Stability of fishing vessels in waves and wind

J. L. Mantari Centre for Marine Technology and Engineering (CENTEC), Technical University of Lisbon,

Instituto Superior Técnico, Lisboa, PORTUGAL

ABSTRACT: The The stability characteristics of 27 fishing vessels, mainly from the Portuguese and

Peruvian fishing fleet, are studied. Calculations of ship’s stability for longitudinal and beam waves were

made. The variations of dynamic transverse intact stability of the fishing vessels under 3 operational loading

conditions are calculated and analyzed for 2 representative sinusoidal longitudinal waves. The wave

parameters considered were the following: s=1/20 and (a) /Lpp=1, (b) /Lpp=1.6, with wave crest position

along the wave or vessel’s length. Potential for the occurrence of stability failure due to pure loss of stability

and parametric resonance were found. For beam waves, fishing gear and gusty wind loads were included to

evaluate the energy balance between the heeling and righting moments. Based on these calculations, size,

hull form and others particularities of the fishing vessels, some light on the occurrence of partial or total

stability failure were found. An overview of the International Code on Intact Stability (2008 IS Code) related

to fishing vessels, is made. Finally, conclusions are drawn about 2008 IS Code, and the loss of fishing

vessel’s intact stability in longitudinal and beam waves.

Keywords Stability failure, fishing vessel, stability variations in longitudinal waves, GZ curves, design

criteria, fishing gear forces

1 INTRODUCTION

The safety management systems applied at the

international level in merchant ships do not have

their equivalent in the vessels dedicated to fishing,

and much less to the most numerous sub-sector, the

so called-artisan fishing (Piniella et al. 2009, Kuo

2003).

The safety of fishing vessels remains a key

concern given the high rates of accidents occurring

worldwide. The IMO, FAO and some Classification

Societies have some records or data of the world

fishing vessels, but no representative and trusted

database about casualties of fishing vessels is

available.

It is important to distinguish between casualties

(Antão and Soares 2004) and work accidents

onboard (Antão et al. 2008). The casualties can

occur because of the stability failure of the vessel,

for many reasons well described by (Umeda et al.

1999, Umeda 2002, Francescutto 2007), mostly

including additional factors suggested by Kobylinski

(2003) and others authors. On the other hand, the

accidents onboard occur mainly because the work

environment is affected by: the dynamic stability of

the vessels (Piniella et al. 2008), weather condition,

vessel location, time of the year, vessel

characteristics (Di Jin et al. 2005).

Most of the accidents aboard happen on deck or

in holds (Havold 2009) during the trips to and from

the fishing grounds and many authors believe that

the main reason of accidents on the fishing industry

is human error, which account for between 75% and

96% of all accidents in the industry (Rothblum et al.

2000, Umberti et al 2001), which is maybe higher

but not too different from what is found in

commercial vessels (Guedes Soares et al. 2001,

Antão and Guedes Soares 2008). These ideas are

supported by Kobylinski (2003), in the sense that not

only the “environment” basic element should be

considered in the ship stability analysis in general, it

should consider the four basis elements: ship,

environment, cargo and operations.

The present studies represent an initial effort in

that project by studying a set of 27 fishing vessels

mainly from the Portuguese and Peruvian fleets,

with different configurations and modes of operation

in order to have a better understanding of:

The range of variation that can be expected

in the intact stability characteristics in

longitudinal waves and in this way to guide

the design of the decision support system to

cope with pure loss of stability on a crest

wave and with the likelihood of parametric

roll.

The action of fishing gear forces, wind and

combinations of some fishing vessels in a

fishing trip scenario, and their influence in

the stability failure.

The Subcommittee on Stability and Load Lines

and on Fishing Vessels is also analyzing some of

these problems and their results have been taken into

account in this paper.

This study shows that in occasions the IMO

rough weather criteria may be unconservative.

2 INTACT STABILITY OF FISHING VESSELS

The sea waves are irregular, and despite the regular

wave approximation being unconservative (Umeda

et al. 1999), for reasons of simplicity this paper uses

the well known crest, trough and own sinusoidal

wave to study their effect in the stability of fishing

vessels. In order to reach large variation in the

righting arms, it is common practice to use the wave

length to ship length ratio around 1 and wave

steepness equal to 1/10, as pointed by several

authors and also recommended by the (IMO-

MSC.1/Circ.1200 2006).

The current IMO weather criterion, utilizes the

energy balance method adopted in Japan without

major modifications. This paper assumes that a

fishing vessel with a steady heel angle due to steady

wind has a resonant roll motion in beam waves.

Then, as a worst case, the fishing vessel is assumed

to suffer gusty wind and fishing gear loads (if they

exist) when she rolls toward windward. In the case

of the resonant roll, roll damping moment and wave

exciting moment cancel out. Thus, the energy

balance between restoring and wind heeling energy

can be validated around the equilibrium point.

Furthermore, at the final stage of capsizing the effect

of wave exciting moment can be considered to be

small, since no resonance mechanism exists near the

angle of vanishing stability.

2.1 Transverse stability in longitudinal waves

The intact stability in longitudinal waves, rather

than in still water, gives a better idea of the changes

of restoring energy of the ship in trough, own and

crest waves (which corresponds to a periodic wave

to be superimposed on the waterplane with phase

angles of 0, 90 and 180º, respectively, as shown in

Figure 1). In order to calculate the changes of

stability by means of variation of righting arm, GM

and restoring energy, it is convenient to use

commercial software or the equations presented in

the proposal of new generation intact stability

criteria, submitted by Japan (IMO-SLF 51/4/3). In

this paper all the calculations related to the first part

of this study were carried out using commercial

software GHSTM

.

Figure 1. Changes on righting arm curves in longitudinal waves for a Portuguese fishing vessel “FV 8”.

The longitudinal and quartering seas are some of

the most critical conditions that should be analyzed

and are applicable to all kind of ships. There are

interesting studies about fishing vessels considering

longitudinal and quartering seas. The changes of

stability in longitudinal waves that induces

parametric resonance were studied experimentally

and numerically by Hamamoto and Panjaitan (1996),

Umeda et al. (1999), Neves et al. (1999), Pérez-

Rojas et al. (2003), Ribeiro e Silva et al. (2004) and

several authors. Umeda et al. (1999) studied

experimentally two fishing vessels and came to the

conclusion that quartering seas are more dangerous

than head seas and can lead to more capsizing.

As example of the changes of stability due to the

hull forms, the experimental studies done by Neves

et al. (1999) concluded that a stern deep transom is

more sensitive than a round stern trawler. This is

corroborated in a simple way in this paper, as

mentioned hereafter, and it was used as comparison

parameter to evaluate if the hard chinned hull with a

characteristic classical purse seiner transom is

sensitive or not to the parametric roll resonance

phenomena.

In this simple way of analysis it is not possible to

reach conclusions about parametric rolling

phenomena. However, what this paper is trying to

point out is that stability software can be used for a

preliminary analysis of such changes of stability

based on the righting arm curve obtained for the

most severe wave conditions. This will give some

indications about the susceptibility to parametric

rolling, despite not providing a complete answer

which only specific software like the one of Ribeiro

e Silva et al. (2005) can provide.

2.2 Transverse stability in beam wind and rolling

(weather criterion)

The basic principle of the IMO rough weather

criteria is the balance between restoring and

inclining energy in beam waves and wind, assuming

certain roll amplitude that takes into account the

excitation moment due to waves. The criteria are

used to determine fishing vessel performance in

beam seas and strong winds. These criteria assume

that a fishing vessel has taken a large roll to

windward from a passing beam wave. After the

wave crest passes the vessel quickly rolls to the

upright position due to both the wind pressure on the

lateral plane and the backside of the passing wave.

In Figure 2, the Area “A” represents the amount of

energy associated with the inclining moment that

acts to snap roll the fishing vessel back upright, after

the beam wave passes. Area “B” is the restoring

energy available to counter the fishing vessel

rollback. 1 is the angle of roll to windward due to

wave action, and 2 is the downflooding angle or the

angle of second intersect between steady wind lever

l1 and righting arms curve c or 50 deg, whichever is

less.

2.3 Transverse stability due to fishing gear loads.

Pelagic trawling and purse seining requires

considerable skill to precisely control a fishing

vessel and her gear. It is important to note that it is

very rare, except in special cases, that the heel

caused by wind only would endanger a fishing

vessel (Gefaell, 2005). Usually what happens is that

stability is lost when there is an unusual combination

of wind, waves and fishing loads. An interesting

research even highlighted that there are more fishing

vessels accidents during the fishing and recovery of

gear operation (Wang et al. 2005) than in heavy

weather. These two arguments and those criteria

developed by IMO Subcommittee on safety of

fishing vessels (IMO 1979) motivated this work.

The following analysis are based on a procedure

reported by the IMO after a proposal submitted by

the Soviet Union in 1979 (IMO 1979), but here they

are applied to a traditional pelagic pure seiner, see

Figure 3.

The current purse seiners, for example, have

fishing gears that put in danger a fishing vessel quite

easily, mainly for these which still use the power

block in a high position. As reported before (IMO

1979) the increase of power of the machinery, in

general, increases the heeling moment until a point

that weather criterion is not the only way to guaranty

the stability of the fishing vessel in operation.

However, nowadays in some countries, for example

Peru, there is still a tendency to increase the power

of the machinery like the main engine, winch and

power block.

-10 0 10 20 30 40 50 60 70 80 90-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

Balance of energy of the intact stability at fishing operation

Heel Angle (deg)

Arm

(m

)

Righting arm in still water condition

Heeling arm due to wind and fishing gear loads

O

A

B

Figure 2. Balance of energy for the weather criteria.

WLf

WLo

WLf

WLo

Figure 3. Gear loads on a traditional pelagic purse seiner.

A classical purse seiner has two devices for

fishing. The winch has the function of collecting the

bottom of the net, rings and weights; the winch

produces a load that is represented as P2 in Figure 3.

The power block has the function of fish leaning

toward the side of the vessels, collect the buoys and

the rest of the upper net; the power block produces a

load that is represented as P1 in Figure 3.

The simplified scenario for the calculation of the

heeling moment due to fishing loads is shown in

Figure 3. This uses a coordinate system xyz fixed in

space, and a coordinate system attached to the vessel

x’y’z’.

As illustrated in Figure 3, after an angular

displacement the following orthogonal coordinate

transformation matrix [T] is applied to describe the

position of points A’, B’ and Q’ fixed to a FV:

AZ

AY

T

AZ

AY

'

' ,B

ZB

YT

BZ

BY

'

' ,Q

Z

QY

T

QZ

QY

'

'

where: cossin

sincosT (1)

The moment due to fishing net load P1 at the power

block is given by:

cos)''

(1

sin)''

(11 Q

YA

YPQ

ZA

ZPM (2)

)]cos()sin()[(11 A

YA

QA

ZPM (3)

)1

cos(111

DPM (4)

The moment due to the pull of winch P2 is given by:

)''

(sin2

)''

(22 Q

YB

YPQ

ZB

ZCosPM (5)

)2

cos(222

DPM (6)

where:

1 = P1 angle as shown in Fig. 3;

2 = P2 angle as shown in Fig. 3; D1 = distance from point Q to point A (Power Block);

D2 = distance from point Q to point B (Purse Gallows).

The total heeling moment due to both fishing gear

loads is therefore given by:

)2

cos(22

)1

cos(11

DPDPt

M (7)

The maximum heeling moment, with “ =0” and

“ ” variable, can also be found using a basic

trigonometric theory:

2211maxDPDP

tM cos( 2) (8)

Despite the simplifications used in this static

analysis, both methods are still conservative because

it considers the maximum pull of the fishing gear as

static and therefore dynamic effects due to waves

and current acting on the ship and fishing gear are

ignored.

3 CALCULATION RESULTS

3.1 Fishing vessels studied

In this section a set of 2 sinusoidal longitudinal

waves, which include a subset of 34 waves profiles

for each fishing vessel and each operational loading

condition, with crest wave position along Lpp or ,

were studied. Additionally, a number more

significant of fishing vessels were considered, and

the following calculations were done:

a) Change of draft and displacement at still water,

and at different loading conditions;

b) Calculation of the intact stability of fishing

vessels in waves for vessels larger than 24m, these

calculations were done using the International Code

on Intact Stability (2008 IS Code) (IMO-

MSC.267(85) 2008);

c) Calculation of the intact stability of fishing

vessels in waves for vessels smaller than 24m, these

calculations were done using FAO/ILO/IMO2005

intact stability criteria (FAO/ILO/IMO 2005);

d) Considering the items b and c, variations of

GM, variations of righting lever at 30º, and

variations of restoring energy from 0º to 30º and 0º

to 40º are presented. These calculations were

performed for all the fishing vessels studied in this

Thesis and considering different loading conditions,

when full data were available.

From the 27 vessel studied, see Table 1, 16

fishing vessels present full data, see more details in

the full thesis, and they were studied at different

loading conditions: (C1) 0% cargo, 100%

consumables; (C2) 100% cargo, 35 – 50%

consumables; (C3) 100% cargo, 10 – 20%

consumables.

Some of the fishing vessels studied in this paper

are shown in Figures 4 , see Table 1. They were

classified by hull forms and hull size for their

analysis, as shown in Tables 1. The majority of the

fishing vessels, as mentioned above, were analyzed

at three different operational loading conditions.

However, some of the vessels were studied as they

were analyzed by the corresponding authors in their

respective papers. For example, FV2-FV5, FV9

presented in Table 1 were taken from Pérez-Rojas et

al. (2003, 2006) and they were also studied by

Santos et al. (2008). FV 7 which came from Amagai

et al. (2000). The fishing vessel FV 27 is a modern

Chilean tuna purse seiner. The fishing vessels FV 12

and FV 13 were extensively published by Neves et

al. (1999). The Portuguese fishing vessels are

studied in here for the first time (FV1, FV6, FV8,

FV10, FV11, FV14 and FV15). The rest of fishing

vessels are Peruvian pelagic purse seiners (FV18-

FV26).

3.2 Variation of transverse stability in longitudinal

waves

Figures 5-6 show the roll-restoring energy

variation, from 0 to 30º (left side), at different

operational loading conditions for the 27 fishing

vessels considered in this Thesis. Notice that some

of these fishing vessels present only one operational

loading condition, because they were presented as

they were studied previously. Figure 5 shows the

roll-restoring energy variation of the fishing vessels

“FV3” and “FV5” at operational loading condition

C3, which, in addition to the fishing vessel “FV4”,

(Figure 6) capsized due to stability problems (Pérez-

Rojas et al. 2006). Figure 6 also shows that they

have larger roll-restoring variations compared with

other small fishing vessels of similar size and hull

form. These large variations, in addition to some

other particularities of stability changes, have

influence on the total or partial failure of a vessel.

The causes of partial or total stability failure

according to the IMO criteria are several. This work

aims to provide some preliminary guidance to ship

designers on the possibility of occurrence of

parametric resonance and pure loss of stability in

longitudinal waves.

Table 1. Fishing vessels main characteristics, hull size

Figure 4. Body view of 15 fishing vessels. “FV1”, “FV6”, “FV8”, “FV10”, “FV11”, “FV14” and “FV15” are from the Portuguese fleet and the rest are from Spain and Japan.

Roll restoring energy variation (%), from 0 to 30 deg., with

respect to still water (H/ =0.05, /Lpp=1 )

-75

-50

-25

0

25

50

75

100

125

FV

1

FV

3

FV

5

FV

6

FV

8

FV

10

FV

14

FV

15

FV

16

FV

18

FV

19

FV

20

FV

21

FV

22

FV

23

FV

24

FV

25

FV

26

Ch

ang

es o

f re

sto

rin

g e

ner

gy

(%

)

.

Positive variation

Negative variation

Maximum variation

Figure 5. Changes of righting arm with respect to calm water

(normalized by 100/B), B/T and Lpp/B.

Roll restoring energy variation (%), from 0 to 30 deg., with

respect to still water (H/ =0.05, /Lpp=1 )

-50

-25

0

25

50

75

100

125

150

175

FV

1

FV

2

FV

4

FV

6

FV

7

FV

8

FV

9

FV

10

FV

12

FV

13

FV

14

FV

15

FV

16

FV

17

FV

18

FV

19

FV

20

FV

21

FV

22

FV

23

FV

24

FV

25

FV

26

FV

27

Ch

an

ges

of

rest

ori

ng

en

erg

y (

%)

.

Positive variation

Negative variation

Maximum variation

Figure 6. Changes of restoring energy (%) from 0 to 30

degrees, respect to still water.

Table 2. Change of roll-restoring energy variation in waves (respect to still water) at critical operational loading condition. Wave

parameters: Upper (H/ =0.05, /Lpp=1.6), lower (H/ =0.05, /Lpp=1).

The most rapid increase of roll in a parametric

resonance scenario could be observed when the

vessel experiences an internal roll disturbance

combined with a condition of increasing energy in a

particular sailing condition. This combination of

restoring with a larger-than-calm-water and resisting

the roll with less-than-calm-water can cause the roll

angle to progressively increase to a large and

possibly dangerous level. However, all the fishing

vessels have this combination of roll-restoring

energy. But some of them has the gain of roll-

restoring energy larger than the loss of roll-restoring

energy, i.e. At is larger than |Ac|, see Figure 7, in

such cases the restoring moment tends to accelerate

the vessel back to equilibrium with a excitation

which is even larger than other situation (At < |Ac|),

and potential for resonance phenomena can be shed,

see Table 2.

Figure 7. Fishing vessel model (FV10)

Figure 7 show the model of the FV10 (left side)

and the percentage of gain and loss of roll-restoring

energy up to 30º (right side).

In Table 2, it can be seem that some specific

fishing vessels have particular restoring energy

variations which, combined with low GMsw and

large GM variations in waves could lead to the

occurrence of partial or total stability failure. The

ratios between the absolute value of the percentage

gain and loss of roll-restoring energy up to 30º and

40º, which are less than 1, give us potential for the

occurrence of parametric resonance; see fishing

vessels FV10, FV14, FV15, FV25 and FV26.

Attention is called to these particular fishing vessels

marked in bold in Table 2.

Similar analyses were performed to the vessels

mentioned above (FV12, FV13, FV17), and not only

for the ones which are included in Table 2. As

expected, they showed potential for the occurrence

of parametric resonance, as confirmed by other

authors which have studied these same fishing

vessels Neves et al. (1999, 2002), Ribeiro e Silva et

al. (2004) and De Juana Gamo et al. (2005).

In another hand, it is possible to notice than even

when differences of length are not significant (see

Table 1) it is not possible to reach a general

conclusion about susceptibility to resonance

phenomena, but what is remarkable is that

considering also the hull from (see Table 1) it

becomes possible to reach some conclusions about

the changes of the stability in fishing vessels.

For example, the ITPS (Inclined Transom Purse

Seiner) (see Table 1 and Figures 4 and 8), have

direct relation with the loss of restoring energy in

trough waves for the fishing vessels less than 40m in

length, as shown in Figures 5 and 6, and despite this

kind of waves are the most favourable.

However, according to Ribeiro e Silva et al.

(2005), parametric rolling can occur only when large

transverse stability changes (driven by wave

characteristics, coupled heave and pitch responses,

and hull form parameters such as hull flare, end

sections shape, and main deck position) are

combined with low damping (reduced speed).

Hence, hard chinned hulls may also have larger roll

damping forces due to viscous effects at the hard

chinned, and turn to be less sensitive to parametric

rolling than soft type hull forms.

Figure 9 shows the Ince-Strutt diagram for /Lpp

[0.84, 1.6] and wave steepness of 1/20. Table 3

presents the susceptibility analysis of parametric

rolling of the 16 fishing vessels studied in this paper.

This Table presents results for /Lpp [0.84, 1.6]

and wave steepness of 1/20. Similarly to Table 3, the

threshold values were calculated by using Hayashi

(1953) and ABS (Shin et al. 2004) method. From

Table 3 it can be inferred that FV1 (Portuguese),

FV16 and FV20 (Peruvian), do not present

vulnerability to parametric resonance in head seas

for the defined wave parameters and its determined

forward speed for susceptibility criteria (Vpr).

Moreover, FV1 and FV20 do pass the check of 2008

IS Code adapted to longitudinal wave scenarios

(Mantari et al. 2011a). Opposite occur to the rest of

fishing vessels at COLC and sailing condition

(vessel speed and wave parameters), because they do

not pass the frequency and/or damping threshold

condition for parametric resonance, i.e. they have

vulnerability to parametric resonance in head seas.

Therefore, their severity should be also determined.

Figure 8. Transom of different kinds of fishing vessels, DT,

ITPS, without transom.

The FV18, FV22 and FV23 do not pass: (a) the

frequency and damping threshold condition; (b) the

check of 2008 IS Code adapted to longitudinal wave

scenarios (Mantari et al. 2011a), for the same

abovementioned wave parameters, and for these

reasons her severity should be also determined.

However, the results that came up from this

study, related to these vessles, should be treated

carefully, because: (a) the present method used to

calculate parametric resonance of this particular

vessel is not suitable (the GM variation can no be

modeled as a sinusoidal function); (b) The ITPS

fishing vessels less than approximately 40m in

length, which have chinned hull, seem to be

beneficial to the avoidance of parametric resonance

(Mantari et al. 2011a). Then further studies are

needed.

FV25 and FV26 do not pass: (a) the frequency

and damping threshold condition; (b) the check of

2008 IS Code adapted to longitudinal wave

scenarios; and (c) present potential for stability

failure. Therefore, for more reason, their severity

should be determined as well.

Finally, it is important to point out that the

analysis of the changes in stability in waves gives

indications about the susceptibility to parametric roll

but it is still necessary to consider the dynamic effect

of waves on fishing vessels.

Table 3. Susceptibility analysis of parametric rolling.

Ince-Strutt diagram ( =0.03)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.1

0

0.1

5

0.2

0

0.2

5

0.3

0

0.3

5

0.4

0

0.4

5

p

q

q1 q2 FV1 FV6 FV8FV10 FV14 FV15 FV16 FV18FV19 FV20 FV21 FV22 FV23FV24 FV25 FV26 q1h q2h

Figure 9. Linear and high order approximation for the

boundary of the first instability zone (Ince-Strutt diagram).

/Lpp [0.84, 1.6], wave steepness of 1/20.

3.3 Stability under operational loading condition in

beam waves

Peruvian and Portuguese purse seiners as the ones

presented in Figure 10 are studied in this thesis.

The fishing vessel “FV6”, when the fishing gear

loads, as presented in Table 4, are considered,

comply successfully with the energy balance

analysis, but they become dangerous and lead to

total failure when the gusty wind is also included,

see Figure 11.

The fishing vessel “FV8”, when only the fishing

gear loads are considered, comply successfully with

the energy balance analysis, except by fastened

condition, but they become dangerous and lead to

the total failure when the gusty wind is also

included, see Figure 12. It is important to remark

that only partial winch pull were used for this fishing

vessel, which is not the case for the fishing vessel

“FV6”, see Table 4. The unfavorable hydrostatics

and her low displacement play against her intact

stability, in a critical fishing trip scenario.

Additionally, due to the difference between the

Atlantic and Pacific Ocean, for this Portuguese

fishing vessels is reasonable use wind speed of 26

m/s, as mentioned above. Then it is even more

unfavorable when this wind is considered.

After the several calculations made on the fishing

vessels “FV8”, with different fishing gear forces and

scenarios of fishing trip scenarios (not include in this

Thesis for lack of space), it can be concluded that

this particular fishing vessel has over dimensioned

machinery on deck. Then, preventive action should

be taken to asses her intact stability during a critical

fishing trip scenario. Fortunately, the Portuguese

fishing fleet, particularly this fishing vessel (as

fishing vessel “FV8”), fish around 13.5 tons of fish

(Mantari et al. 2011a). Then it seems that is very

difficult to reach such tension on the cables or net as

presented in Table 4. This is maybe why there is not

casualties reported due to fishing gears forces

(Antão and Guedes Soares 2004). However, in each

of the fishing trip scenarios, for example pursing, the

cable can get fastened and then the tension on this

cable can reaches these values (see Table 4), then

special attention need to be taken to such situations.

In the Peruvian fleet, for a fishing vessel of

similar size as “FV8”, she normally could fish more

than 100 tons (Mantari et al. 2011a). Then, fish

recovering (fishing trip) is dangerous, and it is

possible to reach these tension values or forces as

presented in the Table 4. Moreover, it is believed

that casualties due to fishing gear forces are

frequently (Mantari et al. 2009a).

This study also shows that in particular fishing

trip scenario the IMO rough weather criterion is

unconservative.

Figures 11-12, show that the combined effect of

the fishing gear and moderate to whole gale wind

description can be larger than the requirements of

the weather criterion as pointed out also in IMO

(1979), Tadanobu Machii et al. (1989), Gefaell

(2005), Mantari et al. (2009, 2009a, 2011b).

Finally, with respect to the fishing gear heeling

moment, it can be said that few or limited number of

research articles are available in the literature. A

literature survey shows few articles dealing with

fishing gear forces, and any article dealing with

fishing gear forces combined with waves or winds. It

is perhaps due to the fact that nowadays there is not

abundance of natural resources (fish), which may

cause danger in a fishing trip scenario. However,

exist the possibility that the net may be fastened at

the bottom and generate a stability failure.

Moreover, some countries have still abundance of

fish and the tendency to increase machinery onboard

still exist, as mentioned above. Therefore, the

fishing gear forces acting individually of in

combined action with waves and winds should be

considerer for further research.

Table 4. Fishing gear forces (Tons) acting on the 7 fishing vessels.

4 CONCLUSIONS

In this paper the changes of restoring energy

with waves were studied for several fishing

vessels, identifying the effect of fishing vessels

size and hull form. These calculations indicate

how the stability is sensitive to the changes from

one wave profile to another in longitudinal waves,

which can be related with the susceptibility of the

vessel to parametric roll. Potentials for stability

failure are given.

With respect to the fishing gear heeling

moment, the calculations presented in this paper,

show that fishing gear heeling moments are more

important than the heeling moments produced by

the weather criterion, and, effectively, a

combination of them leads to capsizing even when

the operational load condition is normal.

For general understanding and acceptance, the

new IMO intact stability criterion should be

completed, i.e. it should consider all the aspects

related to the stability and cover all the variants

that can exist.

At the moment the IMO stability criterion does

not assure safety, neither, in longitudinal and

beam waves, making a decision support system

very useful for the safety of certain fishing

vessels.

201918171615141311 12109876543210

COZINHA

PORÃO (104.8 m^3)

MESSE ALOJAMENTOS

CASA

DE

BANHO

PAIOL

DA

AMARRARUFO

PA

IOL

DO

PR

OP

UL

SO

R D

E

PR

OA

E D

O S

ON

AR

CASA DAS

MÁQUINASCOMBUSTÍVEL

(7.1 M^3)

COMBUSTÍVEL

(2.6 M^3)

COMBUSTÍVEL

(1.2 M^3)

COMBUSTÍVEL

(2.0 M^3)

ÁGUAS NEGRAS

(2.4 M^3)

COMBUSTÍVEL

(0.5 M^3) COMBUSTÍVEL

(1.6 M^3)

ÁGUA

DOCE

(2.5 M^3)

CO

MB

US

TÍV

EL

(3.5

M^3

)

Figure 10. General arrangement of two purse seiners fishing vessels, Portuguese (smaller) and Peruvian (bigger).

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3Intact stability at fishing operation, U=15m/s

Heel angle (deg)R

igh

tin

g a

rm (

m)

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3Intact stability at fishing operation, U=19m/s

Heel angle (deg)

Rig

hti

ng

arm

(m

)

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3Intact stability at fishing operation, U=26m/s

Heel angle (deg)

Rig

hti

ng

arm

(m

)

GZ

C1, hauling

C2, pursing

C3, hauling

C4, pursing

C5, fastened

H.WindUm/s Arm

H.W.Um/s + C1, hauling

H.W.Um/s + C2, pursing

H.W.Um/s + C3, hauling

H.W.Um/s + C4, pursing

H.W.Um/s + C5, fastened

Figure 11. Inclining arms due to external forces (wind and fishing gear loads) and restoring arms of the fishing vessel FV6.

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3

0.4Intact stability at fishing operation, U=15m/s

Heel angle (deg)

Rig

hti

ng

arm

(m

)

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3

0.4Intact stability at fishing operation, U=19m/s

Heel angle (deg)

Rig

hti

ng

arm

(m

)

-10 0 10 20 30 40 50 60-0.1

0

0.1

0.2

0.3

0.4Intact stability at fishing operation, U=26m/s

Heel angle (deg)

Rig

hti

ng

arm

(m

)

GZ

C1, hauling

C2, pursing

C3, hauling

C4, pursing

C5, fastened

H.WindUm/s Arm

H.W.Um/s + C1, hauling

H.W.Um/s + C2, pursing

H.W.Um/s + C3, hauling

H.W.Um/s + C4, pursing

H.W.Um/s + C5, fastened

Figure 12. Inclining arms due to external forces (wind and fishing gear loads) and restoring arms of the fishing vessel FV8.

ACKNOWLEDGMENT

This work has been performed within the project

“SADEP-Decision support system for the safety of

fishing vessels subjected to waves”. The project has

been financed by the Foundation for Science and

Technology (“Fundação para a Ciência e a

Tecnologia”), from the Portuguese Ministry of

Science and Technology, under contract

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