This article post aim to discuss the generally used equations, formulas, factors to determine a suitable port fender design. All formulas and equations are only intended as reference only. If you have a project, drop us an email so our technical staff can advise you.

Contributed by Wang.

A solution to absorb collision & prevent damage

Since the early days of floating crafts & small wooden boats, fenders were woven from ropes to absorb collision during berthings. Similar to the products we have today, they came in various sizes and patterns to serve different needs. The primary function of such a “soft-contact” system is to prevent the vessel from sustaining damage as the ship or boat is being moored against the quay wall. However, the vast amount of variations may confuse some looking to purchase certain fenders for their new-built port or jetty. In short, impact forces during the vessel berth, abrasive action, among other factors must be taken into consideration as well as the block safety coefficient to provide some allowance. The multi dimensional forces may cause extensive damage to the jetty structure AND the ship at the same time if a less suitable fender is used (or worse, a low performance fender system is deployed). So, it is about absorbing contact and distributing the force onto a larger surface area to prevent damage. Aside from mostly uniformly distributing collision force, it also increases impact time to lower the reaction force in whole.

Yes, it is important to have a structure of this kind to prevent damage to the quay wall or jetty or harbour.

Quite simply, determining a suitable marine fender system comes down to considering:

Amount of Energy Absorbed and Maximum Impact Force Imparted

Common Selection Process: All Conditions must be Carefully Studied

It is important to keep in mind that the local marine condition is as big a factor as the ships the quay is accomodating. Both aspects affect the choice of “marine bumpers” used. So it is not surprising to see two different types of fender systems being deployed in the same city, but to accommodate different types of ships. Harbor conditions are also rarely the same. Successful previous local experience must be considered. The best way to figure out what type of port fender is suitable for your berthing structure would be to carefully study your own local marine condition that includes:

Site condition and depth
Local temperature range & weather
Wind velocity
Direction of ship when berthing
Tidal range & wave height
Berthing structure
Type of ships, along with class, configuration, size
Velocity of ship approaching the quay wall during berthing
Exposure of harbor basins
Available docking assistance

Before diving into this guide, one has to understand that the design criteria differ from one person to another. So this article is aimed to act as jsut a reference for many. For detailed project designing & fender choosing, kindly contact a professional team to design suitable marine fender system

Prior to designing and doing any calculations, one has to prioritise one’s design standard and criteria.

Are there any specific codes and standards that you need to conform to?
Intended useful life of product? Some fenders are longer lasting than others.
Safety factor?
Designated vessels for berthing calculations?
Velocity range?
Costs: From installation fees, to maintenance costs. All has to be thoroughly considered.

Guide:

The law of energy conversation is the basis for all fender design selection. When choosing fenders, it is vital to base calculations and considerations on the largest (heaviest) vessel sizes to be berthed at the wharf. Besides, vessels are getting larger as ship design evolves from time to time. It is important to take into consideration those expected to arrive in the near foreseeable future.

Fender Energy Absorption = Energy Delivered upon impact – Energy absorbed by pier

To understand how much energy absorption is needed, one needs to first determine the energy that will be delivered to the quay wall upon initial impact.

Secondly, one has to then carry out calculation to find out the energy that requires to be absorbed. For linearly elastic structures, the energy is ½ the maximum static load level times amount of deflection. Some allowance should be added. If the structure is very rigid, one can assume no energy absorption from the pier.

Minus the energy amount absorbed by pier and one can determine the fender energy absorption value that is required for a safe berth.

Then, one can choose a suitable fender type and design from a wide range of available marine fenders in the market today: from super cone type, arch type, cylindrical shaped, to floating types like Yokohama fenders and foam fenders. Be sure to select a manufacturer that adheres to PIANC2002 and/or other standards to ensure great quality fender products.

GT Gross Tonnage Total volume of cargo + vessel NT Net Tonnage Total volume of cargo on vessel DPT Displacement Tonnage Total weight of the cargo-filled vessel when vessel is loaded to the draft line DWT DeadWeight Tonnage Weight of cargo + people (including crew) + fuel + food on the vessel LOW Light Weight Vessel weight BW Ballast Weight Weight of the vessel when water is added in the ballast

Types of Berthing Approach:

Side Berthing:

‘Dolphin’ Berthing:

End Berthing:

Lock Entrances:

Ship-to-ship (STS) Approach:

This article only discusses berthing calculations for side berthing. If you have a Ship-to-ship (STS) operation or End Berthing, certain equations may be different. Contact our team for assistance.

Effective Berthing Energy formula for Side Berthing:

This is the most common berthing method for docks. The berthing energy is calculated with the equation:

EB = Berthing energy (kJ, N*m, or lbF*ft)

EB = 0.5 × WD × VB × VB × CM × CE × CC × CS

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WD = Water displacement of the vessel (kg, tons, lbs)

WD = Water displacement of the vessel (kg, tons, lbs). This is the Total Displacement Tonnage(DPT) of the vessel.

VB = Berthing velocity of the vessel at the moment of impact (m/sec, ft/sec)

VB = Berthing velocity of the vessel at the moment of impact (m/sec, ft/sec). Berthing velocity is an important parameter in fender system design. It depends on the size of the vessel, loading condition, port structure, and the difficulty of the approach. The most appropriate method to determine berthing velocity is based on actual previous statistical data. If that is not possible, the most widely used reference would be the Brolsma table, adopted by BSI, PIANC and other standards. However, it is important to keep in mind that the best option is still to base on previous statistical information.

CM = Virtual mass factor

CM = Mass Coefficient/Virtual mass factor: During the sudden stop of movement as a vessel comes into contact with the berth, the mass of water moving with the vessel adds to the energy acting upon the vessel and fender. This situation is referred to as “Added Mass Coefficient” or “Mass Factor”. Weight of water moving that adds to that is called “ Additional Weight” in these berthing studies.

As the vessel is stopped by the fenders, the momentum of the water continues to push against the vessel and this actually increases its overall mass, so CM has to be calculated. There are 2 ways to calculate its mass coefficient.

The most commonly used “Vasco Costa (1964) method”:

Formula B:

C E = Eccentricity factor

C E = Eccentricity factor. The reaction force will give a rotational movement at the moment of contact. This will dissipate an amount of the energy. There are 2 formulas to determine the eccentricity factor:

= Eccentricity factor. The reaction force will give a rotational movement at the moment of contact. This will dissipate an amount of the energy. There are 2 formulas to determine the eccentricity factor:

You require these info:

Distance between center of mass (vessel’s) to the point of impact (R)
Velocity vector angle (v)
Radius of gyration (K)
Berthing angle(α)

NOTE:

K: Radius of vessel rotation (usually 1/4 of the vessel’s length)

R: Distance of the line paralleled to wharf from the vessel’s Center of Gravity (CG) to the contact point. Common cases are 1/4 to 1/5 of vessel’s length.

CB: Block Coefficient, which is related to the hull shape.

WD: Water displacement of the berthing ship(kg, Tons, lbs)

: Sea Water density(1.025 Tons/m3)

LBP: Length between perpendiculars. Please see sketch below for better explanation:

x: Distance from bow to point of impact

B: Beam(m, ft)

Formula (i): The more detailed calculation to find out C E :

If the beam, length and draft information are not available, this table can be used to estimate:

Typical Block Coefficients(CB) Type of Vessel CB
BS 6349 CB
PIANC 2002 Tankers 0.72~0.85 0.85 Bullk Carriers 0.72~0.85 0.72~0.85 Container Ships 0.65~0.75 0.60~0.80 General Cargo 0.60~0.75 0.72~0.85 RoRo Vessels 0.65~0.70 0.70~0.80 Ferries 0.50~0.65 0.55~0.65

Formula (ii): The more simple formula to find out C E :

This method can lead to a serious underestimation of Berthing Energy when the berthing angle (α) is greater than 10° and/or the point of impact is aft of quarter-point(x > LBP/4).

To verify your calculations, one can check the calculated C E values to ensure they generally fall within the following limits:

For more information, please visit kenuo.

Quarter-Point Berthing x = L/4 Ce = 0.5 Third-Point Berthing x = L/3 Ce = 0.6 ~ 0.8 Mid-Vessel Berthing x = L/2 Ce = 1

CC = Berth configuration factor

CC = Berth configuration factor. This is the part of berthing energy absorbed by the cushion effect of water between the approaching vessel and the quay wall. The smaller the draft (D) of the vessel is, or the larger the under keel clearance(KC), the more trapped water can escape under the vessel, and would give a higher CC value. Also, if the berthing angle of the vessel is greater than 5°, we can consider CC = 1. Different dock types would have different variations.

= Berth configuration factor. This is the part of berthing energy absorbed by the cushion effect of water between the approaching vessel and the quay wall. The smaller the draft () of the vessel is, or the larger the under keel clearance(), the more trapped water can escape under the vessel, and would give a highervalue. Also, if the berthing angle of the vessel is greater than 5°, we can consider= 1. Different dock types would have different variations.

Closed Dock case
A closed Dock would be a wharf, where you have a concrete wall going directly to the sea ground. In this case the quay wall will push back all the water that is being moved by the vessel. This creates a resistance factor that can be calculated as follows:

If KC ≤ D / 2, CC ≈ 0.8

If KC > D / 2, CC ≈ 0.9

Open / Semi-Closed Dock case
A semi-closed dock is when water can flow underneath the dock, but the depth changes below the dock. Open dock is usually a dock with piles underneath and the water can flow freely underneath the dock. In such case we can assume the following value of 1.

CC ≈ 1

CS = Softness factor

CS = Softness factor. This is the energy absorbed by the deformation of the vessel’s hull and fender. Usually, we can assume CS ≈ 0.9.

When selecting the size of fenders, it should be selected base on the consideration of kinetic energy of contact between two vessels or between vessel and berthing facilities may be absorbed by a single fender. The following tables are given for determining the energy absorption depends on approaching velocities for various ships.

Energy absorption for ship-to-Jetty (for reference only)

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Energy Absorption of Oil Tankers at ¼ point Berthing (kJ)

Table (i) Energy Absorption of Oil Tankers at ¼ point Berthing (kJ)

DWT Assumed

Weight(t)

Approaching velocity (m/s) 0.10 0.12 0.15 0.18 0.20 0.25 0.30 0.40 300 668 1.7 2.5 3.8 5.5 6.8 11.0 15.0 27.0 500 1,091 2.8 4.0 6.3 9.0 11.0 17.0 25.0 45.0 700 1,558 4.0 5.7 8.9 13.0 16.0 25.0 36.0 64.0 1,000 2,228 5.7 8.2 14.0 18.0 23.0 36.0 51.0 91.0 2,000 4,294 11.0 16.0 28.0 35.0 44.0 68.0 99.0 175 3,000 6,470 17.0 24.0 37.0 53.0 66.0 103 149 264 4,000 8,363 21.0 31.0 54.0 69.0 85.0 133 192 341 5,000 10,594 27.0 39.0 61.0 88.0 108 169 243 432 6,000 12,184 31.0 45.0 70.0 101 124 194 280 497 7,000 14,084 36.0 52.0 81.0 116 144 225 323 575 8,000 16,066 41.0 59.0 92.0 133 164 256 369 656 10,000 20,373 52.0 75.0 117 168 208 325 468 832 12,000 23,851 61.0 88.0 137 197 243 380 548 974 15,000 29,493 75.0 108 169 244 301 470 677 1200 17,000 33,056 84.0 121 190 273 337 527 759 1350 20,000 38,623 99.0 142 222 319 394 616 887 1580 25,000 45,946 117.0 169 264 380 469 733 1050 1880 30,000 56,093 143.0 206 322 464 572 894 1290 2290 35,000 63,084 161.0 232 362 521 644 1010 1450 2570 40,000 72,771 186.0 267 418 601 743 1160 1670 2970 45,000 77,986 199.0 286 448 645 796 1240 1790 3180 50,000 89,818 229.0 330 516 742 917 1430 2060 3670 60,000 104,300 266.0 383 599 862 1060 1660 2390 4260 65,000 114,637 292.0 421 658 948 1170 1830 2630 4680 70,000 122,108 312.0 449 701 1010 1250 1950 2800 4980 80,000 136,972 349.0 503 786 1130 1400 2180 3140 5590 85,000 143,359 366.0 527 823 1180 1460 2290 3290 5850 100,000 166,004 423.0 610 953 1370 1690 2650 3810 6780 120,000 200,083 510.0 735 1150 1650 2040 3190 4590 8170 150,000 251,896 643.0 925 1450 2080 2570 4020 5780 10280 200,000 327,735 836.0 1200 1880 2710 3340 5230 7520 13380 250,000 401,268 1020 1470 2300 3320 4090 6400 9210 16380 330,000 548,670 1400 2020 3150 4530 5600 8750 12600 22390 370,000 627,016 1600 2300 3600 5180 6400 10000 14400 25590 480,000 795,540 2030 2920 4570 6580 8120 12680 18260 32470

Energy Absorption of Ore Carriers at ¼ point Berthing (kJ)

Table (ii) Energy Absorption of Ore Carriers at ¼ point Berthing (kJ)

DWT Assumed

Weight(t)

Approaching velocity (m/s) 0.10 0.12 0.15 0.18 0.20 0.25 0.30 0.40 1,000 2,360 6.0 8.7 14.0 20.0 24.0 38.0 54.0 96.0 2,000 4,429 11.0 16.0 25.0 37.0 45.0 71.0 102 181 3,000 6,453 16.0 24.0 37.0 53.0 66.0 103 148 263 4,000 8,341 21.0 31.0 48.0 69.0 85.0 133 192 340 5,000 10,301 26.0 38.0 59.0 85.0 105 164 237 420 6,000 12,574 32.0 46.0 72.0 104 128 200 289 513 8,000 16,332 42.0 60.0 94.0 135 167 260 375 667 10,000 20,516 52.0 75.0 118 170 209 327 471 837 12,000 24,345 62.0 89.0 140 201 248 388 559 994 15,000 29,572 75.0 109 170 244 302 471 679 1210 20,000 38,068 97.0 140 219 315 388 607 874 1550 25,000 45,116 115 166 259 373 460 719 1040 1840 30,000 54,874 140 202 315 454 560 875 1260 2240 40,000 71,143 181 261 408 588 726 1130 1630 2900 50,000 86,432 220 318 496 714 882 1380 1980 3530 60,000 101,383 259 372 582 838 1030 1620 2330 4140 70,000 119,062 304 437 683 984 1210 1900 2730 4860 80,000 132,125 337 485 758 1090 1350 2110 3030 5390 90,000 149,528 381 549 858 1240 1530 2380 3430 6100 100,000 175,960 449 646 1010 1450 1800 2810 4040 7180 150,000 256,357 654 942 1470 2120 2620 4090 5890 10460 200,000 319,149 814 1170 1830 2640 3260 5090 7330 13030 270,000 426,459 1090 1570 2450 3520 4350 6800 9790 17410

Energy Absorption of Freighters at ¼ point Berthing (kJ)

Table (iii) Energy Absorption of Freighters at ¼ point Berthing (kJ)

DWT Assumed

Weight(t)

Approaching velocity (m/s) 0.10 0.12 0.15 0.18 0.20 0.25 0.30 0.40 700 1,585 4.0 5.8 9.1 13.0 16.0 25.0 36.0 65.0 1,000 2,237 5.7 8.2 13.0 18.0 23.0 36.0 51.0 91.0 2,000 4,357 11.0 16.0 25.0 36.0 44.0 69.0 100 178 3,000 6,606 17.0 24.0 38.0 55.0 67.0 105 152 270 4,000 8,712 22.0 32.0 50.0 72.0 89.0 139 200 356 5,000 10,795 28.0 40.0 62.0 89.0 110 172 248 441 6,000 13,515 34.0 50.0 78.0 112 138 215 310 552 7,000 15,557 40.0 55.0 89.0 129 159 248 357 635 8,000 17,703 45.0 65.0 102 146 181 282 406 723 9,000 19,625 50.0 72.0 113 162 200 313 451 801 10,000 21,630 55.0 79.0 124 179 221 345 497 883 12,000 26,052 66.0 96.0 150 215 266 415 598 1060 15,000 31,477 80.0 116 181 260 321 502 723 1280 17,000 36,784 94.0 135 211 304 375 586 845 1500 20,000 41,748 107 153 240 345 426 666 959 1700 30,000 60,483 154 222 347 500 617 964 1390 2470 40,000 79,393 203 292 456 656 810 1270 1820 3240 50,000 98,306 251 361 564 813 1000 1570 2260 4010

Energy Absorption of Passenger Ships at ¼ point Berthing (kJ)

Table (iv) Energy Absorption of Passenger Ships at ¼ point Berthing (kJ)

DWT Assumed

Weight(t)

Approaching velocity (m/s) 0.10 0.12 0.15 0.18 0.20 0.25 0.30 0.40 500 845 2.2 3.1 4.9 7.0 8.6 13.0 19.0 34.0 1,000 1,709 4.3 6.2 9.8 14.0 17.0 27.0 39.0 70.0 2,000 3,500 8.9 13.0 20.0 29.0 36.0 56.0 80.0 143 3,000 5,282 13.0 19.0 30.0 44.0 54.0 84.0 121 216 4,000 7,105 18.0 26.0 41.0 59.0 73.0 113 163 290 5,000 8,912 23.0 33.0 51.0 74.0 91.0 142 205 364 6,000 12,083 31.0 44.0 69.0 100 123 193 277 493 7,000 13,873 35.0 51.0 80.0 115 142 221 319 566 8,000 15,346 39.0 56.0 88.0 127 157 245 352 626 9,000 16,986 43.0 62.0 97.0 140 173 271 390 693 10,000 18,661 48.0 69.0 107 154 190 298 428 762 15,000 26,283 67.0 97.0 151 217 268 419 603 1070 20,000 33,423 85.0 123 192 276 341 533 767 1360 30,000 47,952 122 176 275 396 489 765 1100 1960 50,000 71,744 183 264 412 593 732 1140 1650 2930 80,000 111,956 286 411 643 925 1140 1790 2570 4570

Energy Absorption of Barges or Lighters at ¼ point Berthing (kJ)

Table (v) Energy Absorption of Barges or Lighters at ¼ point Berthing (kJ)

G/T Assuming Weight ( t ) Approaching velocity ( m/s ) 0.20 0.25 0.30 0.35 0.40 0.50 0.60 50 85 0.9 1.4 2.0 2.7 3.5 5.4 7.8 100 161 1.6 2.6 3.7 5.0 6.6 11.0 15.0 150 241 2.5 3.8 5.5 7.5 9.8 15.0 22.0 200 319 3.3 5.1 7.3 10.0 13/0 20.0 29.0 300 496 5.1 7.9 11.0 15.0 20.0 32.0 46.0

Energy Absorption of Container Ships at ¼ point Berthing (kJ)

Table (vi) Energy Absorption of Container Ships at ¼ point Berthing (kJ)

G/T DWT Assumed Weight (t) Approaching velocity ( m/s ) 0.10 0.15 0.20 0.25 0.30 0.40 8,000 12,000 26,752 68 154 273 427 614 1090 9,000 14,000 33,567 86 193 343 535 771 1370 16,626 16,004 38,172 97 219 390 609 876 1560 21,057 20,400 48,995 125 281 500 781 1120 2000 23,600 23,650 55,560 142 319 567 886 1280 2270 30,992 27,203 64,264 164 369 656 1020 1480 2620 38,826 33,287 79,599 203 457 812 1270 1830 3250 41,127 27,752 67,121 171 385 685 1070 1540 2740 51,500 28,900 68,664 175 394 701 1090 1590 2800 57,000 49,700 105,199 268 604 1070 1680 2420 4290

Energy Absorption of Fishing Vessels at ¼ point Berthing (kJ)

Table (vii) Energy Absorption of Fishing Vessels at ¼ point Berthing (kJ)

Type G/T Assumed Weight ( t ) Approaching velocity ( m/s ) 0.20 0.25 0.30 0.35 0.40 0.50 0.60 Whale

factory

ship

10,000

17,000

20,000

34,058

53,494

66,217

348

546

676

543

853

1060

782

1230

1520

1060

1670

2070

1390

2180

2700

2170

3410

4220

3130

4910

6080

Whale ship 400

800

1,000

1,797

3,263

3,950

18.0

33.0

40.0

29.0

52.0

63.0

41.0

75.0

91.0

56.0

102

123

73.0

133

161

115

208

252

165

300

363

Trawler

Vessel

400

800

1,000

2,000

3,000

2,297

3,693

4,458

7,173

9,863

23.0

38.0

45.0

73.0

101

37.0

59.0

71.0

114

157

53.0

85.0

102

165

226

72.0

115

139

224

308

94.0

151

182

293

403

146

236

284

457

629

211

339

409

659

906

Skipjack

vessel

100

200

126

202

390

779

1.3

2.1

4.0

7.9

2.0

3.2

6.2

12.0

2.9

4.6

9.0

18.0

3.9

6.3

12.0

24.0

5.1

8.2

16.0

32.0

8.0

12.9

25.0

50.0

12.0

19.0

36.0

72.0

Mackerel

vessel

100

112

266

525

1.1

2.7

5.4

1.8

4.2

8.4

2.6

6.1

12.0

3.5

8.3

16.0

4.6

11.0

21.0

7.1

17.0

33.0

10.0

24.0

48.0

Tuna

long-liner

150

200

400

590

780

1,681

6.0

8.0

17.0

9.4

12.0

27.0

14.0

18.0

39.0

18.0

24.0

53.0

24.0

32.0

69.0

38.0

50.0

107

54.0

72.0

154

Round

Haul netter

100

191

377

0.8

1.9

3.8

1.1

3.0

6.0

1.7

4.4

8.7

2.3

6.0

12.0

3.1

7.8

15.0

4.8

12.0

24.0

6.9

18.0

35.0

Towing

net vessel

100

300

500

204

361

1,138

1,838

1.0

2.1

3.7

12.0

19.0

1.6

3.3

5.8

18.0

29.0

2.3

4.7

8.3

26.0

42.0

3.1

6.4

11.0

36.0

57.0

4.0

8.3

15.0

46.0

75.0

6.3

13.0

23.0

73.0

117

9.1

19.0

33.0

105

169

General

fishing

vessel

100

150

195

350

500

0.8

2.0

3.6

5.1

1.2

3.1

5.6

8.0

1.8

4.5

8.0

11.0

2.4

6.1

11.0

16.0

3.1

8.0

14.0

20.0

4.9

12.0

22.0

32.0

7.1

18.0

32.0

46.0

Energy Absorption of Ferry Boats at ¼ point Berthing (kJ)

Table (viii) Energy Absorption of Ferry Boats at ¼ point Berthing (KJ)

G/T Assumed Weight (t) Approaching velocity ( m/s ) 0.20 0.25 0.30 0.35 0.40 0.50 0.60 50 124 1.3 2.0 2.8 3.8 5.1 7.9 11.0 100 246 2.5 3.9 5.6 7.7 10.0 16.0 23.0 200 430 4.4 6.9 9.9 13.0 18.0 27.0 39.0 300 664 6.8 11.0 15.0 21.0 27.0 42.0 61.0 500 1,012 10.0 16.0 23.0 32.0 41.0 65.0 93.0 1,000 1,796 18.0 29.0 41.0 56.0 73.0 115 165

After having the effective berthing energy value, one can then choose the suitable type of marine fender design / system. Performance has to be compared in order to design the most suitable system. For example, deflection curve, energy absorption and reaction of a cylindrical fender is different from an arch-shaped fender. One has to compare alternatives and then determine which one is more suitable for use. This is when previous records of fender systems deployed play a big role in advising the suitability for the particular marine condition.

Energy Absorption:

The obvious factor in designing a fender system. This value has to be higher than the effective impacting energy of ships.

Reaction Force:

This value has to be less than the vessel’s allowable reaction force to prevent damage to the hull surface (or in extreme cases, the structure as a whole).

Environmental Condition:

It is vital to determine how harsh the working conditions for the fenders will be. One will have to choose accordingly its durability to handle strong waves, winds, or extreme weather. If the working condition is very demanding, it is possible you will have to replace the fenders quite often.

Berthing Angle:

A fender that can accept a situation’s angular compression has to be considered. An angular compression does not result in a simplistic linear energy absorption curve so this has to be a main priority when choosing a rubber fender design.

Fender (or Panel) Surface Pressure

Surface pressure value of fender has to be less than the vessel’s allowable hull surface pressure. For certain fenders like super cell type and cone type, they most commonly come with frontal frames/panels that distributes the pressure. So to decrease surface pressure value, one can increase the surface area of the panel.

Trustworthy Supplier

Choose a quality rubber fender manufacturer. Some people always assume that prices and quality can not come together but it is possible in today’s manufacturing innovation and high tech automation processes. Manufacturers are spending less time doing low importance repetitive work and focusing on Quality Control (QC) processes assisted by great process flow.

Fender Arrangement and Spacing In Between

After choosing what type and size of fenders to use, the next step is determining the number of fenders. To do that, one has to take into consideration fender spacing. The spacing between fenders play a very important role in determining a fender system’s success. Should one opt to save cost and have too great a spacing between fenders, accidents might happen where vessel berthing might hit the dock structure. British Standards recommend that for a continuous quay, the installation pitch is recommended to be less than 15% of the vessel.

The maximum spacing between fenders (S) can be calculated with this equation:

Maximum Spacing between Fenders,

Note:

RB = Bow Radius of Board Side of Vessel (m, ft).

If radius info is not available, one can use this estimation to find out the info:

PU = Uncompressed Height of Fender incl. Panel (m, ft)

C = Fender Height in Rated Compression.

= Fender Deflection (m, ft)

For arrangement consideration especially distance between fenders, it is important to keep in mind that one should not only have the largest vessel type in mind. As smaller vessel might face problems berthing if one only design for large vessels.

This shows an improper design as smaller vessels berthing at the dock would crash into the wall:

This might be a possible solution for this situation:

Of course, aside from fender spacing, all aspects from angular compression energy absorption to hull pressure per unit needs to be considered as well. If a particular type does not satisfy requirement, one should consider other options.

Choosing a Suitable Frontal Panel

To choose a suitable panel, one has to consider hull pressures allowed for the berthing vessels. The following table shows a rough guide of allowable hull pressures of certain popular type of vessels. (just for reference):

Allowable Hull Pressures

Vessel Type Hull Pressure KN/m2 Tankers 150~250 ULCC & VLCC(Coastal Tankers) 250~350 Product & Chemical Tankers 300~400 Bulk Carriers 150~250 Post-Panamax Container Ships 200~300 Panamax Container Ships 300~400 Sub-Panamax Container Ships 400~500 General Cargo 300~600 Gas Carriers 100~200

Calculation:

P: Hull Pressure(N/m2, psi)
ΣR: Combined Reaction Forces of all rubber fenders
A1: Valid Panel Width excluding lead-in chamfers(m)
B1: Valid Panel Height excluding lead-in chamfers(m)
PP: Permissible hull pressure(N/m2, psi)

Another option: WITHOUT frontal frames.

Rubber fenders like arch fenders and cylindrical fenders do not come with frontal frames. The fender body itself comes into contact with the vessel’s hull during berthing. One has to carefully consider the hull pressure exerted.

Selecting the Chains

A common fender system with frontal frame usually involve a Weight Chain, Tension Chain and Shear Chain.

Chain Function Weight Chain Normally installed at a static angle of 15 – 25° to the vertical, its main function is to sustain the weight of the entire frame panel structure Tension Chain Protect the fender against damage when compressed Shear Chain Fixed at 20 – 30° to the horizontal, shear chain exists to avoid damage while the fender is in shear deformation

Some installation do not involve shear chain, but a fender system would definitely be more resistant to shear damage with them.

h1: Static offset between brackets(m, ft)
Ф2: Dynamic Angle of Chain(°)
h2: Dynamic offset between brackets at F(m, ft)
D: Fender compression(m, ft)
R: Reaction Force of rubber units behind the frontal panel(N, Lbs)
W: Weight of the panel face(N, Lbs)
FL: Safe working Load of chain(N, Lbs)
L: Bearing length of chain(m, ft)
n: number of chains acting together
μ: Friction coefficient of face pad. Usually equals 0.15 for UHMW-PE facings.
FM: Minimum Breaking Load(N, Lbs)
FS: Safety Factor(2~3 times)

Tips on choosing suitable chains:

Chain sizes should be as exact as possible. An overly tight chain or an overly loose chain would fail the system.
Safety factor has to be considered. At least 2 to 3 times of the work load.
Open link type is more preferable.

Installation tips:

One must consider installation during the early design process and not after choosing the fenders and finalising the purchase as the maintenance, wear allowances and protective nets/coatings will affect their useful life.
Chains should not be installed twisted. They might break due to a reduction in load capacity.

A small tip after preliminary choosing the type of fenders to use, make sure you do not make these 5 top mistakes that causes structural failures for marine fenders.

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