J Mar Sci Technol DOI 10.1007/s00773-016-0373-2
ORIGINAL ARTICLE
The overall motion induced interruptions as operability criterion for fishing vessels S. Gaglione1 • V. Piscopo1 • A. Scamardella1
Received: 6 October 2014 / Accepted: 11 February 2016 Ó JASNAOE 2016
Abstract A new index, namely the overall motion induced interruptions (OMII), is proposed as a seakeeping criterion for fishing vessels, to compare ships having different hull forms and dimensions by means of an only parameter, in a human centred approach, mainly related to the onboard risk level. Therefore, the first aim of the paper is to investigate the factors affecting fishing vessels’ seakeeping performances to improve them to reduce the high number of injuries occurring during fishing operations, mainly related to both risk perception and harsh weather conditions. Despite the classical approach, where motion induced interruption is determined for a certain sea state with regard to several location points, the new index accounts for all crew members’ positions on the working deck, all heading angles the vessel may experience during fishing operations, based on relevant operating scenario, and all sea states the ship may encounter in the fishing area. The influence of position, heading angles and sea states on the attained risk level is fully investigated, analysing seakeeping performances of four fishing vessels with different hull forms and dimensions. Finally, a new operability criterion is proposed, based on OMII, to investigate the influence of ship size and operating scenario on the risk of injuries during fishing operations. Main factors affecting fishing vessels’ seakeeping performances are fully & V. Piscopo
[email protected] S. Gaglione
[email protected] A. Scamardella
[email protected] 1
Department of Sciences and Technology, The University of Naples ‘‘Parthenope’’, Naples, Italy
discussed, paying attention to relevant correlation with ship roll natural period. Keywords Overall motion induced interruptions Fishing vessels Operability criterion
1 Introduction Over the last decades many attempts have been undertaken to increase merchant ships’ seakeeping qualities, paying attention not only to relevant behaviour in a seaway, but also to derived responses related to on board comfort and risk level. Ship mission effectiveness, in fact, is determined by readiness and availability of its equipment, but it is also influenced by crew members’ operability. In this respect, as each individual is responsible of a certain workload portion, ship operability could be degraded by even a small number of crew members’ reduced performances. Ship motions may cause a great variety of physiological symptoms and biomechanical events that may degrade ship mission effectiveness, reducing crew members’ ability of performing essential commands, communication functions, navigation tasks, maintenance responsibilities and even food preparation (Stevens and Parsons [1]). Therefore, the influence of crew members’ operability on seakeeping qualities mainly depends on ship typology, becoming essential in all cases when relevant mission consists of working operations entirely performed at sea, as for fishing and offshore service vessels. Over the last years specific attempts to better understand fishing vessel seakeeping performances have been carried out by several researchers (Fonseca and Guedes Soares [2]; Maimun et al. [3]; Tello et al. [4]), even if there is still concern with relevant behaviour at sea, due to the high
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number of accidents occurred during fishing operations and mainly associated with large amplitude motions and accelerations in harsh sea conditions (Tello et al. [5]). Many researchers investigated the causes of occupational accidents on board fishing vessels of Italian (Boccadamo and Scamardella [6]), Norwegian (Bye and Lamvik [7]) and Portuguese (Anta˜o and Guedes Soares [8]) fleet among others, founding that both safety culture and risk perception, as well as weather conditions, significantly increase the rate of work accidents at sea. These considerations explain all efforts devoted to improve fishing vessels’ seakeeping qualities and decrease the risk of injuries, also by means of an on board decision support system, as stressed by Tello et al. [5], that could advise the skipper when motions become unacceptable, providing some guidance about how changing ship operational conditions. In any moving scenario, in fact, the potential for losing balance, sliding or in such cases lifting-off is always present and dramatically increases in harsh weather conditions. From this point of view, the motion induced interruption (MII) theory developed by Graham [9] allows to estimate the number of sliding and tipping occurrences, leading crew members to temporarily abandon the allotted task, to keep themselves upright. Sliding and tipping events are mainly due to high lateral/vertical accelerations that, in turn, depend on: sea state, heading angle between vessel route and prevailing sea direction, position on the working area. All these factors affect a reliable estimation of the on board safety level, as MIIs are generally evaluated at few points on ship main deck, for an assigned sea state. In this respect, in fact, crew members generally move on working area during fishing operations, so that they do not occupy the same position. Furthermore, the influence of heading angles on MII occurrences is generally disregarded, even if operating scenario has to be taken into consideration, due to possible couplings between wave and ship natural periods, mainly depending on the encounter frequency, that in turn depends on wave frequency, vessel speed and route. In this respect, the first aim of the present work is to define a new index, namely the overall motion induced interruptions (OMII), mainly based on MII theory, that allows comparing vessels having different hull forms and dimensions by means of an only parameter, and more reliably estimate and eventually mitigate the on board risk level. Despite of classical MII approach, it allows to account for: (1) all positions crew members may occupy on the working deck; (2) all heading angles experienced during fishing operations, based on the assumed operating scenario; (3) all sea states the vessel may encounter in the fishing area during its lifetime. Four fishing vessels, having dimensions ranging from 19.5 to 63.5 m, are assumed, as a test example, to investigate the influence of crew members
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position on MII occurrences. Subsequently, the influence of both heading angles and wave zero-crossing period is explored, due to possible couplings between wave and ship natural periods. After this preliminary analysis, OMII is determined for the analysed fishing vessels, considering two different operating scenarios in Mediterranean Sea Region. Some considerations about the dependence of OMII on ship roll period are carried out too, to account for possible variations of both displacement and loading conditions. The second aim of the present work is to define a new operability criterion for fishing vessels, based on OMII, to decrease the on board risk of injuries. In this respect, a human centred approach is followed assuming that the best fishing vessel is the safest one, i.e. the one obtaining the highest operability index (OI) for all possible fishing operational conditions. Finally, the influence of both operating scenario and ship roll natural period on OI is further investigated, showing that they are key elements to be accounted to mitigate the risk of injuries on board fishing vessels.
2 Fishing vessels’ operability assessment 2.1 Seakeeping performance criteria Ship mission effectiveness has to be assessed evaluating the effects of motion amplitudes and accelerations on all involved subsystems, such as hull, machinery and crew members, among others (Tello et al. [5]). According to ITTC seakeeping committee final recommendations (ITTC [10]), both motion responses and derived criteria have to be checked. The former mainly involve the root mean square (RMS) of vertical/lateral displacements and accelerations; the latter, instead, include propeller emergence, slamming, bow emergence and wetness index, among others. The correct choice of right seakeeping criteria, together with relevant limit values, strongly influences the ship operability assessment. In this regard, not many data are available in literature for fishing vessels, apart from those ones proposed by Odabasi et al. [11], Fonseca and Soares [2], Sario¨z and Narli [12]. Anyway, the most comprehensive study on fishing vessels’ seakeeping performances is probably due to Tello et al. [4, 5]. They found that exceeded criteria are mainly associated with pitch and roll motions, identifying their dependence on vessel hull forms, which in case of roll motion have enhanced performances for U than V-shaped cross sections, despite of pitch motion, for which the opposite holds true. Furthermore, both transverse metacentric height GMT and vessel displacement variations play an important role, as for fishing vessels having a considerable breadth, GMT may be
J Mar Sci Technol
increased so as ship roll period could match the fundamental wave one, placing the vessel in a dangerous operational condition. Past efforts in the assessment of fishing vessels’ operability have been always devoted to check motion and derived responses against prescribed limit values, at some chosen location points on bridge and working deck. Nevertheless, the risk level in fisheries is still high, as Anta˜o and Guedes Soares [13] concluded, after a study on maritime accidents occurred in Portugal over a period of 20 years, founding that it is necessary to improve both operation and safety, especially for small fishing vessels, representing 89 % of accidents in the studied sample. Boccadamo and Scamardella [6], after carrying out a survey on the Italian fishing fleet, found that work accidents occurred mostly at sea or in the fishing area (around 80 %) and that weather conditions played an important role in increasing relevant rate (around 60 %). Bye and Lamvik [7], as well as Anta˜o and Guedes Soares [8], studied the causes of occupational accidents on board Norwegian and Portuguese fishing vessels, respectively, founding that one of accidents’ main causes has to be ascribed to safety culture and risk perception, too. To reduce accidents at sea, it is therefore necessary to mitigate the risk level on board fishing vessels, providing some guidance about how changing ship operational conditions to make motions acceptable (Tello et al. [5]). In this respect, starting from the MII, a new global index for sliding and tipping occurrences is proposed, accounting for all locations crew members may occupy on working deck during fishing operations, as well as for all sea states the vessel may encounter during its lifetime, each one with a certain probability of occurrence, depending on fishing area wave scatter diagram. The influence of heading angles on accidents’ occurrence needs to be further investigated too, not only to find the relevant range to avoid during fishing operations, but also to mitigate the risk of injuries and accidents at sea. In the following, the OMII will be defined for sliding, longitudinal (f/a) and lateral (s/s) tipping occurrences and subsequently applied to seakeeping analysis of four fishing vessels, to investigate the influence of hull forms, sea states and operating scenarios on the attained risk level. 2.2 Theoretical background Seakeeping criteria relating ship operability to human factors are generally subdivided into whole-body vibration (WBV) and whole-body motion (WBM) problems, at frequencies above and below 1 Hz, respectively (Collwell [14]). WBV problems are mainly related to manual control and vision at frequencies above 1 Hz, even if significant biodynamic effects have been encountered at lower
frequencies, as reported by Wiker et al. [15]. WBM problems, instead, involve both Motion Induced Interruptions (MII), due to sliding or lose of balance, and long-term Motion Induced Fatigue (MIF), mainly related to sleep disturbances due to heavy roll. A Motion Induced Interruption (MII) occurs when local motions cause a person to lose balance or slide, thereby interrupting whatever task is performed in all non-seated situations, such as standing, walking or lifting (Crossland and Rich [16]). The MII concept was introduced for the first time by Applebee et al. [17], to evaluate the performances of crew members working on flight decks and investigate relevant loss of postural control. Anyway the most comprehensive study on the argument has been certainly carried out by Graham [9] and Graham et al. [18, 19], who extended the procedure to frequency domain and introduced the lateral force estimator (LFE), more suitable for practical seakeeping purposes, to predict sliding and losing of balance events (tipping). In this respect sliding, f/a and s/s tipping estimators connect heave, pitch and roll accelerations to friction and tipping coefficients; the MII per unit time is subsequently determined, in the frequency domain, as the number of upcrossings of relevant threshold values. Sliding and tipping estimators are quite similar and mainly depend on gravity g and horizontal/vertical accelerations in the ship reference system. In this respect, a sliding event occurs along port or starboard directions when forces due to ship motions overcome the frictional ones between individual’s shoes and deck. A tipping event, instead, occurs when moments of forces parallel to ship deck about individual’s foot, in the longitudinal or transverse plane for f/a and s/s tipping occurrences, respectively, are greater than those due to normal forces that, in turn, consist of vertical acceleration components, including gravity. Relevant threshold values, instead, depend on friction ls and tipping d/h and b/h coefficients, where h is the human body centre of gravity height above deck, while d and b are the half-foot length and half distance width, respectively. Denoting by g1, g2 and g3 (g4, g5 and g6) the motions (rotations) along (around) the ship longitudinal, transversal and vertical axes, respectively, and assuming that longitudinal accelerations are small if compared to lateral ones, MII estimator functions and relevant threshold values are listed in Table 1 for port and starboard conditions. It is noticed that the subscript P denotes any point having coordinates (xP, yP, zP) respect to a reference system having origin at the ship centre of mass, with x axis forward positive and rotated by l (heading angle) as regards the prevailing sea direction, y and z axes portside and upward positive, respectively. Hence, MII estimator functions can be determined as regards a local reference system, with axes parallel to the ship ones and origin located at the human body centre of gravity P, fixed upon the ship.
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J Mar Sci Technol Table 1 Motion induced interruptions estimator functions and threshold values Sliding
f/a tipping
s/s tipping
Sliding estimator
Threshold value
f/a tipping estimator
Threshold value
s/s tipping estimator
Sp ¼ g€2P gg4 ls g€3P
ls g
Tf ¼ 13 h€ g5 dh g€3P
d hg
Tp ¼ 13 h€ g4 g€2P gg4 bh g€3P
Ss ¼ þg€2P þ gg4 ls g€3P
Ta ¼
þ 13 h€ g5
d € h g3P
The friction coefficient ls depends on deck conditions and is generally assumed equal to 0.70, according to Baitis et al. [20] for dry decks. On the contrary tipping coefficients, mainly associated with location on main deck and performed task, differ from one axis to another, as it was verified by a series of experiments conducted by the Defence Evaluation and Research Agency in a Large Motion Simulator on several Royal Navy sailors (Crossland and Rich [21]). In the following longitudinal d/h and lateral b/h tipping coefficients are assumed equal to 0.17 and 0.25, according to Baitis et al. [22]. A Motion Induced Interruption event occurs when any estimator function is higher than relevant threshold value. In this respect, MII occurrences per unit time depend on (1) sea state, by relevant wave spectrum, (2) heading angles and (3) position on main deck, by means of the previously defined sliding/tipping estimator functions. Relevant spectral moments can be easily determined as follows (Nocerino [23]): Z1 mn;ðH1=3 ;Tz Þ ;lk ;ðx;y;zdeck Þ ¼ xne jGðxe ; l; x; y; zÞj2 Sz ðxe Þdxe j
0
ð1Þ having denoted by xe and Sz(xe) the wave encounter frequency and spectral density, respectively, and by G(xe, l, x, y, z) the sliding/tipping transfer function. The number of upcrossings per unit time of a certain threshold value t allows estimating the number of MII for both sliding and tipping events for a given sea state, heading angle and position on ship main deck, assuming that they follow the Rayleigh distribution (Nocerino [23]): MIIðH1=3 ;Tz Þ ;lk ;ðx;y;zdeck Þ j vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi um 1 u 2;ðH1=3 ;Tz Þj ;lk ;ðx;y;zdeck Þ t exp t2 2m0;ðH1=3 ;Tz Þ ;lk ;ðx;y;zdeck Þ ¼ j 2p m0;ðH1=3 ;Tz Þ ;lk ;ðx;y;zdeck Þ
Ts ¼
13 h€ g4
Table 2 Risk level and MII occurrences per hour
þ g€2P þ gg4
Threshold value b hg
b€ h g3P
Risk level
MII
1. Possible
6
2. Probable
30
3. Serious
90
4. Severe
180
5. Extreme
300
apply different techniques to maintain equilibrium (Dobie [24]), but there is also a certain long-term adaptation that allows to explain some differences between civilian and crew members in MII occurrences, as also stated by McCauley and Pierce [25]. Anyway, the predicted incidence of loss of balance events is in any case useful and widely applied for practical purposes, to evaluate crew performances and compare different hull forms, in terms of attained risk level and personnel safety. Before the development of MII theory, criteria for personnel operations were simply defined in terms of roll, pitch and vertical acceleration limit values. On the contrary, the MII model contemporarily accounts for roll and pitch amplitudes, as well as vertical and lateral accelerations, connecting the number of MII events to the attained risk level, as shown in Table 2 (Graham [9]). Anyway, as stated by Crossland and Rich [21], it is necessary to point out that the connection between risk level and MII occurrences strongly depends on the performed task; in this sense, as example, the permissible number of MII occurrences is certainly higher for watch standing than weapon reloading tasks (Steven and Parsons [1]). From this point of view, no many suggestions are available in literature, apart from the one suggested in The North Atlantic Treaty Organization Standard Agreement 4154 (STANAG 4154 [26]), where a limit value of one MII per minute is reported.
j
ð2Þ It is noticed that the LFE approach significantly simplifies the problem of postural stability control, as it assumes human body is rigid and unable to counteract external forces, which implies the number of MII occurrences is generally overestimated. In fact, not only people
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2.3 The overall motion induced interruptions Motion Induced Interruptions are influenced by several parameters, i.e. vessel speed, heading angle, sea state and position on the working area (Scamardella and Piscopo [27]). Therefore, if a more reliable evaluation of MII occurrences is required, a new index accounting for all
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having denoted by Adeck the deck area devoted to crew members’ working operations, whose location and extension mainly depend on ship type and mission. If Nc location points, each one having coordinates (x, y, zdeck)i, map the deck area, Eq. 3 becomes: OMIIðH1=3 ;Tz Þj ;lk ¼
Nc 1 X MIIðH1=3 ;Tz Þj ;lk ;ðx;y;zdeck Þi Nc i¼1
ð4Þ
Table 3 Scatter diagram for Mediterranean Sea Region H1/3 (m)
TZ (s)
0–1
60
140
102
35
7
1
0
345
1–2
15
96
138
77
24
5
1
356
2–3
3
32
66
50
20
6
1
178
3–4
1
9
24
23
11
4
1
73
4–5
0
3
8
9
5
2
1
28
5–6
0
1
3
4
2
1
0
11
6–7
0
0
1
2
1
1
0
5
7–8
0
0
1
1
1
0
0
3
6–7
7–8
8–9
9–10
45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
5–6
N
OMII ¼
Ns Nc l X X 1 X pj pl MIIðH1=3 ;Tz Þ ;lk ;ðx;y;zdeck Þ i j Nc j¼1 k¼1 i¼1
ð5Þ
The index can be determined for sliding, f/a and s/ s tipping events, evaluating relevant MII on the basis of estimator functions and threshold values listed in Table 1. The sea state probability density function depends on fishing area wave scatter diagram: in the following the Mediterranean Sea Region will be assumed as reference (see Table 3). It is noticed that, by the dispersion relation and the wave maximum steepness for deep water conditions (Lewis [30]), wave breaking occurs only in two cases, namely H1/3 = 3–4 m and Tz = 3–4 s and H1/3 = 5–6 m and Tz = 4–5 s, each one with 0.1 % probability of occurrence. Hence, the incidence of cases for which Strip Theory is not applicable is totally negligible and the OMII index is not influenced by the occurrence of wave breaking condition. As concerns the heading angle probability density function, two different operating scenarios will be considered: (a) all heading angles have the same probability of occurrence (see Fig. 1a); (b) transverse headings are avoided (see Fig. 1b). Anyway in both cases heading angles in the range 0°–45° are disregarded, due to possible ship manoeuvring problems experienced during fishing
% pµ
4–5
% pµ
3–4
Previous expression allows to estimate the mean value of MII per unit time on ship main deck for any heading angle lk, having probability of occurrence pl, and any sea state, having probability of occurrence pj and characterized by a certain combination of significant wave height H1/3 and zero-crossing period Tz. Denoting by Ns and Nl the number of sea states and heading angles, having pj and pl probability of occurrence, respectively, OMII can be finally rewritten as follows:
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180
these variables can be defined, following an approach similar to the one proposed by Scamardella and Piscopo [28, 29] for the motion sickness influence (MSI). Let us define, for the k-th heading angle lk and the j-th sea state, characterized by a certain combination of significant wave height H1/3 and zero-crossing period Tz, the OMII as the mean MII, estimated on the entire working area, according to the following equation: R Adeck MIIðH1=3 ;Tz Þj ;lk ;ðx;y;zdeck Þ dA OMIIðH1=3 ;Tz Þ ;lk ¼ ð3Þ j Adeck
µ [deg]
(a)
µ [deg]
(b)
Fig. 1 Probability density function vs. heading angle a 1st scenario, b 2nd scenario
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J Mar Sci Technol Fig. 2 Fishing vessels’ hull forms
DWL DWL
FV1
FV2
DWL DWL
FV3
FV4
Table 4 Fishing vessels’ main dimensions D (m)
T (m)
CB
CWP
6.00
3.20
2.72
0.52
0.85
8.00
4.20
3.60
0.52
0.81
D (t)
FV
L (m)
B (m)
FV1
19.45
FV2
32.97
FV3
49.71
9.25
4.50
3.83
0.50
0.74
902.2
0.40
0.25
0.79
FV4
63.51
12.50
6.00
5.10
0.55
0.77
2278.0
0.40
0.25
0.98
Kxx/B
Kyy/L
GMT (m)
GML (m)
163.6
0.40
0.25
0.74
14.33
502.2
0.40
0.25
0.76
26.33
operations. Furthermore, it is noticed that ships could experience both involuntary and voluntary speed reductions, the former mainly due to added drag and reduced propulsive efficiency in a seaway, the latter instead caused by increased slamming and deck wetness events, as well as unacceptable accelerations on working areas. Involuntary speed reductions are generally small except for large, full and low-powered ships (Lewis [30]) but, for increasing sea states, motion amplitudes can become so severe that the captain fears for the ability of his crew to carry out their functions and for possible damages to ship structures, systems and payload. In this respect, the only recourse that the captain has is either to reduce the vessel speed and/or to change the heading with respect to waves. Anyway, the process by which a ship captain makes his decision to voluntarily reduce the ship speed or change the ship-wave heading direction is necessarily subjective (Lewis [30]). Hence, in actual analysis it is assumed that the service speed is independent from both sea states and heading angles, so that ship operability depends only on relevant seakeeping qualities and vessels, having different hull
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Troll (s)
Tpitch (s)
Theave (s)
V (kn)
5.6
2.6
3.7
8
7.3
3.2
4.3
10
49.28
8.3
3.6
4.6
12
60.32
10.1
4.1
5.4
14
forms and dimensions, can be each other compared, by means of the OMII index, independently from the onboard decision making system.
3 Seakeeping analysis 3.1 Main data Four fishing vessels, having different hull forms and dimensions, with an overall length ranging from 19.5 to 63.5 m, are analysed. Seakeeping analysis has been carried out by means of a commercial code, suitable for both monohulls and catamarans, based on linear strip theory (Salvesen et al. [31]). It is noticed that the non-dimensional roll damping factor due to viscous effects, defined as the ratio of actual to critical damping, is set equal to 0.075, as far as common values lie in the range between 0.050 and 0.100 for typical hull forms, without roll suppression devices (Lewis [30]). Fig. 2 shows relevant hull forms, while Table 4 reports main dimensions and some data useful for
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1
OMII/OMIImax
OMII/OMIImax
1 0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
x[m]
-2 0
x[m]
2 4 6 8 10
-2.5
-1-0.5 -2 -1.5
0 0.5
1 1.5
2 2.5
0 2 4 6 8
y[m]
10
(a)
-1-0.5 -2 -1.5
1 1.5
2 2.5
y[m]
(c)
1
1
OMII/OMIImax
OMII/OMIImax
-2.5
0 0.5
0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
-2 0
x[m]
2 4 6 8 10
-2.5
0 0.5 -1 -0.5 -2 -1.5
1 1.5
2 2.5
x[m]
0 2 4 6 8
y[m]
10
(b)
-2.5
-1-0.5 -2 -1.5
0 0.5
1 1.5
2 2.5
y[m]
(d)
Fig. 3 MII distribution for various heading angles—Hs = 2.5 m— Tz = 3.5 s—sliding occurrences per hour on board FV1. a heading b heading angle = 90°; angle = 45°; MIImax = 10.471,
MIImax = 0.644, c heading angle = 135°; MIImax = 0.145, d heading angle = 180°; MIImax = 0.202
seakeeping analysis. Denoting by kxx (kyy)the roll (pitch) gyradius as fraction of ship breadth (length), relevant natural periods can be determined according to the following formulas, where GMT (GML) is the transverse (longitudinal) metacentric height, CB (CWP) is the block (water plane) coefficient and T is the ship immersion (Lewis [30]):
together with a service vessel speed corresponding to Fn = 0.30. Besides, the working area is the main deck afterward half, as superstructures are generally located in the forward half one, according to common fishing vessels’ general arrangement.
2p kxx 2p kyy Troll ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffi ; Tpitch ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffi ; gGMT gGML sffiffiffiffiffiffiffiffiffiffiffi 2TCB Theave ¼ 2p gCWP
ð6Þ
In all cases the full loading condition, with a centre of mass height above keel KG = 0.80D, is assumed as reference,
3.2 Influence of location and heading angles The influence of crew members’ position on sliding and tipping occurrences is preliminarily investigated, as combined vertical/lateral accelerations significantly vary along the ship length and breadth. Figures 3, 4 and 5 plot sliding, f/a and s/s tipping occurrences on board fishing vessel FV1, at four heading angles, namely 45°, 90°, 135°
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1
OMII/OMIImax
OMII/OMIImax
1 0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
-2 0
x[m]
x[m]
2 4
1 1.5
6 8 10
0 2
2 2.5
4
10
1 1.5 0 0.5 -1 -0.5 -2 -1.5 y[m] -2.5
8
(a)
2 2.5
(c)
1
OMII/OMIImax
1
OMII/OMIImax
10
1 1.5 0 0.5 -0.5 -1 y[m] -2 -1.5 -2.5
6
0 0.5 -1 -0.5 -2 -1.5 y[m] -2.5
0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
-2 0
x[m]
0
x[m]
2 4
1 1.5
6 8 10
2 2.5
0 0.5 -1 -0.5 -2 -1.5 y[m] -2.5
(b)
2 4 6 8
2 2.5
(d)
Fig. 4 MII distribution for various heading angles—Hs = 2.5 m— Tz = 3.5 s—f/a tipping occurrences per hour on board FV1. a heading b heading angle = 90°; angle = 45°; MIImax = 43.413,
MIImax = 10.408, c heading angle = 135°; MIImax = 0.145, d heading angle = 180°; MIImax = 0.202
and 180°, with a wave zero-crossing period Tz = 3.5 s and a significant wave height H1/3 = 2.5 m. These plots are reported as a reference, because similar results have been obtained independently of wave zero-crossing period and ship dimensions. In all cases, in fact, while at quartering seas the MII distribution is quite homogeneous, at beam and head seas it significantly varies, with a maximum in correspondence of the farthest from ship symmetry plane and centre of mass location point. This variability explains the need of a new index, such as the OMII, that allows accounting for all crew members’ positions on main deck and all sea states the ship may encounter during its lifetime, based on relevant fishing area wave scatter diagram.
The influence of operating scenario on OMII is investigated too, as shown in Figs. 6, 7 and 8, where sliding, f/a and s/s tipping occurrences on board all the analysed fishing vessels are plotted for different zero-crossing periods and a significant wave height of 2.5 m. In all cases OMII2:5;Tz ;lk decreases for increasing zero-crossing periods, showing a maximum between beam and quartering seas, quickly decaying beyond this range. Coloured areas refer to possible, probable and serious risk level, as listed in Table 2. In all cases sliding occurrences are lower than f/a and s/s tipping ones that, in turn, are each other comparable, in terms of maximum values and distribution. It is also interesting to underline that the shape of OMII2:5;Tz ;lk curves is almost the same for all the examined vessels, so
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1
OMII/OMIImax
OMII/OMIImax
1 0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
-2 0
x[m]
0
x[m]
2 4 6 8 10
0 0.5 -1 -0.5 -2 -1.5 -2.5
1 1.5
2
2 2.5
4 6
10
0 0.5 -1 -0.5 -2 -1.5 -2.5
8
y[m]
(a)
1 1.5
2 2.5
y[m]
(c)
1
1
OMII/OMIImax
OMII/OMIImax
10
0 0.5 -1 -0.5 -2 -1.5 -2.5
0.8 0.6 0.4 0.2
0.8 0.6 0.4 0.2
0
0
-10
-10 -8
-8 -6
-6 -4
-4 -2
-2 0
x[m]
x[m]
2 4 6 8 10
0 0.5 -1 -0.5 -1.5 -2 -2.5
1 1.5
0 2
2 2.5
4 6 8
y[m]
1 1.5
2 2.5
y[m]
(b)
(d)
Fig. 5 MII distribution for various heading angles—Hs = 2.5 m— Tz = 3.5 s—s/s tipping occurrences per hour on board FV1. a Heading angle = 45°; MIImax = 39.124, b heading angle = 90°;
MIImax = 4.448, c heading angle = 135°; MIImax = 0.238, d heading angle = 180°; MIImax = 0.202
as the influence of operating scenario is almost the same, independently of ship dimensions, at least in the analysed range.
tipping occurrences for each sea state, according to the following formula:
3.3 Influence of wave zero-crossing period Sliding, f/a and s/s tipping occurrences obviously increase with significant wave height, but it is not so simple to understand the influence of wave zero-crossing period, due to possible couplings with roll, pitch and heave ship natural frequencies. In this respect, relevant influence is investigated determining the total number of sliding, f/a and s/s
N
OMIITOT;ðH1=3 ;Tz Þj ¼
Nc l X 1 X pl Nc k¼1 i¼1
OMIIsliding þ OMIIf =a þ OMIIs=s ðH
Þ
1=3 ;Tz j ;lk ;ðx;y;zdeck Þi
ð7Þ Figures 9 and 10 plot the OMIITOT;ðH1=3 ;Tz Þ distribution vs. wave zero-crossing period for both operating scenarios and several significant wave heights in the range 0–5 m. In all cases OMIITOT;ðH1=3 ;Tz Þ decreases for increasing wave
123
45 42 39 36 33 30 27 24 21 18 15 12 9 6 3 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, mk
OMII2.5, Tz, µk
J Mar Sci Technol 45 42 39 36 33 30 27 24 21 18 15 12 9 6 3 0
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
(a) 45 42 39 36 33 30 27 24 21 18 15 12 9 6 3 0
(b)
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, mk
OMII2.5, Tz, µk
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
45 42 39 36 33 30 27 24 21 18 15 12 9 6 3 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
(c)
(d)
Fig. 6 OMII2:5;Tz ;lk distribution versus heading angles—sliding occurrences per hour. a Fishing vessel FV1, b fishing vessel FV2, c fishing vessel FV3, d fishing vessel FV4
zero-crossing periods, showing a maximum at Tz = 3.5 s, corresponding to a modal period of ITTC Bretschneider Spectrum of 4.9 s, so very close to ship natural frequencies (see Table 4). The influence of ship dimensions is very clear too, as sliding and tipping occurrences decrease for increasing vessel dimensions, even if relevant curves have almost the same shape. Furthermore, the influence of heading angles is remarkable too, as OMIITOT;ðH1=3 ;Tz Þ decreases by about 70 % from the first to the second operating scenario. Also in this case coloured areas refer to possible, probable and serious risk level, respectively. 3.4 OMII estimation and dependence on roll period Table 5 reports OMII values for sliding, f/a and s/s tipping occurrences on board the analysed fishing vessels: obtained results show a clear dependence on ship dimensions, heading angles and operating scenario.
123
Two main results are achieved: (1) OMII decreases by 70 % from the first to the second operating scenario; (2) OMII not only decreases for increasing vessel dimensions, as it could be predictable, but it also shows a clear dependence on ship roll period, according to the following formula: pffiffiffiffiffiffiffiffi OMII ¼ m Troll þ q ð8Þ where slope m, constant term q and correlation coefficients q2 are listed in Table 6. In this respect, it has to be pointed out that f/a tipping estimator (see Table 1) depends on heave and pitch accelerations, only. Anyway, for increasing pitch and heave natural periods, roll period increases in turn, what implies that OMII index can be expressed as function of Troll, even if roll natural period is not directly involved in its evaluation. By Eq. 8 OMII depends, by means of ship roll period, on transverse metacentric height GMT. In this respect, already in a preliminary project phase, loading condition
150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, µk
OMII2.5, Tz, µk
J Mar Sci Technol 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
(b)
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, mk
OMII2.5, Tz, µk
(a) 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
(c)
(d)
Fig. 7 OMII2:5;Tz ;lk distribution versus heading angles—f/a tipping occurrences per hour. a Fishing vessel FV1, b fishing vessel FV2, c fishing vessel FV3, d fishing vessel FV4
has to be optimized, avoiding excessively high GMT values compatibly with stability requirements, to decrease, in turn, the OMII and consequently the on board risk level.
4 A new operability index for fishing vessels The high number of injuries on board fishing vessels and the need of increasing the safety level suggest defining a new OI, accounting for sliding and tipping occurrences. The new OI depends on: (1) fishing vessel operating scenario, by relevant heading angle probability density function (see Fig. 1a, b); (2) fishing area, by means of wave scatter diagram (see Table 3); (3) a weight factor, allowing to account for fishing vessel operability, in terms of mean number of sliding, f/a and s/s tipping occurrences, for any sea state and heading angle. In this respect, the best fishing vessel will be the safest one, i.e. the one obtaining the highest score in the range 0–1, according to the following formula:
OI ¼
Ns X j¼1
pj
Nl X
pl OIl;j
ð9Þ
k¼1
where pj (pl) is the probability of occurrence of each sea state (heading angle). In Eq. 9 OIl,j is a weight factor, whose dependence on OMII, for any sea state and heading angle, is obviously questionable. The limit suggested in STANAG 2154 [26] of 1 occurrence per minute or, what is the same, 60 events per hour is a reasonable value beyond which crew members’ operability is dramatically compromised, so as OIl,j is almost zero. Besides, in the range 0–60 events per hour a certain decrease of crew members’ operability is predictable, too. In this respect, assuming that crew operability is degraded by about 50 % when the risk level becomes possible (6 occurrences per hour) and it is almost zero, when the STANAG limit of 60 events per hour is exceeded, the following best-fit weight factor distribution is suggested that, in turn, depends on the mean number
123
150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, µk
OMII2.5, Tz, mk
J Mar Sci Technol 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
(a) 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
(b)
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
OMII2.5, Tz, mk
OMII2.5, Tz, µk
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Tz=3-4 s Tz=4-5 s Tz=5-6 s Tz=6-7 s Tz=7-8 s Tz=8-9 s Tz=9-10 s
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
180 175 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45
Heading angle [deg]
Heading angle [deg]
(c)
(d)
Fig. 8 OMII2:5;Tz ;lk distribution versus heading angles—s/s tipping occurrences per hour. a Fishing vessel FV1, b fishing vessel FV2, c fishing vessel FV3, d fishing vessel FV4
of sliding, f/a and s/s tipping occurrences OMIITOT according to Eq. 7, for any sea state and heading angle: OIl;j ¼ e
OMIITOT;ðH 1=3 ;Tz Þj ;lk 10
ð10Þ
Table 7 reports the OI for all the analysed fishing vessels and both operating scenarios. The influence of heading angles is appreciable, as it is possible to increase the OI by a value ranging from 12.7 to 26.9 %, depending on vessel dimensions, in the analysed ship size range. Furthermore, it is predictable that the above-mentioned increase may grow up to 40 % for small fishing vessels, having roll period equal or less than 5 s. Furthermore, by the obtained results, the new OI shows a clear dependence on ship roll period, according to the following equation: pffiffiffiffiffiffiffiffi OI ¼ aTroll þ b Troll þ c ð11Þ
123
where a, b, c constants and correlation coefficient q2 are listed in Table 8, for the first and the second operating scenario. Furthermore, Fig. 11 shows that two ways can be followed to decrease the on board risk level. First of all ship loading condition can be optimized in a preliminary project phase, avoiding high GMT values, compatibly with stability requirements, to increase the ship roll period and consequently the OI. Furthermore, guidance has to be provided to crew members to avoid, as far as possible, transverse beam seas, shifting the OI from the first (lower curve) to the second (upper curve) operating scenario.
5 Conclusions The OMII has been proposed to evaluate fishing vessels’ seakeeping performances, considering the on board safety level as a key element, due to the high number of injuries
90
90
80
80
70
70
60
OMIITOT,H1/3,Tz
OMIITOT,H1/3,Tz
J Mar Sci Technol
H1/3=0-1 m
50
H1/3=1-2 m
40
H1/3=2-3 m H1/3=3-4 m
30
H1/3=4-5 m
60
H1/3=3-4 m
20 10 5.5
6.5
7.5
8.5
0 3.5
9.5
H1/3=2-3 m
30
10 4.5
H1/3=1-2 m
40
20
0 3.5
H1/3=0-1 m
50
H1/3=4-5 m
4.5
5.5
Tz [s]
90
90
80
80
70
70
60 H1/3=0-1 m
50
H1/3=1-2 m
40
H1/3=2-3 m H1/3=3-4 m
30
H1/3=4-5 m
8.5
H1/3=3-4 m
0 3.5
9.5
Tz [s]
H1/3=2-3 m
30
10 7.5
H1/3=1-2 m
40
10 6.5
9.5
H1/3=0-1 m
50
20
5.5
8.5
60
20
4.5
7.5
(b)
OMIITOT,H1/3,Tz
OMIITOT,H1/3,Tz
(a)
0 3.5
6.5
Tz [s]
H1/3=4-5 m
4.5
5.5
6.5
7.5
8.5
9.5
Tz [s]
(c)
(d)
Fig. 9 OMIITOT;H1=3 ;Tz per hour distribution vs. wave zero-crossing period—1st scenario. a Fishing vessel FV1, b fishing vessel FV2, c fishing vessel FV3, d fishing vessel FV4
occurring during fishing operations. In this respect, the OMII allows to more reliably estimate the safety level, accounting for sliding and tipping events on the entire working area and not only at some chosen location points. Furthermore, all sea states the vessel may encounter in the fishing area, each one with a certain probability of occurrence, are considered under different operating scenarios the vessel may experience during fishing operations. A new operability criterion, mainly based on OMII, is subsequently suggested, to compare vessels having different hull forms and dimensions, in a human centred approach. In this sense, the best fishing vessel will be the safest one, i.e. the one obtaining the highest OI score. Three main results have been achieved:
2.
1.
All these considerations suggest there is a wide space to improve safety on board fishing vessels already at an early design stage comparing, by means of the proposed operability index, vessels having different hull forms, paying attention to both loading condition and transverse
The rate of sliding and tipping events is significantly influenced by: position occupied by crew members on working area, heading angles and sea states, so as the MII alone cannot provide a reliable estimate of the on board risk level.
3.
The OMII, in terms of total number of sliding and tipping occurrences, decreases for increasing roll period. In this respect, transverse metacentric height GMT plays an important role for the on board safety level, so as excessive values have to be avoided, without compromising the ship transverse stability, to increase the relevant operability index. The operating scenario is another key point to be accounted. It has been found, in fact, that sliding and tipping events are maxima in the heading angle range between quartering and beam seas, quickly decaying beyond it, so that an increase of OI between 15 and 40 % could be reached, avoiding the above dangerous conditions.
123
45
45
40
40
35
35
30
OMIITOT,H1/3,Tz
OMIITOT,H1/3,Tz
J Mar Sci Technol
H1/3=0-1 m
25
H1/3=1-2 m
20
H1/3=2-3 m H1/3=3-4 m
15
H1/3=4-5 m
30 25
H1/3=0-1 m
20
H1/3=2-3 m H1/3=3-4 m
15
10
10
5
5
0 3.5
4.5
5.5
6.5
7.5
8.5
H1/3=1-2 m
H1/3=4-5 m
0 3.5
9.5
4.5
5.5
6.5
Tz [s]
45
45
40
40
35
35
30
30
25
H1/3=0-1 m H1/3=1-2 m
20
H1/3=2-3 m H1/3=3-4 m
15
H1/3=4-5 m
H1/3=0-1 m
20
H1/3=2-3 m H1/3=3-4 m
5
5 6.5
7.5
8.5
H1/3=1-2 m
15 10
5.5
9.5
25
10
4.5
8.5
(b)
OMIITOT,H1/3,Tz
OMIITOT,H1/3,Tz
(a)
0 3.5
7.5
Tz [s]
H1/3=4-5 m
0 3.5
9.5
4.5
5.5
6.5
Tz [s]
7.5
8.5
9.5
Tz [s]
(c)
(d)
Fig. 10 OMIITOT;H1=3 ;Tz per hour distribution vs. wave zero-crossing period—2nd scenario. a Fishing vessel FV1, b fishing vessel FV2, c Fishing vessel FV3, d fishing vessel FV4
Table 5 Sliding, f/a and s/s tipping occurrences per hour OMII
FV1
FV2
FV3
FV4
1st scenario
2nd scenario
1st scenario
2nd scenario
1st scenario
2nd scenario
1st scenario
2nd scenario
Sliding
0.395
0.141
0.252
0.092
0.191
0.067
0.099
0.035
f/a tipping
6.714
2.023
5.233
1.507
4.557
1.227
3.627
0.998
s/s tipping
4.093
1.266
3.120
0.948
2.624
0.760
1.936
0.578
Table 6 OMII regression coefficients
OMII
1st scenario M
123
2nd scenario Q
2
q
M
Q
q2 0.9938
Sliding
-0.3646
1.2485
0.9924
-0.1314
0.4491
f/a tipping
-3.8134
15.6410
0.9919
-1.2835
5.0091
0.9735
s/s tipping
-2.6679
10.3650
0.9965
-0.8599
3.2802
0.9873
J Mar Sci Technol Table 7 Operability Index for both operating scenarios Operability index
FV1 1st scenario
2nd scenario
1st scenario
2nd scenario
1st scenario
2nd scenario
1st scenario
2nd scenario
OI
0.709
0.900 (?26.9 %)
0.780
0.921 (?18.1 %)
0.805
0.929 (?15.4 %)
0.830
0.935 (?12.7 %)
Table 8 OI regression coefficients
FV2
Operability index
OI
Fig. 11 Operability index vs. ship roll period
FV3
FV4
1st scenario
2nd scenario 2
A
B
C
q
A
B
C
q2
-0.1290
0.8642
-0.6134
1.000
-0.0426
0.2795
0.4771
0.9998
1.00 0.95 0.90 0.85
OI
0.80 0.75 0.70 1st scenario
0.65
2nd scenario 0.60 0.55 0.50 5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
Troll [s]
metacentric height GMT and finally accounting for both stability and seakeeping requirements. Furthermore, safety may be improved during normal operating conditions too, by means of an ad hoc on board decision support system, mainly based on OMII and providing guidance in avoiding dangerous sea conditions, in the assumption that higher the operability index is, safer the fishing vessel will be. Acknowledgments The work has been financed by the Department of Sciences and Technology of the University of Naples ‘‘Parthenope’’, under the Research Project: PROGETTO INSIST ‘‘Innovazione Tecnologica nei Sistemi di Trasporto’’ POR Campania FSE 2007/2013 CUP B25B09000040007—Research Stream: ‘‘Ottimizzazione della tenuta al mare di mezzi navali ai fini del miglioramento del Comfort e della Sicurezza dei passeggeri e del personale imbarcato’’; ‘‘Sicurezza della Navigazione: Sistema di Monitoraggio dei moti nave e dei loro effetti sulle persone imbarcate ai fini del miglioramento della sicurezza e dell’ergonomia a bordo’’—B.U.R.C. n.23 14 April 2009—Legge regionale 28/03/2002 n.5 (year 2008).
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