COMFORT ON BOARD EVALUATIONS FOR HIGH SPEED

VESSELS

A. D. Alkan YTU GIDF Department of Naval Architecture and Marine Engineering,

Yıldız Technical University, Istanbul, Turkey

ABSTRACT: Dynamic nature of sea is a vital issue that certainly influences vessel operational performance

and safety in a seaway resulting excessive dynamic loads, motions and accelerations. The literature reveals

that absolute vertical accelerations in multiple axes and vibrations due to impacts on hull body are the most

influencing parameters on motion sickness incidence (MSI). Actually the MSI seems to be the most adverse

discomfort phenomena on humans among the others, those are motion induced interruptions (MII), motion

induced fatigue (MIF), high impact injuries (HII) and the like. Obviously motion quality and its discomfort

influences on humans are desired to be controlled and optimised in initial design stage by naval architects

however reliable quantitative evaluations of discomfort levels are needed. In the case of high speed vessels,

their usual light weight and high speed demand require a delicate evaluation on human comfort. This paper

presents a state-of-art review of the current literature on comfort on board highlighting concrete design

guidelines for high speed vessels.

1. INTRODUCTION

Dynamic nature of seaway influences ship hull body

and thus crew and passengers who may encounter

with adverse effects due to excessive dynamic loads,

motions and accelerations. Ship motions increase the

energy loss of human body on board and produce an

increased level of fatigue and drowsiness in long

voyages (Arribas and Pineiro, 2007). As several

authors Rolnick and Lubow (1991) observed that

people like car drivers and pilots usually do not get

sick as they do control their motion themselves,

whereas passive passengers and crew do. The most

common adverse effect borne by accelerations of

ship motions is defined as motion sickness

(kinetosis) or seasickness incidence (MSI). The term

‘motion sickness’ is used to refer not only to

vomiting and nausea but also drowsiness, headaches,

sweating, stomach awareness, loss of appetite, and

various cardiovascular and endocrinal changes

(Money, 1991; Uijtdehaage et al., 1993). In fact the

symptoms of MSI in general are pallor, cold

sweating, nausea and vomiting due to motion (Bos

and Dallinga, 2006). Another discomfort

phenomenon is Motion Induced Interruption (MII)

that may occur when ship motions become

sufficiently large having low-frequency, large-

amplitude and long-term exposure individuals

experience slide or lose balance unless they

temporarily abandon their allotted task to pay

attention to keeping upright (McNamara and Baitisi

1980). The physical fatigue associated with ship

motions is described by the term Motion Induced

Fatigue (MIF) referring a bio-dynamic problem.

Whole Body Vibrations (WBV) is a result of short

or long-term exposures of human body with vessel

responses to the environment (Table 1). Thus,

operations on a moving platform often induce

fatigue and degrade mental effort leading to

decreased human performance. In the cases of the

imposition of higher frequency vibrations induces

corresponding motions and forces within the human

body, creating discomfort and possibly resulting in

degraded health (Griffin, 1990). Among all

discomfort phenomena over individuals motion

sickness is rated the worst (Turan et al., 2005).

IX HSMV Naples 25 - 27 May 2011: Keynote 1

Comfort on board is expressed as wellbeing quality

of individuals (passenger and/or crew) in floating

objects in operations. The current article focuses on

evaluation techniques of motion sickness of high

speed vessels providing with concrete information of

the problem that would be useful for design

applications.

Table 1. Phenomena describing comfort on board

Phenomenon Frequency

Motion Sickness

(MSI)

Low-frequency, short- and long-

term exposure (habituation)

Motion-Induced

Interruption (MII)

Low-frequency, large-amplitude,

short-term event

Motion-Induced

Fatigue (MIF)

Low-frequency, large-amplitude,

long-term exposure

Whole-Body

Vibration (WBV)

Medium/High-frequency, tolerable

exposure determined by severity of

motion

2. EVALUATION OF MOTION SICKNESS

INCIDENCE

The MSI is a vestibular related discomfort implying

both real and illusory motion exposure perceived by

our senses. Motion effects may drive an autonomic

response that can lead emesis if not blocked

(Dahlman, 2009). The MSI performance of a vessel

is desired to be within the limits given by standards

for human effectiveness (see Table 2). The MSI

prediction algorithms used today is based on the

work of O’Hanlon and McCauley (1974) and the

ISO Standard 2631-1. Figure 1 shows predicted MSI

rating obtained by the procedure of O’Hanlon and

McCauley. Ship Motion Simulator developed by Mc

Cauley et al. (1976) suggested that it is mainly the

vertical component of ship motion that causes sea

sickness.

Table 2: Seakeeping performance criteria for human

effectiveness in rms (NORDFORSK 1987).

Vertical Acc. Lateral Acc. Roll Motion Description

0.20 g 0.10 g 6.0° Light Manual Work

0.15 g

0.07 g 4.0° Heavy Manual

Work

0.10 g

0.05 g 3.0° Intellectual

Work

0.05 g

0.04 g 2.5° Transit

Passengers

0.02 g

0.03 g 2.0° Cruise Liner

80

60

40

20

0

0.06 0.10

0.16 0.25

0.40 0.63

0.50

0.20

0.10

0

0.30

0.40

0.60

ARMS (g)

f (s)

MSI (%)

Figure 1. Predicted MSI by Bos and Bles (1998).

Among the research efforts in the evaluation of the

MSI the most recent and robust model seems to be

the works of Bos et al. (see Bos and Bles, 1998; Bos

and Dallinga, 2006; Bos et al., 2007; Turan et al.,

2005 ). Referring the findings of the European

project COMPASS, Bos and Dallinga (2006)

reported that observation of Griffin (1990) at sea and

the ISO (ISO, 1997) gave a more generic description

of motion sickness in terms of a Motion Sickness

Dose Value (MSDV). Thus MSDV is expressed as

taMSDV w= , (1)

( )∑=i iiw awa , (2)

where t is the time of exposure, aw denotes

frequency weighted (wi) acceleration and ai the

specific

acceleration component at the frequency (band) i.

The proposal revealed also that next the local

vertical motion, the local sway motion contributes

was the second most important contributor to

seasickness. The quantification should carefully take

into account roll motion affect on lateral

acceleration. Following the analogy of the ISO

approach, better physical description was obtained

by using av instead of aw (or awz) only, with

222 )( wzwywxhv aaaka ++= , (3)

awx and awy as recorded in a ship fixed frame of

reference. The coefficient kh represents weight of the

horizontal acceleration vector-sum with the vertical

component. Finally they define an illness rating (IR)

as

IX HSMV Naples 25 - 27 May 2011: Keynote 2

MSDVKIR ⋅= ,

taKIR v⋅= , (4)

Where K is the proportionality constant highly

depended on age, gender and sickness history of

individuals (scaled from 0 to 3).

3. DISCUSSION OF MSI CONSIDERATIONS ON

DESIGN

Motion sickness incidence is functionally

characterized by ship motions and environmental

influences exposed by individuals. MSI is desired to

be an optimal between human and non human

subsets. The social aspect of MSI is important that a

fixed standard does not valid for all individuals since

that the habituation, susceptibility based upon

physiological characteristics and personality factors

would vary. Thus a reliable the quantification of

MSI requires taking into account all accelerations in

the 6 degree of freedom as well as social references

of age, gender and sickness history. Particularly for

the latter multidisciplinary research efforts have

been in progress considering the current literature.

The major priority in optimizing the MSI for a ship

design is human health and wellbeing. The optimal

MSI defines and efficient person-machine system

that would perform the continuity of safe riding, task

force and mission effectiveness.

The MSI quantification for high speed vessels

requires a careful analysis of ship motions using

appropriate tools. The importance of survey studies

has been sufficiently demonstrated in the literature

as well as the experimental ones that certainly define

acceptable convergence with the computed data

(Khalid et al., 2010).

An approximate model of the MSI evaluation can be

embedded in a concept design model that can define

a feasible concept design space. Actually some

robust numerical techniques such as artificial neural

networks and expert systems are able to set the

relations between ship motions/accelerations and

design variables. As current author has implemented

previously, the computed RAOs of motions and

accelerations of statistically sufficient number of

candidate vessels can be modelled (Alkan, Nabergoj

and Trincas, 2005). The RAOs model is expressed in

function of a set of design variables composed of

main dimensions and other significant parameters

for a constant speed of advance and wave parameter.

The model can be extended to compute statistical

response spectrums by inserting seaway statistical

data of given seaway that would be input for MSI

evaluations.

Human element in the design should be considered

earlier. Locating critical stations near the effective

center of rotation of a ship is advantageous. The

design should consider head movements of

individuals. Minimized head movements are desired

to overcome motion induced sickness and fatigue.

The operator should be aligned with a principal axis

of the hull. The design should not accommodate

combining provocative sources of motion sickness.

The reflect of human element on ship design

requires a multidisciplinary team effort.

High speed small crafts produce instantaneous and

higher accelerations with respect to large ones.

Researchers demonstrated that specially designed

seats for the use of operators and individuals

remarkably lowered motion induced effects

(Dobbins et al. 2008).

4. CONCLUSIONS

Evaluation of comfort on board for high speed

marine vehicles has a difficult nature surrounded by

human element, ship motions, ocean environment

and ship itself. The motion sickness constitutes the

most dominant influence on the comfort on board

quality of marine vehicles. The design impact of

motion sickness must properly take role in the

concept design level. The naval architects should

endeavour incorporating ‘human factor engineering

principles’ in ship design.

5. REFERENCES

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