Container Securing System for ships

CARGO SECURING MANUAL
By Capt. Pawanexh Kohli

This Manual is in Accordance with Resolution A.489(XII),
the Recommendation on the Safe Stowage and Securing of
Cargo Units and other Entities in Ship's, as adopted by the
International Maritime Organization (IMO).

M.V. ---------------
of Liberia.

COMPANY
(Ship and Company Name and other selected data removed by Author)

DNV APPROVED MANUAL
VESSEL DNV + 1A1, + MV, + KMC, EO, corr

THIS DOCUMENT AUTHORED BY CAPT. PAWANEXH KOHLI IN 1995 WHILE
MASTER OF THE REFERENCED SHIP. THE DOCUMENT HAS REMAINED
PROPRIETERY TO CAPT. KOHLI THOUGH BROUGHT INTO OFFICIAL USE.

FOCUS TOPIC: CONTAINER LASHING ON A CARGO SHIP

THIS MANUAL IS DEDICATED TO ALL THOSE WHO SAILED THE LOVELY KSECS.

INTRODUCTION

Extent of this Manual:

To specify arrangements and securing gear provided on board the M.V. ------------- for the correct application to and
the securing of cargo units, based on forces that may arise during adverse weather conditions.
To ensure, for the safety of ship and protection of cargo and personnel, that securing gear is used as specified.
To provide information on the safe working load of any specific item of cargo securing gear provided.
To provide information on the maintenance of such cargo securing gear.
To provide a reference/instruction guide to the vessel's crew.

The ------------- is a Reefer Cargo vessel Designed to carry refrigerated Cargo and a limited number of containers. The
vessel is owned and operated by -------------- (and/or subsidiaries). The Vessel carries reefer fruit cargo in loose boxes or in
pallets. This Manual will discuss securing arrangements and equipment for unitized cargo (palletized cargo and containers
only).

This manual is arranged in the following chapters:

i ) This Introduction and Vessel's Particulars.

Chapter 1. Location and details of fixed securing arrangements.
Chapter 2. Location and stowage of portable securing gear.
Chapter 3. Details of portable securing gear, inventory of items and their strength.
Chapter 4. Correct application of portable securing gear.
Chapter 5. An indication of the forces expected to act on cargo units.

Vessel Particulars:

Name: ------------- Type: Refrigerated Cargo Ship
Keel Laid: Mar 1989 Delivered: Dec 1989
Length Overall: 159.656 meters Breadth (mld): 23.510 meters
Depth (mld): 14.97 meters Displacement: 19302 tons
Block Coefficient: 0.5780 Class: DNV +1A1, +MV, +KMC+, EO
GRT: 10749 NRT: 6841
Summer Draft: 9.957 meters Freeboard: 3.350 meters

The vessel has four Reefer Cargo Holds, each divided into 4 decks (A, B, C, D).

Container capacity is provided on foc'sle deck, upper deck, hatch tops and in Hold 3. See following Fig. 1. for General
Arrangement for Deck Containers.

This vessel is is provided with side boards in each Cargo hold where required for pallet stow.

The vessel can also carry small cars under deck. The air circulation holes on the deck gratings can be used as lashing points
for the car lashing gear.

Author: Captain Pawanexh Kohli

5D 4D 3D 2D 1D BAY NO.: DECK

TROPICAL STAR

Drawings by Capt. Kohli

5D 4D 3D 2D 1D
4H 3H 2H 1H BAY NO.: HATCH

M.V. -------------
Fig: 1 - Arrangement for Deck stow of Containers

Note: 4D can stow 20 feet containers also.


CHAPTER 1: Location and details of fixed securing arrangements.

Container and fixed fitting Table :

Quantity of Containers Tier Quantity of fixed Fitting
Conic Guides Lashing Eyes
F'csle 4 FEU 1 12 nil
deck

Upper 32 FEU or 2 60 48
Deck 24 FEU + 16 TEU

Hatch 12 FEU 1 32 nil
Cover

Hold 3 12 TEU 4 12 Bottom Lock 6 TP Foundations
Apertures
TOTAL 48 FEU - 104 + 12 48 + 6

Permissible Container Loads :

On Hatch Cover ............................... 32 Metric Tons per Stack for One (1) tier of 40 ft.

On Deck ........................................... 25 Metric Tons per Stack for One (1) tier of 40 ft on Foc'sle Deck.

50 Metric Tons per Stack for Two (2) tiers of 40 ft on Upper Deck.

Under Deck ........................................ 80 Metric Tons per Stack for Four (4) tiers of 20 ft in Hold 3.

Container Securing System :

a) Only Twist Lock system without Lashing on Hatch covers and Foc'sle deck.
b) Twist Lock system with Lashing on Upper deck.
c) Twist Lock system with Buttresses and Bridge Fittings in Hold 3.

Permissible Deck Loads :

Deck A to D ........................................... 1.70 T/M2

Hatch A to D ........................................... 1.75 T/M2

Pallet Securing System :

Hatch Side Boards and Portable Inflatable Dunnage Bags, supplemented by Wood Shoring where required.

Side Shoring (Where Fitted):

In Hold 1 = decks A, B, C and D.
In Hold 2 = decks A, B, C and D.
In Hold 3 = deck D.
In Hold 4 = decks B, C, and D.


FOCSLE DECK ARRANGEMENT:-

Hatch 1

Bay 1

FOC'SLE DECK PLAN

= Conic guide on deck

= Conic guide on stanchion

FIG.1-1. - Fixed Securing System On Foc'sle Deck

This diagram (Fig. 2.) shows the fixed securing arrangements for 40 'containers on the foc'sle deck (for stowage
on Hatch top 1 and Bay 1). Note that fixed guides for the Conic Base Locks are provided for each container
position. There are no eye pads for portable Lashing rods as twist locks with bridge fittings suffice.

STACK LOAD TABLE :

COMPARTMENT No of Stacks Stack Load

ON HATCH Hatch top 1, 2, 3, 4 3 each 32 MT

Bay 1 (foc'sle) 4 25 MT

ON DECK Bay 2 to 5 (40' cntnrs) 4 each 50 MT

Bay 4 (20' containers) 8 37.5 MT

IN HOLD 3 Hold 3 (20' containers) 3 80 MT


UPPER DECK ARRANGEMENT:-


Center Line
Hatch 4 Hatch 3 Hatch 2

Bay 5 Bay 4 Bay 3 Bay 2

UPPER DECK PLAN

= Conic guide on deck = Lashing Pad Eyes = Conic guide on stanchion

FIG.1-2. - Fixed Securing System On Upper Deck

This diagram (Fig. 23) shows the fixed securing arrangements for 40 'containers on the upper deck (for stowage on Hatch tops 2 to 4 and Bays 2 to 5). Note that fixed
guides for the Conic Base Locks are provided for each container position. Additional guides are provided for stowing 20' containers in Bay 4. There are eye pads at
each 40' position in Bays 2 to 4 for portable Lashing rods.


Conic Guide Units (Single/Double): These are also known as Dovetail Shoes. They are the bottom fixed securing
arrangement on all Hatch tops and Deck stow positions. The portable Bottom Locks are fitted in these units. These may be
mounted on raised stools of appropriate height to compensate for camber.

CONIC GUIDE UNIT (Single)

36 ± 1
8.0 ± 0.5
189 ± 1

190 ± 2
180 ± 2

213 ± 2

CONIC GUIDE UNIT (Twin)

36 ± 1
8.0 ± 0.5
189 ± 1

203

190 ± 2
180 ± 2

416 ± 2

Fig. 1-3. - Conic Guide Units on Deck and Hatch Tops.


Fig. 1-3.1. - D-Ring (Lashing Eye) on Deck.
Conic Guide Units: Breaking Load -
Manufacturer- Ozean Service & Reparatur

D-Ring on Deck: Breaking Load - 49 tons
Manufacturer- Ozean Service & Reparatur

UNDER DECK ARRANGEMENT:-

2nd Deck

Foundation for TP Element
Detail "A" (Fig 4-5)

Twist Lock

Bottom Lock Aperture
Use Tw ist Lock

Port Stbd
CL

FIG 1-4. - ARRANGEMENT FOR CONTAINER STOW/SECURING IN HOLD 3.

Fig.. 4 shows the fixed securing arrangements for 20' containers in Hold 3. Here, 20' containers are stowed athwart ship (3
rows) and can go upto 4 tiers. The diagram shows the apertures/raised pots (4 x 3 available) for the bottom locks (twist
locks) and the fixed foundations for the Thrust Pad (TP) Elements. See Fig. 3-7. for details of TP Elements.


CHAPTER 2: Location and stowage of portable securing gear.

DECK STORE (Mast Ho. 2)

Bay 5 Bay 4 Bay 3 Bay 2 Bay 1

Poop Deck Foc'sle Deck
Accomodation

Fore Peak

Store
Hatch # 3 Hatch # 2 Hatch # 1
Twist Locks

Bridge Fitting

Turn Buckle
LASHING BIN

M.V. -------------
FIG. 2-1.

Portable securing gear is located in the Deck store and in a Lashing Bin the locations of which are indicated on the diagram above.

The Deck Store (Stbd side aft of Hatch 2) is used to stow the Lashing rods when they are not in use.

The Lashing Bin is used to stow the Bridge Locks, Twist Locks & Base Locks and the Turnbuckles. The Lashing Bin is designed into three sections, segregating its
contents as shown in the diagram above.

Spare Lashing equipment is stowed in the Forepeak Store.


CHAPTER 3: Details of portable securing gear & Inventory of items.

This Chapter describes the functions and design characteristics of the portable lashing gear carried on the vessel.
An Inventory of items and their location on board is also indicated.
1. Turn Buckle

1 Turn Buckle
L= 1380 - 925 mm
42 mm

42 mm

L= 1190 - 865 mm

Fig. 3-1

Features: Pipe Body with two Swivel Hook Bolts OR one Hook bolt and one Jaw Bolt.
Size: As per Sketch
Finish: Galvanized.
Location: Lashing Bin
Inventory: 44 pcs.
Maintenance: Regular greasing and inspection.
SWL:

Locking nuts are provided to prevent inadvertent opening of the turn buckles. In any case they are to be checked for
tightness frequently during a sea voyage.

2. Bottom Cone Lock (Base Lock or Dovetail twist lock)

Locking Cone Head
2

Locking Lever

47 mm

Base Slides into Guide
Bottom Cone Lock Fig. 3-2

Features: Base plate slides into Guide on Deck.
Flange Thickness: 47 mm
Finish: Galvanized.
Inventory: 144 pcs.
Maintenance: Inspection and Oiling.
SWL:


3. Twist Lock

3 Twist Locks

lock

28 mm Locking Lev er

lock

Fig. 3-3

Features: Left hand locking or Right Hand Locking
Flange Thickness: 28 mm
Finish: Galvanized.
Inventory: 206 pcs. (LH 99 pcs, RH 107 pcs)
Maintenance: Inspection and Oiling.
SWL:

These twist Locks are used to interlock container tiers. They are available on board as right hand or left hand locking.
(Painted to indicate locking side).

4. Lashing Rod
Lashing Rod
4
L=2380 mm

D=25 mm

Fig. 3-4

Features: Eye on one end and slip hook on other end. No Corner Hooks needed.
Diameter: 25 mm.
Finish: Galvanized.
Location: Deck Store (Mast Ho. 2)
Inventory: 64 pcs
Min BL: 36 tons.

These Lashing Bars are used to secure containers on upper deck stow positions when carried in two tiers or more. When, in
the case of carrying High Cube containers, these rods are too short, extension rods are appended to it.
Lashing rods and turnbuckles can turn slack during the course of a voyage and need to be checked frequently.


5. Bridge Lock

190mm

5 Bridge Lock
Fig. 3-5

Features: Max Opening 190 mm.
Finish: Galvanized.
Inventory: 48 pcs.
Maintenance: Inspection and Greasing to keep free.
Min BL:

Bridge Locks are used across the top of adjoining containers and are optional when securing single tier containers. Care has
to be taken that these are checked and re-tightened in the duration of the voyage.

6. Lashing Rod Extension

6 D=30mm

32mm

L=360 mm

Lashing Rod Extension
for High Cubes
Fig. 3-6

Features: Used to extend Lashing Bar when loading High Cubes.
Length: 360 mm
Finish: Galvanized.
Location: Deck Store
Inventory: 48 pcs
Min BL: 42 tons All Drawings by Capt. Kohli

These are used to extend the length of the cross lashing rods as and where required. The hook end is attached to the lashing
rod and the eye attached to the turn buckle.


7. T.P. Element (Buttresses)

7 Adjustable TP Element

L=750 to 800 mm
MBL=30 T.

Drawing by Capt. Kohli
Fig. 3-7

Features: Adjustable Length.
Finish: Galvanized.
Location: Deck Store
Inventory: 6 pcs.
Maintenance: Inspection and Greasing. To be kept free.
Min BL: 30 tons
Manufacturer:

8. Inflatable Dunnage Bags: Two types available on board-

Maker: Type 1 Air Pac Type 2 Cargo Pack
Max Gap: 400 mm 450 mm
Max Pressure: 1.5 KPa/2.0 PSI 1.5 KPa/2.0 PSI
Size: 2000 x 850 mm 1000 x 1850 mm.

Inventory of items:

Lashing Gear Quantity on Board Location

BASE CONES 144 Lashing Bin
TWIST LOCKS 206 Lashing Bin
BRIDGE LOCKS 48 Lashing Bin
ROD EXTENSIONS 48 Deck Store
LASHING RODS 64 Deck Store
TP ELEMENTS 6 Deck Store
TURN BUCKLES 44 Lashing Bin
INFLATABLE DUNNAGE BAGS 700 For'd Store


CHAPTER 4: Correct application of portable securing gear.
The Provisions for securing cargo, contained in this chapter, should be interpreted as minimum requirements.
Additional Lashing should be taken to that prescribed here if so considered by the Master. The Master should in
applying portable securing gear, take into account the following factors:
1. duration and geographical area of voyage
2. sea conditions which may be expected
3. vessel's design and characteristics
4. dynamic forces under expected weather conditions
5. type and weight of cargo carried and their intended stowage pattern

Container Cargo:-
Containers on Foc'sle Deck:

The following diagram shows the general lashing arrangement when carrying containers on the foc'sle deck, i.e.
on Bay 1 and Hatch top 1. This arrangement also applies to single tier stow on all other positions.

5 5

2

2

Lef t Hand Lock

5
2
Bottom Base Lock Bridge Lock

FIG. 4-1. - Arrangement of Securing System On Raised Foc’sle


Containers on Upper Deck:

The following diagram shows the general lashing arrangement when carrying containers on the upper decks, i.e.
on Bays 2 to 5 and Hatch tops 2 to 4.
The vessel normally carries a maximum of two tiers and cross lashing bars from the outside of each stack
suffice. When carrying 3 tiers (usually empty container on the third tier) criss-cross lashing arrangement is
suggested. SEE DIAGRAM BELOW.


5

3 HIGH

5

2 HIGH

3 3

4 4

1 1

2
2 6 2

Drawing by Capt. Kohli

Lef t Hand Lock

1 3

Turn Buckle 2
Bottom Base Lock Twist Lock

L=2380mm 6
4
L=360 mm
5
Lashing Rod Extension
Lashing Rod Bridge Lock for High Cubes

FIG. 4-2. - Arrangement for Securing System On Upper Deck (40')


20' Containers on Bay 4 :

FIG. 4-3. - Securing Arrangement for 20' containers on Deck.

Bay 5 - 40' containers

Twist Lock
5

20' container 20' container

3
Bridge Locks

PLAN VIEW - 2nd tier
Bay 4F, 4A
4

1
20' container 20' container

6 2
BAY 4 - Looking Aft

Lashing Rod & Turnbuckle

For'd

Bay 3 - 40' containers

When Stowing 20' containers in Bay 4, each 40' stow position is effectively divided into two - for'd and after.

To secure two high 20' containers in Bay 4, bridge locks are used to secure each stack with the adjoining one. Lashing rod
system need not be used. It is not possible to secure lashing bars between two fore/aft containers within Bay 4.

Base locks are used at the Bottom tier and Twist Locks are used between each tier.


Handling Method of Lashing Rod :

A
End Hole of 2nd tier Container

Bottom tier Container

Lashing Rod

A. Insert Hook of lashing rod into lower end hole of the second tier container - raise the rod, line up the hook with the
end hole, insert.

B

End Hole of 2nd tier Container

Bottom tier Container

Lashing Rod

B. Swing the other end to cross lash and attach to the turnbuckle. Tighten the turnbuckle to secure the lash.

Bowed / slacked or overfastened lashing is not desirable. Hand adjust to proper tension with the turn buckle.


20' Containers in Hold :

The following diagram shows stowage pattern and lashing arrangement in Hold.

Bridge Fittings

TP Element
See Detail "A"

Twist lock

Port Stbd AFT FOR'D
CL
FIG. 4-4. - Arrangement for Securing System In Hold.


TP Elements (Buttresses) :

The following diagram "Detail `A' shows securing arrangement for TP Element when loading 4 high 20' containers in Hold
3.

2nd Deck

4th tier Container

3rd tier Container
Foundation for TP Element

Adjustable TP Element

L=750 to 800 mm
MBL=30 T.

Fig. 4-5 - Detail "A" (TP Element) Drawings by Capt. Kohli

The TP Elements (Buttresses) are fastened on one end to the foundation on the 2nd Deck (A deck) of Hold 3.
The other end, shaped like a double cone fits into the upper and lower corner pockets of the 3rd and 4th tier containers. The
TP Element is then screwed tight. This then acts as a thrust pad and prevents athwartship racking movement of the
containers in Hold 3.


Palletized Reefer Cargo:-
When carrying palletized reefer cargo, the side boards on the hatch sides are erected to present a vertical side to the end
pallets. This enables a secure tight stow . Additionally, portable Inflatable Dunnage Bags are used as required to ensure a
tight stow. When the hold is partly full, wooden shoring is applied, observing prudent seamanship, to prevent shifting of
cargo.

< 400 - 450 mm
Side Boards (Fixed Side Shoring)
Dunnage Bag

CARGO PALLETS

Cargo Hold Deck

Cargo Hold Side

Fig. 4-6. -Pallet stow/securing arrangement in Reefer Holds

Carrying cars Under deck:-
To secure cars under deck, the air circulation holes on the deck gratings are used as lashing holes for the car lashing hooks.
As vessel does not usually carry such cargo, the portable lashing is obtained when necessary. No stock on board.

Car Lashing Straps

Automobile
Cargo Hold Deck Grating

Air Holes in Grating

Fig. 4-7. -Securing of Cars under deck. Drawings by Capt. Kohli

NOTE: Effective new IMO regulations, Cars must be certified free of fuel before they can be carried under deck or where the cargo space
is not certified suitable for dangerous goods. Enhanced ventilation systems need to be provided for car carriage.


CHAPTER 5 : An Indication of Forces Acting on Cargo Units.
A cargo unit stowed on board will be subjected to the same movements the vessel experiences at sea. The most important,
for securing purposes, are:

1. Rolling. 3. Heaving.
2. Pitching. 4. Wind Force.

Fig 5-1 showing the various motions effecting containers.

Wind Force

Heave Motion

Pitch Motion
Roll Motion


Of the above mentioned motions, the time period involved and the amplitude of motion are significant.

The time period of roll motion is obtained from the formula "Roll Tr = 0.7B GMT". In general a value of GM is
selected so that the period of roll is around 12 to 16 seconds (a convenient relationship- GMT=0.06B). This leads us to
"Tr=2.86 B". A maximum roll amplitude of 30 degrees is specified.

Pitch time period is "Tp = 0.5 Lpp". A maximum pitch amplitude of 8 degrees is used.

Heave period is "Th = 0.5 Lpp". The Heave amplitude is Lpp 80 m.

Wind force is considered to act constantly, athwart ship only and at the maximum of 40 m/s. The magnitude of wind
force is 1.8 tonnes on the sides of a 20' container and 3.6 tonnes on a 40' container.

The centre of motion (though constantly changing the affect of such changes is small), is considered to be:
1. on the centreline of the vessel.
2. at the long. centre of floatation.
3. at the waterline or at one half of the moulded depth, whichever is greater.


Possible Modes of Failure:

Subject to the Forces acting on a container stack, the following modes of failure are possible:

i) Racking on containers' structure
ii) Shearing of fittings between containers
iii) Compression on containers' corner posts
iv) Tipping (pull out) on container corners

Fig 5-2 : Modes of Failure of a Container Stack

1 2
1. Racking on end walls 2. Shearing on corner Fittings

3 4

3. Compression on corner posts 4. Tipping force on corner Fittings


The Forces acting on a container stack can be resolved into vertical and transverse directions.

P H
Roll
y
roll static
Wind
Heav e
roll dy namic

d+

H
roll degrees O
roll degrees

Roll

d-
P
Heav e

Wind

H

Roll

Heav e
P

In the figure above, O is the motion centre, d+ & d- are the vertical distances (positive or negative) from this centre. The
transverse distance from O is shown as y. The force P is the pressure acting normal to deck and H is the sliding force
normal to deck. Both have been resolved from the forces that arose due to:
i) Rolling (dynamic and static)
ii) Heave, and
iii) Wind (acts on above deck boxes).


Formulae Used:

TABLE 5.1 - Ship's Motions

Maximum Period in
Motion for -------------
Amplitude Seconds
Roll Ø = 30 degrees T = 2.86
r B 300 in 13.27 secs.

Pitch ß = 8 degrees Tp= 0.5 Lpp 080 in 5.90 secs.
TABLE 5-2:
Heave Lpp T = 2.86 1.74 m in 5.90 secs. Components of
80 m. h B
Force-

Component of force, in tonnes
Pressure
Source Sliding (parallel to Deck)
(normal to Deck) "P"
transverse "H" longitudinal "J"
STATIC
Roll W cos Ø W sin Ø
Pitch W cos ß W sin ß
Combined W cos 0.71 Ø cos 0.71 ß W sin 0.71 Ø
DYNAMIC
Roll 0.07024W Ø. y 0.07024W Ø. dr
T r2 Tr2

Pitch 0.07024W ß . z 0.07024W ß . dp
Tp 2 Tp 2

Heave:
Roll 0.05W Lpp . cos Ø 0.05W Lpp . sin Ø
Th 2 Th 2

Pitch 0.05W Lpp . cos ß 0.05W Lpp . sin ß
Th 2 Th2

Wind 8.25 AV2 cos Ø x 10 -5

Where :-
Ø = roll in degrees W = weight of container in tonnes Tr = Roll period
ß = pitch in degrees Lpp = Length 'tween perpendicular Tp = Pitch period
Th = Heave period A = surface Area V = wind velocity
y = transverse distance from centre of motion z = longitudinal distance from centre of motion
d = vertical distance from centre of motion

Reference: IMO Publications


FORCES ON A CONTAINER IN THE STACK:
The components of force on each container are summed up for each set of motions.
In Rolling Condition: In Pitching Condition:
Pmax=W[(1+0.05Lpp Th2)cosØ + 0.07024 Øy Tr2 ] Pmax=W[(1+0.05Lpp Th2)cosß + 0.07024 ß z Tp2 ]
Hmax=W[(1+0.05Lpp Th2)sinØ + 0.07024 Ød Tr2 ] Jmax=W[(1+0.05Lpp Th2)sinß + 0.07024 Ø d Tp2 ]

In the combined condition (roll & pitch) the ax calculated angles are assumed at a factor of 0.71.
When calculating the forces on a supported (lashed) container stack, the flexibility of container walls (mm/t), flexibility of
lashing (mm/t), effective modulus of elasticity (t/mm2), tension in each support, etc. are to be taken into account.

In a container stack the vertical force P, is divided equally between the four corner posts, that is P/4 per corner. The sliding
force H is divided between the ends (sides) of the container, that H/6 at the top and H/3 at the bottom. The wind force is
taken half to the top frame and half to the bottom (further divided for end walls).

Considering a 2 tier container stack on the -------------, using the following symbols,
h = container height metres b = container breadth metres Q = Wind force in tonnes
H1 , H2 = Transverse (sliding) force tonnes (per tier) P1 , P2 = Vertical force (per box) tonnes

The forces in a stack are given by:

a) Racking per end wall:

Tier 2 racking = H2 . + Q .
6 4
Tier 1 ½ (H2 + H1/ 3 ) + 3Q/4

b) Shear force per bottom corner:

Tier 2 = 1.1 ( H2/ 4 + Q/4 )
Tier 1 = 1.1 ( H2/ 4 + H1/ 4 + Q/2 )
factor 1.1 is used to relate the shear to the connecting fitting between containers.

c) Downward Pressure force, per corner:

Tier 2/1 = P2 / 4 ± h ( H2/ 6 + Q/4 )
b

Tier 1/ base = P2 + P1 ± h/b ( 2 H2/ 3 + H1/ 6 + Q )

ISO STANDARDS FOR CONTAINERS:

Racking Force: the allowable limit is 15 tonnes in the end walls and 7.5 tonnes in the side walls.

Corner post compression: a limit is placed by the capability of the container below to withstand compression in its corner
posts. The limit is 2.25 x the rated weight of the container, i.e. 45 tonnes for a 20' box and 67.5 tonnes for a 40' box. (not a
significant factor unless 5 or more tiers are stowed).

Vertical tension (tipping force): the allowable pull out force on the corner castings is 20 tonnes at the bottom and 15 tonnes
at the top. The safe working load of the twist locks must be greater than this.

Shear: the top and bottom of the corner casting is of substantial thickness and the limiting factor for shear is the strength of
the twist lock. A minimum allowable shear strength of 15 tonnes is recommended.

Reference: IMO Publications


CALCULATIONS SPECIFIC TO M.V. ------------:

Two situations are considered. A two high stack of 40' containers (25 tonnes each) and a two high stack of 20' containers
(37.5 tonnes total). In each case the stacks are considered to be unsupported (NO LASHING) - for the purpose of
calculating the forces on an unsupported stack.
Bay 5 position is assumed as that is the furthest from the LCF (centre of motion) for 40' two high containers. Bay 4 aft is
assumed for the same reason for 20' boxes. In both cases the outboard stack is assumed, also to get a maximum (transverse)
separation from the centre of motion. Centre of motion is taken at waterline at draft 7.30m (max. Banana draft); LCF at
draft 7.30m is -2.726m.

1. BAY 5 outboard - 40' containers, 2 tiers of 25 t each. Stack weight = 50 tonnes, y = 11.97m, d = 6.966 & 9.56 m

Components of forces acting:-

In Rolling Condition:
P (pressure force normal to deck) = 29.56 t. (P 1 & P2 )
H (transverse sliding force parallel to deck) = 17.08 ( H1 ) and 17.86 (H2 ) t.

In Pitching Condition:
P = 37.88 t (P1 & P2 )
J (longitudinal sliding force parallel to deck) = 6.99 (J 1 ) and 8.03 (J2 )

In Combined (roll and pitch) Condition:
P1 & P2 = 31.53 t.
H1 = 10.56 t H2 = 11.11 t
J1 = 1.995 t. J2 = 5.21 t

Calculating the forces in the stack:-

Racking Force per Shear force per Downward pressure
Wall (t) bottom corner (t) per corner (t)
Side wall End Wall
In Rolling condition:
Tier 2 - 3.87 5.9 11.51
Tier 1 - 14.47 11.59 34.28
In Pitching condition:
Tier 2 1.54 - 3.20 11.85
Tier 1 5.80 - 6.11 29.69
In Combined condition:
Tier 2 1.07 2.75 4.04 10.81
Tier 1 3.55 10.02 7.94 29.33

Wind speed of 40 m/s has been applied on the sides. When calculating racking (longitudinal) of side walls, wind has been
considered to act on the ends. All other cases wind force is acting on the sides (larger area) at a force of 3.6 tonnes per
container.

It is seen that racking force in end wall of the bottom tier approaches the ISO limit of 15 tonnes in the rolling condition (3%
less than limit).

In the above mentioned example, twist locks, bridge locks and "V" lashing rods from outer containers is suggested.


2. BAY 4 aft, outboard - 20' containers, 2 tiers, bottom of 20 t and upper tier of 17.5 t. Stack weight = 37.5 t

Components of forces acting:-

In Rolling Condition:
P1 = 23.6 t. P2 = 20.7 t.
H1 = 13.67 t. H2 = 12.5 t.

In Pitching Condition:
P1 = 26.6 t. P2 = 23.3 t.
J1 = 5.59 t. J2 = 4.89 t.

In Combined (roll and pitch) Condition:
P1 = 22.62 t. P2 = 19.7 t.
H1 = 8.45 t H2 = 7.78 t
J1 = 1.60 t. J2 = 3.65 t

Calculating the forces in the stack:-

Racking Force per Shear force per Downward pressure
Wall (t) bottom corner (t) per corner (t)
Side wall End Wall
In Rolling condition:
Tier 2 - 2.53 3.93 7.86
Tier 1 - 11.05 8.19 24.27
In Pitching condition:
Tier 2 1.04 - 1.84 7.17
Tier 1 4.00 - 3.87 18.84
In Combined condition:
Tier 2 0.74 1.75 2.63 6.78
Tier 1 2.70 6.65 5.45 19.50

Wind speed of 40 m/s has been applied on the sides. When calculating racking (longitudinal) of side walls, wind has been
considered to act on the ends. All other cases wind force is acting on the sides (larger area) at a force of 1.8 tonnes per
container.

It is seen that the ISO limits are not exceeded. The closest is the racking in end walls in rolling condition, where it is 22%
less than the 15 tonnes limit. Twist locks and bridge locks suffice in this situation. In any case, no lashing rods can be used
between Bay 4 for'd and Bay 4 aft - any lashing rods taken on one end would not be considered to affect the unlashed end.
The stack would in effect be considered to be unlashed, supported by twist locks and bridge locks only.

Summary:
Calculations show that on -------------, single tier containers need only be supported with twist locks. With two high
containers, in the case of 20' boxes, twist locks and bridge locks will suffice. In the case of two high 40' boxes, though no
force limits are exceeded, the additional support of lashing rods ("V" lashing) is preferred.

These are of course the minimum requirements. In actual practice, the vessel has sufficient stock of gear to secure lashing
rods, twist locks and bridge locks on all containers. It is always advisable to err on the safe side.


Container Securing System for ships

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