Rolling trails with the mv Langkloof of the South African Marine Corporation Ltd

R e p o r t No. 125»

LABORATORIUM VOOR

SCHEEPSBOUWKUNDE

T E C H N I S C H E H O G E S C H O O L DELFT

r

ROLLING T R I A L S '.VITH THE M.V. "LANGKLOOF" OF

THE SOUTH AFRICAN MARINE GORPORATION L T R

AT MARCH 2 2 , 1965„

By J . H o V u g t s O

SUMMARY.

The tonnage w e l l o f t h e f r u i t c a r r i e r m . V c " L a n g k l o o f " was p a r t l y f i l l e d w i t h w a t e r t o a c t a s an a n t i - r o l l i n g t a n k o f the f r e e s u r f a c e t y p e . R o l l a n g l e s w i t h and w i t h o u t w a t e r i n the t a n k were m e a s u r e d . The c o n d i t i o n s under w h i c h t h e t e s t s were done a r e d e s c r i b e d . The r e -s u l t -s o f t h e mea-surement-s a r e p r e -s e n t e d i n t h e form o f h i -s t o g r a m -s o f t h e r o l l a n g l e s . I t i s e x p l a i n e d why no i n f o r m a t i o n a s r e g a r d s t h e r o l l damping p e r f o r m a n c e o f t h e t a n k c o u l d be o b t a i n e d o INTRODUCTIONo The v e s s e l i s s u b j e c t e d to a v e r y u n c o m f o r t a b l e r o l l i n g motion when i n b a l l a s t . An a t t e m p t to r e d u c e t h i s r o l l i n g c o u l d be made by p a r t l y f i l l i n g t h e tonnage w e l l i n t h e m i d s h i p tween d e c k a r e a i n o r -d e r t o g e t an a n t i - r o l l i n g t a n k o f t h e f r e e s u r f a c e type» A p r e v i o u s t h e o r e t i c a l e s t i m a t i o n o f the t a n k e f f e c t had shown t h a t 3 0 t o ^0 p e r -c e n t r e d u -c t i o n i n r o l l i n g -c o u l d be e x p e -c t e d .

To v e r i f y t h i s s t a t e m e n t r o l l a n g l e s were measured w i t h and w i t h -o u t w a t e r i n t h e t a n k , w i t h t h e i n t e n t i -o n t-o c-ompare t h e tw-o c a s e s and to i n d i c a t e the improvement, i f p o s s i b l e . To be a b l e to do so i t i s ne-c e s s a r y t h a t t h e e x t e r n a l ne-c o n d i t i o n s ( e e a s t a t e ) r e m a i n t h e same d u r i n g a s e r i e s o f t e s t s . U n f o r t u n a t e l y t h i s c o n d i t i o n c o u l d not be f u l f i l l e d . T h e r e f o r e no q u a n t i t a t i v e i n f o r m a t i o n c a n be s u p p l i e d a s r e g a r d s t h e e f f e c t i v e n e s s o f t h e t a n k installation»

The t e s t s were c a r r i e d out i n t h e Bay o f B i s c a y on t h e 2 2 n d o f March I965» w h i l e t h e s h i p was on i t s way from Rotterdam t o Capetown»

2

-THE LOADING CONDITION.

The v e s s e l l e f t R o t t e r d a m on t h e 2 0 t h o f March I 9 6 5 i n b a l l a s t . 1 1 The d r a f t f o r w a r d was 1 1 - f t = 3 , 5 0 • and a f t 1 8 ^ f t = 5 , 5 6 m. W i t h a Bean d r a f t o f | ( l l | + 1 8 ^ ) = 1^^^ f t o r | ( 3 , 5 0 + 5 , 5 6 ) = 4 , 5 3 m t h e h y d r o s t a t i c c u r v e s i n d i c a t e a d i s p l a c e m a n t o f 86OO l o n g t o n s o r 8 7 3 8 m e t r i c t o n s .

At t h e day o f tho t e s t s t h e c h i e f o f f i c e r c a l c u l a t e d the m e t a c e n -t r i c h e i g h -t , c o r r e c -t e d f o r f r e e s u r f a c e s , bu-t w i -t h o u -t a n -t i - r o l l i n g t a n k , t o be 7 . 7 1 f t = 2 , 3 5

A c c o r d i n g t o t h e f o r m u l a :

i n w h i c h k = 0 , ^ B i s t h e t r a n s v e r s e r a d i u s o f g y r a t i o n , t h e n a t u r a l r o l l i n g p e r i o d s h o u l d be a b o u t 1 0 , 9 s e c . The r e c o r d i n g s o f t h e r o l l i n g a n g l e on a time b a s e i n d i c a t e d a n a t u r a l p e r i o d between 9 and 1 0 s e c .

MEASURING BrjUIPI-SNT.

R o l l a n g l a s were m e a s u r e d w i t h a g y r o and r e c o r d e d on a S e f r a m pen r e c o r d e r . A l s o t h e peak v a l u e o f t h e s t a r b o a r d r o l l a n g l e d u r i n g e a c h c y c l e was i n d i c a t e d i n i n t e r v a l s o f two d e g r e e s and t h e number o f peak v a l u e s i n e a c h i n t e r v a l was c o u n t e d .

The e q u i p m e n t was i n s t a l l e d a t t h e p i l o t ' s c a b i n on t h e n a v i g a t i n g b r i d g e d e c k .

ROLLING T E S T S .

R o l l r e c o r d i n g s were t a k e n i n t h e Bay o f B i s c a y on t h e 2 2 n d o f March 1 9 6 5 . A r e c o r d i n g w i t h t h e tonnage w e l l p a r t l y f i l l e d w i t h w a t e r was a l -ways e n c l o s e d by two r e c o r d i n g s w i t h t h e t a n k empty. Two c o n d i t i o n s were c o n s i d e r e d , namely a beam s e a and a bow s e a . A f t e r t h e l a s t s e r i e s o f t e s t s p i p i n g i n t h e t o n n a g e w e l l was s l i g h t l y damaged by a w a s h p l a t e , g o t l o o s e by t h e w a t e r a c t i o n . To p r e v e n t f u r t h e r damage t h e c a p t a i n had t o s t o p any f u r t h e r f i l l i n g o f t h e t a n k .

3

-D u r i n g t h e t e s t s t h e w e a t h e r was g e n e r a l l y good w i t h a moderata s e a . Tha w e a t h e r f o r e c a s t i n t h i s a r e a f o r t h e n i g h t o f 2 1 s t to 2 2 n d

March w a s : "South to s o u t h w e s t t h r e e o r f o u r . R a i n a t t i m e s . C o a s t a l f o g p a t c h e s . M a i n l y good away from c o a s t s " , and f o r t h e 2 2 n d March: " B i s c a y s o u t h w e s t , m a i n l y f o u r t o s i x , b u t t h r e e i n s o u t h s h o w e r s . a o o d " o T e s t c i r c u m s t a n c e s a r e s u m m a r i z e d i n t h e f o l l o w i n g tabie» Time o f b e -g i n n i n -g o f t a s t D u r a t i o n o f r e c o r -d i n g Tonnage w e l l 9 . 1 5 h r Run 2 I 0. 3 0 h r Run 3 1 2 . 0 5 h r Run k 1 6 . 1 5 h r Run 5 1 7 . 3 0 h r 21 min. empty 2 0 min. f i l l e d with h =1 , 5 8 m 2 5 rain. empty P o s i t i o n N i f 6 " l 5 ; . / 7 ° 2 7 ' C o u r s e 3 5 0 Speed a c -c o r d i n g 1 6 ^ - I 7 k n 1 8- I 8 ^ k n t o l o g 3 5 0 1 3 5 18 2 0 min. empty N 4 5 ° 2 8 ' ; W 8 ° 9 ' 2 0 7 17 2 0 m i n . f i l l e d with 46-,5m3 h = 1 , 6 5 m 2 0 7 17 Run 6 1 8 . 1 3 h r 21 B i n . 2 0 5 1 5 , 5

D i r e c t i o n beam s e a on beam s e a on beam s e a on bow s e a on bow s e a on bow s e a on o f s e a p o r t s i d e p o r t s i d e s t a r b o a r d s t a r b o a r d s t a r b o a r d s t a r b o a r d

s i d e s i d e s i d e s i d e

TANK ACTION.

The a c t i o n o f t h e a n t i - r o l l i n g t a n k depends on t h e c r e a t i o n o f a h y d r a u l i c jump o r b o r e , l a g g i n g about one q u a r t e r o f a p e r i o d ( o r n i n e t y d e g r e e s ) b e h i n d t h e r o l l i n g m o t i o n o f t h e v e s s e l . When t h e t a n k was f i l l ed i t was n o t i c e d t h a t t h e b o r e a c t u a l l y e x i s t e d and t h a t i t had t h e c o r -r e c t p h a s i n g w i t h -r e s p e c t to t h e s h i p ' s m o t i o n . So t h e o b s e -r v e d phenomena i n t h e t a n k f u l l y a g r e e d w i t h t h e e x p e c t a t i o n s , C o n s e q u e n t l y t h e c o u n t e r a c t i n g moment, w h i c h i s opposed to t h e s h i p ' s r o l l i n g , was c e r t a i n l y d e v e l -oped..

-- h .

U n f o r t u n a t e l y t a n k f i l l i n g and e m p t y i n g t o o k a l o n g time and t h e s e a s t a t e i n the Bay o f B i s c a y changed v e r y q u i c k l y , s o t h a t no two r e c o r d i n g s w i t h t h e a n t i r o l l i n g t a n k i n and out o f a c t i o n can be c o n s i d e r e d to have been t a k e n under the same e x t e r n a l c o n d i t i o n s . T h e r e -f o r e no q u a n t i t a t i v e i n d i c a t i o n o -f any e -f -f e c t o -f t h e t a n k c a n be given» However, the i m p r e s s i o n o f the c a p t a i n and t h e o f f i c e r s was t h a t t h e s h i p r o l l e d e a s i e r when t h e t a n k was f i l l e d . As was known b e f o r e h a n d , the s i z e o f the t a n k i s too s m a l l to dominate t h e r o l l i n g m o t i o n , s o a s p e c t a c u l a r improvement c o u l d not be e x p e c t e d .

T h e s e t e s t s show c l e a r l y t h a t i t w i l l be h a r d l y p o s s i b l e to l e a r n a n y t h i n g about t h e t a n k ' s e f f e c t i v e n e s s from s e a t r i a l s when the s e a s t a t e c a n n o t be measured q u a n t i t a t i v e l y a t t h e same time f o r r e f e r e n c e o O n l y t h e n a t h o r o u g h a n a l y s i s can be made.

TEST RESULTS.

A l l r e s u l t s p r e s e n t e d h e r e b y have to be c o n s i d e r e d by t h e m s e l v e s . I t i s not p o s s i b l e to compare any o f two r e c o r d i n g s t a k e n , b e c a u s e o f t h e r a p i d c h a n g i n g o f t h e e x t e r n a l s e a c o n d i t i o n s . T h e r e f o r e from t h e measurements no i n d i c a t i o n can be o b t a i n e d o f the damping e f f e c t o f

t h e t a n k .

1o Beam s e a .

The number o f r o l l s t o t h e s t a r b o a r d s i d e i n i n t e r v a l s o f two de-g r e e s i s p r e s e n t e d i n f i de-g . 1. The t o t a l number o f r o l l s f o r r u n 1 , 2 and 3 was 1 1 9 , H I and 123 r e s p e c t i v e l y . I n the f i g u r e s t h e s e num-b e r s have num-been r e d u c e d t o an e q u a l num-base o f 100 r o l l s .

A p a r t from the change i n s e a c o n d i t i o n t h e g r e a t d i f f e r e n c e between r u n 1 and 3 way be due to the f a c t t h a t r u n 1 and r u n 2 were t a k e n w i t h t h e beam s e a on the p o r t s i d e and r u n 3 v;ith t h e beam s e a on t h e s t a r b o a r d s i d e . T h e r e f o r e i n the f i r s t r u n an i n i t i a l h e e l to s t a r b o a r d and i n t h e l a s t one an i n i t i a l h e e l t o p o r t may have been p r e -s e n t , w h i l e o n l y t h e peak v a l u e -s o f the -s t a r b o a r d r o l l -s c o u l d be c o u n t e d . The l 8 0- d e g r e e s c o u r s e change was o r d e r e d by t h e c a p t a i n f o r r e a s o n s o f n a v i g a t i o n .

From f i g o 1 the a v e r a g e r o l l a n g l e and t h e s i g n i f i c a n t r o l l a n g l e

were c a l c u l a t e d ; t h e l a t t e r b e i n g t h e a v e r a g e o f t h e one t h i r d p a r t o f the l a r g e s t r o l l s . The f i g u r e s have t o be c o n s i d e r e d a s i n d i c a t i v e f o r a c t u a l l y c o n t i n u o u s c u r v e s and no h i s t o g r a m s s h o u l d be u s e d f o r

5 -t h e i r d e -t e r m i n a -t i o n . r u n a v e r a g e a n g l e s i g n i f i c a n t a n g l e ' I 5 , 2 7,^ 2 k,6 3 2 , 9 4 , 1 2c Bow s e a .

The same i n f o r m a t i o n f o r t h e case o f a bow s e a i s p r e s e n t e d i n f i g . 2 . The nuBiber o f r o l l s was 1 3 9 , 1 0 9 , 1 1 3 r e s p e c t i v e l y , b u t i n t h e f i g u r e t h e y have a g a i n been r e d u c e d t o 1 0 0 r o l l s .

As t o t h e s e a s t a t e i t must be r e m a r k e d t h a t e s p e c i a l l y i n t h i s s e -r i e s t h e s e a c o n d i t i o n changed v e -r y q u i c k l y and i t was w o -r s t when .

t h e tank was f i l l e d . T h i s f a c t was f u l l y c o n f i r m e d by t h e s h i p ' s o f f i c e r s . As no q u a n t i t a t i v e i n f o r m a t i o n o f t h e s e a s t a t e i s p r e -s e n t no a n a l y -s i -s c a n be made.

The a v e r a g e and s i g n i f i c a n t r o l l i n g a n g l e s a r e g i v e n below.

r u n a v e r a g e a n g l e s i g n i f i c a n t a n g l e 5 4 , 3 6 , 8 6 4 , 0 6 , 1 INCLINOMETER CHECK. • I t was f e l t t h a t t h e i n c l i n o m e t e r e x a g g e r a t e d r o l l i n g a n g l e s l a r g e ¬ l y . A t t h e c a p t a i n ' s r e q u e s t i t was t r i e d t o c a l i b r a t e t h e i n c l i n o m e t e r r e a d i n g s w i t h t h e a i d o f t h e r o l l - g y r o . A g r a p h o f t h e r e s u l t s i s g i v e n i n f i g . 3 . As c a n be s e e n t h e i n c l i n o m e t e r n e a r l y a l w a y s i n d i c a t e s t o o l a r g e a n g l e s , a t l e a s t f o r r o l l i n g p e r i o d s o f a b o u t 9 s e c . S c a t t e r i s l a r g e and r e a d i n g s a r e v e r y i n a c c u r a t e . T h i s i s c e r t a i n l y due t o t h e f a c t t h a t t h e i n c l i n o m e t e r i s s e n s i b l e t o a t h w a r t s h i p s a c c e l e r a t i o n s and t h a t i t s own momentum p r e v e n t s i t from i n d i c a t i n g s h i p ' s a n g l e s i n -s t a n t l y .

•

ACKTfO/JLEDG EMENT.

Thank must be o f f e r e d t o t h e c a p t a i n and s h i p ' s o f f i c e r s f o r t h e i r e x c e l l e n t c o o p e r a t i o n i n t h e t e s t s c

- 1 3 ,

O 2

6 8 10 12 U

• M

2 6 8 10 12 U

R o U a m p l i t u d e in d e g r e e s ( s t a r b o a r d r o l l s )

BOW SEA

RUN 5.

Tank f i l l e d .

RUN 6.

Tank empty.

6 8 10 12 U

» R o l l a m p l i t u d e in d e g r e e s ( s t a r b o a r d r o l l s )

1 2 ~ U

F I G :

2.

PRELIMINARY REPORT ON ROLLING TRIALS WITH THE

"LANGKLOOF" OF THE SOUTH AFRICAN J4ARINE CORPORATION LTD.

By I r J.H. VugtSo R e p o r t N r o 1 2 5 » S h i p b u i l d i n g L a b o r a t o r y o T e c h n o l o g i c a l U n i v e r s i t y - D e l f t o 6 A p r i l 19650 D a t e : 2 2 n d March

I 9 6 5 .

- 1

P r e l i m i n a r y r e p o r t on r o l l i r i K t r i a l s w i t h t h e

m.v. " L a n g k l o o f " o f t h e S o u t h A f r i c a n M a r i n e C o r p o r a t i o n Ltdo

By I r J.Ho Vugts»

The l o a d i n K c o n d i t i o n o

The v e s s e l l e f t R o t t e r d a m on t h e 20th March I965 i n b a l l a s t . The d r a f t f o r w a r d was 11 j f t = 3 , 5 0 » and a f t i s j f t = 5,56m. W i t h a

h y d r o s t a t i c c u r v e s i n d i c a t e a d i s p l a c e m e n t o f 860O l o n g t o n s o r 8738 m e t r i c t o n s . At t h e day o f t h e t e s t s t h e c h i e f o f f i c e r c a l c u l a t e d t h e m e t a c e n -t r i c h e i g h -t , c o r r e c -t e d f o r f r e e s u r f a c e s , b u -t w i -t h o u -t a n -t i - r o l l i n g -t a n k , to be 7o71 f t =

2,35

M e a s u r i n g equipmento

R o l l a n g l e s were measured w i t h a g y r o and r e c o r d e d on a S e f r a m pen r e c o r d e r . Moreover t h e p e a k v a l u e o f t h e s t a r b o a r d r o l l a n g l e d u r i n g e a c h c y c l e was i n d i c a t e d i n i n t e r v a l s o f two d e g r e e s and t h e number o f peak v a l u e s i n e a c h i n t e r v a l was counted»

The equipment was i n s t a l l e d a t t h e p i l o t ' s c a b i n on t h e n a v i g a t i n g b r i d g e d e c k .

T = 2Tr k

2

-R o l l i n g t e s t s .

R o l l r e c o r d i n g s were t a k e n i n t h e Bay o f B i s c a y on 22nd March 1965. A r e c o r d i n g w i t h t h e tonnage w e l l p a r t l y f i l l e d w i t h w a t e r was a l w a y s e n c l o s e d by two r e c o r d i n g s w i t h t h e t a n k empty. Two c o n d i t i o n s were c o n s i d e r e d , namely a beam s e a and a bow s e a . A f t e r t h e l a s t s e -r i e s o f t e s t s p i p i n g i n t h e tonnage w e l l waa s l i g h t l y damaged by a w a s h p l a t e , g o t l o o s e by t h e w a t e r a c t i o n . To p r e v e n t f u r t h e r damage

t h e c a p t a i n had t o s t o p any f u r t h e r f i l l i n g o f t h e t a n k .

D u r i n g t h e t e s t s t h e w e a t h e r was g e n e r a l l y good w i t h a moderate s e a . The w e a t h e r f o r e c a s t f o r t h e n i g h t o f 21st t o 22nd March w a s :

" S o u t h tö southwest t h r e e o r f o u r . R a i n a t t i m e s . C o a s t a l f o g p a t c h e s . M a i n l y good away from o o a a t s " , and f o r t h e 22nd March: " B i s c a y s o u t h -w e s t , m a i n l y f o u r t o s i x , b u t t h r e e i n s o u t h s h o -w e r s . Good".

T e s t c i r c u m s t a n c e s a r e summarized i n t h e f o l l o w i n g t a b l e o

Rxin 1 Run

2

3

5

6

Time o f b e g i n -n i -n g o f t e s t

9.15

10.30

12.05

16.15

17.30

21

20

25

20

20

21

4 4

,5 m3

=

1 , 5 8

46

,5 m3

1,65

^4

^28*

;W8

°9'

-

₅₅₀

₃₅₀

₁₃₅

₂₀₇

₂₀₇

₂₀₅

1 6 | -

17

18 - 1 8 |

18

₁₇

₁₇

_15,5

D i r e c t i o n o f beam s e a on beam s e a on L- beam sea on bow s e a on bow s e a on bow s e a on s e a •port s i d e p o r t s i d e s t a r b o a r d s t a r b o a r d s t a r b o a r d s t a r b o a r d

Tank a c t i o n o

The a c t i o n o f t h e a n t i - r o l l i n g t a n k depends on t h e c r e a t i o n o f a h y d r a u l i c jump o r b o r e , l a g g i n g about one q u a r t e r o f a p e r i o d ( o r n i n e t y d e g r e e s ) b e h i n d t h e r o l l i n g motion o f t h e v e s s e l . vVhen t h e t a n k was f i l l ed i t was n o t i c e d t h a t t h e bore a c t u a l l y e x i s t e d and t h a t i t had t h e c o r -r e c t p h a s i n g w i t h -r e s p e c t to t h e s h i p ' s m o t i o n . So t h e o b s e -r v e d phenomena i n t h e t a n k f u l l y a g r e e d w i t h t h e e x p e c t a t i o n s . C o n s e q u e n t l y t h e c o u n t e r -a c t i n g moment, opposed t o t h e s h i p ' s r o l l i n g , w-as c e r t -a i n l y developpedo

Tank effect»

The i n f o r m a t i o n c o l l e c t e d d u r i n g t h e t e s t s h a s to be worked o u t and w i l l be r e p o r t e d l a t e r . U n f o r t u n a t e l y t a n k f i l l i n g and e m p t y i n g t o o k a l o n g t i a e and t h e s e a s t a t e i n t h e Bay o f B i s c a y changed v e r y q u i c k l y , so t h a t no two r e c o r d i n g s w i t h t h e a n t i - r o l l i n g t a n k i n and o u t o f a c t i o n c a n be c o n s i d e r e d t o have been t a k e n under t h e same e x t e r n a l c o n d i t i o n s . T h e r e f o r e no q u a n t i t a t i v e i n d i c a t i o n o f any e f f e c t o f t h e t a n k c a n be g i -ven » However, t h e i m p r e s s i o n o f t h e c a p t a i n and t h e o f f i c e r s was t h a t t h e s h i p r o l l e d e a s i e r when t h e t a n k was f i l l e d . As known b e f o r e h a n d , t h e s i z e o f t h e t a n k i s too s m a l l t o dominate t h e r o l l i n g m o t i o n , s o a s p e c t a c u l a r improvement c o u l d n o t be e x p e c t e d .

T h e s e t e s t s show c l e a r l y t h a t i t w i l l be h a r d l y p o s s i b l e t o l e a r n a n y t h i n g about t h e t a n k ' s e f f e c t i v e n e s s from s e a t r i a l s when t h e s e a s t a t e c a n n o t be measured q u a n t i t a t i v e l y a t t h e same time f o r r e f e r e n c e . Only t h e n a t h o r o u g h a n a l y s i s c a n be made. I n c l i n o m e t e r . I t waa f e l t t h a t t h e i n c l i n o m e t e r e x a g g e r a t e d r o l l i n g a n g l e s l a r g e l y . At t h e c a p t a i n ' s w i s h i t was t r i e d to c a l i b r a t e t h e i n c l i n o m e t e r r e a d i n g s w i t h t h e a i d o f t h e r o l l - g y r o . A g r a p h o f t h e r e s u l t s i s g i v e n . Aa c a n be s e e n t h e i n c l i n o m e t e r n e a r l y a l w a y s i n d i c a t e s too l a r g e an,r:les, a t l e a s t f o r r o l l i n g p e r i o d e o f about 9 s e c . S c a t t e r i s l a r g e and r e a d i n g s a r e v e r y i n a c c u r a t e . T h i s i s c e r t a i n l y due t o t h e f a c t t h a t t h e i n c l i n o m e t e r i s s e n -s i b l e t o a t h w a r t -s h i p -s a c c e l e r a t i o n -s and t h a t i t -s own momentum p r e v e n t -s i t from i n d i c a t i n g s h i p ' s a n g l e s i n s t a n t l y .

Thanks must be o f f e r e d t o t h e c a p t a i n and s h i p ' s o f f i c e r s f o r t h e i r e x c e l l e n t c o o p e r a t i o n i n t h e tests»