in the Baltic Sea
of the ro-ro passenger vessel
The Joint Accident investigation Commission
of Esionia, Finland and Sweden
The Government o f the Republic o f Estonia
Parit=RepoRt mi the E S T O M A Disaster o f 28 Septemtoer 1994
Pursuant to an agreement concluded between Estonia, Finland and Sweden a "Joint Accident Investigation Commission" f o r the investigation o f the cap-sizing o f the passenger vessel E S T O N I A on 28 September 1994 was set up on 29 September 1994. The Commission consists o f three members f r o m each state and is chaired by one o f the Estonian members. Each state has appointed experts to assist the Commission.
This part-report covers main technical findings and conclusions. The final report to be issued later w i l l also cover a l l other factors and circumstances contributing to the accident. The report is unanimous on all points. •
A n d i Meister Kari Lehtola O l o f Forssberg Chairman
U n o Laur Heimo livonen B ö r j e Sten Strom
Enn Neidre Tuomo Karppinen Hans Rosengren
Identical letters to:
The Council o f State o f the Republic o f Finland The Government o f the Kingdom o f Sweden
ie Baltic Sea
The Joint Accident Investigation Commission
ESTONIA: Ministry of Transport and Communications, Viru 9, Tallinn EE0101, Phone +372 6 397 613, Fax +372 6 397 606 FINLAND: PCIMA, Ministry of Justice, Box 62, SF-00811 Helsinki, Phone +358 0 759 082 62, Fax +358 0 759 082 65 S W E D E N : Board of Accident Investigation, Box 12538, S-102 29 Stockholm, P/7one+46 8 737 58 40, F a x + 4 6 8 737 58 52
MV ESTONIA Part-Report
Members and appointed experts of the Commission
E S T O N I A
Members
A n d i Meister, Chairman, Minister of Transport and Communications U n o Laur, Master Mariner
Enn Neidre, Master Mariner
Experts
Kalle Pedak, Director-General Heino J a a k u l a , Naval Architect J a a n Metsaveer, Professor H e i n o L e v a l d , Professor
F I N L A N D
l\/lembers
Kari L e h t o l a , Chairman PCIMA H e i m o l i v o n e n , Rear-admiral, Ret. T u o m o K a r p p i n e n , Dr.Tech. Experts S i m o A a r n i o , Captain K l a u s Rahka, Dr.Tech. P i r j o V a l k a m a - J o u t s e n , Executive secretary S W E D E N IVIembers Olof F o r s s b e r g , Director-General Hans R o s e n g r e n , Master Mariner B ö r j e S t e n s t r ö m , Naval Architect
Experts
Michael H u s s , DrTech. Olle N o o r d , Master Mariner B e n g t S c h a g e r , M.Sc.
In case of discrepancies between the Estonian, Finnish, Swedish and English texts, the English text is to be considered the authoritative version.
The English text has been checked for linguistic correctness by Tim Crosfield, IVI.A. Typographic design Gunnel Göransson
Preface
Shortly before 2 a.m. o n 28 September 1994 the Estonian ro-ro passenger vessel E S T O N I A capsized and sank i n the B a l t i c Sea w h i l s t o n a scheduled passage f r o m Tallinn to Stockholm, A large number o f lives were lost.
The accident is being investigated by a j o i n t Estonian/Finnish/Swedish commission.
The C o m m i s s i o n has previously concluded that the accident was i n i t i -ated b y the l o c k i n g devices f o r the b o w visor b e i n g unable to w i t h s t a n d the loads imposed d u r i n g the prevailing speed, heading and sea conditions. This conclusion is still valid.
This part-report covers m a i n technical f m d i n g s and conclusions. The f i n a l report to be issued later w i l l cover also a l l other factors and c i r c u m -stances f o u n d to have contributed to the development o f the accident. This w i l l include inter alia operational practices, c e r t i f i c a t i o n and inspections, stability i n f o r m a t i o n , weather conditions and training. Rescue operations and resources w i l l be covered as w e l l .
The content o f the current part-report may be amended and editorially m o d i f i e d as part o f the final report but i t is anticipated that all facts and conclusions reported herein w i l l remain unchanged i n substance.
The Commission consists o f the members and appointed experts listed o n the opposite page.
Note
The present part report must be read with its restricted scope in mind and no conchtsions about the causes of the accident should be drawn before the final report is available.
1. If not otherwise stated all times in the report are given in Estonian time = UTG + 2 hrs.
2. W e i g h t ( m a s s ) a n d forces are in this report given in metric t o n s r a t h e r t h a n Sl-units.
MV ESTONIA Part-Report
Index
1 ÖBitroduction and Summary 8
U Introduction 8
1.2 T h e V e s s e l 8
1.3 T h e Voyage 10
2 Summary of Facts and Findings 12
2.1 D e s c r i p t i o n of Affected Installations 12 2 . 1 . 1 ' T h e B o w Visor a n d R a m p installation 12
2.1.1.1 The visor 12 2.1.1.2 The bcMoiïi lock 13 2.1.1.3 The side locks 14 2.1.1.4 Manual visor locks 15 2.1.1.5 The deck hinges 15 2.1.1.6 The loading ramp 15
2.1.1.7 Visor and ramp control system 16
2.2 S u m m a r y of O b s e r v a t i o n s o n the R e c o v e r e d B o w V i s o r a n d on the W r e c k 17 2.2.1 G e n e r a l 17 2.2.2 T h e B o w Visor 17 2 . 2 . 3 T h e B o w A r e a o f t h e Hull 18 2.3 P a r t s R e c o v e r e d for E x a m i n a t i o n 19 2.4 Other O b s e r v a t i o n s 19 2.5 L o c a t i o n of the C o l l i s i o n B u l k h e a d a n d the R a m p 20
3 Analysis and Evaluation 21
3 J T h e B o w V i s o r Attachment D e v i c e s - Strength C o n s i d e r a t i o n s 21 3.1.1 D e s i g n Basis a n d R e q u i r e m e n t s o f t h e C l a s s i f i c a t i o n S o c i e t y 21
3.1.1.1 General requirements 21
3.1.1.2 Bureau Veritas rule requirements for the design load on the visor 21 3.1.2 T h e S t r e n g t h o f t h e B o t t o m L o c k A s s e m b l y 22 3.1.3 T h e S t r e n g t h o f t h e Side L o c k s 2 3 3.1.4 A p p r o v a l o f t h e L o c k i n g D e v i c e s 2 3 3.1.5 T h e H i n g e s o n D e c k 24 3.1.6 C o n t r i b u t i o n f r o m t h e M a n u a l L o c k s 24 3.1.7 T h e V i s o r O p e r a t i n g A c t u a t o r s 2 5
3.2 The Ramp Locking Devices - Strength Considerations 2 5
3.4 Forces Deveaoping D u r i n g ttie FaiBure 28
3.4.1 G e n e r a l c o n s i d e r a t i o n s 28
3.4.2 C o m p a r i s o n w i t h D e s i g n R e q u i r e m e n t s 29
3.4.3 S e a a n d S p e e d C o n d i t i o n s R e q u i r e d to C r e a t e C r u i c a l F o r c e s 2 9
3 J L o c a t i o n off the C o l l i s i o n B y l l r f i e a d and t h e R a m p 30
3.5.1 R e g u l a t o r y R e q u i r e m e n t s 30 3.5.2 D e s i g n C o n s i d e r a t i o n s 30
4
ConeiysDons 31
R e c o m m e n d a t i o n s 32
MV ESTONIA Part-Report
1 Introduction and Summary
1.1 Introduction
The Estonian-flagged ro-ro passenger vessel E S T O N I A capsized and sank shortly b e f o r e 2 a.m.on 28 September 1994 w h i l s t o n a scheduled voyage f r o m T a l l i n n to Stockholm. The vessel had, according to available i n f o r m a -t i o n , 989 passengers and crew members o n board. 137 persons s u r v i v e d the accident.
The accident is b e i n g investigated b y a j o i n t Estonian/Finnish/ Swedish C o m m i s s i o n , set up i n accordance w i t h a decision taken o n 28 September
1994 at T u r k u b y the p r i m e ministers o f the three countries. U n d e r Esto-n i a Esto-n ' c h a i r m a Esto-n s h i p the C o m m i s s i o Esto-n has Esto-niEsto-ne regular members, three from each country. Experts have been assigned to the C o m m i s s i o n to ensure competence i n a l l areas.
The present report is a part-report, covering the f m d i n g s , conclusions and recommendations o f the C o m m i s s i o n regarding the technical causes and development o f the accident. The f i n a l report w i l l also cover a l l other factors and circumstances c o n t r i b u t i n g to the development o f the accident, i n c l u d i n g weather conditions, c e r t i f i c a t i o n and inspections, stability i n f o r -m a t i o n , operational practices, t r a i n i n g and rescue operations and resources. I t w i l l also describe affected institutional organizations.
Several investigations b y appropriate independent institutions have been i n i t i a t e d d u r i n g the w o r k . They include inter alia analysis o f the weather and sea conditions, the wave induced m o t i o n o f the ship, calculation o f h y d r o d y n a m i c forces i n the b o w area, metallurgical investigation o f f r a c -t u r e d surfaces f r o m f a i l e d par-ts and inves-tiga-tion o f an h y d r a u l i c ac-tua-tor
I n r e a d i n g this part-report i t must be noted that the causes and con-clusions quoted herein relate only to technical matters and do n o t describe or e x p l a i n the f u l l sequence o f events n o r any operational issues related to the accident.
1.2 The Vessel
The vessel was a ro-ro passenger ferry, b u i l t as y a r d n e w b u i l d i n g number 590 b y Jos. L M e y e r W e r f t o f Papenburg i n Germany f o r the F i n n i s h f e r r y company R e d e n A B Sally. She was delivered o n 20 June 1980 under the name o f V I K I N G S A L L Y and was p u t i n t o service o n the route between the p o r t o f S t o c k h o l m i n Sweden and the ports o f M a r i e h a m n and T u r k u i n Finland. A f t e r the Sally company merged w i t h E f Q o h n Oy, the vessel was
operated f r o m A p r i l 1990 as SILJA STAR between Stockholm and T u r k u and f r o m January 1991 as W A S A K I N G o n the routes between Vaasa and Umea/Sundsvall i n the G u l f o f Bothnia.
The vessel was the second largest passenger f e r r y i n the B a l t i c Sea i n those days and was one o f the f i r s t " j u m b o " size ferries. A general arrange¬ ment d r a w i n g o f the vessel is shown i n Figure 1.
The vessel was acquired o n 15 January 1993 b y Estline M a r i n e Co L t d and was bareboat chartered to the Estonian company E-line L t d . I t was p u t into the service o f Estline between Tallinn and Stockholm under the name o f E S T O N I A . The operations were conducted b y Estonian S h i p p i n g C o m -pany L t d under a management contract. The companies E-line L t d and Estline were o w n e d equally by the state o w n e d Estonian Shipping C o m -pany L t d and b y the Swedish shipping com-pany N o r d s t r o m & T h u l i n A B . Technical management was subcontracted to N o r d s t r o m & T h u l i n A B .
The vessel was b u i l t after a similar n e w b u i l d i n g , D I A N A I I , delivered to the Swedish shipping company Rederi A B Slite. The E S T O N I A was longer b y an extra m i d s h i p section but the b o w and stem areas were identical i n the t w o vessels except f o r the length o f the bulbous b o w w h i c h was increas-ed b y 0.8 metres i n the E S T O N I A . B o t h ships were b u i l t to the rules o f the classification society Bureau Veritas rules w i t h class n o t a t i o n -l-I 3/3 E, Deep Sea, Ice l A , Car/Passenger Ferry + ( A U T ) . The E S T O N I A was m o d i f i e d i n 1985 w h e n the a f t part o f the h u l l b e l o w the waterline was r e b u i l t to i n -crease buoyancy and stability.
U p o n delivery f r o m the y a r d the vessel was issued a Passenger Ship Safety Certificate i n compliance w i t h the Safety o f L i f e at Sea ( S O L A S ) c o n v e n t i o n b y the F i n n i s h Authorities. The vessel was c e r t i f i e d f o r short international voyages. The permitted number o f passengers was l i n k e d to a note r e f e n i n g to short international voyages between Sweden and F i n l a n d (this note was introduced since certain l i f e saving equipment c o m p l i e d w i t h the 1974 issue o f the S O L A S convention, n o t yet i n f o r c e at the time, rather t h a n the 1960 S O L A S convention). The vessel was under the statutory supervision o f the F i n n i s h B o a r d o f Navigation f r o m the time o f constmc-t i o n u p constmc-to 14 January 1993. The administration had authorized Bureau Veritas to p e r f o r m the related h u l l surveys and inspections. I t was under Estonian supervision f r o m 15 January 1993 to the time o f the accident. The Estonian B o a r d o f N a v i g a t i o n had authorized Bureau Veritas to per-f o r m the statutory per-f u n c t i o n s under the S O L A S and other international con-ventions.
T h e v e s s e l hsiel the follewiswj mam p a r i i e y l a r s :
L e n g t h , over all 1 5 5 . 4 0 m P r o p u l s i o n p o w e r 1 7 , 6 0 0 k W L e n g t h , betw/een p e r p e n d i c u l a r s 137.40 m D e a d w e i g h t 3 2 3 0 t o n s B r e a d t h , m o u l d e d 2 4 . 2 0 m L i g h t w e i g h t 9 7 3 3 t o n s D e p t h t o b u l k h e a d d e c k , m o u l d e d 7.65 m G r o s s t o n n a g e 1 5 , 5 9 8 M a x i m u m d r a f t 5.60 m Max. n u m b e r o f p a s s e n g e r s 2 0 0 0 N u m b e r o f d e c k s 8 Max. service s p e e d 2 1 k n o t s
MV ESTONIA Part-Report
1.3 The Voyage
T h i s section contains a b r i e f summary o f the voyage ending w i t h the acci-dent. A m o r e detailed description o f the voyage and analysis o f operational and other aspects and the rescue operations w i l l be g i v e n i n the f m a l report.
The vessel was o n scheduled service between Tallirm and S t o c k h o l m w i t h departure f r o m Tallinn every second evening at 1900 hrs l o c a l t i m e and a r r i v a l i n S t o c k h o l m the f o l l o w i n g m o r n i n g at 0900 hrs l o c a l time. The vessel departed f r o m S t o c k h o l m o n the same evening f o r arrival the f o l l o w i n g m o r n i n g to Tallinn. The scheduled d u r a t i o n o f the w e s t b o u n d v o y -age was 15 hours.
The vessel departed at 1915 hrs o n 27 September 1994, carrying 803 passengers, 186 crew members and a l o a d o n car deck consisting, accord-ing to customs documentation, o f 38 lorries and trailers, 25 trucks, 11 vans and 26 passenger cars w i t h a c o m b i n e d w e i g h t o f about 1000 tons. The lorries a n d trucks were loaded a f t and the vessel h a d a departure t r i m o f about h a l f a metre b y the stem. The vessel h a d one degree o f starboard list at departure and the p o r t ballast tank was f u l l .
W h e n the E S T O N I A l e f t T a l l i n n the w i n d was southerly, 8 - 1 0 m/s. V i s i b i l i t y was g o o d , w i t h rainshowers. A s the voyage c o n t i n u e d the w i n d increased gradually and veered to south-west. A t m i d n i g h t the weather c o n d i t i o n s were w i n d south-west 1 5 - 2 0 m/s w i t h a s i g n i f i c a n t wave height o f 3.5-4.5 metres. V i s i b i l i t y was generally more t h a n 10 nautical miles.
The weather forcast f o r the m i d n i g h t hours as received b y the vessel p r e d i c t e d southwesterly w i n d , veering to west, v e l o c i t y 1 5 - 2 0 m/s, increas-ing t o w a r d s the m o m i n g , significant wave height 2.5-3.5 m .
The voyage proceeded as n o r m a l w i t h moderate sea conditions and a h e a d i n g o f 2 6 2 ° along the Estonian coast. A l l f o u r engines were operated at n o r m a l cmise p o w e r The vessel t u m e d at about 0030 hrs at a w a y p o i n t located about 5 9 ° 2 0 ' N and 2 2 ° 0 2 ' E to heading 2 8 7 ° f o r the c o n t i n u e d passage t o the S ö d e r a r m entrance to the S t o c k h o l m archipelago.
The sea conditions grew more severe as the vessel l e f t the sheltered water a l o n g the Estonian coast. Speed was around 14.5 knots w i t h some r o l l i n g a n d moderate to occasionally heavy p i t c h i n g . The stabilizing f m s had been activated w h e n passing the waypoint. A t about 0045 hrs the first i n d i c a t i o n s o f something abnormal were n o t e d b y several witnesses. M e t a l -lic sounds were heard i n the vessel.
The engineer i n the engine c o n t r o l r o o m has stated that he later o n -p r o b a b l y at about 0115 hrs - observed o n the T V m o n i t o r that water was c o m i n g i n at the sides o f the f o r w a r d ramp w h i c h appeared to be i n closed p o s i t i o n . Somewhat later again more severe m e t a l l i c impact noises were heard a n d shortly thereafter the ship started to r o l l more severely, develop-ing a starboard list.
Subsequently the b o w visor separated f r o m the b o w and t i l t e d f o r w a r d over the stem. The f o r w a r d ramp was p u l l e d open b y the v i s o r due to
mechanical interference and was finally f u l l y opened, a l l o w i n g large amounts o f water to enter the car deck.
A s the list increased passengers started to rush up the staircases and panic developed at many places. People w h o managed to get onto the boat deck received l i f e jackets. M a n y passengers w h o had gone to sleep were trapped in their cabins and had no chance o f gettmg out i n time.
A s the list increased to about 30 degrees the m a i n engines t r i p p e d due to lack o f lubricating o i l pressure. The generator units stopped somewhat later and the emergency generator started automatically, s u p p l y i n g p o w e r to l i m i t e d lights in p u b l i c areas and on deck.
M A Y D A Y emergency signals were received at 0124 hrs b y eleven shore and ship based radio stations i n the area, i n c l u d i n g the M R C C station at Turlcu.
The vessel continued to heel over and the accomodation decks started to take o n water at about 0130 hrs. F l o o d i n g o f the accomodation c o n t i n u e d w i t h considerable speed and the starboard side o f the bridge was sub-merged at about 0135 hrs as indicated b y the chart r o o m c l o c k w h i c h h a d stopped at this moment. The list was at this stage more t h a n 90 degrees.
Passengers w h o had managed to reach the boat deck and the outer side o f the ship j u m p e d or were swept into the water L i f e rafts had been re-leased or were rere-leased automatically as they became submerged and some people managed to get into them. The weather was severe d u r i n g the n i g h t and caused additional loss o f l i f e . A total o f 94 v i c t i m s were collected f r o m r a f t s and f r o m the water i n the area. A total o f 137 survivors were p i c k e d up b y helicopters and assisting ships d u r i n g the n i g h t and the early m o m i n g hours.
The vessel made a p o r t t u m w h i l s t the starboard list was developing. I t has n o t been possible to ascertain w h a t action was taken o n the bridge at this stage. The ship lost p r o p u l s i o n and d r i f t e d , l y i n g across the seas, w h i l s t flooding continued. I t sank completely at 0148 hrs w h e n the last visible i n d i c a t i o n disappeared f r o m the radar screen o f a F i n n i s h radar station. The p o s i t i o n at the sinking was N 5 9 ° 2 2 ' . 9 , E 2 1 ° 4 1 '.0. The w r e c k had t u m e d to a heading o f 95 degrees as she went d o w n . The b o w v i s o r was later traced about one nautical m i l e west o f the wreck.
A r e v i e w has shown that weather conditions comparable to those d u r i n g the n i g h t o f the accident had occurred only once or t w i c e before w h i l e the vessel was sailing f r o m Tallinn to Stockholm.
•V? MV ESTONIA Part-Report
2 Summary of Facts and
Findings
2.1 Description of Affected Installations
2.1.1 T h e B o w V i s o r a n d R a m p Installation
This section describes the b o w v i s o r and ramp installation. The b a c k g r o u n d and circumstances related to the l o c a t i o n o f the ramp are covered separate-l y i n Section 2.5.
T h e ' b o w v i s o r and ramp installation o f the E S T O N I A was o f a c o n f i g u r a t i o n c o m m o n at the t i m e o f b u i l d i n g . The installation comprised an u p -w a r d - o p e n i n g b o -w v i s o r and a l o a d i n g ramp, h i n g e d at m a i n deck level and b e i n g closed i n a raised position. I n closed p o s i t i o n the upper end o f the r a m p extended into a b o x - l i k e structure o n the deck o f the v i s o r
The s p e c i f i c components related to the b o w v i s o r and ramp installations h a d been designed and supplied b y v o n Tell A B , one o f the established makers o f such systems. The system i n c l u d e d the complete ramp w i t h hinges, operating and l o c k i n g devices and the operating and l o c k i n g de-vices f o r the b o w v i s o r as w e l l as the hydraulic operation and c o n t r o l sys-t e m f o r sys-the complesys-te inssys-tallasys-tion. The i n c o r p o r a sys-t i o n o f sys-the syssys-tem insys-to sys-the ship was shipyard design and installation w o r k .
The general arrangement o f the ramp and v i s o r installation is s h o w n i n Figure 2.
2.1.1.1 The visor
The v i s o r was the most f o r w a r d part o f the vessel's h u l l and was a steel structure similar to the n o r m a l b o w structure o f a vessel. The general shape and design is s h o w n i n Figure 3. The h u l l f o r m h a d considerable f l a r e i n the b o w area, t y p i c a l f o r ro-ro vessels b u i l t at the time. The v i s o r consisted m a i n l y o f the shell plating, being an extension o f the ship's shell p l a t i n g and contour, the deck part, the b o t t o m part, the a f t b u l k h e a d and i a t e m a l h o r i z o n t a l stringers, vertical partial bulkheads and transverse stiffeners. T w o beams o n deck extended a f t o f the v i s o r a f t end and carried the hinge arrangements f o r the p i v o t i n g points o f the v i s o r The v i s o r w e i g h e d about 55 tons.
The deck o f the v i s o r h a d a b o x - l i k e housing between the t w o beams, enclosing the upper part o f the ramp w h e n the ramp was i n closed p o s i t i o n . The geometry was such that the ramp h a d to be i n the f u l l y closed p o s i t i o n i n order n o t to interfere w i t h the v i s o r d u r i n g its opening and closing m o v e -ment.
The visor p i v o t e d around the t w o hinges o n upper deck d u r i n g its nor-m a l opening and closing nor-movenor-ment. I t was secured i n the closed p o s i t i o n b y three hydraulically operated l o c k i n g devices at its l o w e r part. One o f these was m o u n t e d o n the forepeak deck and the other t w o o n the a f t side o f the v i s o r w i t h m a t i n g parts in the h u l l f r o n t bulkhead. A d d i t i o n a l l y , t w o mechanical l o c k i n g devices were located in the area o f the h y d r a u l i c side locks. Three l o c a t i n g horns, one o n the forepeak deck and t w o o n the f r o n t bulkhead engaged recesses i n the visor to absorbe lateral loads.
The visor was supported vertically in the closed p o s i t i o n by the t w o deck hinges and f u r t h e r rested on three points o n the forepeak deck. One o f these was the solid stem post o f the visor, resting o n the ice-breaking stem o n t o p o f the bulbous bow, the other t w o were steel pads o n the forepeak deck. The three l o c k i n g devices kept the visor d o w n i n its closed p o s i t i o n and the l o c a t i n g horns absorbed any side loads that m i g h t develop. L o n g i -t u d i n a l loads were borne b y -the hinges and -the l o c k i n g devices and possi-bly b y direct contact between the visor and the f r o n t bulkhead o f the h u l l .
The visor was supported i n open p o s i t i o n b y the t w o hinges and t w o p a r k i n g devices, consisting o f hydraulically operated bolts engaging lugs o n the hinge beams.
Rubber seals supported b y steel f l a t bars were installed o n the forepeak deck and the f r o n t bulkhead, together m a k i n g a continuous seal against w h i c h the visor abutted w h e n closed.
The v i s o r c o u l d not be seen f r o m the bridge due to the p r o t r u d i n g f o r -w a r d superstructure. The top o f the b o -w f l a g pole could, ho-wever, be seen.
2.1.1.2 The bottom lock
The b o t t o m l o c k i n g arrangement is shown i n Figure 4. I t was sometimes called the " A t l a n t i c l o c k " as i t was not i n c o m m o n use i n early ferries b u t was later introduced to enable similar ferries to cross open oceans. The " A t l a n t i c l o c k " h a d become established b y the time the E S T O N I A was b u i l t . The l o c k i n g device consisted o f a l o c k i n g bolt, movable h o r i z o n t a l l y i n a transverse direction, guided in a b o l t housing. I n extended p o s i t i o n the t i p o f the b o l t engaged a support bushing. The b o l t housing was f i x e d to the forepeak deck b y means o f t w o steel lugs and the bushing was installed i n a t h i r d similar lug. A m a t i n g l u g , attached to the visor itself, was located between the b o l t housing and the support bushing w h e n the v i s o r was i n the closed p o s i t i o n and the extended b o l t then engaged the hole i n the m a t i n g l u g .
Some overall dimensions o f the lugs were g i v e n o n an assembly d r a w i n g issued by the supplier o f the l o c k i n g devices b u t no m a n u f a c t u r i n g d r a w i n g seems to have existed.
The b o l t was m o v e d i n the bolt housing between the retracted p o s i t i o n and the extended p o s i t i o n b y means o f a hydraulic actuator, operated f r o m the c o n t r o l panel f o r the v i s o r and the ramp as described i n subparagraph 2.1.1.7. A spring-loaded mechanical plunger, perpendicular to the bolt, engaged grooves i n the b o l t i n the open and closed p o s i t i o n , respectively.
1*^ MV ESTONIA Part-Report
thereby securing the b o l t mechanically i n its extreme positions, regardless o f h y d r a u l i c pressure. The b o l t was also l o c k e d h y d r a u l i c a l l y at any t i m e because the h y d r a u l i c f l u i d was trapped i n the system, regardless o f whether the h y d r a u l i c system was under pressure or not.
T w o magnetic-type l i m i t switches were installed, b e i n g actuated b y a magnet attached to the bolt. The switches were actuated w h e n the b o l t was i n f u l l y retracted p o s i t i o n and fixUy extended p o s i t i o n respectively. The h y d r a u l i c c o n t r o l system as w e l l as the arrangement and f u n c t i o n i n g o f the switches and the p o s i t i o n i n d i c a t i o n and alarm system are covered sepa-rately i n subparagraph 2.1.1.7. The mechanical switches o f the o r i g i n a l design h a d been replaced b y the magnetic ones at an earlier stage i n the h i s t o r y o f the vessel.
The m a t i n g l u g i n the b o t t o m structure o f the v i s o r consisted o f a single steel l u g , w e l d e d to a transverse beam o f the v i s o r b o t t o m structure and supported b y a bracket as shovm i n Figure 5. The l u g h a d a hole f o r the l o c k i n g b o l t w i t h an o r i g i n a l diameter o f 85 millimetres. The diameter o f the hole h a d increased i n service and after the accident the hole was oval w i t h dimensions about 90 x 105 millimetres. The elongation may have been caused b y wear or b y y i e l d i n g d u r i n g the f a i l u r e o f the l o c k i n g device.
The f a i l u r e mode o f the b o t t o m l o c k installation and related f i n d i n g s are covered i n paragraph 3.1.2.
2.1.1.3 The Side locks
The side locks consisted o f t w o lugs, m o u n t e d to the a f t b u l k h e a d o f the visor and extending, w h e n the v i s o r was closed, into t w o recesses i n the f r o n t b u l k h e a d o f the h u l l , one at each side o f the ramp opening. I n the closed p o s i t i o n h y d r a u l i c a l l y operated bolts engaged holes i n the v i s o r lugs. The arrangement is s h o w n i n Figure 6. The h y d r a u l i c b o l t installa-tions w e r e similar to that o f the bottom, lock, i.e. a b o l t m o v i n g i n a b o l t h o u s i n g and, w h e n extended, engaging a support bushing. The v i s o r l u g inserted between the b o l t housing and the support bushing. The b o l t was m o v e d b y an h y d r a u l i c actuator A mechanical f r i c t i o n plunger was i n -stalled. The p o s i t i o n o f the bolt, f u l l y retracted and f u l l y extended, was sensed b y magnetic-type l i m i t switches.
A d d i t i o n a l hydraulic cylinders were installed at each side to push i n a f o r w a r d d i r e c t i o n o n the visor lugs w h e n the v i s o r was to ó p e n . This instal-l a t i o n was intended to assist i n breaking the v i s o r open i n case i t h a d be-come stuck i n the closed p o s i t i o n due to i c i n g .
The i n s t a l l a t i o n o f the visor side lugs is s h o w n i n Figure 7. I t has been n o t e d b y the C o m m i s s i o n that no detailed d r a w i n g existed f o r these lugs and that t h e i r actual length along the attachment area to the v i s o r was shorter t h a n that indicated o n general arrangement drawings f o r the l o c k i n g installation. The lugs were w e l d e d to the a f t side o f the v i s o r a f t b u l k h e a d w i t h f i l l e t welds. N o w e l d i n g details were g i v e n o n any d r a w i n g .
T w o v e r t i c a l stiffeners were installed o n the f r o n t side o f the p l a t i n g , separated b y a distance slightly larger than the thickness o f the l u g i t s e l f
These stiffeners were installed to satisfy a Bureau Veritas surveyor's re-quirement f o r "local reinforcement o f the ship 's structure b y w a y o f lock-i n g devlock-ices". N o other arrangements were made lock-i n the deslock-ign to transmlock-it the forces f r o m the lugs into the structure o f the visor.
2.7.1.4 Manual visor locks
T w o manual locks were installed, one at each side and m o u n t e d j u s t b e l o w the hydraulic side locks. Each lock consisted o f t w o lugs w e l d e d to the a f t side o f the visor and a hinged eye bolt w i t h nut, mounted between t w o lugs i n the f r o n t bulkhead. I n closed p o s i t i o n the eye bolt was swung into posi-t i o n beposi-tween posi-the posi-t w o lugs i n posi-the visor and posi-the n u posi-t was posi-tighposi-tened d o w n . The arrangement is shown i n Figure 8. The locks had no remote p o s i t i o n i n d i -cating devices.
The manual lock was described i n the supplier's instructions booklet as "reserve". N o advice was given anywhere i n instructions b y the maker, the shipyard or operators as to the use o f these manual locks.
2.1.1.5 Ttie deck hinges
The t w o beams on the deck o f the visor extended about 3 metres a f t o f the a f t edge o f the visor deck. The ends o f the beams carried the hinge arrange-ments. The hinge arrangement is shown i n Figure 9. A heavy steel bushing was w e l d e d into a hole in each o f the t w o side plates o f each beam. The bushings had a bore, carrying a bronze bushing. The deck part o f the hinge consisted o f t w o lugs welded to the deck, carrying between them a steel housing. This deck part was located, i n the installed arrangement, between the t w o bushings o f a visor beam. A shaft was installed t h r o u g h the entire assembly, secured b y l o c k i n g plates bolted to the outer ends o f the hinge bushings.
2.1.1.6 The loading ramp
The ramp was a steel design w i t h f o u r longitudinal beams and a number o f transverse beams. A steel plate made up the upper surface o f the ramp. A d d i t i o n a l stiffeners were arranged between the m a i n beams.
The ramp was longer than the available deck height and therefore p r o -t r u d e d b y abou-t 1.5 me-tres above -the level o f -the upper deck w h e n i n -the raised, i.e. closed, position. This extension was enclosed in the b o x - l i k e h o u s i n g o n the visor deck. Flaps at the t i p o f the ramp were h i n g e d along the f r o n t end o f the ramp and were controlled b y means o f steel cables t o extend w h e n the ramp was lowered. The cables were engaged on bellcranks at the ends o f the f l a p axis. W h e n the ramp was closed these flaps h u n g d o w n to keep its total length as short as possible.
The ramp was hinged at its a f t end to the hull structure b y f o u r hinges. Each hinge consisted o f steel lugs w e l d e d to the h u l l and lugs w e l d e d to the a f t beam o f the ramp. Bushings and hinge pins made up the complete hinge installation. The outer hinges were heavier than the t w o inner ones.
V:: MV ESTONIA Part-Report
Raised bars were w e l d e d onto the sides o f the ramp. F i x e d railings were m o u n t e d o n each side.
The r a m p was manoeuvered b y t w o hydraulic actuators, one at each side. W h e n i n the raised, closed, p o s i t i o n the ramp was p u l l e d i n b y t w o l o c k i n g hooks, engagkig pins i n the side beams o f the ramp. These hooks were h y d r a u l i c a l l y operated v i a a lever mechanism arranged to m o v e past its dead centre d u r i n g the l o c k i n g movement and stay i n this mechanically secured p o s i t i o n .
T w o a d d i t i o n a l l o c k i n g bolts were m o u n t e d along each side o f the ramp. These were hydraulically operated, m o v i n g transversely i n the ramp
coaming. I n the extended p o s i t i o n they engaged b o x - l i k e extensions o n the r a m p side bars.
A l l the l o c k i n g devices had l i m i t switches f o r their retracted and ex-tended positions as described separately i n subparagraph 2.1.1.7.
A r u b b e r seal, supported b y steel f l a t bars, was arranged i n the ramp c o a m i n g and made up a weathertight seal against the surface o f the ramp w h e n the ramp was i n the closed p o s i t i o n .
2 . 11 . 7 Visor and ramp control system
A c o n t r o l system served the ramp and v i s o r installation. The system was supplied b y the maker o f the ramp and v i s o r actuating systems. I t was described i n an instruction booklet, issued b y the s u p p l i e r
The c o n t r o l system consisted o f a high-pressure h y d r a u l i c system w i t h tank and t w o pumps plus the n o r m a l components o f a h y d r a u l i c p o w e r system, p r o v i d i n g hydraulic p o w e r to a control panel and to the operating and l o c k i n g devices o f the v i s o r and the ramp. The control panel was m o u n t e d o n the p o r t side j u s t inside the ramp. I t contained manual control levers f o r separately operating:
— the v i s o r b o t t o m lock — the v i s o r side locks
— the r a m p p u l l - i n hooks and l o c k i n g bolts — the v i s o r opening/closing
— the open visor p a r k i n g plungers — the r a m p opening/closing.
There was no hydraulic or electric interlock between the devices, the indicator lamps being m o n i t o r e d b y the operator f o r proper f u n c t i o n o f each step d u r i n g opening or closing, before the n e x t step was activated.
The i n d i c a t o r lamps were m o u n t e d o n a panel located at the operating station and a second panel was installed o n the bridge, i n the f r o n t panel to the r i g h t o f the seat o f the O f f i c e r o f the Watch.
The panels had red and green lights, p o w e r e d v i a the l i m i t switches o n the actuators f o r the v i s o r and ramp l o c k i n g devices. P o s i t i o n switches were also installed to sense f u l l y - c l o s e d ramp and f u l l y - c l o s e d v i s o r Lights f o r the v i s o r and the ramp were green only w h e n the v i s o r or the ramp, respectively, was f u l l y closed, otherwise they were red. The lights f o r the l o c k i n g devices were w i r e d to be red w h e n the locks were i n the fiiUy
retracted p o s i t i o n and green w h e n they were f u l l y extended, locked. The b o t t o m l o c k had a separate set o f lights, the side locks one set o f lights and the ramp locks one set o f lights. The position switches f o r the side locks and f o r the ramp locks, respectively, were w i r e d i n series so that a l l the devices had to be i n the correct end p o s i t i o n before the relevant l i g h t came on. I f one device was i n an intermediate p o s i t i o n no l i g h t w o u l d be on.
T V cameras were installed f o r m o n i t o r i n g the car deck. One o f these m o n i t o r e d the f o r w a r d ramp area. Display screens were installed i n the engine control r o o m and i n the chart r o o m on the bridge.
2.2 Summary of Observations on the
Re-covered Bow Visor and on the Wreck
2.2.'il (@©6a©ral
N o indications o f structural deviations between the actual o n b o a r d i n -stallations and the o r i g i n a l design have been f o u n d . I t has, however, n o t been possible to fially establish i f any repair w o r k has been carried out o n the affected parts d u r i n g the vessel's lifetime.
The visor was traced o n the seabed and recovered. The m a i n observations that were made on the visor after i t had been brought ashore at Hanko i n F i n l a n d are summarized below.
The visor shell p l a t i n g had an extended indentation o n its f r o n t side, slightly starboard o f the stem.
The solid stem post had l e f t the visor after separation o f the welds. The b o t t o m o f the visor was heavily pounded and distorted. The l u g f o r the b o t t o m l o c k was i n place b u t the surrounding structure was heavily deformed. The hole i n the l u g was oval and the material showed signs o f y i e l d i n g .
The inner vertical bulkheads o f the visor had indentations and score marks o n the p o r t side.
The upper bar i n the visor had heavy impact marks. Other cross-bars h a d lighter marks.
The a f t bulkhead o f the visor had various damage. I n particular the recess f o r the p o r t side locating h o r n h a d been t o r n completely open i n the area b e l o w the recess.
B o t h side l o c k i n g lugs had been t o r n out o f the bulkhead, leaving rectan-gular holes i n the plating.
18 MV ESTONIA Part-Report
The h i n g e bushings at the end o f the hinge beams h a d separated f r o m the b e a m side plates due to f a i l u r e o f the side plates and the welds around the bushings.
The b o t t o m plates o f the hinge beams h a d p o u n d i n g and impact marks a r o u n d the attachment lugs f o r the v i s o r opening actuators and green p a i n t marks. T h e lugs f o r the opening cylinders h a d heavy score marks o n their starboard sides.
The b o x o n the v i s o r deck had impact damage to the p o r t part o f its a f t inner w a l l , i n c l u d i n g bent and dented b u l b bars.
The a f t edges o f the hinge beam b o t t o m plates and the deck p l a t i n g o f the v i s o r h a d heavy p o u n d i n g marks.
The damage is illustrated i n a series o f photographs i n Figure 10.
2 J . 3 T h e B o w A r e a of t h e Hull
D i v i n g a n d R O V inspections o f the b o w area o f the w r e c k revealed certain damage t o the h u l l and the installations i n the b o w area as summarized below.
The deck hinge f i t t i n g s o n deck were undamaged except f o r p o u n d i n g marks o n t h e i r f o r w a r d faces. The v i s o r p a r k i n g support was undamaged.
The deck was t o r n open f r o m the v i s o r operating actuator openings and f o r w a r d . T h e openings continued f o r some length d o w n the f r o n t bulkhead. The deck damage was extensive w i t h uneven fracture surfaces whereas the openings i n the f r o n t bulkhead h a d rather clean cut contours.
The side l o c k lugs remained i n their recesses, engaged o n the l o c k i n g bolts. Part only o f the ripped-out v i s o r a f t p l a t i n g seemed to r e m a i n at-tached to the l u g b o t t o m faces. The clearance between the lugs and the bolts was estimated b y the diver t o be about 10 millimetres.
Various damage to the f r o n t b u l k h e a d was f o u n d and i n particular to its l o w e r part.
The b o t t o m l o c k i n g b o l t housing was t o r n away as w e l l as the support bushing. A l l three attachment lugs were f r a c t u r e d i n their thinnest cross sections. The welds between the lugs and the housing and bushing respec-t i v e l y h a d f a i l e d . The l o c k i n g b o l respec-t remained arespec-trespec-tached respec-t o respec-the p i s respec-t o n r o d o f the actuating c y l i n d e r
There was various damage to the rubber seals and their supporting flat bars o n the front b u l k h e a d and, extensively, o n the forepeak deck.
P o u n d i n g damage was recorded to the shell p l a t i n g edges around the forepeak deck and to the ice-breaking stem o n the bulbous bow. Various scratch marks were noted o n the bulbous bow.
The l o a d i n g ramp was slightly open, w i t h a gap o f about one metre at the top.
The t w o p o r t side hinges at the b o t t o m o f the ramp were t o r n apart. B o t h hydraulic actuators f o r the ramp h a d f a i l e d i n their r o d end pieces. The actuators were i n retracted p o s i t i o n as w h e n the ramp is closed.
Various deep indentations were f o u n d on the beams on the l o w e r side o f the ramp.
The ramp p o r t side beam was damaged in several places, m o s t l y towards the top end.
The lugs f o r the p u l l - i n l o c k i n g hooks were twisted. The hooks them-selves could not be inspected closely.
The boxes on the ramp side bars, m a t i n g the bolts o f the ramp side locks, were twisted to open position, except f o r the lower port side one. The side l o c k bolts were f u l l y extended except f o r the l o w e r port side one w h i c h was only partly extended.
The damage is illustrated i n a series o f photographs s h o w n i n Figure 11.
2.3 Parts Recovered for Examination
The v i s o r was traced on the seabed and was recovered and b r o u g h t ashore f o r investigation. Steel parts o f the visor were r e m o v e d f o r detailed e x a m i -nation f r o m the attachment areas o f the side l o c k i n g lugs and the hinges. One hydraulic cylinder was r e m o v e d f o r internal examination.
The attachment lugs f o r the b o t t o m lock were removed f r o m the w r e c k and b r o u g h t to the surface. One hinge bushing was also recovered.
The l o c k i n g b o l t was removed f r o m the actuator piston r o d b y divers o n 4 December 1994 and brought to the surface. I t was checked f o r wear and deformation. The b o l t was straight. Only a slight difference i n diameter was measured at the contact area between the b o l t and the l u g o f the v i s o r The general diameter o f the b o l t was 79.8 millimetres whereas the m i n i -m u -m -measure-ment across the contact area was 79.4 -milli-metres. N o other damage to the bolt was noted.
W h e n the bolt was recovered f r o m the w r e c k i t was attached to the p i s t o n r o d o f the hydraulic actuator w h i c h remained i n place o n the f o r e -peak deck as shown i n Figure 12. The hydraulic hoses were connected. The actuator was i n fially extended, i.e. locked, p o s i t i o n and the p i s t o n r o d was bent upwards, away f r o m the forepeak deck. The connecting p i n c o u l d be w i t h d r a w n w i t h o u t d i f f i c u l t y and the bolt was brought to the surface.
2 4 Other observations
A student w o r k i n g temporarily i n an o n board maintenance team observed i n A u g u s t 1994 some cracks i n the f i l l e t welds between the hinge beam side plates and the hinge bushings.
The observed cracks were located i n the l o w e r section o f the w e l d beads between the hinge beam side plates and the hinge bushings o n the side
'?0 MV ESTONIA Part-Report
f a c i n g the deck part o f the hinge installation. One crack, about 100 m i l l i -metres l o n g , and one shorter crack were observed i n the starboard hinge lugs. One crack, about 60 millimetres long, was observed i n one l u g at the p o r t h i n g e . The cracks were n o t v i s i b l e w h e n the v i s o r was closed.
2.5 Location of the Collision Bulkhead
and the Ramp
The ramp o f the E S T O N I A was located about 4.2 metres f o r w a r d o f the p o s i t i o n f o r an upper extension o f the c o l l i s i o n b u l k h e a d r e q u i r e d b y the S O L A S 1960 convention, v a l i d at the t i m e o f b u i l d i n g the vessel.
T h é B u r e a u Veritas rules v a l i d at the time h a d n o t f u l l y incorporated the S O L A S requirements regarding the upper extension o f the c o l l i s i o n b u l k -head. Thus, the m i n i m u m 5 per cent o f ship's l e n g t h l i m i t applicable to its l o c a t i o n pursuant t o S O L A S (1960) was n o t a requirement o f the B u r e a u Veritas rules. The rules d i d , however, contain w o r d i n g stating the the classif i c a t i o n society head o classif classif i c e may require an extension o classif the c o l l i s i o n b u l k -head t o the forecastle deck.
The b u i l d i n g s p e c i f i c a t i o n f o r the vessel stated under a heading "Partial C o l l i s i o n D o o r " that "For the intended service n o t r e q u i r e d b y F . B . N . " ( F i n n i s h B o a r d o f N a v i g a t i o n ) . The vessel was g i v e n a Passenger Ship Safety C e r t i f i c a t e i n compliance w i t h S O L A S b y the F i n n i s h A u t h o r i t i e s u p o n d e l i v e r y f r o m the yard. The extent o f p a r t i c i p a t i o n b y representatives o f the F i n n i s h A d m i n i s t r a t i o n d u r i n g the construction o f the vessel is still b e i n g investigated.
M o r e detailed requirements f o r b o w door and ramp installations were later g i v e n i n the 1981 Amendments to the S O L A S c o n v e n t i o n and i n the
1982 U n i f i e d Requirements b y l A C S (International A s s o c i a t i o n o f Classi-f i c a t i o n Societies).
3 Analysis and Evaluation
The Bow Visor Attachment Devices
- Strength Consideratiofis
3.1.1 SgsSgrii B a s i s sinê Kofcgygrdmcirats o f v;Gii<-©ila^-^siifiioa'Èioiiii Svimmf
3.1.1.1 General requirements
The b o w v i s o r itself was b u i l t to scantling requirements s p e c i f i e d i n B u -reau Veritas Rules o f 1977. Compliance w i t h these has n o t been v e r i f i e d i n detail i n this investigation.
The l o c k i n g devices should, according to the B u r e a u Veritas rules v a l i d at the t i m e , cause the b o w door to be " f i r m l y secured". N o detailed proce-dure f o r v e r i f y i n g the l o c k i n g devices was given. Structural reinforcements were specified i n general w o r d i n g to be required at attachment points f o r cleats, hinges and jacks.
T w o notes made b y the Bureau Veritas examiner o f the assembly draw-i n g o f the v draw-i s o r draw-installatdraw-ion stated that "the l o c k draw-i n g devdraw-ices to be subject o f the approval o f the N a t i o n a l A u t h o r i t y " and " l o c a l r e i n f o r c e m e n t o f the ship's structure i n w a y o f l o c k i n g devices, cylinders and hinges to Sur-v e y o r ' s satisfaction".
The design l o a d to be applied to the b o w visor o f a r o - r o vessel has been subject to continuous development based o n n e w data and was n o t w e l l established at the time o f E S T O N I A' S construction.
3.1.1.2 Bureau Veritas rule requirements for the design load on the visor
The B u r e a u Veritas rules d i d n o t specify m i n i m u m pressure heads to be applied to the h o r i z o n t a l and vertical areas o f the v i s o r These loads as calculated b y the yard based o n applied pressure heads amounted to 536 tons v e r t i c a l l y and 381 tons horizontally. The o r i g i n o f the applied pressure heads has n o t been i d e n t i f i e d . The applied loads were, however, o f the same magnitude as those required b y other classification societies at the t i m e .
The loads were, i n the calculations b y the yard, applied evenly to the f i v e attachment points, the hinges included, resulting i n a calculated design l o a d o f 100 tons per attachment point. The B u r e a u Veritas rules d i d n o t i n c l u d e guidance o n the calculation procedure to be applied as no load requirements were specified.
22 MV ESTONIA Part-Report
The procedure apphed d i d n o t produce a set o f forces b e i n g i n static balance w i t h the external forces. The l o a d d i s t r i b u t i o n is statically under-t e r m i n e d . A more deunder-tailed l o a d d i s under-t r i b u under-t i o n analysis w o u l d have s h o w n a design l o a d per l o c k i n g device o f about 135 tons. The pressure head to be a p p l i e d was later more clearly d e f i n e d and the value g i v e n i n the 1982 U n i f i e d Requirements o f LACS w o u l d have resulted i n a desigfi l o a d f o r each l o c k i n g device o f about 200 tons.
The design l o a d o n each l o c k i n g device was used f o r determining a m i n i m u m l o a d carrying cross section o f the attachment o f each device. T h i s was obtained b y a p p l y i n g generally permissible stress levels. The calculations were n o t submitted to B u r e a u Veritas f o r examination. The c a l c u l a t i o n methodology i n c l u d e d a n o m i n a l safety f a c t o r o f about three against the assumed f a i l u r e mode.
3.1.2 ' T h e S t r e n g t h of t h e B o t t o m L o c k A s s e m b l y
The b o t t o m l o c k i n g device f a i l e d i n its attachments to the f o r e peak deck. The f a i l u r e took place i n the plate lugs carrying the b o l t housing and the m a t i n g support bushing and i n the w e l d around the housing and the bush-ing.
The f a i l e d lugs were recovered f r o m the w r e c k and have undergone m e t a l l u r g i c a l and strength e x a m i n a t i o n o f the f r a c t u r e d surfaces and o f the base m a t e r i a l as w i l l be reported i n detail i n an appendix to the f m a l report. A l l i n d i c a t i o n s are that the lugs f a i l e d i n an overload c o n d i t i o n w i t h a l o w n u m b e r o f cycles. The general appearance o f the f a i l e d lugs is s h o w n i n F i g u r e 13. The f a i l u r e i n the w e l d was partly i n the beads and p a r t l y t h r o u g h separation between the w e l d and the h o u s i n g material. The t h i c k -ness o f the w e l d beads was about 3 m i l l i m e t r e s .
The load-carrying capability o f the b o t t o m l o c k assembly has been estimated according to d i f f e r e n t calculations to be i n the range f r o m 90 to m a x i m u m 150 tons. The calculations take into account the cross section o f the f r a c t u r e d surfaces o f the lugs and a c o n t r i b u t i o n f r o m the w e l d j o i n t s .
The actual f a i l u r e l o a d was most l i k e l y less as the lugs may have f a i l e d i n sequence. The gap between the h o u s i n g and the b u s h i n g was 100 m i l l i -metres compared to the 60 m i l l i m e t r e thickness o f the m a t i n g l u g o n the v i s o r The actual transverse p o s i t i o n o f the l u g o n the l o c k i n g b o l t w o u l d i n f l u e n c e w h i c h l u g w o u l d carry the m a j o r part o f the l o a d and thereby f a i l ahead o f the other one. The d e f o r m a t i o n o f the v i s o r l u g indicates that the single l u g f o r the support bushing f a i l e d first.
I t is understood f r o m i n f o r m a t i o n g i v e n b y the y a r d that the l o c k i n g device assembly was manufactured as a shop subassembly that was subse-quently w e l d e d to the forepeak deck. The assembly was w e l d e d u s i n g standard w e l d i n g practice as no detailed d r a w i n g w i t h w e l d i n g data was issued f o r this subassembly.
To satisfy the design calculations o f the yard, the lugs should have had a larger m i n i m u m cross section or the w e l d should have been made a f u l l load-carrying j o i n t , using appropriate m a n u f a c t u r i n g technique.
It is concluded that a load carrying cross section o f the l o c k i n g device, to satisfy the applied design load, was not incorporated i n the actual instal-lation.
3.1.3 '1!'ill©; ^©Str:)!]:!?:/);:!!:" - 3 "3(3^; P ^>mf^e^
The side locks f a i l e d at the attachment o f the lugs to the v i s o r a f t p l a t i n g . N o detailed drawings have been f o u n d , that show the exact dimensions o f the lugs, nor details o f the w e l d i n g o f these to the visor plating. The lugs had a b o t t o m length o f about 380 millimetres as measured at the attach-ment remains o n the visor, compared to about 480 indicated o n general arrangement drawings.
The lugs were r i p p e d out o f the visor p l a t i n g together w i t h part o f the p l a t i n g itself, leaving rectangular holes w i t h fracture surfaces i n shear. The lugs remain i n the wreck. The b o t t o m surface o f one o f the lugs is s h o w n i n Figure 14.
The thickness o f the a f t p l a t i n g o f the visor was 8 millimetres. T w o vertical stiffeners were added b e h i n d each l u g at the request o f the surveyor f o r local reinforcement o f the structure i n w a y o f the l o c k i n g devices. N o other strength c o n t i n u i t y was incorporated b e h i n d the lugs.
The load-carrying capability o f the side l o c k cannot be calculated w i t h certainty as i t is statically undetermined. The force required to p u l l and break the l u g away f r o m the visor i n a d i r e c t i o n tangential to the r o t a t i o n around the hinge points has, however, been estimated to be 9 0 - 1 2 0 tons. I t is concluded that the absence o f s u f f i c i e n t l y detailed m a n u f a c t u r i n g and installation instructions resulted i n the calculated design l o a d c a r r y i n g capability not b e i n g incorporated. O n l y l i m i t e d arrangements were made f o r t r a n s m i t t i n g the loads f r o m the lugs to the structure o f the v i s o r
3.1.4 A p p r e v a l ©v 'Uw Lmhm§ D®vie®s
A w r i t t e n request was made by the manufacturer o f the ramp and the l o c k -i n g dev-ices to the F -i n n -i s h B o a r d o f N a v -i g a t -i o n f o r adv-ice about w h -i c h drawings the A d m i n i s t r a t i o n wanted to see. The A d m i n i s t r a t i o n responded that o n l y where there was any doubt as to interpretation o f applicable rules should drawings be submitted to the A d m i n i s t r a t i o n . The A d m i n i s t r a t i o n assumed that the classification society w o u l d take care o f the r o u t i n e ex-amination. This correspondence refers to drawings produced b y the maker o f the ramp and associated parts and not the installation drawings o f the shipyard. N o indications have been f o u n d that any drawings were submit-ted to the A d m i n i s t r a t i o n f o r special consideration.
MV ESTONIA Part-Report
I n e x a m i n i n g the arrangement drawings the B u r e a u Veritas surveyor made a r e m a r k that the arrangement o f the l o c k i n g devices should be sub-j e c t t o the approval o f the national authority. N o evidence has been f o u n d
i n d i c a t i n g that such installation drawings were submitted b y the y a r d to the F i n n i s h A d m i n i s t r a t i o n .
A c o m m e n t o n the arrangement d r a w i n g b y the surveyor f i i r t h e r stated that the structural r e i n f o r c e m e n t b e h i n d the l o c k i n g devices should be t o the satisfaction o f the attending surveyor This comment seems to have been c o m p l i e d w i t h and a note o n the inspection records f o r the completed i n s t a l l a t i o n requests that t w o vertical stiffeners be w e l d e d o n the front side o f the v i s o r plating.
3.1.5 T h e H i n g e s o n D e c k
The hinge bushings installed i n the end lugs o f the v i s o r hinge beams h a d an u l t i m a t e load-carrying capacity i n tension o f about 3 5 0 tons at each hinge. T h i s includes an estimated c o n t r i b u t i o n f r o m the w e l d j o i n t s . The weakest section was across the lugs and i n c l u d e d the f i l l e t w e l d around the hinge b u s h i n g . The n o r m a l l o a d created w h i l e raising the v i s o r was about
150 tons o n each hinge. The reported cracks i n these welds were i n a loca-t i o n w h i c h was subjecloca-ted loca-to sloca-tress p r i m a r i l y as a resulloca-t o f w i n d loads dur-i n g the v dur-i s o r ' s opendur-ing and closdur-ing and dur-i n partdur-icular dur-i f some t w dur-i s t dur-i n g oc-c u r r e d as a oc-consequenoc-ce that the aoc-ctuators d i d n o t m o v e w i t h the same velocity. The cracks had, due t o t h e i r location, a rather l i m i t e d e f f e c t o n the assembly's c a p a b i l i t y to take f o r w a r d directed loads.
The f a i l u r e o f the lugs at the hinges t o o k place i n tension. The f r a c t u r e surfaces indicate that the f a i l u r e t o o k place i n a m o n o c y c l i c overload con-d i t i o n . T h e lugs ancon-d the welcon-ds o f the hinge bushings have uncon-dergone metal-l u r g i c a metal-l a n d strength investigation w h i c h w i metal-l metal-l be reported i n an appendix t o the f m a l report.
I t is regarded as l i k e l y that the forces to cause the hinges t o f a i l were created w h e n the hinge arms started to contact the upper deck as a conse-quence o f compression o f the v i s o r b o t t o m structure. The leverage thereby created i n c o m b i n a t i o n w i t h the mass forces generated w h e n the v i s o r was p o u n d i n g o n the forepeak deck were more than adequate t o p u l l the hinges apart.
3/S .S C o n t r i b u t i o n f r o m t h e IVIanual L o c k s
The m a n u a l locks at each side consisted o f t w o plate lugs and an eye b o l t rotated to p o s i t i o n between the lugs and tightened. The t o t a l load-carrying capability o f the manual locks has been calculated to be about 70 tons each. I f the manual locks h a d been applied they w o u l d to some extent have c o n t r i b u t e d to the overall load-carrying capability o f the v i s o r locks. The
f a c t that there were no instructions f o r their use indicates, however, that they were not regarded as part o f the operational l o c k i n g system.
The visor had t w o heavy-duty actuators f o r controlled opening and closing o f the visor. These were connected to the v i s o r hinge beams at a distance o f
1.3 metres f r o m the hinges and were m o u n t e d o n r e i n f o r c e d h o r i z o n t a l p l a t f o n n s i n the f r o n t structure o f the h u l l . The actuators were connected hydraulically to a solenoid-type control valve, w h i c h was closed at all times except w h e n the visor was being moved.
W h e n sea loads started to open the visor, an u p w a r d l o a d was also ap-p l i e d to the actuators, w h i c h resisted the oap-pening movement. The leverage f r o m the centre o f attack o f the sea loads compared to that o f the actuators enabled a h i g h p u l l i n g force to be transmitted to the actuators. The p o r t side actuator was at this moment pulled out o f the h u l l w i t h o u t being ex-tended w h i l s t the locked-in hydraulic f l u i d acted to transmit the f o r c e to the l o w e r attachment o f the unit. The vertical f o r c e to p u l l the support structure o f the actuator out o f the h u l l i n shear has been estimated to be around 700 tons, t a k i n g into account the unsymmetrical attachment p o i n t o f the load. The actuator has undergone a detailed investigation w h i c h w i l l be reported i n an appendix to the f i n a l report.
The seals i n the starboard side actuator f a i l e d , preventing the h y d r a u l i c f l u i d f r o m transmitting the load. The piston r o d o f this actuator was there-f o r e extended and the actuator remained connected in the h u l l d u r i n g the i n i t i a l phase o f the movement o f the v i s o r The load i n i t i a l l y taken b y this actuator before the seals f a i l e d cannot be determined but w i l l have been less than the above value o f 700 tons.
3.2 The Ramp Locking Devices
- Strength Considerations
The ramp was secured i n the closed p o s i t i o n b y six l o c k i n g devices, t w o p u l l - i n hooks at the upper end and t w o l o c k i n g bolts along each side o f the ramp.
The upper p u l l - i n hooks were i n closed p o s i t i o n as v e r i f i e d b y video pictures o f the actuator and lever mechanism. It has, however, n o t been possible to determine i n w h i c h mode the hooks failed. A n upper l i m i t o f the load-carrying capability o f a h o o k may have been the load at w h i c h the metal i n the contacting area between the h o o k and the m a t i n g p i n started to y i e l d . This load was approximately 20 tons. It is assumed that the p i n slipped o f f the hook when y i e l d i n g started in the h o o k material, as the bend-over angle o f the hook t i p was small.
MV ESTONIA Part-Report
The side securing bolts were, i n l o c k e d p o s i t i o n , extending into b o x - l i k e structures, w h i c h were w e l d e d to the side bars o f the ramp. These boxes w e r e r i p p e d open f o l l o w i n g failvires i n their welds. The f o r c e required to r i p any one o f these boxes open has been estimated to about 20 tons. One b o x , the l o w e r port-side one, was n o t r i p p e d open and i t is assumed that the l o c k i n g b o l t was n o t f u l l y engaged i n this box. A question remains about the c o n d i t i o n o f this l o c k i n g device at the t i m e o f the accident, b u t this d i d n o t have any e f f e c t o n the overall development o f the accident.
The securing devices f a i l e d sequentially as a result o f l o a d b e i n g ap-p l i e d f i r s t to the ap-p o r t side. A f o r c e aap-pap-plied to the t o ap-p o f the ramap-p fi-om contact w i t h the v i s o r h a d a favourable leverage relative t o that o f the l o c k i n g devices, r e d u c i n g the f o r c e actually r e q u i r e d to break the devices. The contact f o r c e required to d e f o r m the stiffeners i n the deck b o x o f the v i s o r has been estimated to be about 50 tons.
3.3 Probable Failure Sequence of the
Visor and the Ramp
The d i s t r i b u t i o n o f forces o n the visor attachment points cannot be static-ally determined. A complete f i n i t e element analysis o f the v i s o r and the huU .part o f the attachment structure, t a k i n g i n t o accoimt a l l elasticity o f the
structures, w o u l d i n theory p e r m i t calculation o f forces at the i n d i v i d u a l attachment p o i n t , g i v e n that the external loads were k n o w n . Since the ex-ternal loads are undeterminable and q u i c k l y variable i n magnitude and l o c a t i o n , n o means exist f o r accurate calculation o f the loads at each i n d i -v i d u a l attachment point.
The most probable sequence o f events d u r i n g the f a i l u r e has been recon-structed based o n damage observations and calculations. Figure 15 illust-rates this sequence as described below.
The three l o c k i n g devices may have f a i l e d i n any one sequence. The chance that they f a i l e d simultaneously has been considered to be small, t a k i n g i n t o account the u n c o n t r o l l e d play at each l o c k i n g b o l t and the elas-t i c i elas-t y o f elas-the selas-trucelas-ture.
A f t e r f a i l u r e o f the b o t t o m and side locks, the v i s o r operating actuators resisted f i i r t h e r opening movement. The leverage o f the sea loads created s u f f i c i e n t l y h i g h loads o n the actuators to cause these t o be p u l l e d out o f the h u l l or to f a i l internally.
F o l l o w i n g the f a i l u r e o f the locks and the actuators the visor was free to p i v o t a r o u n d its hinge points. The lack o f damage to the p a r k i n g device o n deck indicates that the v i s o r d i d n o t at any m o m e n t rise t o f i i l l y open p o s i -t i o n . Wi-tness s-ta-temen-ts regarding sharp h a m m e r i n g noises f r o m -the b o w area and water c o m i n g u p between the v i s o r and the deck indicate that the v i s o r was p i v o t i n g up and d o w n f o r some time. D u r i n g this part o f the
sequence the visor was beating on its three b o t t o m resting pads, the m a i n one being the v i s o r stem post, w h i c h was i n contact w i t h the ice-breaking stem. The stem post separated f r o m the visor due to f a i l u r e o f the attachment welds i n consequence o f this hammering. The violence o f the p o u n d i n g action caused the stem post to leave the visor w i t h a considerable u p -w a r d velocity, creating a sharp indentation i n the f r o n t o f the v i s o r f o r a lr;!iigi:h f j f about:/ AViefcro;; Glbiovvii M I ÏMgïjrf:; 10.
A f t e r the s o l i d stem post had separated f r o m the v i s o r there was no other strong p o i n t to take the vertical p o u n d i n g , and the b o t t o m part o f the v i s o r structure was d e f o r m e d and compressed b y about 0.2 metres b y beating against the t w o r e m a i n i n g pads, the shell plating p r o t u s i o n around the forepeak deck and the locating horn.
A s the v i s o r was seating lower than n o r m a l due to the compression o f the b o t t o m part, the hinge beams started to contact the m a i n deck, causing heavy upwards and f o r w a r d s loads o n the hinges, resulting i n f a i l u r e o f these. The v i s o r was also beating backwards against the l o w e r part o f the f r o n t bulkliead d u r i n g this movement, adding to a f o r w a r d p u l l i n g f o r c e at the hinges.
A t this stage the visor was still in a position close to the n o r m a l one, g u i d e d because the attachment lugs f o r the l i f t i n g actuators were engaged i n the openings i n the deck. The visor continued to make v e r t i c a l m o v e -ments d u r i n g this phase, indicated b y various damage, e.g. the port-side l o c a t i n g h o r n tore a l o n g opening i n the visor a f t bulkhead. It is also e v i -dent f r o m damage to the a f t end o f the b o t t o m plates o f b o t h v i s o r hinge beams and the m a t i n g hinge f i t t i n g s o n deck that the v i s o r was beating backwards h e a v i l y onto the h u l l . The a f t edge o f the v i s o r deck p l a t i n g was also beating backwards onto the edge o f the h u l l deck, about evenly f o r the f u l l w i d t h f r o m p o r t to starboard.
A t a later stage, possibly due to accumulation o f water inside the v i s o r and due to the mass forces f r o m the p i t c h i n g o f the vessel, the v i s o r started to t i l t f o r w a r d w i t h s u f f i c i e n t force to cause the attachment lugs f o r the l i f t i n g actuators to start cutting openings i n the deck plating. D u r i n g this gradual movement f o r w a r d the a f t w a l l o f the b o x o n the v i s o r deck came i n contact w i t h the top o f the ramp. A s the sea l o a d was on the port bow, the v i s o r was t u m e d somewhat to starboard, thereby causing the contact to be concentrated to the p o r t side.
D u r i n g the continued f o r w a r d s h i f t o f the v i s o r i n a step b y step beating movement, the lugs o f the l i f t i n g actuators continued to cut slots i n the deck p l a t i n g , and the a f t w a l l o f the deck b o x started to push on the upper side o f the ramp. The ramp l o c k i n g devices f a i l e d sequentially. The upper p u l l - i n hooks o f the ramp may have disengaged due to the shock load i n the structure created when the p o r t side actuator was p u l l e d out or later due t o the b o u n c i n g around o f the actuator i n the area as the v i s o r m o v e d up and d o w n . B o t h operating actuators f o r the ramp f a i l e d at their p i s t o n r o d end f i t t i n g s .
