The carriage of deck cargoes is a matter which needs full awareness of the risks involved in it. Although the structural aspects must be considered with respect to the adequate strength of stowage and lashing devices, it is the operational aspects which still lead to casualties. This is particularly the case for timber deck cargoes.
In Bulk Carrier Update No. 2 2004, we asked: “Is there a problem with timber deck cargoes?” That article discussed the discrepancy in reasonable GM values between the damage stability criteria set out in SOLAS Chapter II-1 and the recommendation (three per cent of the ship’s beam) given by the Timber Code (Code of Safe Practice for Ships carrying Timber Deck Cargoes).
The conclusions drawn for newbuildings were
n to include realistic timber loading conditions in the preliminary loading manual which meet the damage stability criteria and the three per cent rule of thumb,
to apply IACS UI SC161 by utilising the buoyancy of timber cargo to increase loading flexibility, and
to separate top side wing tanks from double bottom tanks to lower the GM if necessary.
To follow up on this topic, here we ask: How can the appropriate stowage and securing of timber deck cargoes be ensured?
The inadequate or negligent securing and stowage of timber deck cargoes together with insufficient stability properties due to improper load and voyage planning may lead to cargo shifting and subsequently put the ship in an unsafe condition and endanger life and the ship and cargo.
Casualties observed in recent years where the transverse movement of cargo was the relevant cause involved ships carrying packaged timber deck cargoes, while no serious casualties have been reported for ships carrying logs. It is not surprising that transverse movement typically takes place in heavy weather when the cargo stow is subject to wave impacts and extreme accelerations due to the ship’s motions.
The typical scenario observed involves an easing of the lashing tension, so that upper layers of cargo stow start to move, putting timber packages below under high racking loads which will collapse and consequently destroy the compact stowage of deck cargo.
Although the Timber Code outlines recommendations and guidelines for how to stow and secure timber deck cargoes, the industry recognised that most of the measures stated were outdated. The industry claimed that the prescribed methods no longer suite modern ship arrangements and are not easy to comply with in a rational manner.
Therefore, at its 82nd session in December 2006, the Maritime Safety Committee tasked the DSC subcommittee to look into the concerns expressed in its working programme and produce a result by 2010. Subsequently, during its 12th session, the DSC subcommittee established a working group to deal with this subject under the chairmanship of Sweden and with the participation of DNV as the only class society.
Since then, the working group has drafted a revised version of the Code which will be used as a working document for the subsequent DSC meetings.
When drafting the revised code, particular attention has been paid to the safe, rational and efficient securing of timber deck cargoes.
One shortcoming is the availability of data regarding the behaviour and characteristics of typical timber deck cargoes. Consequently, in February 2008, practical tests sponsored by MariTerm of Sweden were performed using logs and packaged timber.
Tests have been performed regarding:
The friction resistance of different material combinations in wet, dry and snowy surface conditions for packaged timber cargo and logs;
The racking strength of packaged timber cargo
Loop-lashed packaged timber cargo
Unsecured logs stowed athwartships
The determination of the required strength of uprights supporting longitudinally stowed logs
The main objective is, as stated, to provide an adequate stowage and securing arrangement for timber deck cargoes which prevents the cargo from sliding and collapsing, taking into consideration the nature of the timber cargo and the loads acting on it throughout a planned voyage.
The draft version of the revised Timber Code is divided into three chapters and a number of annexes. While the first chapter describes the general background and definitions, chapter 2 focuses on the general recommendations for the stowage and securing of timber deck cargo. This chapter also highlights general safety aspects, such as stability, visibility and load line criteria, as well as operational aspects like permitted loading weights, voyage planning and pre- and post-loading operations.
The stowage of timber deck cargo should comply with the basic principle of making the cargo stow as solid and compact as practical to
Prevent slack in stow which would cause easing of lashing;
Produce a binding effect within the stow; and
Reduce free spaces within the stow to a minimum.
The securing of timber deck cargo should follow the principal methods of
Transverse blocking of cargo over its full height by means of uprights;
Transverse blocking of the base layer by timber rails or an equivalent means or in combination with lashing arrangements;
Different types of lashing arrangements;
Frictional securing; and
A combination of the aforementioned methods.
Chapter 3 outlines design principles to be used when developing cargo securing arrangements. Typical design criteria for different securing arrangements are provided, allowing for the appropriate strength calculation of lashing and fastening equipment.
In general, securing arrangements for timber deck cargoes should be based on accelerations, the physical properties of the cargo and equipment and appropriate safety factors as stated in the Code of Safe Practice for
Cargo Stowage and Securing (CSS).
Each cargo securing arrangement for timber deck cargoes is to be documented in the Cargo Securing Manual and accompanied by a lashing plan showing at least the following:
The maximum cargo weight for which the arrangement is designed;
The maximum stowage height;
The required number and strength of blocking devices and lashings;
The required pretension in lashings;
Other cargo properties of importance for the securing arrangement, such as friction, rigidity of timber packages, etc.;
Illustrations of all the securing items that might be used; and
Any restrictions regarding maximum accelerations, weather criteria, etc.
The revised Timber Code will be a big step forward to reduce the risk to life, ships and cargoes due to the transportation of timber deck cargo.