A disposable wave buoy

R e p o r t No. 397

LABORATORIUM VOOR

SCHEEPSBOUWKUNDE

TECHNISCHE HOGESCHOOL DELFT

r n

by M. B u i t e n h e k

L J

P r e p a r e d f o r t h e Symposium on O f f s h o r e Data A c q u i s i t i o n systems, o r g a n i z e d by t h e S o c i e t y f o r Underwater Technology o f t h e

U n i v e r s i t y o f Southampton i n September '19'jk

1

A DISPOSABLE V/AVE BUOY

M. B u i t e n h e k ^

Summary

A d e s c r i p t i o n i s g i v e n o f a s i m p l e v a v e h e i g h t m e a s u r i n g buoy w h i c h i s i n e x p e n s i v e enough t o be d i s p o s e d o f a f t e r i t has been u s e d once t o m e a s u r e t h e s e a s t a t e i n t h e e n v i r o n m e n t o f a c o i r i m e rc i a l l y r u n s h i p .

1 • I n t r o d u c t i o n

A. wave h e i g h t m e a s u r i n g buoy has been d e v e l o p e d b y t h e S h i p b u i l d i n g L a b o r a t o r y o f t h e D e l f t U n i v e r s i t y o f T e c h n o l o g y f o r d a t a ' a c q u i s i t i o n o f t h e c o n d i t i o n o f t h e s u r f a c e o f t h e s e a . The buoy s u p p l i e s c o n t i n u o u s l y d a t a o f t h e v e r t i c a l a c c e l e r a -t i o n s -t o w h i c h -t h e f l o a -t i n g body i s s u b j e c -t e d .

The v e r t i c a l p o s i t i o n o f t h e body ( a n d t h e accelerom.eter) i s m a i n t a i n e d b y means o f a s t i f f arm w i t h a l e n g t h o f 1 m e t e r and a t h i n s t e e l w i r e w i t h a l e n g t h b e t w e e n 2 and hO m e t e r s and a w e i g h t o f 100 N a t t h e end.

The l e n g t h r e q u i r e m e n t depends on t h e e x p e c t e d s i g n i f i c a n t wave p e r i o d . D u r i n g t h e l a u n c h i n g , t h e s t e e l w i r e i s wound upon a c a r d b o a r d case and w i l l be r o l l e d o u t when t h e buoy t o u c h e s t h e s u r f a c e o f t h e sea.

The f r e q u e n c y m o d u l a t e d m e a s u r i n g s i g n a l i s t r a n s m i t t e d b y r a d i o t o a r e c e i v e r on b o a r d o f a s h i p . The p r i n c i p a l d e s i g n c o n s i d e r a t i o n has been t o f i n d a compromise between good t e c h n i c a l s p e c i f i c a t i o n s and r e l a t i v e l y l o w c o s t s because o f t h e r e q u i r e m e n t t o l o s e o f t h e buoy a f t e r l a u n c h i n g f r o m m e r c h a n t s h i p s .

The wave buoys have been u s e d i n e x p e r i m e n t s o n b o a r d t h e S.S. " A n t l a n t i c C r o W i "

( r e f . 1 ) .

B o t h a n a l o g and d i g i t a l d a t a - r e d u c t i o n methods c a n be a p p l i e d t o compute h i s t o -gramjnes ^ c o v a r i a n c e f u n c t i o n s and p o w e r - d e n s i t y specti'a o f wave h e i g h t s a n wave p e r i o d s by means o f d o u b l e i n t e g r a t i o n and a square bandpass f i l t e r .

2. R e q u i r e m e n t s o f t h e d e s i g n

Because t t i e r e c o v e r y o f a m_easui'ing d e v i c e f r o m t l i e sea i s a t i m e consi.uiiing and exT)ensive j o b , t h e buoy i s d e s i g n e d and c o n s t r u c t e d as a d i s p o s a b l e one.

_H U n i v e r s i t y o f T e c h n o l o g y , D e l f t , L a b o r a t o r y o f S h i p b u i l d i n g Mekelweg 2, D e l f t , The N e t h e r l a n d s

2 The t a i l buoys a r e i n t e n d e d t o be l a u n c h e d f r o m o r d i n a r y m e r c h a n t s h i p s b y t h e n o r m a l c r e w , w i t h o u t i n t e r f e r i n g w i t h t h e s h i p s s c h e d u l e . The f o l l o w i n g r e q u i r e m e n t s w i l l be met: - r e l i a b l e i n f o r m a t i o n o f t h e v e r t i c a l a c c e l e r a t i o n s - r e l i a b l e o p e r a t i o n - s h o c k p r o o f - easy t o h a n d l e by one p e r s o n - i n e x p e n s i v e 3 - F u n c t i o n a l d e s c r i p t i o n

The absence o f any f i x e d r e f e r e n c e n e c e s s i t a t e s t h e use o f a f l o a t i n g body f r o m w^hich t h e i n f o r m a t i o n a b o u t t h e wave h e i g h t and t h e wave p e r i o d must be o b t a i n e d f r o m t h e v e r t i c a l a c c e l e r a t i o n - s i g n a l b y means o f d o u b l e i n t e g r a t i o n .

P r o c e e d i n g from, a l i n e a r accelerom.eter w h i c h i s c o n n e c t e d t o t h e v e r t i c a l a x i s o f t h e buoy, c a r e must be t a k e n t h a t t h i s a x i s has t o be s t a b i l i s e d i n t h e c o r r e c t d i r e c t i o n

h. S t a b i l i z a t i o n o f t h e v e r t i c a l p o s i t i o n

A s t i p u l a t i o n f o r t h e c o r r e c t d a t a r e d u c t i o n o f t h e a c c e l e r a t i o n s i g n a l i s , t h a t t h e p i c k - u p keeps t h e v e r t i c a l p o s i t i o n r e g a r d l e s s o f t h e shape o f t h e wave. I n c o n n e c t i o n w i t h t h e s i n g l e use c f t h e buoy, e x p e n s i v e s t a b i l i z a t i o n p r i n c i p l e s a r e l e f t o u t o f c o n s i d e r a t i o n . I n f i g u r e 1 a s c h e m a t i c d i a g r a m i s g i v e n , on t h e b a s i s o f w h i c h t h e o p e r a t i o n o f t h e t a i l buoy can be i l l u s t r a t e d .

A t h i n w i r e , t o w h i c h a w e i g h t G i s c o n n e c t e d a t t h e end i s , v i a a s h o r t s t i f f c o n s t r u c t i o n , c o n n e c t e d t o t h e f l o a t i n g body.

A d i s t u r b i n g moment M, caused by t h e m.oving sea surfa.ce, w i l l t u r n t h e buoy a r o u n d a h o r i z o n t a l a x i s .

The r i g h t i n g m.Gment i s b r o u g h t a b o u t by t h e p r o d u c t o f t h e l e n g t h L l o f t h e s t i f f t a i l and t h e f o r c e F l w h i c h i s t h e p e r p e n d i c u l a r r e s o l u t i o n o f t h e t e n s i o n i n t h e w i r e .

For L2 >> L l a p p l i e s , t h a t t h e a n g l e a approaches z e r o , t h e r e f o r e t h e r i g h t i n g moment may be '.•.'ritten as:

F1L1 --^ L l G s i n 3

The l a i ' g e r t h e a n g l e o f r o t a t i o n 0, t h e l a r g e r t h e r i g h t i n g moment w i l l be. The above c o n c l u s i o n i s based on a s t a t i c s i t u a t i o n .

3

The dynamic b e h a v i o u r i s k e p t o u t o f c o n s i d e r a t i o n . V/ith t h e d e c i s i o n o f t h e l e n g t h o f t h e w i r e , a l l o w a n c e w i l l be made f o r t h e o r b i t a l movement o f t h e wave. The

l e n g t h o f t h e w i r e w i l l be chosen i n such a way, t h a t a t t h e p l a c e o f t h e w e i g h t , t h e wave movement i s r e d u c e d s u f f i c i e n t l y .

I n t h e measurements r e p o r t e d p r e s e n t l y , t h e f o l l o w i n g l e n g t h s o f w i r e have been used: On t h e I J s s e l m e e r On t h e N o r t h Sea On t h e A t l a n t i c Ocean 2 . 5 m 1 2 m ^ 0 m

D u r i n g t h e s e measurem^ents i t has been e s t a b l i s h e d t h a t b y means o f t h i s t a i l s t a b i l i z a t i o n t h e v e r t i c a l p o s i t i o n w i l l be k e p t w i t h i n a d e v i a t i o n o f + o r - 5 d e g r e e s . 5 - B l o c k d i a g r a m o f t h e t a i l buoy I n f i g - o r e 2 t h e b l o c k d i a g r a m i s s h o ™ o f t h e e l e c t r o n i c p a r t o f t h e b u o y , con-s i con-s t i n g o f t h e f o l l o w i n g p a r t con-s : - t h e a c c e l e r o m e t e r - t h e c a r r i e r o s c i l l a t o r , n e c e s s a r y f o r t h e power o f t h e sensor - t h e d e m o d u l a t o r - t h e volta-ge c o n t r o l l e d o s c i l l a t o r - t h e t r a n s m i t t e r and a n t e n n a - t h e s t a b i l i z e d power s u p p l y - t h e b a t t e r i e s 5 . 1 The a c c e l e r o m e t e r

The f o l l o w i n g demands have been m.ade o f t h e s e n s o r : f r e q u e n c y r e s p o n s e h y s t e r e s i s m.easuring r a n g e o v e r l o a d r a n g e 0 - 5 cps < 0 , 2 ^ F.S. ± 1 g 2 0 t i m e s - i t has t o be i n e x p e n s i v e

I n t h e d e s i g n e d system an a.ccelercm.eter has been chosen w h i c h i s e q u i p e d w i t h an i n d u c t i v e p i c k - u p .

5 . 2 The c a r r i e r o s c i l l a t o r

The consequence o f t h e use o f an i n d u c t i v e sensor i s t h e n e c c e s s i t y o f a power o s c i l l a t o r . The chosen f r e q u e n c y amounts t o 8 0 0 0 c p s .

5 . 3 The d e m o d u l a t o r

The p h a s e - s e n s i t i v e demodulator i s used t o e l i m i n a t e t h e b e f o r e m e n t i o n e d 8OOO cps o s c i l l a t o r s i g n a l . Of t h e r e m a i n i n g s i g n a l , t h e a m p l i t u d e and t h e p o l a r i t y a r e p r o p o r t i o n a l w i t h t h o s e o f t h e a p p e a r i n g a c c e l e r a t i o n . 5. i i The V o l t a g e C o n t r o l l e d O s c i l l a t o r ( V . C. 0 . ) Because v a r i o u s a t m o s p h e r i c s can t a k e p l a c e d u r i n g t h e t r a n s m i s s i o n by r a d i o o f t h e a c c e l e r a t i o n s i g n a l , w h i c h may i n f l u e n c e t h e a m p l i t u d e o f t h e s i g n a l , t h e i n f o r m a t i o n i s c o n v e r t e d i n t o a change o f t h e f r e q u e n c y . 5 . 5 The t r a n s m i t t e r a n d t h e antenna W i t h t h e h e l p o f a c r y s t a l c o n t r o l l e d t r a n s m i t t e r (± 27 Mc) t h e f r e q u e n c y modul a t e d a c c e modul e r a t i o n s i g n a modul i s t r a n s m i t t e d b y an M t r a n s m . i t t e r . For t h e t e s t -models t h e used t r a n s m i t t e d power w^as ± 2 0 0 m W a t t .

More o r l e s s dependent on t h e s i t u a t i o n i n t h e v i c i n i t y o f t h e r e c e i v i n g a n t e n n a , t h e r a n g e has been d e t e r m i n e d t o be:

f o r wave h e i g h t s o f about 2 m : i 3 3 km f o r wave h e i g h t s c f about 7 m : ^ 11 km To i n c r e a s e t h e d i s t a n c e r a n g e , t h e t r a n s m i t t e d power has t o be i n c r e a s e d t o a b o u t 2 W a t t . 5 . 6 The s t a b i l i z e d power s u p p l y Because t h e v o l t a g e o f t h e b a t t e r i e s i s n o t c o n s t a n t , t h e power i s s t a b i l i z e d e l e c t r o n i c a l l y i n o r d e r t o i n c r e a s e t h e s t a b i l i t y o f t h e mieasuring p a r t . 5 . 7 The b a t t e r i e s

The f o l l o w i n g demands have been m.ade o f t h e b a t t e r i e s : - s u f f i c i e n t power, a l s o a t l o w t e m p e r a t i r r e - r o b u s t m e c h a n i c a l p e r f o r m a n c e - p e r m a n e n t l y good c o n n e c t i o n w i t h t h e e l e c t r o d e s , even a f t e r l a u n c h i n g o f t h e body - l e a k p r o o f . 6. C a l i b r a t i o n and t h e s e n s i t i v i t y o f t h e t a i l buoy

VJith each s e p a r a t e buoy a s t a t i c c a l i b r a t i o n i s e x e c u t e d i n a s i m p l e way, b y

t i u ' n i n g t h e a c c e l e r o m e r e r o r t h e c o m p l e t e buoy over a, known a n g l e . The s e n s i t i v i t y ( c p s p e r ™/sec2) i s d e t e r m i n e d f r o m t h e v a l u e s a t 0 ° and 9 0 ° w i t h r e g a r d t o t h e v e r t i c a l .

5

7 - The coniTDOsition o f t h e "buoy

I n f i g u r e 3 t h e composite d r a w i n g i s shown o f t h e complete t a i l buoy.

To make t h e t r a n s p o r t e a s i e r i t i s p o s s i b l e t o u n f a s t e n t h e d i f f e r e n t p a r t s and t o mount them on t h e s p o t i n a s i m p l e way.

8 . The w i r e r e e l and t h e s t a b i l i z a t i o n w e i g h t

The p e r f o r m a n c e has t o meet t h e f o l l o w i n g r e q u i r e m e n t s : - i n e x p e n s i v e

- s i m p l e t o assemble when t h e buoy i s g e t t i n g r e a d y - n o t v u l n e r a b l e d u r i n g t h e t r a n s p o r t

- n o t -AiJLnerable dui'ing t h e l a u n c h i n g e s p e c i a l l y w h i l e d r o p p i n g f o r m a l a r g e h e i g h t

- r e l i a b l e p e r f o r m a n c e

I t has been f o u n d t h a t t h e f u n c t i o n s o f t h e w i r e r e e l and t h e s t a b i l i z a t i o n w e i g h t have t o be d i s c o n n e c t e d .

E a r l i e r i n t h e d e v e l o p m e n t , t h e w i r e had been wound on t h e s t a b i l i z a t i o n w e i g h t , w h i c h had t h e shape o f a s p o o l . I t i s f o u n d , t h a t t h e f o r c e i n t h e w i r e became t o o h i g h a t t h e moment when t h e buoy t o u c h e d t h e w a t e r .

The extreme f o r c e had been caused by t h e h i g h d e c e l e r a t i o n o f t h e f l o a t i n g body and t h e r o t a t i o n i n e r t i a o f t h e s t a b i l i z a t i o n w e i g h t .

W i t h t h e p r e s e n t c o n s t r u c t i o n t h e t w i n e d s t e e l w i r e ( d i a m . 1 mmi) i s wound on a c a r d b o a r d r e e l , a f t e r w h i c h t h e w i r e i s f a s t e n e d w i t h a l a y e r o f paper t a p e .

A f t e r t o u c h i n g t h e w a t e r s u r f a c e t h e w e i g h t i s n o t stopped b y t h e w i r e w h i c h f r e e l y unwinds from^ t h e r e e l b u t p r i m ^ a r i l y has been b r a k e d by t h e r e s i s t a n c e o f t h e w e i g h t mioving thjrough t h e w a t e r .

Q. The l a u n c h i n g

The t a i l buoy, t h e w'ire r e e l and t h e s t a b i l i z a t i o n w e i g h t have been f a s t e n e d t o each o t h e r w i t h t h e h e l p o f sna,pshackles .

Th.e t r a n s m . i t t e r i s s e t i n t o a c t i o n by rem.oving a s m a l l magnet cn t h e o u t s i d e o f t h e buoy. A f t e r t h e c o m p l e t e system has been l a u n c h e d , t h e w i r e ean f r e e l y unwind and a f t e r a s h o r t t i m e , t h e s t a b i l i z s . t i o n w e i g h t w i l l be i n p o s i t i o n a t t h e d e s i r e d deo'th.

6

A t t h e f u l l s c a l e measurements ( r e f . l ) t h e l a u n c h i n g s have p e r f o r m e d s u c c e s f u l l y f r o m t h e p l a t f o r m , s i t u a t e d ± 15 m above t h e sea s u r f a c e , w h i l e t h e s h i p s p e e d was

± 2k k n o t s .

1 0 . D a t a r e d u c t i o n

The r e c e i v e d s i g n a l c o n s i s t s o f t h e f r e q u e n c y m o d u l a t e d a c c e l e r a t i o n s i g n a l . Dependent on t h e q u e s t i o n i n w h i c h way t h e m e a s u r i n g d a t a have t o be o f f e r e d , a s e l e c t i o n w i l l have been made o f t h e d i f f e r e n t r e d u c t i o n methods.

I n d e p e n d e n t o f t h e used m.ethod, t h e f o l l o w i n g remarks have t o be made:

- owing t o t h e n o t optimum s t a b i l i z a t i o n o f t h e t a i l b u o y , a l t h o u g h t h e r o l l i n g m o t i o n r e m a i n s s m a l l a c c o r d i n g t o o b s e r v a t i o n s , a h o r i z o n t a l a c c e l e r a t i o n com-ponent i s i n t r o d u c e d c a u s i n g a r e c t i f y i n g e f f e c t , w h i c h makes i t i m p o s s i b l e t o t r e a t t h e s i g n a l s f r o m D.C. ( d i r e c t c u r r e n t ) .

because t h e a c c e l e r a t i o n s i g n a l has t o be i n t e g r a t e d t w i c e t o o b t a i n t h e i n f o r -m.ation about t h e wave h e i g h t , a l l o w a n c e has t o be made f o r t h e d r i f t o f t h e m o d u l a t o r i n s i d e t h e buoy and a l l o w a n c e has t o be made a t t h e r e c e i v i n g s i d e f o r t h e d r i f t o f t h e d e m o d u l a t o r and b o t h i n t e g r a t o r s .

- because d u r i n g t h e e x p e r i m e n t s o t h e r c o n v e r s a t i o n s b y r a d i o t a k e p l a c e , atmos-p h e r i c s have t o be a.ccounted f o r .

T h i s d e m o n s t r a t e s t h e n e c c e s s i t y o f t h e use o f band f i l t e r s . Some examples o f r e d u c t i o n methods a r e :

- ' o n - l i n e r e d u c t i o n w i t h t h e h e l p o f a "Frequency t o v o l t a g e " c o n v e r t e r , band f i l t e r s and i n t e g r e . t o r s .

I n p u t o f t h e s i g n a l i n a "Real-Tim.e" c o r r e l a t o r and a Spectrum D i s p l a y p r o d u c e s t h e c o v a r i a n c e f u n c t i o n and t h e e n e r g y d e n s i t y s p e c t r u m o f t h e wave h e i g h t . - o f f - l i n e r e d u c t i o n w i t h t h e h e l p o f a,n i n s t r u m e n t a t i o n t a p e r e c o r d e r .

By c o u n t i n g d u r i n g e q u a l t i m e i n t e r v a l s t h e f r e q u e n c y m o d u l a t e d a c c e l e r a t i o n s i g n a l , t h e i n f o r m a t i o n i s o b t a i n e d a b o u t t h e a m i p l i t u d e and t h e f r e q u e n c y o f t h e o r i g i n a l m.easiuring s i g n a l .

The a u t o c o v a r i a n c e f u n c t i o n and t h e e n e r g y d e n s i t y s p e c t r i m i can be o b t a i n e d

T

The f i r s t e x p e r i m e n t s have been c a r r i e d o u t t o t e s t t h e o p e r a t i o n o f t h e t a i l buoy and t o compare t h e r e s u l t s w i t h t h o s e o f t h e f i x e d wave h e i g h t p l a t f o r m

" T r i t o n " i n t h e N o r t h Sea. The r e s u l t s a r e g i v e n i n f i g u r e h.

The r e f e r e n c e r e c o r d s o f t h e T r i t o n measiired d u r i n g t h e same t i m e as t h e r e c o r d s o f t h e t a i l buoy appeared n o t t o be u s e f u l .

T h e r e f o r a c o m p a r i s o n has been made w i t h r e c o r d s t a k e n b e f o r e and a f t e r t h e e x p e r i m e n t s w i t h t h e t a i l buoy.

A second c o m p a r i s o n has been made w i t h a wave r i d e r . The wave r i d e r i s a wave h e i g h t m e a s u r i n g buoy made b y "Data w e l l " w h i c h i s e q u i p e d w i t h an i n t e r n a l l y s t a b i l i z e d p i c k - u p . Because i n t h e wave r i d e r t h e a c c e l e r a t i o n s i g n a l i s c o n v e r t e d i n t o a wave h e i g h t s i g n a l b e f o r e t r a n s m i s s i o n , t h e d a t a o f b o t h buoys have been computed on t w o t o t a l l y d i f f e r e n t ways. The r e s u l t s o f t h e c o m p a r i s o n a r e shown i n f i g i u r e 5

-D u r i n g f u l l s c a l e m-easurements on b o a r d o f t h e C o n t a i n e r s h i p " A t l a n t i c Crown", s a i l i n g f r o m Le Havre t o New Y o r k , t h e t a i l buoys have been used under r e a l c o n -d i t i o n s ( r e f . 1 ) .

A l t h o u g h e v e r y l a u n c h e d buoy worked p e r f e c t l y t h e t r a n s m i t t i n g r a n g e a p p e a r e d t o o s m a l l f o r a l o n g t e r m r e c o r d on b o a r d o f a f a s t s h i p . For t h a t k i n d o f r e c o r d s t h e t r a n s m i t t i n g power o f t h e t a i l buoys has t o be i n c r e a s e d .

I n f i g i u r e 6 and 7 two wave h e i g h t s p e c t r a have been g i v e n o f t h e r e c o r d s near New F o u n d l a n d . 12._ D e s i g n d a t a . S u p p l y ± 9 v o l t Fj'equency o f m o d u l a t i o n 2300 cps S e n s i t i v i t y 500 cps/g R a d i u s o f a c t i o n 1 0 - 3 3 to: T r a n s m d t t e d power 250 ra\j F r e q u e n c y o f t r a n s m i s s i o n 27 I'lc D i s j n e t e r o f t h e buoy O.H3 rn L e n g t h o f t h e a n t e n n a 1.50 m L e n g t h o f t h e w i r e 2 - Uo m

8 Weight o f t h e buoy 1 0 0 N S t a b i l i z a t i o n w e i g h t 1 0 0 N Remark I n t h e f u t u r e t h e t r a n s m i t t e d power w i l l be i n c r e a s e d t o 1 o r 2 V/att i n o r d e r t o e n l a r g e t h e r a d i u s o f a c t i o n . R e f e r e n c e s 1 . Beukelmian W. and B u i t e n h e k , M. : " F u l l s c a l e measiu:ements and p r e d i c t e d s e a k e e p i n g p e r f o r m a n c e o f t h e C o n t a i n e r s h i p " A t l a n t i c C r o i m " ,

N e t h e r l a n d s S h i p Research C e n t r e TNO, R e p o r t I 8 5 S, November 1 9 7 3

2 . P a s v e e r , F.J.:

" S p e e d - c o r r e c t e d d e m o d u l a t i o n and o n - l i n e p r o c e s s i n g o f d a t a f r o m a n a l o g t a p e "

D e l f t U n i v e r s i t y o f T e c h n o l o g y C o m p u t a t i o n C e n t r e , P r o c e e d i n g s o f 7 t h AICA Congress, F r a a g 1973.

9

LIST OF FIGURES

F i g u r e 1 Schematic d i a g r a m o f t h e s t a b i l i z a t i o n 2 E l e c t r o n i c b l o c k d i a g r a m o f t h e t a i l buoy 3 Composite d r a w i n g o f t h e t a i l buoy

h Comparison between t h e wave s p e c t r u m by t h e f i x e d p l a t

-f o r m and t h e t a i l buoy

5 Com.parison between t h e wave s p e c t r u m by t h e wave r i d e r and t h e t a i l buoy

6 Measured wave spectr-om d u r i n g f u l l s c a l e measurements T Measured wave s p e c t r u m d u r i n g f u l l s c a l e m.easurements

10 CO^ITENTS Summary 1. I n t r o d u c t i o n . 2 . R e q u i r e m e n t s f o r t h e d e s i g n . 3 . F u n c t i o n a l d e s c r i p t i o n . h. S t a b i l i z a t i o n o f t h e v e r t i c a l p o s i t i o n . 5. B l o c k d i a g r a m o f t h e t a i l buoy. 5.1 The a c c e l e r o m e t e r . 5.2 The c a r r i e r o s c i l l a t o r . 5-3 The d e m o d u l a t o r .

5.U The v o l t a g e c o n t r o l l e d o s c i l l a t o r (V.C.O.). 5 . 5 The t r a n s m i t t e r and t h e a n t e n n a ,

5 . 6 The s t a b i l i z e d power s u p p l y . 5 . 7 The b a t t e r i e s .

6. C a l i b r a t i o n and t h e s e n s i t i v i t y o f t h e t a i l buoy. 7 . The com.position o f t h e buoy.

8 . The w i r e r e e l and t h e s t a b i l i z a t i o n w e i g h t . 9 . The l a u n c h i n g . 10. Data r e d u c t i o n , 11 . R e s u l t s . R e f e r e n c e s L i s t o f f i g u r e s

I G

accelero

-meter

demodulator

voltage

controlled

oscillator

transmitter

carrier

oscillator

stabilized

power

batteries

supply

Fig

.2

E l e c t r o n i c b l o c k d i a g r a m of t h e t a i l b u o y .

0.3 0.2 O 0) O) 0.1 t r i t o n 1 3 0 0 _ 1330 hr t a i l b u o y 1 4 0 o _ 1445 hr t r i t o n 1 5 0 0 _ 1530 hr

ü)

Vsec

Fig.4 C o m p a r i s o n b e t w e e n the wave s p e c t r u m by

the fixed platform and t h e tailbuoy.

0.5 1.0 1.5

0)

^ Vsec

. 5 C o m p a r i s o n b e t w e e n t h e wave s p e c t r u m by

the w a v e r i d e r and t h e tailbuoy.

O 0.5 1.0 1.5

(JL) B^Vsec

F i g . 7 M e a s u r e d wave s p e c t r u m during

full s c a l e m e a s u r e m e n t s .