FINCANTIERI Approach to High Speed Vessel, Operability and Comfort Levels

INTERNATIONAL SEMINAR

COMFORT ON BOARD AND OPERABIHTY EVALUATION OF H I G H SPEED MARINE VEHICLES Genoa. CETENA S.p.A.

25 November 1994

I

F I N C A N T I E R I APPROACH TO HiGH SPEED VESSEL OPERABILITY AND COMFORT

L E V E L S '

Luigi GROSSI. Ottavio PINTO, Stefano SAIONE FINCANTIERI C.N.I.

Naval Shipbuilding Division, Hydrodynamic and Acoustic Depanment.

ABSTRACT

Scope of the present paper is lo give a general idea ofprocedures adopted by Fincantieri for the assessment of op-erabihty of high speed ferries, taking into account seakeeping performances, vibration and noise.

Most of these procedures derive from past experiences in tlieoretical previsions correlated with model andfull scale measurements carried out on high speed vessels, either mihtary or civil

A presentation of llie major results is included as well

1. INTRODUCTION

In past times generally tlie operability of strips in sea slates have been evaluated based upon criteria tliat take into account hull stmctiu'e damage, propulsion plant, equipment and sj'steins elTiciency.

At the same time, conxfort onboard has become a commercial issue for fast ferries, where passengers are not generally acclimatised onboard ships, different types of vessels are in competition and tlierefore comfort on-board could represent a choice factor from passengers point of view.

On the other hand it is obvious tliai tlie efficiency of a ship is related to the efliciency of her crew.

A modem assessment of operability of a ship has to take into account tlie following factors:

• stnicliual integrity and systems efliciency; • crew and passengers seaworthiness and comfort.

Due to the importance of these factors in design pro-cedure of high speed vessels, Fincantieri faces them at the very first stage of the project.

2. DESIGN PROCEDURE

Design procedure for the assessment of liigh speed vessels operability is therefore divided into three phases during the first stages of tlie project (immediately after

availability of rough body plan and general anangemenl plan):

• ship systems and hull structure integrity assess-ment;

• crew and passengers seasickness analysis; • crew and passengers noise exposure.

These three phases are mainly based upon seakeeping, noise and vibration analysis.

2.1 Systems Efficiency and Hull integrity. In the first stage tlieoretical se;ikeeping computations give all the data of sliip motions necessary for operabil-ity analysis bases upon systems and htdl integroperabil-ity. Criteria generally adopted are STANAG 4154 opera-tional limits based upon the following parameters:

• max value of fore perpendicular vertical accelera-tion;

• max slamming probability; • deck wetness.

These limits are sometimes integrated with other cri-teria:

• propeller emergency probability;

• vertical acceleration distribution fi^om fore to after perpendicular.

For the most signiGcanl projects, the requested data are obtamed from lowing tank seakeeping tests.

The above mentioned parameters are usefiil also to characterise the sldp.

Fig. 1 compares two similar ships with a completely difierent vertical accelerations behaviour,

f'

2.2 Crew and Passengers seasickness analysis.

1/

Motion sickness seems lo be caused by a lot of exter-nal factors and parameters, but mairüy by:

• the experienced vertical acceleration at a certain location along tlie sliip;

• the frequency contents of these accelerations; • the exposure lime.

Oilier causes and external factors influence tlie phe-nomenon such as: sex, age, fatigue, lianger, anxiety, dif-ferent smells, to be or not in closed rooms niüiout win-dows, working or not, reading or not, etc.

However, all tliese factors are relaled to tlie passenger and his particular status; they do not depend on tlie seakeeping qualities of llie ship.

All these secondarj' factors were not taken into ac-count in om investigations and only the first three were analysed in order to have an objective evaluation of comfort onboard.

The procedme adopted m Fincantieri takes into ac-count die analysis of llie results coming from experi-mental tests in motion simulators witli not acclimatised volunteers and therefore they represent om "'protol}'pe of passenger".

Comfort analyses should take into account all tlie three factors and llieir interdependencies: die accelera-tion level at a certain frequencj' for a certain exposure lime must be compared wiUi limits dial give standard indication on die behaviom of people present onboard.

In die range from 0.01 Hz to 10 Hz, Uiat well repre-sents die frequenc}' range of motions both for conven-tional and fast sldps, diree types of recommended'limits can be found in die literature:

• ISO Standard 2631 "fadgue-decreased .proficienc)' boundaries" (1 Hz lo 80 Hz);

• ISO Standard 2631/3 "severe discomfort bounda-ries" [1] (0.1 Hz lo 0.63 Hz);

• O'Hanlon & McCauley Modon Sickness Incidence niethod.

The first two guides define and give numerical values for limits of exposme for vibration transmitted to Uie human body. The ddrd one is a calculaüng mediod to evaluate MSI (Modon Sickness Incidence: die percent-age of subjects who vomited wiüiin 2 homs).

ISO Standard curves at different ex-posure times rep-resent die lindt with a nonunal MSI equal to 10% so, i f the acceleradon level for a certain frequeiic>' is beyond ÜÜS limit in a voyage of two hours, we can have more Uian 10% of passengers feeling sick.

In our analysis a global nominal curve has been con-sidered. Tlds curve represents tlie limit for a MSI = 10 % wilh 2 homs' exposure time and in particular i l con-sists of: . .

1. 0.1-5^1.63 Hz: O'Haidon & McCauley curve wiUi MSI=10%andt = 21irs;

2. 0.63^^10 Hz: ISO Standard 2631

Below 0.1 Hz the same limit as die O'Hanlon & Mc-Cauley curve for 0.1 Hz has been kept.

Tlds figme only represents a MSI = 10 % wiUi ex-po-sme dme equal to 2 lus: a sldp owner could be inter-ested in seeing what is die findt, for example, for 4.5 hrs (that is its voyage time) or lo fix a MSI = 5%.

For this reason, we have used a simplified method presented in Ref. 4 that gives some simple formidas in order lo change the limits at different MSI or exposme times.

To cliange MSI from 10% die following expressions can be used:

MSI f o r M S I < 2 0 %

MSl{az)^20 + m log -log(l.47)

f o r 2 0 % < M S l < 80% where az is die RMS vertical acceleration linut for die desired MSI percentage and AZ is die same value at

10% of MSI.

To change die acceleration limits at different exposure times die following ex-pression, provided by ISO can be used:

where az(t) causes die same MSI level after an expo-sme time I as az (Ij) after expoexpo-sme time t j .

As mentioned in Uie foregoing, diese figmes can be utilised to calculate die acceleration limit curve versus frequency at difierent MSI and exposme time (= voyage time), according lo operators' specific needs.

This limit curve can, finally, be superimposed with a one-ddrd octave band analysis on acceleration responses al a cenain longitudinal or fransversal location of the ship for a certain sea state, heading and speed.

These one-ddrd octave band acceleration responses can be calculated from the responses measmed during seakeeping model tests or for example from seakeeping malliemadcal models.

If diese complete responses (in the frequency range) are nol available, a prelindnary investigation can be

made comparing the limit curve with RMS values ofthe vertical acceleration al a certain frequency.

The comparison of these responses and die limit curve can give designers and operators Uie indication on the degree of comfort present onboard wilh all Üie interde-pendencies amon^Uie above mentioned three parame-ters, r

I

t •* ^ 2.3 Crew ..and Passengers noise exposure.

To define airborne noise for a ship means necessary to find die right balance between two different require-ments; the noise of the sldp connected to its movement and the necessity to secme in its spaces no dangerous level for ears, speech communications, and comfort.

The ship is, first of all, a mean of Uansport. One of tlie principal somce of noise is its engine and its ma-chinery. For Idgh speed vessel could not be neglected the contribute conung from die flow around the hull.

So it's impossible fix in this case die same airborne noise levels fixed for a static construction Idee die levels required in a building, for example.

Two are the significant ways Uuough the noise spreads: the airborne and die structural noise. Usually lintits for airborne and stnictmal noise are established for the engine and all the principal machinery that con-tribute to die noise.

To reduce the airborne noise propagadon could be necessary to increase the weight of walls around die area of source of noise or build a box around it.

To reduce the structmal noise could be necessary use elastic connections, simple or double suspension, or work on die structmal parameters: ddckness, ribs, struc-tural intersections, damping.

Usually, the most noisy areas are the propulsion room, machinery spaces and the lower zone of die slup sensi-ble to hydrodynandc-noise: cavitation, flow, sprays, waves etc.

As you go away from the boUom where generally are mounted engine and machinery lower level of noise can be obtained.

Three could be generally the criteria to define accept-able noise levels :

• Consequence of noise exposme on the health; • Consequence of noise ex-posme on die comfort; • Consequence of noise exposure on die speech

communication.

Speaking on comfort die effects of noise on Human health could be neglected, so in the following paragraph will be briefly treated about die last two criteria.

Consequence of the noise exposure on the "omfort. Some sounds cause annoyance. Noise is unwanted sound. Many different parameters acts on die amioyance caused by noise. Some of these are acousdcal and some not acoustical. Tlie principal acoustical parameters are: Sound level (An increase of sound level causes an

in-crease of the quantity of sound heard in the time (intensity)); Frequeucies (Around 2000- 8000 Hz noises are more annoying, whUe under the 500 Hz and upper die 10000 Hz, has not be shown sign of annoy-ance at the same pressme level); Time of exposure (A short sound necessities of more pressure level Üian a longer one lo cause the same amioyance) and die type of the noise Spectrum.

Consequence of the noise exposure on the speech communicatiou

When a person speaks, acoustic waves me generated. Tliese waves are different at any moment in frequency and pressure. The average over all level of speech is not easily detemtined because the variation of die normal tone of voice is greatly depending on many parameters.

The A weighted noise levels for most speakers meas-med at a distance of 1 meter from Uieni are usually be-tween 50 mid 65 dBA when Uiey are required to speak widi a normal tone of voice as result from die Table a.

To miderstand the words it's necessary dial the acous-tic level near die ear of the listener wifl exceed the background noise.

The understanding of die speech commimication de-pends, also, on the emission level of the voice and on the distance between the speaker and listener in addition to odier factors as: the velocity in speaking, the faiidliar-ity widi the words used by die speaker and Uieir clear-ness and so on.

Normally are employed tests lo detennine how well speech can be understood by die listener. These are called intelligibility tests. A speech commuiUcation is defined as good if die 95 % of words is correctly under-stood by die listener. Usually it happens until 5 m if die backgromid noise level is < 50 dB A and die speaker use a normal tone of voice.

Above die 50 dB A of background level the speaker, instinctively, will increase his "normal" level of voice, 10 compensate the increase ofthe background noise.

ff the distance speaker-listener is not much more than 1 meter could be made "normal" conversadons widi background noise of about 65 dB A . Tlds voice effort if 11 is not continuous could be carried for long time. So a level of background noise'of 65 dB A could be consid-ered as an acceptable level for all the space in wldch a "normal" conversation could be made.

Increasing the distance behveen speaker and listener mitil 2-4 meters tlds level goes down to 55 dB A.

Wilh a relaxed tone of voice die background noise could not be more Idglier Uian 45 dB A. Tlds could be taken as a good noise level for a bedroom.

In the Table b are given, approximately, die conver-sation lone of voice level as fmicdon of background noise

3. EXAMPLES OF PRACTICAL APPLICATION

MDV1200 (Figure 2) represenls Üie new generation of car ferry monolnills, according to the increasing mar-ket inlerest in Mgh speed applied lo passengers/cars feny service. i

In recent y e ^ Fincanderi has carried oul several fidl test campaigns al the major Emopean model basin (INSEAN - Rome, SSPA - Göteborg, DMI - L}'ngby) on models of Deep-V monohulls. Purpose of diese tests was boUi lo validate and optimise performances and to inves-dgate the influence on resistance and seakeeping quali-des. of difierent parameters such as L/B, B/T rados, deadrise angle, bow and stem shapes.

The experience of Fincantieri in high speed mono-hulls is not only related lo die Deep-V concept but also lo hard-cldne send-planning monohulls and in particu-lar to "DESTRIERO" Vessel, die fastest realisation of dus concept. The extensive model tests campaign, car-ried out at SSPA and die relevmil predicting metiiods were validated by die successfid results obtained during sea-trials.

The huU of MDVl200 was bom from die above men-tioned experiences and die obtained data were suitably exploited in order to make quite reliable predictions. Tlie hud was optimised trying to reach a good compro-mise between die well-proven seakeeping qualities of die Deep-V concept and Uie excellent speed perfomi-ances of die hard-cldne semi-planning hulls.

The following aspects were considered determinant and qualifying results for Uie improvement of Uie Deep-V concept for this type of service:

• service speed aromid 40 knots;

• low acceleration levels mnidsldps (less dian about 0.025 g RMS m Sea State 4)

• sniall ddferences for tiiese levels between after and forward part of passenger area and therefore low values of pitch angle (less Uian 0.3 deg RMS in Sea Stale 4);

• low speed losses in rough weaUier;

• high roll damping and consequent low lateral mo-dons.

The vessel lias a Uransport capacity of 450 passengers widi luggage and 120 cms (4 m average lenglh) ar-ranged on lluee different decks:

• lower car deck, holding 42 cars wiUi a total avail-able mea of ~ 500 ni^;

• main car deck, holding 78 cars widi a total avail-able mea ofa 900 ni^;

• passenger and main deck.

Vehicles can be embarked/disembarked bodi ftom an aft ramp/door and from a fonvard ramp and visor.

3.1 Seasickness analysis for MDV1200

In September 1992, Seakeepmg Tests were carried out at Danish Maritime Institute on a model of Fincantieri's MDV 1200.

Tlic tests were performed at Uie foUowing conditions: • Sea Slate 4 (Significant Wave Height Hl/3 = 2.1

m), Head Sea and for Uie speeds of 25, 30 and 35 knots;

• Sea Slate 5 (Significant Wave Height Hl/3 = 3.3 m), Head Sea and for die speeds of 25. 30 and 35 knots;

The following vertical acceleration responses were measmed and collected during Uiese tests:

e vertical accelerations at Fore and After Perpen-dicidms;

• vertical accelerations al Bridge location;

• vertical accelerations at longitudinal position of Cenfre of Gravity.

From diese measmemenls heave displacement and pitch angle were calculated, loo.

A one-ddrd octave band mialysis for Uie vertical ac-celeration responses al Centre of Gravity and al Bridge, measmed during seakeeping model tests, were per-formed and compmed with die comfort Uiidts.

For Uie comfort analysis of MDV1200, the previous figmes have been utilised to calculate two fandlies of limit curves:

• curves for Motion Sickness Incidence variable from 1% lo 20 % at a conslanl ex-posure time of 2 hrs;

• curves for exposure times vmiable from 0.5 hrs lo 2 lus at a MSI index kept constant at 5%.

The results of die motion sickness analysis is shown in die following diagrams:

• Figs. 3 and 4: seasickness analysis at LCG and Bridge respectively, for Sea Stale 4 a( different speeds and at an exposme time of 2 hrs;

• Figs. 5 and 6: seasickness analysis al LCG mid Bridge respectively, for Sea Stale 5 al different speeds and al an exposure time of 2 lus;

• Figs. 7 and 8: seasickness analysis at LCG and Bridge respectively, for Sea Slate 4 al different speeds mid at an e.\posme time of 4 hrs;

• Figs. 9 and 10: seasickness analysis at LCG and Bridge respectively, for Sea Stale 5 at different speeds and al an exposure time of 4 lus;

From Uie results of Uiese diagrams die following con-siderations can be made:

a. die sldp offers an exceUent behaviom from Uie point of view of passenger seasickness, especially for Uiose seated amidships for all considered

speeds boüi for Sea Stale 4 (no seasickness) and Sea State 5 ( 1 % of MSI);

b. however, in all passenger areas, die MSI is less Uian about 1% in Sea State 4 for an exposure time of 2 lus and only in Sea State 5 a MSI = 10 % is reached in U^ Bridge locadon.

}

3.2 Ship^bóard noise prediction methods.

r.-To predict sidpbomd noise and lo determine the ob-jecUve noise and vibraUon levels, computer programs liave been used based on the calculation procedmes described in SNAME Design Guide (Ref. 5) and on Fincantieri's experimental data.

The logical scheme of die used method (with the indi-cadon of lhe used program) is shown in Fig. 11.

ASSORB: Program calculates die room Sabine con-stant values. The infonnation inputted includes the di-mensions ofthe room, the material type on each smface and die contribution of no-boundary smface areas.

PRELOC: Program computes Uie conUibution to die airborne noise in a receiver area of die stnichire borne noise conung from maclunery vibration.

The infonnation that usually needs as input regards mounting configuration, foundation, path between ma-cldnery (type of structmal intersections along die paUi (T. L, T intersections) source and receiver space, radiat-ing smface characteristics (material, thickness, distance between ribs) of the receiving room and Ihe source (inachiner)') acceleration levels.

LOC: Program computes die airborne noise in a compartment or due to the airborne noise levels in Ihe sunounding compartments.

The input necessary information is: die airborne noise in the sunomiding compartments, die cliaraclerisdcs of die wall or deck dividing the compartments (density. Young modulus, ribs, thickness) the chmacierisdcs of the receiver spaces.

T.B.L.: Program computes the airborne noise in a compartment due to the flow mound die hull. Tlds com-ponent is relevant for Idgh speed. The input are : speed of the vessel, distance between compartment and bow, characteristics of the hull (ddckness, ribs etc.), die cliaracteristics of the compartment (Assorb).

OPFBELD: Program computes the airborne noise from somce (exliausl gas and intake air) to a any point taking in to account the orientation between somce and receiver, their distance and die presence or not of ob-stnictions and reflections during the path source - re-ceiver.

In Fig. 12 is shown an application of slupboard noise prediction niethods for FINCANTIERI MDV 1200 vessel.

The contribution of Uie exhaust gas and air intake, the flow moimd the hull and structure borne noise has been considered.

Tlie HVAC contribution has been neglected, assum-ing that ils sound pressme levels are lower than the oUier somces.

The nmnbers written in the figme are the total dBA levels for each compartment resulting from all the somces considered.

4. CONCLUSIONS

Modem approach lo lugh speed vessels operability has to take into account not only hull and systems integrity, but also people on bomd efficiency.

Available tools, such as computer codes and model tests can issue all the data for a reliable and a more real-istic analysis.

REFERENCES

f l ] Inlernalional SlandardlSO 2631/3.

"Evaluation of human exposure lo whole body vi-bration. Pari 3: Evaluation of whole body z-axis vertical vibration in lhe frequency range 0.1 lo 0.63 Hz".

1985-05-01.

f2J O'Hanlon ti: McCauley.

"Motion Sickness Incidence as a Function of Ac-celeration of Vertical Sinusoidal Motion". Aerospace Med 45 (4): 366-369. 1974. f3J A.R.J.M. Lloyd

"Seakeeping - ship behaviour in rough weather". Ellis Horwood Series in Marine Technology. ELUS HOR WOOD LW/ITED. 1989.

f4J A. Soars, J. Schmidt

Advanced Multi-Hull Designs "Motion sickness evaluation on ships".

Paper presented al "The eighth International High Speed Craft Conference".

London. 21-23 January 1992.

f5J Design Guide for Shipboard Airborne Noise Control - Teclmical and research bulletin n° 3-73 - The Society of Naval Architect and Marine Engineers -1983

f6J J. C. Webster: "Effetti del rumore sulla comunica-zione verbale" byManuale di controllo del rumore - Tecnicbe Nuove - 1992

TONE O F V O I C E A W E I G H T E D SOUND L E V E L dB WfflSPERED 40 RELAXED 57 NORMAL 59 RAISED 65 STRONG 74 SHRIEKED 82 VERY STRONG 88 Table a Communica tion

Background Noise Levels dBA

<50 dB 50-70 dB 70 - 90 dB 90 - 100 dB 110-130 dB

Face to Face Voice

normal distance less than 6 m Voice raised distance until 2 m Voice raised distance until 0.5 m Very strong voice distance untill 0.25 m Impossible

Telephone Good Satisfactor

y Difficult Necessity of acoustic box Needs of special equipment s

Interphone Good Satisfactor

y

Unsatisfie d

Impossible Impossible

TRAGHETTO V E L O C E MDV 1200 T - VERSIONE CODAG

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT LCG - H1/3 = 2 m

Exposure Time = 2 hrs

1 1 \ \

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT BRIDGE - Hl/3 = 2 m

Exposure Time = 2 hrs r-.

1 _r 1 . 1

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT LCG - H1/3 = 3 m

Exposure Time = 2 hrs -:.

z

%

<

ENCOUNTER FREQUENCY (THIRD OCTAVE BAND CENTER) [Hz]

10 -« Vs = 25 knots -• Vs = 30 knots -* Vs = 35 knots IS02631/3 MSI = 1% IS02631/3 MSI = 5% IS02631/3 MSI = 10% • iS02631/3 MSI = 20% IS03MG2.XLC

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT BRIDGE - Hl/3 = 3 m

Exposure Time = 2 hrs

z

i

5

ENCOUNTER FREQUENCY CTHIRD OCTAVE BAND CENTER) [Hz]

10 Hi Vs = 25 knots -• Vs = 30 knots Vs = 35 knots IS02631/3MSI = 1% IS02631/3 MSI = 5% IS02631/3 MSI = 10% IS02631/3 MSI = 20% IS03MB2.XLC

MDV 1200 - SEASICKNESS ANALYSIS AT LCG - Hl/3 = 2 m

Exposure Time = 4 hrs

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT BRIDGE - Hl/3 = 2 m

Exposure Time = 4 hrs r:._ .

i

<

ENCOUNTER FREQUENCY (THIRD OCTAVE BAND CENTER) [Hz]

10 -• Vs = 25 knots -* Vs = 30 knots Vs = 35 knots 1302631/3 MSI = 1% IS02631/3 MSI = 5% IS02631/3 MSI = 10% - !S02631/3 MSI = 20% IS02MB4.XLC

MM/ATS-FG

MDV 1200 - SEASICKNESS ANALYSIS AT LCG - Hl/3 = 3 m

Exposure Time = 4 hrs

ENCOUNTER FREQUENCY (THIRD OCTAVE BAND CENTER) [Hz]

10 - * — Vs = 25 knots Vs = 30 knots -* Vs = 35 knots IS02S31/3MSI = 1% IS02631/3 MSI = 5% IS02531/3 MSI = 10% - IS02631/3 MSI = 20% 1S03MG4.XLC

MDV 1200 - SEASICKNESS ANALYSIS AT BRIDGE - Hl/3 = 3 m

Exposure Time = 4 hrs

1

EXPERIMENTAL DATA Of i' UACC M A O H l ï s ï l E S A N D APPARATUS CONNECTIONS FOUNDATIONS SIGMA ATTPAR ASSORB AIRBORNE NOISE IN SHIP SPACES T B L L O C SPEED AND POSITION ALONG THE H U U AIRBORNE NOISE uurrsiN ACCOMODATIONS ASSORB NOISE IN TURBULENT BOUNDARY LAYER FLOW S T R U C T U R E S VIBRATIONS INDUCED ON THE HULL SOUND POWER UMITBIN NOISE SOURCE SPACES

A T T P A R - A S S O R B

AIRBORNE NOISE IN ACCOMODATION AREAS DUE TO TURBULENT FLOW

F I N C A N T I E R I M D V

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