Structural Safety and Analytic Comparison of Mooring Bollards

I Putu Sindhu Asmara

, Budianto

, Tri Tiyasmihadi

, Fais Hamzah

Zullaiqa Nurrochmah

and Putu Gede Bayu Agastya

Safety and Risk Engineering, Politeknik Perkapalan Negeri Surabaya, Surabaya, Indonesia

Shipbuilding Engineering, Politeknik Perkapalan Negeri Surabaya, Surabaya, Indonesia

Marine Engineering, Politeknik Perkapalan Negeri Surabaya, Surabaya, Indonesia

Marine Engineering, Aachen University of Applied Sciences, Aachen, Germany

Keywords

Bollards, Structural Safety, Assessment, Analytical Hierarchy Process.

Abstract

Winch bollard, which came into the market of marine products in 2004, can replace the package of deck

machinery components normally used for mooring, including winches, capstan, wrapping drums, and bollard.

While mooring line configuration studies are widely available, there are few cases presenting the design and

selection of the bollard types for its fabrication concern in the shipyard. This paper aims to assess the structural

strength of winch bollard using finite element analysis and compares it to three other designs of mooring

bollards. The other designs of the bollard structure consider the different materials of Grade A and Grade

AH32 for the conventional bollard and the usage of hook types. All of the bollard designs fulfil the required

load capacity and the requirement for the safety factor from the classification society of Biro Klasifikasi

Indonesia. The authors have compared and selected one of them to be applied to a hospital ship using the

analytical hierarchy process. The criteria used for the selection are function, manufacturing process, and cost.

INTRODUCTION

Mooring equipment including winches, chokes,

bollards, bitts, capstan, etc., is mandatory to be

installed on the deck as the part of the mooring system

between the vessels and jetty to face the

environmental loads such as tide, current, and wind to

prevent them from drifting away (Chao,2010). The

hydrodynamic calculation determines the

environmental loads and leads to the calculation of

the number of mooring lines and components, the

stress analysis of its fitting to the deck, deck stress

analysis. In this study, the authors focus on the

structural strength and selection of the bollard types.

The maker of the equipment has designed the strength

of the component according to the safety

requirements from the International Association of

Classification Society. However, in some application

cases, especially for vessels voyaging in a national-

territorial zone, the shipyard prefers to design and

fabricate its local product fulfilling the national

classification society (Chao,2010).

https://orcid.org/0000-0001-7359-9366

https://orcid.org/0000-0002-4155-5008

https://orcid.org/0000-0002-0802-6542

Chao analysed (JIS, 1995) type and (DIN, 2001)

type bollards’ ultimate loading capacity and its stress

analysis on the fitting to the hull foundation structure

of the deck. The study figured out the curve of

mooring force-displacement according to the finite

element analysis and experiment data. Another study

performed by ( Kuzu, 2017) compared the

conventional

type of mooring system involving

mooring ropes and

windlass to the vacuum and

magnetic mooring

systems. The study applied the

analytical hierarchy

process considering the criteria of

environment effect,

operation safety, operation cost,

as well as the

flexibility to ship movement,

environment condition,

and operating limitation. In

this study, the authors do

another search on the

strength assessment and

analytical comparison of

bollard options of the

conventional mooring system.

A bollard is made of pipes and mounted

perpendicular to the deck, or made of cast iron shaped

to resemble a pole. The he bollard has a load capacity

and lifetime to withstand the environmental forces

Sindhu Asmara, I., Budianto, ., Tiyasmihadi, T., Hamzah, F., Nurrochmah, Z. and Bayu Agastya, P.

Structural Safety and Analytic Comparison of Mooring Bollards.

DOI: 10.5220/0010964100003260

In Proceedings of the 4th International Conference on Applied Science and Technology on Engineering Science (iCAST-ES 2021), pages 1299-1304

ISBN: 978-989-758-615-6; ISSN: 2975-8246

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

1299

acting on the hull of the ship. The fitting of the

bollards on the main deck will expose them to water

and cause rust. Besides, the friction caused by the

rope will erode the bollard. The thickness of the pipe

and plate material will determine the strength and

lifetime of the bollard. In general, damage to the

bollard occurs due to the impact load. The load

happens during the mechanisms of the mooring

approach between the jetty and the deck. It would be

nice if the construction of the bollard has resistance

to water, weather, and rope friction.

The dimension of the bollard and the material

used for the design affects the ultimate capacity of the

bollard, so it is necessary to optimize the design of the

bollard by considering material having a different

ultimate strength. The strength analysis and selection

of bollards for a hospital ship are studied considering

the usage of the material specification. The material

specification for the existing design is Grade A and

Grade AH32 for one of the alternative bollards. The

AH32 grade material has a higher strength than

structural steel hull material. The maximum stress or

safety factor that occurs in the construction of

existing bollards with grade A material and new

bollards with grade AH32 material is at the same

level. The structural model and stress analysis of two

bollards and two other types are analysed using the

software of Fusion 360. The four alternatives of

bollard design are selected using the AHP method to

determine the proper product that fit the needs of

consumers or user.

METHOD

Determining an appropriate bollard to be installed

a hospital ship requires a proper research

methodology of designing, analysing, and selecting

the options. Firstly, providing the alternatives of

mooring configuration on the deck needs a literature

study on the available system provided by the

industries and shipyards, as well as the possible

variation of material used to design the bollard. This

step includes surveying and collecting data obtained

from the shipyard, such as the particular dimension of

the ship and the availability of bollard material for

production. The second step is to determine the load

capacity of components based on the ship's particular

dimension and environmental data of mooring

location.

The third step continued with data processing for

mooring calculation to determine the required bollard

load capacity, as well as developing the structural

model of the bollards and performing its stress

analysis according to the bollards load capacity

loading. This analysis aims to obtain the same level

of displacement and safety factor of the bollard

design options. Finally, from the results of the bollard

design options, the last step is to choose the bollard

using the AHP method to determine the best-chosen

bollard, according to the criteria of function,

manufacturing, and cost.

The design options are developed based on a

bollard capacity and its specifications from the

standard of Japan Industry Standard, available in the

JIS F 2001-1990 catalogue, as shown in Table 1 and

Table 2. Fig. 1 presents a detailed drawing of the

standard bollard. The material used on the JIS type

bollard is the grade A material having a yield strength

of 235 MPa. An alternative design uses AH32 grade

material with a higher yield strength of 315 MPa. The

AH32 grade material is steel hull material provided

by the standard of ship construction issued by the

(American Bureau of Shipping, 2004). The data

included

in Table 3 shows the mechanical

properties of

material grade A and grade AH32. The

parameters for

the calculation of wind and current

forces used in this

study are the most influenced

environmental

conditions in the jetty, can be shown in

Table 4.

Table 1: Size of bollard, JIS F 2001-1990.

Nominal

Diameter

Bedplate

B L Min. h Min.t3 l R

400 550 1630 160 14 400 45

Table 2: Bollard bedplate size, JIS F 2001-1990.

Post

D D1 H H1 t t1 t2 h1 e b

406.4

485 749 600

135

1000

Table 3: Mechanical properties material of bollard.

Grade

Tensile Test

Yield point

𝑚𝑚

)

Tensile strength

𝑚𝑚

)

Elongation

(L = 5.65

√

𝐴)%

235min 400 - 520 22

AH32 315 450 - 590 21

Table 4: Environmental data.

Wind-blown

projections,

Aw (m2)

Wind velocity,

Vw (m/s)

Sectional area

of the ship

submerged in

water, Ac

(

)

Current speed,

Vc (m/s)

1628.56 12.6 2200 0.2

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Figure 1: Detailed of bollard, JIS F2001-1990.

After obtaining the data, the current and wind

forces are calculated using (1) and (2) to (5),

respectively (Triatmojo, 2010). Bending stress is the

result of the

mooring force and bollard stem height,

as seen in (6)

and (7). Finally, the authors compare

the stress to

stress analysis performed using Fusion

360 software.

Rα = CC ∙ γw ∙ Ac ∙

(

𝑉𝑐

⁄

2𝑔

)

(1)

where:

Rα

is the force due to current (N),

is the

coefficient current pressure

γw

is the density of

seawater mass (1025kg/m

is the longitudinal

submerged cross-sectional area of the ship (m

is the current velocity (m/s), and g is cceleration of

the gravity.

Rw = 0.42 ∙ Pα ∙ A , for ⍺ = 180°(from bow) (2)

Rw = 0.50 ∙ Pα ∙ Aw, for ⍺ = 0° (from stern) (3)

Rw = 1.10 ∙ Pα ∙ Aw, for ⍺ = 180°(from side) (4)

Pα = 0.063𝑉

(5)

where:

𝐑𝐰 is the force due to wind (N), 𝐏𝛂 is the pressure

of the Wind (kg/m2), 𝐕 is the wind speed (m/s), and

𝐀𝐰 is the wind-field projected (m

I = 1

⁄

64 ∙ π ∙

(

− Di

)

(6)

σ = (

M∙y

)

(7)

where:

M is the bending moment acting on the bollard

(Nm), Do and Di are the ouside and inside diameter

of the bollard, respectively.

Table 5: Saaty’s scale and its association with verbal

judgment.

Verbal descri

tion Saat

’s scale

Indifference 1

- 2

Moderate preference 3

- 4

Strong preference 5

- 6

Very strong or demonstrated 7

- 8

Extreme preference 9

The authors apply the method of the analytical

hierarchy process to select the most rational type of

bollard structure from the four alternatives. The

criteria of design complexity, function, strength,

manufacturing process, maintenance, and price make

the selection is rational. The selection method uses

Saaty’s scale (Brunelli, 2015) associating with verbal

judgment to

scale the pairwise comparisons between

the criteria

shown in Table 5. The decision-maker

of the

shipbuilder has also provided a pairwise

comparison

matrix between the selection criteria.

RESULT

The models of the optional bollards structure are

the

JIS type, DIN type, hooked bollard, and winch

bollard can be seen in Figs. 2 to 5, respectively. In

alternatives 1 and 2, the concept designs of the

bollards are the same, the double-bollard type. The

differences are baseplate shape and plate thickness. In

concept 3, the design of the bollard uses the quick

release hook type. A Quick-release hook is a

fastening tool that uses an automatic system to make

the mooring process more efficient. In alternative 4,

the design of the bollard uses the bollard winch type.

Winch bollards are double bollards with an automatic

mooring system where the body of the bollard can

spin and pull the rope when the ship is mooring. All

of the four design concepts fulfill the required

capacity of the 60 tons SWL.

Figure 2: Stress analysis of alternative 1.

Structural Safety and Analytic Comparison of Mooring Bollards

1301

In Fig. 2, the bollard structure stress analysis of

option 2 shows a higher level than that of option 1,

which is 69.40 MPa. In Fig. 3, the result of the stress

analysis for the quick release hook type is 46.65 MPa.

The maximum stress on the structure of the winch

bollard is 52.68 MPa, shown in Fig. 4.

Figure 3: Stress analysis of alternative 2.

Figure 4: Stress analysis of alternative 3.

Figure 5: Stress analysis of alternative 4.

Table 6: Comparison of structural safety analysis.

Altern Displacement Strain Stress Safety

atives (mm) (MPa) factor

1 0.1439 2.077E-04 39.15 6.002

2 0.3309 4.803E-04 69.40 4.539

3 0.0813 3.784E-04 46.65 4.437

4 0.3375 3.789E-04 52.68 5.980

Table 6 shows a comparison of the analysis

results,

including safety factors, displacement, strain,

and

stress. The design has complied with the strength

criteria of (BV, 2017) that the minimum safety factor

1.5.

Selection of the Options

The selection of design concepts performed after

identifying shipbuilder preferences applies the

criteria of design complexity (C1), function (C2),

strength (C3), manufacturing (C4), maintenance

(C5), and price (C6). Table 4 shows a pairwise

comparison matrix that describes the relative

contribution or influence of each element to the goal

or criteria that are a level above it. Table 5 shows the

calculation of the criteria eigenvalues and tests their

consistency. Table 6 shows the calculation of the

average value for each row, hereinafter referred to as

the criteria eigenvalues. Table 7 is a sample of

alternative data with the values taken according to the

data collected.

Table 7: Weighing between the selection criteria.

Criteria C1 C2 C3 C4 C5 C6

C1 1 5 1/5 7 5 7

C2 1/5 1 1/9 1 3 1

C3 5 9 1 9 7 5

C4 1/7 1/1 1/9 1 3 1

C5 1/5 1/3 1/7 1/3 1 1/3

C6 1/7 1/1 1/5 1/1 3 1

sum 6.69

17.33

1.77 19.3 22 15.

Table 8: Normalized Criteria Matrix.

Criteria C1 C2 C3 C4 C5 C6

C1 1/

6.69

17.33

0.2/

1.77

19.33

5/22

15.33

0.2/

6.69

17.33

0.11/

1.77

19.33

3/22

15.33

6.69

17.33

1.77

19.33

7/22

15.33

0.14/

6.69

17.33

0.11/

1.77

19.33

3/22

15.33

0.2/

6.69

0.33/

17.33

0.14/

1.77

0.33/

19.33

1/22

0.33/

15.33

0.14/6.69

1/17.33 0.2/1.77 1/19.33

3/22

1/15.33

Table 9: Criteria Eigenvalues.

Criteri

C1 C2 C3 C4 C5 C6

Averag

0.15 0.29 0.11 0.36 0.23 0.46 0.27

0.03 0.06 0.06 0.05 0.14 0.07 0.07

0.75 0.52 0.57 0.47 0.32 0.33 0.49

0.02 0.06 0.06 0.05 0.14 0.07

0.07

0.03 0.02 0.08 0.02 0.05 0.02 0.04

0.02 0.06 0.11 0.05 0.14 0.07 0.07

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Table 10: Alternative-criteria comparison.

Alternatives C1 C2 C3 C4 C5

1 80 86 98 92 86 83

2 80 83 80 89 86

3 89 80 95 80 80 80

4 98 89 92 86 83 98

sum 347 338 365 347 335 344

Table 11: Alternative Matrix Normalization.

Alternative

C1 C2 C3 C4 C5 C6

80/

347

86/

338

98/

365

92/

347

86/

335

83/

347 338 365 347 335

344

347 338 365 347 335

344

347 338 365 347 335

344

Table 12: Alternative Eigenvalues.

Alternatives

C1 C2 C3 C4 C5 C6

1 0.231 0.254 0.268 0.265 0.257 0.241

2 0.231 0.246 0.219 0.256 0.257 0.241

3 0.256 0.237 0.260 0.231 0.239

0.233

4 0.282 0.263 0.252 0.248 0.248 0.285

Table 13: Alternative-criteria eigenvalues.

Alternatives

C1 C2 C3 C4 C5 C6

0.061 0.017 0.132 0.017 0.009 0.018

0.061 0.017 0.108 0.017 0.009 0.018

3 0.068 0.016 0.128 0.015 0.009 0.017

4 0.075 0.018 0.124 0.016 0.009 0.021

Table 14: Final assessment results.

Alternatives Final result

1 0.255

2 0.229

3 0.253

4 0.263

Table 15: Comparison of Existing and New Bollard.

No Variable Existing bollard

Winch bollard

1 Material Grade A Grade AH32

2 Yiel

Strength 235

315

3 Tensile Strength 400 - 520 450 - 590

4 Stress 39.15 MPa 52.68 MPa

5 Safety Facto

6.002 5.98

6 Operational Manual

Automatic with

moto

Table 8 shows the calculation of the alternative matrix

normalization. Table 9 shows the calculation of the

alternative eigenvalues obtained from the

of results

dividing the criteria value into alternatives and the

number of each criterion. Table 10 present the

eigenvalues of alternative-criteria which is calculated

by multiplying the average of criteria eigenvalues

with the alternative eigenvalues for each

corresponding criterion. Table 11 shows the final of

selection result by summing the alternative-criteria

values. The eigen final result shows that the most

rational bollard is alternative 4. The winch bollard has

the highest score and rationally to be recommended

for fabrication. Table 12 presents the specification

comparison of alternative 4, the selected bollard to

alternative 1, the existing bollard installed in the

previous vessel.

Figure 6: Winch Bollard.

Winch bollard modeling is shown in Figure 6.

This

type of bollard saves space on the deck and can

perform automatic mooring operations so that it is

more effective than the standard (manual) method

currently available. The performance of this winch

bollard is that the bollard body can rotate and pull the

rope when the ship is mooring with just one person

operating equipped with speed control.

The advantages of the winch bollard are:

The operation is carried out by just one person.

Automatic mooring system.

Easier and time-savings

Optimal and safe control using the foot pedal.

There is speed control.

Low noise during operation.

CONCLUSIONS

The structure of the winch bollard have been designed

and the safety factor is 5.980 which is almost the same

level with the safety factor of the existing JIS type

bollard, 6.002. The study proves that the benefit of the

winch bollard affect the decision-maker to provide

Structural Safety and Analytic Comparison of Mooring Bollards

1303

the highest weighing to this alternative. The future

works of this research is to develep the detail design

and prototype of the winch bollard.

ACKNOWLEDGEMENTS

The authors would like to acknowledge to Politeknik

Perkapalan Negeri Surabaya for providing the

publication fund.

REFERENCES

S. R. Chao, J. Choung, C. M. Oh, and K. S. Lee,. (2010).

Ultimate load capacities of mooring bollards and hull

foundation structure. Ocean Engineering, vol. 37, pp.

770-776, 2010.

JIS (Japanese Industrial Standards), 1995. JIS-F2001,

bollards.

DIN (Deutsche Industrie Normen), 2001. DIN-82607,

double bollard.

A. C. Kuzu, O. Arslan. (2017). Analytical Comparison of

Different Mooring System. Conference of IAMU AGA,

Varna, Bulgaria.

ABS, 2004, Guide For Building and Classing Floating

Production Installations. USA: American Bureau of

Shipping.

B. Triatmojo, Hidrologi Terapan, 2010, Yogyakarta, Beta

Offset.

Brunelli, Matteo 2015. Introduction to the Analytic

Hierarchy Process. SpringerBriefs in Operations

Research. P. 83. 978-3-319-12502-2 (electronic).

10.1007/978-3-319-12502-2.

BV( Bureau Veritas), 2017. Rules for Certification of

Lifting Appliances onboard Ships and Offshore Units,

Chapter 2: Design Assessment, Section 3: Structural

Assessment.

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