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TagsContainerization Ships Cargo Transport
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Total Pages16
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1

UK P&I CLUB

Container lashing and stowage
In general terms, by a process of evolution, the
lashing systems in use on small container vessels and
post-panamax are very similar

UK P&I CLUB
IS MANAGED
BY THOMAS
MILLER

Page 2

2

In the early years of containerisation, existing general
cargo vessels were converted with the removal of
‘tween decks and the addition of cell guides into the
cargo holds. On deck, the hatchcovers were
strengthened and fittings added for lashings. However,
the containers on deck were seldom stowed above one
high and so were secured to the vessel by ‘traditional’
cargo ship methods.

Often seen still trading today, are a few of the ‘first
generation’ vessels built during the late sixties and
early seventies. These ships were the first to be
designed and built as pure container carriers. The
holds and hatchcovers were as wide as possible, and
container posts were fitted on deck to facilitate loading
of deck-stowed containers out to the ship’s side (see
Figure 2 ).

Lashing of containers on deck

Figure 1: Typical midship section of an early vessel conversion

For this generation of vessel, two systems of securing
the cargo were common. One relied on the use of
twistlocks in conjunction with lashing bars or chains,
and the second relied on the use of stacking cones and
bridge pieces in conjunction with lashing bars or
chains. Gradually, due to the increased utilisation of
differing height containers, the second method became
redundant and it became common practice to use
twistlocks throughout the stow. This method normally
allowed containers to be stacked three high and, in
some cases, four high if the fourth tier was light in
weight or empty.

For first generation vessels, computer technology was
not available onboard to speedily calculate dynamic
loads acting on container lashings and frames. The
shipboard computer (if any) was only used to calculate

The use of a computer lashing program, together with the IMO requirement for every vessel to
carry onboard an approved Cargo Securing Manual, should mean a reduction in collapsed
stows and losses overboard

Centreline Girder

Dunnage

Twin Hatchcovers

Main
Deck

Chain or Wire
Lashings

Tier 82

Old
’Tween
Deck

4th TIER

3rd TIER

2nd TIER

1st TIER

ROW
06

ROW
05

ROW
04

ROW
03

ROW
02

ROW
01

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Figure 8 and photo above right: Excessive compression
force on container corner post, leading to failure of the post

roll can be determined using the following rule-of-thumb
formula:

The case illustrated, with a GM of 0.9m, leads to a
natural roll period of 16 seconds. This would lead to
quite a long roll, with the loadings increasing to the
maximum, and then reducing until the vessel becomes
upright, and then rolls back the other way.

A detailed breakdown of the forces in each stack is
obtained, displaying the relevant forces acting on each
container. The programs assume, as a default, that all
containers are stowed with their door ends aft, but this
can be altered by the user. As an example, an excerpt of
a printout from the Seamaster program is shown
opposite. The bottom line for each row of containers
indicates the maximum allowable forces (MAF) for the
forces identified in the column directly above,
highlighted in blue. If a force exceeds the MAF it is
highlighted in red.

Racking force: The first two columns are the
transverse forces tending to distort the container ends,
primarily due to a rolling action. This should not exceed
a MAF of 15t. If a lashing is applied, the force varies
between the forward and aft ends of the container
because of the different ‘stiffness’ of the door and
closed ends.

Corner shear: This is closely related to racking, but is
the force tending to shear off the twistlocks. It should
not exceed a SWL of 15t for a standard twistlock.

Compressive force: This is the force acting on the
container corner posts and fittings, and is the result of
tilting the stack and the vertical acceleration. It should
not exceed 45t for a standard 20’ container corner
post, or 67.5t for a 40’ container’s corner post. Larger
compression forces are allowed for corner castings at
the base of a stack (83.8t).

Separation force: This is the tipping force which is
acting to ‘pull out’, or separate the corner fittings and
should not exceed 15t for the top fitting, and 20t for the
bottom. It is shown as a negative value in the force
table. This force does not refer to the tensile loadings
on the twistlocks.

Lashing tension: This is the tension in the applied
lashings. Lashing rods should only ever be applied
hand tight, not over-tightened with large spanners, as
this induces unnecessary tension in the lashing rod,
reducing the angle of roll at which the SWL would be
exceeded. The Germanischer Lloyd (GL) limit for
lashing rods is 23t SWL; turnbuckles are rated at 18t.
Seamaster uses the LRS 1999 rules for reporting (see
excerpt from a printout opposite).

The examples of the Seamaster printout are from an
actual incident involving container loss in heavy
weather. They illustrate the advantages of using a

Period ( T
R
) =

0.7 Beam
� GM

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WITH LASHING BRIDGE – Report for Deck Bay 54 on the basis of LRS 1999 Rules
(with 78 kn wind & 24.9° roll, assuming draught = 12.6 & GM = 0.90m)

Row 12 Deck Bay 54
Tier Ht(ft) Wt(t) Wind(t) Cl Door Fwd < LASHINGS > Aft
88 9.5 19.5 4.3 Aft length type length type
86 9.5 26.2 4.3 Aft
84 9.5 21.4 4.3 Aft 3.92 St 30 3.92 St 30
82 9.5 26.2 4.3 Aft
Rolling: Racking Force Corner Shear Compression Forces Lash Tension
Tier Fwd Aft Side Fwd Aft Fwd Aft Fwd Aft Fwd Aft
88 2.9 2.9 0.0 4.2 4.2 9.2 9.2 0.3 0.3
86 11.2 11.2 0.0 2.1 -2.9 49.9 62.8 -6.5 -6.5
84 6.8 -2.3 0.0 6.5 1.5 64.7 65.9 -9.7 -0.6 23.2 38.9
82 15.2 6.1 0.0 11.6 6.6 91.6 81.2 -20.3 -2.2
(MAF) (15) (15) (10) (15) (15) (67.5/83.8)(-15.0/-20.0)

Row 11 Deck Bay 54
Tier Ht(ft) Wt(t) Wind(t) Cl Door Fwd < LASHINGS > Aft
88 9.5 21.2 4.3 Aft length type length type
86 9.5 22.0 4.3 Aft
84 9.5 26.3 4.3 Aft 3.92 St 30 3.92 St 30
82 9.5 26.3 4.3 Aft
Rolling: Racking Force Corner Shear Compression Forces Lash Tension
Tier Fwd Aft Side Fwd Aft Fwd Aft Fwd Aft Fwd Aft
88 3.1 3.1 0.0 4.5 4.5 9.9 9.9 0.4 0.4
86 11.3 11.3 0.0 1.6 -3.4 49.7 62.6 -7.2 -7.2
84 6.5 -2.7 0.0 6.8 1.8 65.4 66.6 -9.2 -0.1 23.3 39.2
82 15.8 6.7 0.0 11.9 6.9 93.1 82.6 -20.4 -2.2
(MAF) (15) (15) (10) (15) (15) (67.5/83.8)(-15.0/-20.0)

NO LASHING BRIDGE – Report for Deck Bay 54 on the basis of LRS 1999 Rules
(with 78 kn wind & 24.9° roll, assuming draught = 12.6 & GM = 0.90m)

Row 12 Deck Bay 54
Tier Ht(ft) Wt(t) Wind(t) Cl Door Fwd < LASHINGS > Aft
88 9.5 19.5 4.3 Aft length type length type
86 9.5 26.2 4.3 Aft
84 9.5 21.4 4.3 Aft
82 9.5 26.2 4.3 Aft 3.68 St 30
Rolling: Racking Force Corner Shear Compression Forces Lash Tension
Tier Fwd Aft Side Fwd Aft Fwd Aft Fwd Aft Fwd Aft
88 2.9 2.9 0.0 4.2 4.2 9.3 9.3 0.3 0.3
86 11.2 11.2 0.0 9.5 9.5 31.1 31.1 -6.6 -6.6
84 20.3 20.3 0.0 7.6 13.9 77.8 63.1 -25.1 -25.1
82 17.3 28.7 0.0 12.7 19.0 107.4 107.3 -39.8 -54.4 18.6
(MAF) (15) (15) (10) (15) (15) (67.5/83.8)(-15.0/-20.0)

Row 11 Deck Bay 54
Tier Ht(ft) Wt(t) Wind(t) Cl Door Fwd < LASHINGS > Aft
88 9.5 21.2 4.3 Aft length type length type
86 9.5 22.0 4.3 Aft
84 9.5 26.3 4.3 Aft
82 9.5 26.3 4.3 Aft 3.68 St 30
Rolling: Racking Force Corner Shear Compression Forces Lash Tension
Tier Fwd Aft Side Fwd Aft Fwd Aft Fwd Aft Fwd Aft
88 3.1 3.1 0.0 4.5 4.5 10.0 10.0 0.4 0.4
86 11.3 11.3 0.0 9.1 9.1 30.7 30.7 -7.3 -7.3
84 20.0 20.0 0.0 7.9 14.3 78.8 63.8 -24.4 -24.4
82 17.7 29.4 0.0 13.0 19.4 109.0 108.9 -39.7 -54.6 19.0
(MAF) (15) (15) (10) (15) (15) (67.5/83.8)(-15.0/-20.0)

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The example shows a marginal case where slightly
more stressful conditions could cause the stack to
collapse. Ship motions would be important and even
the over-tensioning the lashings might be sufficient to
bring about failure.

This demonstrates that if the rules of good stowage are
broken even with relatively modest loads then there are
potentially serious consequences. If the stack included
heavier containers, i.e. units of 20 tonnes and greater,
then bad stowage would probably, if not certainly,
cause collapse if the vessel were to meet adverse
conditions.

It would be wrong to assume that bad stowage will
cause a container collapse. There are other
components to the equation. In addition, the vessel will
have to encounter heavy weather and experience ship
motions of amplitudes approaching design working
limits. There are additional factors, which can influence
events. Containerships can be very large vessels and
lashing systems are of very substantial scale. Such
large arrangements can easily conceal defects, both in
lashings themselves and their manner of application.
The safest condition is one, which has complied with
the basic stowage rules.

A containership master must be prepared to use all
available tools in the ISM system in order to report
defective stowage to the vessel operators and
designated person ashore. It is a fundamental
requirement of ISM that defects of this type are
reported.

There have been examples of vessels performing
multiple chartered voyages, with overloaded and
defective stowage conditions, and with no record of
any protest by the master to charterers through owners.
A containership master should remember to use all the
tools available, in order to check stowage and security.
Modern vessels have computer programs to enable
lashing integrity to be checked at the push of a button.
These facilities must not be overlooked.

Container lashing and stowage:
Original versions of these articles first appeared as part of Carefully to
Carry 7, published in January 2004

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UK P&I CLUB
IS MANAGED
BY THOMAS
MILLER

For further information please contact:
Loss Prevention Department, Thomas Miller P&I Ltd
Tel: +44 20 7204 2307. Fax +44 20 7283 6517
Email: [email protected]

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