The International Load Line Convention of 1966

The International Load Line Convention of 1966 (ICLL 66) has been recognized by nearly every seafaring nation. The first international freeboard regulations took effect in 1904. They were modelled closely on the freeboard restrictions introduced in Great Britain in 1890 on the initiative of the British politician and social reformer Samuel Plimsoll (1824-1898). The idea of using a freeboard index line to mark this was also based on the British pattern. One particularly heavy area of responsibility was thus lifted from the shoulders of the captains. Problems associated with freeboard appeared with the emergence of steamships. Sailing vessels normally had greater freeboard to enable them to achieve the highest possible speed at greater heeling angles under sail pressure. All freeboard regulations so far have been largely based on statistically evaluated empirical data. It is difficult to demonstrate numerically to what degree the chances of the ship surviving depend on the freeboard. Hence there were widely contrasting opinions when the freeboard regulations were introduced.

The ICLL 66 is structured as follows:

Chapter I—General

All the definitions of terms and concepts associated with freeboard and the freeboard calculation, and a description of how the freeboard is marked. Chapter II—Conditions for the assignment of freeboard Structural requirements under which freeboard is assigned. Chapter III—Freeboards

The freeboard tables and the regulations for correcting the basis values given by the tables. This is the most complicated and also central part of the freeboard regulations. Chapter IV—Special regulations

For ships which are to be assigned a timber freeboard. Like Chapter II, this concerns structural requirements. These special regulations will not be discussed here.

The agreement is valid for cargo ships over 24 m in length and for non-cargo-carrying vessels, e.g. floating dredgers. An increased freeboard may be required for tugs and sailing craft. Vessels made of wood or other material or which have constructional characteristics which render an application of the regulations unreasonable or infeasible are subject to the discretion of the national authorities. The agreement states that fishing vessels need only be treated if engaged in international fish transportation or if an application for freeboard is made. Warships are not subject to the freeboard regulations.

Chapter I—General Definitions (Reg. 3)

Length—The ship's length L is the maximum of Lpp and 96% Lw, both measured at 85% of the depth.

Perpendiculars—In the freeboard regulation, the forward perpendicular is located at the point of intersection of the waterline at 85% depth with the forward edge of the stem. The aft perpendicular is established using the rudder axis. This somewhat anomalous approach due to the forward perpendicular makes sense, since the draught (to which usually the length is related) is not available as an input value. The draught is only known after the freeboard calculation is finished.

Chapter II—Structural requirements (Regs 10-26)

The requirement for the assignment of freeboard is that the ship is sufficiently safe and has adequate strength. The requirements in detail are:

1. The national ship safety regulations must be adhered to.

2. The highest class of a recognized classification society (or the equivalent strength) must be present.

3. The particular structural requirements of the freeboard regulation must be satisfied. Particular attention should be given to: external doors, sill heights and ventilator heights, hatches and openings of every kind plus their sealing arrangements on decks and sides, e.g. engine room openings, side windows, scuppers, freeing ports and pipe outlets.

Chapter III—Freeboards

Reg. 27 of the freeboard regulations distinguishes two groups of ships:

Type A: all vessels transporting exclusively bulk liquids (tankers). Type B: all other vessels.

Freeboard calculation procedure

The freeboard is determined as follows:

1. Determine base freeboard F0(L) according to Table 1.5.

2. Correct F0 for CB,0.85D D 0.68, D D L/15, sheer D standard sheer, superstructures and bow height < minimum required bow height.

The corrections are:

a. Correction for ships with 24 m < L < 100 m (Reg. 29):

E is the ' effective length of superstructure'. A superstructure is a decked structure on the freeboard deck, extending from side to side of the ship or with the side plating not being inboard of the shell plating more than 4% B. A raised quarterdeck is regarded as superstructure (Reg. 3(10)). Superstructures which are not enclosed have no effective length. An enclosed superstructure is a superstructure with enclosing bulkheads of efficient construction, weathertight access openings in these bulkheads of sufficient strength (Reg. 12), all other access openings with efficient weathertight means of closing. Bridge or poop can only be regarded as enclosed superstructures if access to the machinery and other working spaces is provided inside these superstructures by alternative means which are available at all times when bulkhead openings are closed. There are special regulations for trunks (Reg. 36) which are not covered here. E d S for an enclosed superstructure of standard height. S is the superstructure's length within L. If the superstructure is set in from the sides of the ship, E is modified by a factor b/Bs, where b is the superstructure width and Bs the ship width, both at the middle of the superstructure length (Reg. 35). For superstructures ending in curved bulkheads, S is specially defined by Reg. 34. If the superstructure height dv is less than standard height ds (Table 1.5a), E is modified by a factor dv/ds. The effective length of a raised quarter deck (if fitted with an intact front bulkead) is its length up to a maximum of 0.6L. Otherwise the raised quarterdeck is treated as a poop of less than standard height.

Table 1.5 Freeboard tables; intermediate lengths are determined by linear interpolation. The freeboard of ships longer than 365 m is fixed by the administration

A; tankers (Rule 28)

Table 1.5 Freeboard tables; intermediate lengths are determined by linear interpolation. The freeboard of ships longer than 365 m is fixed by the administration

A; tankers (Rule 28)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

24

200

80

841

136

1736

192

2530

248

3000

304

3278

26

217

82

869

138

1770

194

2552

250

3012

306

3285

28

233

84

897

140

1803

196

2572

252

3024

308

3292

30

250

86

926

142

1837

198

2592

254

3036

310

3298

32

267

88

955

144

1870

200

2612

256

3048

312

3305

34

283

90

984

146

1903

202

2632

258

3060

314

3312

36

300

92

1014

148

1935

204

2650

260

3072

316

3318

38

316

94

1044

150

1968

206

2669

262

3084

318

3325

40

334

96

1074

152

2000

208

2687

264

3095

320

3331

42

354

98

1105

154

2032

210

2705

266

3106

322

3337

44

374

100

1135

156

2064

212

2723

268

3117

324

3342

46

396

102

1166

158

2096

214

2741

270

3128

326

3347

48

420

104

1196

160

2126

216

2758

272

3138

328

3353

50

443

106

1228

162

2155

218

2775

274

3148

330

3358

52

467

108

1260

164

2184

220

2792

276

3158

332

3363

54

490

110

1293

166

2212

222

2809

278

3167

334

3368

56

516

112

1326

168

2240

224

2825

280

3176

336

3373

58

544

114

1359

170

2268

226

2841

282

3185

338

3378

60

573

116

1392

172

2294

228

2857

284

3194

340

3382

62

600

118

1426

174

2320

230

2872

286

3202

342

3387

64

626

120

1459

176

2345

232

2888

288

3211

344

3392

66

653

122

1494

178

2369

234

2903

290

3220

346

3396

68

680

124

1528

180

2393

236

2918

292

3228

348

3401

70

706

126

1563

182

2416

238

2932

294

3237

350

3406

72

733

128

1598

184

2440

240

2946

296

3246

74

760

130

1632

186

2463

242

2959

298

3254

76

786

132

1667

188

2486

244

2973

300

3262

78

814

134

1702

190

2508

246

2986

302

3270

B (Rule 28)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

l (m)

F (mm)

24

200

80

887

136

2021

192

3134

248

3992

304

4676

26

217

82

923

138

2065

194

3167

250

4018

306

4695

28

233

84

960

140

2109

196

3202

252

4045

308

4714

30

250

86

996

142

2151

198

3235

254

4072

310

4736

32

267

88

1034

144

2190

200

3264

256

4098

312

4757

34

283

90

1075

146

2229

202

3296

258

4125

314

4779

36

300

92

1116

148

2271

204

3330

260

4152

316

4801

38

316

94

1154

150

2315

206

3363

262

4177

318

4823

40

334

96

1190

152

2354

208

3397

264

4201

320

4844

42

354

98

1229

154

2396

210

3430

266

4227

322

4866

44

374

100

1271

156

2440

212

3460

268

4252

324

4890

46

396

102

1315

158

2480

214

3490

270

3128

326

4909

48

420

104

1359

160

2520

216

3520

272

4302

328

4931

50

443

106

1401

162

2560

218

3554

274

4327

330

4955

52

467

108

1440

164

2600

220

3586

276

4350

332

4975

54

490

110

1479

166

2640

222

3615

278

4373

334

4995

56

516

112

1521

168

2680

224

3645

280

4397

336

5015

58

544

114

1565

170

2716

226

3675

282

4420

338

5035

60

573

116

1609

172

2754

228

3705

284

4443

340

5055

62

601

118

1651

174

2795

230

3735

286

4467

342

5075

64

629

120

1690

176

2835

232

3765

288

4490

344

5097

66

659

122

1729

178

2875

234

3795

290

4513

346

5119

68

689

124

1771

180

2919

236

3821

292

4537

348

5140

70

721

126

1815

182

2952

238

3849

294

4560

350

5160

72

754

128

1859

184

2988

240

3880

296

4583

74

784

130

1901

186

3025

242

3906

298

4607

76

816

132

1940

188

3062

244

3934

300

4630

78

850

134

1979

190

3098

246

3965

302

4654

The ICLL 66 generally uses the block coefficient at 0.85D, denoted here by CB,0.85D.

The depth D is defined in ICLL 66 in Reg. 3(6). It is usually equal to the usual depth plus thickness of the freeboard deck stringer plate. The standard D is L/15. R = L/0.48 for L< 120 m and R = 250 for L > 120 m. For D < L/15 the correction is only applicable for ships with an enclosed superstructure covering at least 0.6L amidships, with a complete trunk, or combination of detached enclosed superstructures and trunks which extend all fore and aft. Where the height of superstructure or trunk is less than standard height, the correction is multiplied by the ratio of actual to standard height, Table 1.5a.

Table 1.5a Standard height [m] of superstructure

L [m]

Raised quarterdeck

All other superstructures

<30

0.90

1.80

75

1.20

1.80

>125

1.80

2.30

The standard heights at intermediate ship lengths L are obtained by linear interpolation.

The standard heights at intermediate ship lengths L are obtained by linear interpolation.

d. Correction for position of deck line (Reg. 32):

The difference (actual depth to the upper edge of the deck line minus D) is added to the freeboard. This applies to ships with rounded transitions between side and deck. Such constructions are rarely found in modern ships.

e. Correction for superstructures and trunks (Reg. 37):

350 + 8.3415(L - 24) 24 m < L< 85 m aF [mm]= — 860 + 5.6756(L - 85) 85 m < L< 122 m 1070 122 m < L

This correction is multiplied by a factor depending on E (see item a) following Table 1.5b. For ships of Type B:

For Ebridge < 0.2L, linear interpolation between values of lines I and II.

For Eforecastle < 0.4L, line II applies.

For Eforecastle < 0.07L, the factor in Table 1.5b is reduced by 0.05(0.07L — f)/(0.07L), where f is the effective length of the forecastle.

Table 1.5b Correction Factor for superstructures

E/L =

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Type A

0

0.07

0.14

0.21

0.31

0.41

0.52

0.63

0.753

0.877

1

Type B with

I without detached bridge

0

0.05

0.10

0.15

0.235

0.32

0.46

0.63

0.753

0.877

1

forecastle

II with detached bridge

0

0.063

0.127

0.19

0.275

0.36

0.46

0.63

0.753

0.877

1

Values for intermediate lengths E are obtained by linear interpolation.

Values for intermediate lengths E are obtained by linear interpolation.

f. Correction for sheer (Reg. 38):

The standard sheer is given by Table 1.5c. The areas under the aft and forward halves of the sheer curve are:

48 3

Table 1.5c Standard sheer profile [mm]

Aft Perp. (A.P.) 1/6 L from A.P. 1/3 L from A.P. Amidships

Amidships 1/3 L from F.P. 1/6 L from F.P. Forward Perp. (F.P.)

yi = 25 § + 10 y 2 = 11.1 § + 10 y3 = 2.8 § + 10

The 'sheer height' M is defined as the height of a rectangle of the same area: M = (Aa + AF)/L. The freeboard is corrected as:

For superstructures exceeding the standard height given in Table 1.5a, an ideal sheer profile can be used:

SA is the length of the superstructure in the aft half, SF in the fore half. y is here the difference between actual and standard height of superstructure.

This equivalent area is especially relevant to modern ships which are usually built without sheer, but with superstructures. Reg. 38 contains many more special regulations for ships with sheer which are usually not applicable to modern cargoships and not covered here.

g. Correction for minimum bow height (Reg. 39):

The local freeboard at forward perpendicular (including design trim) must be at least:

76.16L(1 - 0.002L)/(max(0.68, CB,o.85D) C 0.68) FFP,min [mm] = for L < 250 m

If this bow height is obtained by sheer, the sheer must extend for at least 15% L abaft F.P. If the bow height is obtained by a superstructure, the superstructure must extend at least 7% L abaft F.P. For L < 100 m, the superstructure must be enclosed.

h. The freeboard must be at least 50 mm. For ships with non-weathertight hatches the minimum freeboard is 150 mm.

The result is the Summer freeboard. This provides the basis for the construction draught and is regarded as the standard freeboard. It is the freeboard meant when using the term on its own. The other freeboard values are derived from the Summer freeboard (Reg. 40):

'Winter', 'Winter-North Atlantic', 'Tropics', 'Freshwater' and 'Freshwater Tropics'.

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