t i n g t h e w o r t h i -ness o f t h e I K H c o n c e p t f o r t h e d e s i g n a p p l i c a t i o n s o f l a r g e c o m m e r c i a l vessels.

Acknowledgments

The c o n c e p t p r e s e n t e d i n t h i s p a p e r w a s d e v e l o p e d d u r i n g t h e p r i n c i p a l a u t h o r ' s Ph.D. s t u d y at N e w c a s t l e U n i v e r s i t y a n d s p o n s o r e d b y t h e Korea Science a n d E n g i n e e r i n g F o u n d a t i o n G r a n t n o : M 0 6 - 2 0 0 4 - 0 0 0 - 1 0 5 3 9 a n d Dr. Sasaki Funds. The basis h u l l f o r m used i n this s t u d y is a c o u r t e s y o f M r . D a n i e l W i n t e r s o f O r b i s L t d . F i n a l l y t h e e x p e r i m e n t a l v a l i d a t i o n s o f t h e IKH c o n c e p t is b e i n g s p o n s o r e d b y t h e EU - FP7 p r o j e c t STREAMLINE ( 2 3 3 8 9 6 FP7SST2008RTD1). The a u t h o r s t h e r e f o r e g r a t e f u l l y a c k n o w l -edge the above c o n t r i b u t i o n s m a k i n g t h e I K H research a n d t h i s p a p e r possible.

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A l l e n s t r o m , B., R i i s b e r g - J e n s e n , S., 2 0 1 1 a . S t r e a m l i n e : I n c l i n e d K e e l C o n c e p t W P 1 1 . 5 , B a s i s H u l l . SSPA R e p o r t n o . R E 4 0 0 8 4 8 1 7 - 1 1 - 0 0 - A . A l l e n s t r o m , B., R i i s b e r g - J e n s e n , S., 2 0 1 1 b . S t r e a m l i n e : I n c l i n e d K e e l C o n c e p t W P 1 1 . 5 , D e s i g n H u l l . SSPA R e p o r t n o . R E 4 0 0 8 4 8 1 7 - 1 2 - 0 0 - A . B e e k , T . V . , 2 0 0 4 . T e c h n o l o g y G u i d e l i n e s f o r E f f i c i e n t D e s i g n a n d O p e r a t i o n o f S h i p P r o p u l s i o n s . M a r i n e N e w s , W a r t s i l a . B u r r i l l , L C , E m e r s o n , A., 1 9 6 3 . P r o p e l l e r c a v i t a t i o n : f u r t h e r t e s t s o n 1 6 i n . p r o p e l l e r m o d e l s i n t h e k i n g ' s c o l l e g e c a v i t a t i o n t u n n e l . T r a n s . NECIES 7 8 , 2 9 5 - 3 2 0 . C i p i n g , J . , L i a n g q u a n , C , W e i m i n g , T., 1 9 8 9 . I n v e s t i g a t i o n o n r e s i s t a n c e a n d p r o p u l s i v e q u a l i t i e s o f l a r g e f u l l s h i p w i t h l o w r e v o l u t i o n l a r g e d i a m e t e r p r o p e l l e r . I n : P r o c e e d i n g s o f t h e I n t e r n a t i o n a l S y m p o s i u m o n S h i p R e s i s t a n c e a n d P o w e r i n g P e r f o r m a n c e , p p . 1 8 4 - 1 9 0 .

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