Inspection of the compatibility of docks with different types of vessels

Introduction

Docks represent the connection between land and sea, since they are the only structures where vessels can carry out processes such as loading and unloading of hydrocarbons. However, for the correct development of these activities, it is necessary to consider certain aspects, one of them being the compatibility of docks with vessels.

As there are different types of vessels, with specific characteristics, the mooring and management activities of these means of transport must be developed once their correct and safe handling has been confirmed. It is here where the need to guarantee the compatibility between these structures with the possible models of vessels of the oil industry stands out.

The following content will explore the essential aspects for the compatibility inspections of docks with vessels, the necessary characteristics that these infrastructures must have, as well as the criteria to be considered when implementing such an evaluation process.

Dock classification according to their features

Gravity docks

Gravity docks are port structures built on a solid base, taking advantage of their own weight to contain the land and resist the thrust of the vessels and loads that are handled on them.

In particular, they have a lower specific surface area (surface area per unit volume) compared to other types of docks. This means that, in relation to their volume, they have a smaller surface area exposed to water and air, which allows a considerable reduction in the rate of deterioration by factors such as corrosion and erosion¹.

Piling docks

These are port structures composed of an elevated platform supported by vertical piles that are driven into the ground or seabed. These piles transmit the loads of the platform, including the weight of ships, cranes, cargo and people, to the surrounding ground.

Among its main features we have:

• Adaptability: They can be built on land with low bearing capacity or in deep waters where the construction of a gravity dock would be too costly.
• Seismic behavior: Due to their lower mass, these structures have a better relationship with seismic forces compared to other types of piers.
• Fast construction: Precast piles can be installed quickly, which speeds up the construction process.
• Versatility: They can be designed for different uses, such as ship berthing, hydrocarbon loading and unloading, maritime access and much more.

Screen docks

This type of dock is composed of a concrete diaphragm wall designed to transmit the loads to the ground by embedment, and to the back of the dock by means of an anchoring system¹. These structures can be formed by sheet piles, either metal or concrete, or by a continuous concrete diaphragm. This type of pier is characterized by its high specific surface area, which implies greater contact with the environment and, consequently, a shorter service life compared to other piers.

The main function of screen springs is to provide stability and resistance to loads, although their durability is affected by prolonged exposure to environmental conditions and wear.

Criteria for compatibility of docks with vessels

Types of vessels

• Handy/Handymax: They are traditionally used for smaller cargoes as they have a capacity of less than 60,000 DWT². Their length limits are between 150 and 200 meters, being the most common due to their size, which allows them to access the vast majority of ports. Their moderate load capacity and dimensions make them easy to handle and moor, so they do not require special adaptations.
• Aframax: This type of tanker is of medium size and has a capacity of between 80,000 and 120,000 DWT. Due to their characteristics, they are used in short and medium-distance oil trade, ideal for those regions with low production.
• Capesize: These are large vessels dedicated to bulk transportation, carrying from 80,000 to 175,000 DWT, however, due to their size they cannot transit through the Panama and Suez canals. Due to their large size, they can only dock in ports with specific infrastructure and sufficient draft to handle these vessels.
• VLCC / ULCC: Very Large Crude Carriers (VLCC) and Ultra Large Crude Carriers (ULCC) are the oil tankers with the largest cargo capacities, ranging from 150,000-320,000 DWT and 320,000-550,000 DWT². Among their main characteristics, VLCCs have great flexibility, while ULCCs can cover long transport routes. However, being the largest vessels, they require terminals specially built for their dimensions and capacities.

Types of marine fenders

Marine fender systems in docks are devices designed to mitigate damage during the interaction between ships and piers. This important task is accomplished by absorbing the kinetic energy of ships, transforming it into reaction forces manageable by the pier structure and the ship’s hull.

There are several types of fenders, each with specific shapes and strengths, adapted to the particular needs of each port. The proper selection of fenders requires detailed technical advice based on the characteristics of the project to ensure maximum efficiency, protection, and compatibility of docks with vessels. Among the best-known fenders we have:

• Cellular fenders: They are made of rubber and have a cylindrical shape with a hollow center, resulting in a low reaction force. These fenders are widely used due to their versatility, durability, and high energy absorption capacity, essential factors for reducing operating costs and maximizing long-term profitability³.
• Cone fenders: Their design allows them to withstand strong impacts from large vessels, such as oil tankers and cruise ships. Among the main characteristics of these marine fenders are their conical shape and their mounting by means of flanges. Additionally, they have similar properties to cellular fenders and can be used in various conditions.
• Tire fenders: Considered as one of the best options to avoid collisions, they are maritime protection devices designed to withstand significant impacts³. They consist of a cylindrical rubber bag filled with compressed air, which allows them to float partially submerged in water. For added protection, they can incorporate a net of tires or chains on their outer surface.
• Bow fenders: Used mainly on small and medium-sized vessels, these fenders are ideal for docks with limited space or difficult access. Their integral design allows them to be fixed to both vertical and horizontal surfaces, providing effective cushioning against high levels of impact without damage.
• Pile fenders: These are highly customizable protection systems that ensure a single point of contact between the vessel and the fender at any water level. They are designed specifically for a type of vessel, providing the highest protection to the vessel. To secure vessels in different scenarios, they are customized to specific characteristics, as well as used in conjunction with other types of fenders³.

Types of moorings

• Long moorings: The most common method of securing a boat, this type of mooring is worked longitudinally in order to avoid bow-stern displacements. During the process, they are placed as far as possible in the corresponding direction (bow or stern) to maximize their retention force. In addition, they allow the vessels to be properly positioned at the berth.
• Cross moorings: They are placed perpendicularly to the bow-stern line of a vessel, and can be located in the center of these areas. Their purpose is to keep the vessel close to the dock and the mooring area, preventing any kind of displacement from the berth. These moorings are extremely useful in providing additional stability and ensuring that the vessel remains in its desired position during berthing.
• Spring moorings: These are those moorings that, starting from the bow or stern of a boat, are directed in an inclined way towards the opposite area, thus forming a diagonal arrangement. Their purpose is to avoid the longitudinal movements of the moored boats, through an effective fastening.
• Elbow moorings: It is a type of mooring carried out with the purpose of avoiding blows between the case of a vessel and the docks, and as a form of support for the process of unmooring. It is carried out by means of ropes fixed to the bow or stern of a vessel so that it is moored to a buoy located in a port or dock. Simultaneously, from the opposite side of the vessel, another line is used and moored to the dock in question. It should be noted that these lines must be placed perpendicular to the point of departure to ensure the effectiveness of the mooring.

Compatibility inspection methods

Load analysis

This is one of the most effective ways to evaluate the compatibility of docks with vessels, because this methodology determines the limits of dynamic and static loads that vessels impose on the pier structure through contact points and tensioned mooring lines. For a more accurate analysis, it is considered that mooring loads are influenced by external factors such as wind, currents, waves, long wave resonance, tides, flows, etc⁴.

Conducting a load analysis involves collecting data on ship characteristics and local environmental conditions, creating ship-tie-fender system models, evaluating external forces and mooring stresses, and finally validating them through field testing. The result is the assurance that the dock design and mooring systems are suitable for maneuvering the types of vessels under consideration.

Review of dock dimensions and draft

The longitudinal characteristics, in conjunction with the draft of a vessel, which is the vertical distance between the water surface and the bottom of the hull, are parameters that must be carefully evaluated to ensure that any type of vessel has sufficient space to be maneuvered, and also to avoid the risk of running aground.

Maritime safety and operability are intrinsically related to the proper sizing of docks, since a dock that is too small or too large can complicate the development of port activities. Revisions of dock sizing and draft facilitate safe navigation, allowing safe and efficient maneuvers, minimizing the risk of collisions and injuries.

Simulations and pilot tests

Maneuvering simulation systems and pilot tests, based on precise mathematical formulations, allow the recreation and optimization of the design of navigation and ship handling areas⁵. Their main attraction is the elimination of the need for human intervention, allowing fast and objective execution. In order to improve the accuracy of the simulations, relevant information provided by pilots, as well as studies and analyses generated at the docks are implemented.

Among the main advantages of these ship dock compatibility tests is the ability to make objective comparisons considering different scenarios and the preliminary evaluation of maneuvering spaces. It should be noted that this methodology must be performed numerous times to confirm the reliability of the results, thus allowing a statistical analysis of the maneuvers. This method is ideal to represent the behavior of a ship in various circumstances, contributing to safety and efficiency in the design and operation of docks.

Conclusions

The importance of carrying out dock and vessel compatibility inspections lies in the need to ensure the correct and safe maneuvering of vessels during critical processes such as the loading and unloading of hydrocarbons. Since there are different types of vessels, each with specific characteristics, it is essential to verify that the piers are capable of supporting and handling the vessels adequately.

The compatibility of docks with vessels, in addition to guaranteeing operational efficiency, works as a way of protecting port infrastructures. On the other hand, these evaluations give way to the adaptation of docks considering specific needs and characteristics, a fundamental aspect to maintain the safety and functionality of the facilities and the processes that take place in them.

References

1. Structuralia (2018, June 12). Structural characteristics of the main types of port docks. Retrieved June 15, 2024 from https://blog.structuralia.com/caracteristicas-de-los-principales-tipos-de-muelles-portuarios
2. Bilogistik (2019, October 22). Vessel types by size. Retrieved June 15, 2024, from https://www.bilogistik.com/blog/tipos-buque-segun-tamano/.
3. Walker Rubber. (n.d.). Marine Fenders: The 5 Different Types. Retrieved June 15, 2024, from https://www.walker-rubber.co.uk/blog/the-walker-rubber-blog-1/marine-fenders-the-5-different-types-17
4. Ministerio de Obras Públicas Dirección de Obras Portuarias (n.d.). Guide for design, construction, operation and conservation of maritime and coastal works. Retrieved June 16, 2024 from https://www.abcpuertos.cl/documentos/MOP/MOP_Vol_2_Estados_de_Carga_Parte_3.pdf.
5. Instituto Mexicano de Transporte. (2023). Simulaciones de maniobras de embarcaciones en tiempo acelerado en Lázaro Cárdenas y Manzanillo. Retrieved June 17, 2024 from https://imt.mx/archivos/Publicaciones/PublicacionTecnica/pt730.pdf