An Assessment of Stability and Strength of a Container Ship for Safety Compliance in Cargo Loading Plans

Abstract

According to accident case studies, one of the causes of accidents involving container ships was often the incorrectly declared weight of the container. For this reason, the International Maritime Organization introduced an amendment to the International Convention for the Safety of Life at Sea, requiring the verification of container weight declared in the transport document. It partially solved the problem of accurate determination of container ship stability, although an error of 5% by weight is accepted. In this study, using the Macs3 program, the weight of 100 containers was changed by 5% to assess how such a situation affects the ship’s stability. It was found that even a slight change in the weight can affect stability. There are other problems that have to be addressed, e.g., loading of the containers as per positions in the loading plan or sharing information about mass distribution inside. In the last part, Ishikawa’s diagram was used to determine the relationship between the causes and their effect on the accident of MSC Napoli in an attempt to determine other factors that may have contributed to the container ship’s accident and highlight the need to systematize the rules and tools connected to container ship weighing.

1. Introduction

Today, with thousands of vessels used to transport goods by sea, a substantial part of international trade is handled by container ships. The loading of this type of vessel is very fast, versatile, and efficient. The largest container ships carry cargo on intercontinental routes. This ensures the fast transport of containers around the world and reduces the costs but increases the manoeuvring problems of these big vessels [1]. Containers to and from small ports are transported using feeders—smaller ships, often equipped with their handling equipment. With a capacity of up to about 1000 TEU, feeders handle ports that larger vessels cannot reach due to their manoeuvrability. Container ships are specialized vessels, adapted to carry only containers. However, the diverse construction of containers makes it possible to use different ways of transporting goods without having to adapt the ship’s construction to them [2,3,4,5]. The biggest challenge in container carriage is the loading plan. This is related to the stability of the ship, which directly translates into the safety of the carriage itself [6,7,8]. Incorrect positioning of containers on the ship and misdeclared container weight are factors that can have a negative effect on the ship’s system, leading to stack collapse or incorrect separation of dangerous cargo, which can lead to fire [9]. A combination of these factors can lead to damage, loss of cargo, crew fatalities, and even total loss of stability and sinking [10,11,12]. It is therefore essential to plan the loading of container vessels using a loading calculator. Planning and correct loading of vessels is an important tool for determining the safety of ship operation [13,14].

The mandatory stability requirements specified by the IMO [15,16] are contained in the International Intact Stability Code (

Table 1. Summary of mandatory stability requirements. Authors’ work is based on [17].

Criterion	Requirement
Area (A) under the righting arm curve	A0–30° ≥ 0.055 m⋅rad A0–40° ≥ 0.090 m⋅rad A30–40° ≥ 0.030 m⋅rad
Righting arm (GZ)	GZφ ≥ 30° ≥ 0.20 m
Angle corresponding to the maximum of the righting arms	φGZmax ≥ 25°
Initial metacentric height (GM)	GM ≥ 0.15 m
The weather criterion, where a and b are surface areas in the figure below, is based on: [17]	b ≥ a
List of the ship under static wind pressure perpendicular to the plane of symmetry	φ0 ≤ 16° or φ0 ≤ 0.8° φdeck edge entering the water

). They are based on experience from the design and accident analysis of seagoing ships. The criteria presented in the Code apply to typical conditions [17].

These criteria are mandatory for all ships covered by the SOLAS Convention or the Load Line Convention. For some ships, classification societies may recommend increasing certain requirements [2,18,19]. For example, the initial metacentric height in the loading condition with containers on deck shall not be less than 0.15 m, but the Polish Register of Shipping recommends that this height should not be less than 0.20 m [20].

The crew of each ship, when planning loading, take into account the criteria listed in Table 1, which are understood as follows:

⚜

The criterion for areas under the righting arm curve. The area found under the righting arm curve shall not be less than 0.055 m⋅rad, calculated from 0° to 30° of the heel, not less than 0.090 m⋅rad, calculated from 0° to 40° of the heel or up to the angle of flooding (the angle of flooding, in this case, being the angle of heel at which the inner spaces of the ship are flooded with seawater through openings) if the angle of flooding is less than 40°, and not less than 0.030 m⋅rad, calculated for 30° to 40° of the heel, or from 30° to the angle of flooding if the angle of flooding is less than 40° [17].

⚜

Righting arm curve, where the righting arm is at least 0.2 m at an angle of heel equal to or greater than 30°. The maximum righting arm must occur at an angle of the heel of not less than 25°. The righting arm of the vessel in the upright position must increase sufficiently rapidly (the vessel must be sufficiently ‘tough’—it must ‘hold’ sufficiently firmly its equilibrium position). The greatest value of the righting arm (the greatest ability of the ship to return to the equilibrium position) will not occur if the heel angle is too small [17,20].

⚜

The criterion of initial metacentric height—metacentric height is a measure of the ship’s initial stability at small angles of the heel. When its value is high, the ship is considered stiff and will come rapidly to the equilibrium. If the value is low, the rolling will be gentler, but in the event of failure, the ship may lose stability and capsize [21].

⚜

The weather criterion, taking into account the effect of wind and ship motions. According to the weather criterion, the ship’s stability is considered to be sufficient when the conventional wind, under conventional conditions, including wave rolling, does not cause exceeding of the heeling angle of 50° immersion of openings considered to be open, and ship capsizing. These requirements are deemed to be met when the ship’s heeling angle does not exceed 50°, the angle of flooding, or the angle of capsizing. Detailed requirements for this criterion are contained in the Rules for the Classification and Construction of Sea-going Ships, Part IV, Chapter 2 “Stability—Basic Requirements and Criteria” (point 2.1.2) [17,20].

In practice, ship-specific stability information is contained in the “Information on Stability for the Master” or “Stability calculation aids”. Meeting all the requirements does not guarantee the total safety of the ship. Therefore, it is very important to avoid unfavourable weather conditions that could cause flooding of the deck, shifting of cargo, or increased roll, and lead to serious accidents such as Eugen Maersk’s fire due to the stack’s collapse [22], heavy weather damage of Svendborg Maersk [23], or CMA CGM G. Washington’s and MSC Zoe’s container loss [24,25].

The initial loading plan for a container ship is currently created by the shipowner’s representative ashore—a planner, who uses a stability program. A version of the loading plan is sent to the ship and checked by the chief officer, commonly responsible for loading.

Since 1 July 2016, according to the amended SOLAS Convention, each container must have its weight verified before loading. The freight forwarder is responsible for the verification. The SOLAS amendments indicate two methods that can be used to determine the weight of a container at the end of its process. One method requires the container to be weighed with its cargo after it has been packed and secured [26,27]. The other method involves adding the weight of the container and the individual items loaded into it [26,27]. Weight estimation is not permitted. In both methods, the weighing equipment must fulfil national certification and calibration requirements [26,27].

Data obtained from [28] show, that despite the mandatory weight measurement regulations introduced by the IMO, containers still weigh more than indicated in the documentation. This leads to an erroneous assessment of stability and weakening of the ship’s structure due to significant stresses [17].

Although the requirement to check container weight before loading was a significant step forward, there are still some vague points in the container packing process and incidents still take place where the weight of a container is believed to have been declared incorrectly (CMA CGM George Washington, MSC Zoe) [29].

A proper loading plan requires determining factors and environmental parameters in which the vessel is to operate. For this reason, many researchers have addressed this problem. For example, Douglas Edward Perrault in his work analyzes data on the influence of wavelength and wind force in the context of the stability of ship-going vessels [30]. A considerable contribution is a work presented by Barrass and Derrett (now in its seventh, completed edition), which provides a comprehensive introduction to all aspects of stability and strength, ship squat, and the effects of used shipbuilding materials [31]. Numerous practical examples are included to help officers gain qualifications related to this subject. Yongming, S. and Shuhong, S. in their study [32] described the effect of ballast water exchange operations at sea on ship stability and strength. Wang et al. [33] characterized the BLOCK Algorithm, which helps to solve ship reloading problems, related to container jamming in the hold or on deck. Caibula [34], on the other hand, pointed out that the stability of a vessel is also affected by auxiliary equipment (commonly used in small general cargo ships and small container ships). Model tests confirmed that Ultra Large Container Ships are more sensitive than expected to parametric rolling because of low GM values in full load conditions combined with low speeds due to port congestion and Easterly swells in the wintertime. This shows how important it is to properly assess the ship’s stability [35]. Moreover, the EMSA 2019–2024 strategy prioritizes specific safety issues related to container vessels—in particular, loss of containers and fires onboard [9]

One of the reasons why regulations can be difficult to supervise is that there are different methods for calculating the weight of containers. Partly, this is because the system is filled with differing procedures and also differing qualities of equipment and devices, e.g., weighbridges, depending on the financial capacity of the parties concerned. Improved enforcement of regulations would increase their effectiveness, so it is desirable that the provision for verifying the weight of a container is further revised.

Therefore, in this paper, it has been decided to simulate (using the MACS3 program) the degree of irregularities in container loading in relation to their planned and actual weight. The differences are indicated in the criteria affecting the ship’s stability and the consequences of incorrect load on the stability of container ships.

2. Literature Review

Nowadays, researchers research the automatization of the container loading process. Systems for helping to moor larger container vessels were described in [36], which can be a step forward for making this type of ship fully autonomic. Intelligent loading systems, described among others by Qingcai Wu, Qiucheng Xia, and Maochuan Wu in [37] ensure that the ship has appropriate strength, stability, and draft difference, considering the size of the container and the type of goods, so the limits of stacking weight and capacity are in compliance. This requires a flow of data, including the real container’s weight and position onboard the ship. The problem of container localization onboard the ship can be solved using the patent of Tan H., Huang J., Bu F. Song H., and Warf G. K. [38], describing a method of automatic positioning. It proposes the installation of a device providing the position information about a container. The data obtained are used to compute the relative position of the container in the container ship, which is later compared with a stowage plan.

The research carried out for the TopTier JIP project shows that lashing performed according to Cargo Securing Manuals became impractical, as the numbers of tiers, bays, and rows increased significantly. The lashing calculations that used to be flag state approved during the build stage are now performed via computer before each loading/discharge port call. The computer provides the exact view of the planned stowage arrangement and weight distribution. Algorithms can evaluate any loading condition with related extreme motion levels and securing forces. This is why correct data about every single container becomes more and more important [35,39].

The correct container weight information is crucial for such systems to work properly. For the moment, it is the shipper who is responsible for correctly declaring the weight to the port and shipping line. This is why companies started to implement penalties for wrongly declared container weight [27]. Moreover, guidelines were issued to mitigate the risk of declaring the weight incorrectly in case of incorrect, ambiguous, altered, or missing declaration of weight [40].

The misdeclaration of a container’s weight has been considered the most significant risk for container shipping [41]. After the IMO amendment, research was conducted on the implementation of this regulation.

In the port of Tg. Priok, the amendment had no major effect, as containers were already weighed at the gates. However, introducing new methods of measurement raises the costs—costs of weighing and issuing certificates. Therefore, one of the objectives of the regulation was to raise efficiency, which is, for the moment, not possible as it leads to new costs, and because of this, is inefficient and affects the ports’ charge for the shipping [42].

The implementation of the amendment was also studied in the port of Hong Kong. It showed that the guidelines issued by the port were not as clear as the ones of the IMO [43].

Research conducted in Australia shows that the IMO amendment had a positive effect—increased safety of shipping companies and operators of the terminals. On the other hand, the financial costs of shippers rose and implementation of new procedures resulted in time delays [44].

Also, the case study on PT. Albasia showed that during the process of weighing the containers, there was an addition of production costs and extended length of the weighing process which resulted in delays in the arrival to the destination country [45].

Most of the studies highlight the importance of simplifying the working process and implementing information technology to increase the information exchange [46].

The problems faced may lead to the attempts of not following the rule, especially in the case of less developed ports, which may not have the funding to fully implement it. It clearly shows that further work needs to be carried out to develop better and safer solutions.

3. Research Material and Methodology

The research was conducted using the MACS3 Basic Loading Program, approved by all leading classification societies. The program included the BELCO Container Management Module, allowing the creation of the valid stowage plans for container ships.

In order to determine the effect of misdeclared container weight on the stability of a ship in a particular loading condition, an example container ship of 2882 TEU was loaded with 2500 20-foot containers, with the appropriately selected amount of water in the ballast tanks (

Table 2. The way of ballasting of examined ship’s ballast tanks. Authors’ work.

Name of the Tank	Weight [t]	Volume [m3]	Filling [%]	Free Surface [mt]
Fore peak TK	0.0	0.0	0.0	0.0
BW TK 4.01	0.0	0.0	0.0	0.0
BW TK 4.03	677.4	660.9	100.0	0.0
BW TK 4.04	614.0	599.0	100.0	0.0
BW TK 4.05	467.0	455.6	100.0	0.0
BW TK 4.06	435.6	425.0	100.0	0.0
BW TK 4.07	707.4	690.1	100.0	0.0
BW TK 4.08	629.9	614.5	100.0	0.0
BW TK 4.09	574.2	560.2	100.0	0.0
BW TK 4.10	549.8	536.4	100.0	0.0
BW TK 4.15	876.5	855.1	100.0	0.0
BW TK 4.16	817.4	797.5	100.0	0.0
BW TK 4.17	514.5	502.0	100.0	0.0
BW TK 4.18	513.7	501.2	100.0	0.0
Heeling TK 4.19	327.3	319.3	70.0	0.0
Heeling TK 4.20	139.9	136.5	30.0	0.0
BW TK 4.21	569.6	555.7	100.0	0.0
BW TK 4.22	567.7	553.9	100.0	0.0
REEFER TK 4.24	56.7	55.3	100.0	0.0
Aft peak TK	0.0	0.0	0.0	0.0

) and the number and distribution of containers (Figure 1) in order to depart from the port on an even keel and without the list. The weight of the lightship was 11,950 t and the deadweight was 37,580 t. Water in the ballast tanks was assumed to have a density of 1.025 t/m³. The initial trim was 0.03° by stern (0.12 m) and the initial list was 0.02° to starboard. The deadweight reserve was 820 t.

In the initial analysis, each loaded container had a mass of 10 t. Then the mass of 100 randomly chosen containers was changed to 10.5 t and the two loading states were compared. The ship’s stability was assessed using the MACS3 stability program used at the Maritime University of Szczecin. This program performs stability and strength calculations of the ship, for various loading states of the container ship, taking into account the criteria shown in Table 1.

Ishikawa’s diagram was used as a graphical analysis of the effect of factors and their interrelationships that cause a specific problem, as well as an analysis of the effects caused by the operation of such relationships [41]. The diagram arranges the causes chronologically and logically according to the defined problem. The tool was used to examine the accident of MSC Napoli in 2008. The data to perform the analysis were obtained from the accident investigation report introduced in [42].

4. Analysis of the Loading Status of an Example Container Ship (Results and Discussion)

Figure 2 shows a simulation of the loading of containers into the examined ship. In the simulation, 2500 20-foot containers weighing 10 t were loaded, with the ballast tanks filled so that as many containers as possible could be loaded, while meeting the stability criteria. For the purpose of the simulation, the fuel, lubricating oil, and freshwater tanks were assumed to be filled at 70%.

The program was used to verify whether the stability requirements for this vessel were met (

Table 3. Stability criteria for a ship loaded with 10 t containers. Authors’ work.

Stability Results/without d. Cont.—SeeBG
Lever Balance—OK!	Actual	Limit
GM’ (corrected)	0.421	0.421	m
Angle due to transverse Moment	0.016	3.000	degr.
Angle due to Wind + transverse Moment	0.016	18.000	degr.
GZ Lever at 30 Degrees	0.463	0.455	m
Statical Stability Range	53.962	50.000	degr.
Area up to 30 Degrees	0.100	0.055	mrad
Area up to 40 Degrees	0.191	0.090	mrad
Area between 30 and 40 Degrees	0.091	0.030	mrad

).

Loading was done so that the GM reached the limit and bending moments were close to their maximum values (

Table 4. Shearing forces and bending moments for sea conditions acting on the frames of a container ship loaded with 10-ton containers. Authors’ work.

Frame No.	Shear Forces			Bending Moments			Torsion
				Sea
	Existing [kN]	Limits [kN]	rel. [%]	Existing [kN]	Limits [kN]	rel. [%]			rel. [%]
35	25,600	29,850	86	345,456	454,300	76	max. Mom.	Limit
52	30,532	35,000	* 87	722,320	1,021,200	71	(kNm)	(kNm)
77	8763	27,850	31	1,111,023	1,313,300	85	41,690	79,900	52
94	8468	50,900	17	1,213,676	1,882,500	64	Area of T.	Limit
110	5746	50,900	11	1,261,864	1,891,500	67	(kNm2)	(kNm2)
131	−2449	−50,900	5	1,226,878	1,891,500	65	2,449,933	7,801,000	31
148	−8431	−50,850	17	1,098,927	1,809,600	61
168	−17,293	−50,200	34	825,294	1,271,900	65
185	−17,072	−47,650	36	524,022	805,400	65
204	−7947	−23,300	34	241,115	420,200	57
222	7541	18,900	40	144,461	148,000	* 98

* marks max. percentage.

).

Many countries customarily accept an allowable margin of error of up to 5% of the container weight [28]. Accident investigations (e.g., Ever Smart [47]) indicate that the difference between the actual weight and the verified weight is more than 5%. To determine the effect of the difference between the declared and actual weight of a container, the weights of 100 randomly selected containers were changed from 10 t to 10.5 t (Figure 2). The weight of the container in a single position can differ due to the weight misdeclaration or situating it in a position that was not assigned to it. The present situation does not specify which case was taken under consideration. It was stated that both situations took place to make the scenario as close to reality as possible.

This change did not significantly affect the ship’s draught or list. (The final trim was 0.03° by stern (0.11 m) and the final list was 0.02° to starboard. The deadweight reserve was 770 t.) However, the metacentric height was significantly affected and was below the permissible value (

Table 5. Stability criteria for a ship loaded with 10 t and 10.5 t containers. Authors’ elaboration.

Stability Results/Without d. Cont.—SeeBG
Lever Balance—OK!	GM not OK!	Actual	Limit
GM’ (corrected)		0.416	0.425	m
Angle due to transverse Moment		0.016	3.000	degr.
Angle due to Wind + transverse Moment		0.016	18.000	degr.
GZ Lever at 30 Degrees		0.459	0.456	m
Statical Stability Range		53,859	50,000	degr.
Area up to 30 Degrees		0.099	0.055	mrad
Area up to 40 Degrees		0.190	0.090	mrad
Area between 30 and 40 Degrees		0.091	0.030	mrad

). This problem can be solved using appropriate ballasting of the tanks. However, this will take time and also requires sufficient space in the tanks to compensate for the increased weight of the containers.

In the examined situation, the ballasting may cause exceeding of sheer forces or bending moments, as they are close to the limits (e.g., at frame 222,

Table 6. Shearing forces and bending moments for sea conditions acting on the frames of a container ship loaded with 10 t and 10.5 t containers. Authors’ elaboration.

Frame No.	Shear Forces			Bending Moments			Torsion
				Sea
	Existing [kN]	Limits [kN]	rel. [%]	Existing [kN]	Limits [kN]	rel. [%]			rel. [%]
35	25,627	29,850	86	345,864	454,300	76	max. Mom.	Limit
52	30,560	35,000	* 87	723,082	1,021,200	71	(kNm)	(kNm)
77	8741	27,850	31	1,111,843	1,313,300	85	41,852	79,900	52
94	8460	50,900	17	1,214,300	1,882,500	65	Area of T.	Limit
110	5749	50,900	11	1,262,429	1,891,500	67	(kNm2)	(kNm2)
131	−2466	−50,900	5	1,227,304	1,891,500	65	2,466,056	7,801,000	32
148	−8441	−50,850	17	1,099,119	1,809,600	61
168	−17,299	−50,200	34	825,336	1,271,900	65
185	−17,065	−47,650	36	524,069	805,400	65
204	−7958	−23,300	34	241,033	420,200	57
222	7552	18,900	40	144,324	148,000	* 98

* marks max. percentage.

). Also, the deadweight reserve in this situation is 770 t, which doesn’t allow the ballasting of a great amount of water.

The deadweight reserve in this situation is 770 t, which means that only 770 t of ballast can be taken so the ship is still afloat. In this situation, only three ballast tanks can still be ballasted, and this will cause exceeding of allowable bending moments.

Such a situation may contribute to the weakening of the hull structure through reducing the safety margin between the total experienced bending moment and the strength of the hull. This is considered one of the favourable circumstances of the MSC Napoli accident in the Dover Strait in 2008, which resulted in the ship breaking in two parts [48].

In the report, the following possible causes were mentioned: the ship’s speed was not sufficiently reduced in bad weather conditions, no sufficient bucking strength in the way of the engine room, buckling strength calculations were not compulsory in the amidship area, load on the hull was probably increased by the whipping effect, and an insufficient safety margin between the hull’s design loading and its ultimate strength [48].

Based on the mentioned report, an Ishikawa cause and effect diagram was created (Figure 3).

The probable main causes of these accidents include improper storming, discrepancy between the actual weight of the containers and the declared weight, frequent loading of the ship at its limits, and exceeding the maximum bending forces.

These causes depended on human actions. It can be seen that two of the three mentioned accidents were related to the loading status of the ship. One of the main problems related to cargo on a container ship is indicated here—incorrect declaration of cargo weight.

The position of 700 containers loaded on the deck of MSC Napoli was checked. Of these units, 53 (7%) were in either the wrong position or declared as the wrong container. The general agreement in the container industry allows 10% of loaded containers not to be in the planned position. Moreover, the post-accident audit indicated that the weights of many containers onboard were inaccurate. About 660 dry, remaining containers were weighed.

The weight of 20% of them was more than 3 tonnes different from the declared weights.

The problem of the containers’ weight was the reason for the SOLAS amendment, making weighing of the containers compulsory before loading. However, the problem still exists, as shown by the accident of CMA CGM G. Washington, losing 137 containers in the North Pacific Ocean in 2018. The investigation identified several factors that affected the container stow on the deck: acceleration forces exceeding the structural strength of containers during the large rolls, parametric rolling not recognized by the crew, structural failure of containers, transport of 53 ft containers, having different limits than ISO containers (which were exceeded), inaccurate declared weight of some containers, and the final cargo bayplan not being amended to reflect weights measured in port. Force limits were not exceeded in this case, although one stack in bay 18 was 100% [24].

The post-accident comparison showed that the total terminal weight for the 2469 containers (30,394 t) was 736 t (2.4%) lower than the total declared verified gross mass and 65% of the containers’ VGMs were within ±5% of the terminal weights. Of the remaining 35%, 10% were over 1 t lighter than their declared VGM, with the largest variance being 8 t, and 2% were over 1 t heavier than their declared VGM, with the largest variance being 16 t [24].

5. Conclusions

The changed SOLAS Convention, forcing shippers to weigh containers before loading seems to be just the beginning of forming new rules applying to container vessels, as there are still many problems to be solved:

-

In the case under consideration, the weight of 4% of the loaded containers was changed by 0.5 t, which was sufficient for one of the most important parameters, the metacentric height, not to meet the requirement. For this reason, it would be advisable to improve and standardize the process of weighing containers before loading. It is also evident that an attempt should be made to minimize the measurement error since even a slight change in the weight of a container can affect stability.

-

The container weight verification process should be independent of third parties. In addition, to avoid inaccuracies, it should take place just before the container is loaded onto the ship. One way of doing this would be to use a flat scale that first weighs the container with the truck carrying it and then, after the container has been lifted by crane, the truck itself. The resulting container weight seems to be the most reliable, and weighing alone would not affect the loading rate.

-

An update to the loading plan after routine container weighing—the terminals start to weigh containers again on their own, but these data are not always compared to the ones declared. Although the IMO, MCA, and WCS guidance are clear about it, the importance of this practice must be highlighted.

-

No information is available about the distribution of cargo in the container space, which necessitates the estimated center of gravity to be assumed through mathematical calculations.

-

Containers loaded onto a ship are not always placed in the positions specified in the loading plan, and plans are often updated after the ship’s departure.

-

Cargo Securing Manuals are in many cases impractical, as the capacity, number of rows, bays, possible stowing configuration, and loading conditions cannot be inserted in a single paper document. The lashing calculations are now often done using a computer. However, there are no general mandatory requirements or performance criteria.

-

Decision support tools in bad weather conditions should be spread onboard ships, making the crew more aware of parametric rolling and whipping effects.

-

Bureau International des Containers, appointed by the IMO, formed two databases, containing technical details for individual containers. Both databases are incomplete, hence, it is not possible to assess all the containers before loading. Such databases should be developed as stack collapses are also connected with structural failures of containers.

-

Ishikawa’s analysis can easily contribute to estimating the effect of individual causes, as well as the elements contributing to these causes, and can rank the importance of their effect on the damage to the ship (in the case in question, human error in loading containers on the MSC Napoli).

Despite the implementation of further restrictions and preventive measures, container ships are still prone to accidents. This is why further work needs to be carried out into this matter. This will be the topic of the authors’ further works.

The aim of the article was to gather all unsolved problems regarding container weight declaration in an attempt to raise awareness and contribute to the implementation of further changes. It also introduces the general methods that can be developed to solve the problems mentioned. The article investigated the problem of the verified gross mass of containers in light of the last IMO amendment, measuring the performance and effectiveness of the regulation. The main conclusions of the research are that there is still space to improve the law and that there is a need to help all concerned parties in terms of adapting to the existing changes.