Fenders - Best practice examples
What you need to know about type approval testing. 📚
In order to obtain a product type approval or type examination certificate for a fender, the respective tests need to be witnessed or performed and verified by an independent and certified third party.
• The minimum test scope typically includes performance testing, durability testing, verification of correction factors and physical properties as published in the catalogue.
• A product type approval is usually valid for five years and needs to be renewed after the validity period or if any product specifics or the production location changes.
Verification testing; to ensure you truly get what you ordered.
The tests for final fenders and material used, serve to demonstrate the performance and material quality of the product. The tests are typically performed on the actual material and fenders that are produced for a project.
Once the specific parameters and requirements for a project have been determined, it is the manufacturer’s task to ensure the final fenders and the material used are compliant with the client’s individual project requirements. Verification testing ensures that final fenders have been produced according to the respective project specifications and/or catalogue values.
🔍 What is shear compression testing?
As an alternative to a simple compression test, a combined shear compression testing is recommended. This durability test combines shear deflection with axial deflection. At SFT, the combined shear and compression test equipment allows for almost any fender size to be tested, yet the number of compression cycles is inherently limited for the largest fenders. For scale models, 25,000 and more test cycles are possible and have already been successfully tested under full time external auditing.
Why makeshift or DIY test presses are no comparison to purpose-built frames. 🔎
Fender testing is a complex and capital-intensive topic, not only in theory but also in practice. Even more important is a reliable and 'fit for us' testing equipment, as test frames are an elementary part of the performance testing process. It is necessary that calibration is performed per test equipment components, but it is most important that items are calibrated as a group as well. ⚠️ There are test companies and institutes in the market that offer fender testing with makeshift test frames, that are by no means comparable to purpose built test frames of the manufacturer.
🔍Why and when to perform fundamental testing?🔎
WHY? Fundamental testing is carried out using a scale model to establish catalogue performance data and to determine correction factors which are the fundamental data for a product type approval.
WHEN? Since these tests are designed to establish fundamental data during the development of a fender type or for a one-time specification, fundamental testing is not suitable to be performed for every fender project due to the high time and cost expenditure.
What is the principle of durability testing?
Durability testing, as part of fundamental testing, is performed once per fender type on a fender not smaller than the smallest commercially sold fender of the same model. The test procedure imposes long-term fatigue on the fender in a short period of time and evaluates its durability.
📏 Edge distance – Choose the right clearance. 📐
The edge distance of the chain brackets and fender anchors, is a vital part of a fender system design. Especially existing structures pose challenges as modifications of the structure are often difficult. Sometimes, the edge distance is forgotten when designing substructures for new constructions and issues could be avoided by consulting with fender manufacturers about general fender system layout including chain positioning. Therefore, we recommend to consider the following during the design stage of fender projects:
Why physical property testing cannot be performed on the final product. 🔎
It is sometimes asked within the industry why physical properties testing can typically not be performed on the final fender itself instead of preparing test samples from the compound before production. Testing physical properties from final fenders is unusual and very difficult, since it would involve cutting larger pieces out of a final fender which could damage the fender. The reason for this is that a lot more material is needed for the physical properties testing than for the traceability testing.
Fender shear chains, what to consider❓ 🔗
Shear chains are recommended for applications where large shear forces are expected, e.g. at ferry terminals or when vessels are winched along the quay.
➡ Installed at an angle of 40° - 45° when fender is undeflected, resulting in about 30° under deflection
➡ Makes an arch movement during compression; therefore, small angle is required, otherwise chains would extent too much and not engage when needed
➡ Need to be installed in the fender center or above and below the fender for proper functioning
➡ Typically, biggest chain of the system, each side takes the full load
➡ Quay wall area and fender location need to allow enough space for shear chain installation and sufficient edge distance for brackets - particularly important for first and last fender position on a quay wall
Why the weight chain is the most important chain for a fender system.
A panel fender system consists of the rubber unit, the steel panel, and the chain system, i.e. – tension and weight chains, and sometimes shear chains.
Did you know that the weight chain of a fender system is the only chain working 24/7? It supports the weight of the panel and avoids sagging – the other chains are only active when the fender is being compressed.
What you should know:
↪ The ideal angle between the substructure and the chain should be 30-35° to provide full support for the fender panel
↪️ If the angle is larger, like 50°, the chain cannot support the panel: all the weight and force of the panel is introduced into the rubber unit (P2)
↪️ The rubber unit might develop cracks, especially at the top flange areas (P3)
Tension Chains 🔗 Why are they important?
Tension chains (or restraint) chains are an essential component of a panel fender system, and works in several ways:
🔸1) Balance the forces in the fender system, maintains position and alignment of the panel
🔸2) Prevent mooring lines being caught behind the panel (when installed at the top of the panel)
Vessel’s Belting / Rub-rails - how can they damage fender panels.
Beltings are like steel bumpers on vessel hulls. They are usually located just above the water line, and most used on ferries, cruise ships, and barges.
If vessels have beltings, it is essential that fender panels have been designed correctly with chamfers and corresponding load cases. A chamfer is like a bevel, placed on certain sides of the fender panel. During tidal variations or un-/loading, vessels slide up and down or along the panel, and chamfers avoid snagging of beltings during these movements.
Final clarification that chemical composition of rubber compound does not reveal the quality of a fender. 🔧
A lot has been discussed about compounding and chemical composition for rubber fenders within the maritime industry. PIANC Working Group 211, dealing with the new “Guidelines for the design of fender systems”, has achieved a breakthrough recently and can finally provide clarity for the industry:
Independent rubber experts stated:
🔸 The chemical composition and density of rubber compound does not indicate the quality of a fender
🔸 A TGA test is suitable for traceability between tested samples and the final product
🔸 A TGA test will not reveal a high- or low-quality product
Fender design is not about believes; it is about facts.🔍
🔸Fenders are an integral element in maritime safety and the protection of people, port infrastructures, and vessels.
🔸Quality and performance of all fender types is vitally important. But there are no rules dictating how to manufacture safe, reliable and durable marine fenders.
🔸International guidelines and standards such as PIANC2002 and BS6349 exclusively refer to the physical properties of the finished fender, which is a true indicator of quality.
🔸A TGA test on the other hand sheds light on the different components and their quantities, used in a compound but does not give any indication about quality. That means, TGA is telling the user what the compound contains, but is not judging the compound by its ingredients.
Why it is important to be aware of the anticipated load cases. 🔍
The load case for a fender panel is unique for each project and influence its design and cost. It is important that the load case for the fender panel is defined exactly in the specifications but more important: realistically.
If the actual load case differs from the specification, various problems and risks occur during operation.
The video on LinkedIn shows the consequences for a steel panel which is designed for flat contact only, but used with beltings:
A vessel with beltings imparts a line load onto the panel; this concentrated load case is so severe, that the panel might break in the contact area.
◀️🔄▶️ What is the problem of inverted Cone Fenders❓
Cone Fenders have different flange sizes on each side: a wider bottom flange and a smaller head flange. Designers often pay only little attention to the installation of these fenders, and some projects end up with the smaller flange installed to the substructure. This ‘inverted’ cone fender impacts the durability and stability of the fender system and the safety at the berth. The weight of the steel panel and rubber unit of an ‘inverted’ cone fender introduces a large moment into the head section of the fender over the full stand-off distance, leading to irregular compression, potential cracks and permanent deformation of the rubber unit.
Pneumatic Fenders – what you should know.🔍
Pneumatic Fenders can be produced with different methods and each has its own advantage when compared correctly. Wrapped fenders typically consist of a homogeneous fender body with continuous nylon tired cord. Others like molded fenders are made from several sections that are put together in the final steps of the manufacturing process. If made from several sections, the tire cord is not continuous and only stitched at the critical connections of the sections which is problematic. The ISO 17357 standard only focuses on materials, design, layers as well as testing and does not indicate a production method. Both production methods are therefore fully compliant with ISO 17357-1:2014.
Physical Properties Testing.
Physical properties testing cannot be performed on the final product, which is why these properties have to be tested on conform sample rubber sheets. Testing can also be done by the customer themselves when a rubber sheet made from the same compound as used for their fenders is tested. Each property and standard have their own conditioning parameters like storage conditions or timing of the test, and the testing processes have to strictly follow that. If tests are not done according to the mandated parameters, results could vary from the requirements. Always double check condition time and storing requirements with the respective standard or consult your fender manufacturer.
Fender Selection - why this cannot be automated. 🔍
Fender manufacturers offer a wide range of fender types suitable for different requirements. The purpose of fenders is to absorb the kinetic energy of berthing vessels, and on the other hand, to transfer the reaction force via different components of the fender system onto the vessel hull and into the berth substructure. High energy absorption while having acceptable reaction forces is key to a good fender system design. However, simply calculating the berthing energy requirements results in a long list of suitable fender types and sizes. How to select the right fender?
Technical Specifications - Three technical details in specifications you should not miss. 📝
Project specifications serve to ensure a common basis for equipment suppliers/manufacturers, and for clients to detail their specific project needs.
Quotations are based on specifications – or at least they should be. Unfortunately, some companies try to cut corners of specifications, offering their products at lower prices as they are not quoting in accordance with the specification.
RPD Values - Why using RPD values in designing fender panels could avoid liability claims.
The most important difference between CV (constant slow velocity) and RPD (rated performance data) values, is that CV values are based on laboratory test values while RPD values reflect operational conditions. When designers use CV values only for the selection of the fender units and for designing the size of the steel panel accordingly, forces will be underestimated. Why is that? CV values are based on constant slow velocities of 0.0003-0.0013 m/s. Due to the viscoelastic characteristics of rubber, fenders behave differently when compressed with different speeds: slow speed leads to lower forces, high speed leads to higher forces.
Fender System Design - What has a dinner recipe 🍲 and fender design 📏 in common?
Imagine a dinner recipe with the best organic ingredients, but the recipe is imbalanced. The result is that dinner will not be satisfactory. The same principle applies to fender systems. Incorrect fender system designs (recipe) have a costly impact on the operation. Even a high-quality, durable rubber unit (organic ingredient) cannot compensate for an imbalanced design. The chain layout for example is an important topic not to be scoffed at. The picture shows two fender systems - one with chains, one without.
Specifying Load Case - Importance of specifying the load case for the fender exactly.
It is important that the load case for the fender panel is specified exactly but more important: realistically.
The problems during operation start, when the actual load case differs from the specification.The video shows the consequences for a steel panel which is designed for flat contact only, but used with beltings :
Carbon Black - Three facts how Carbon Black influences the quality of rubber compound.
Carbon Black (CB) is a well-known active filler which reinforces the rubber compound and has positive effects on physical properties such as tensile strength, tear resistance and abrasion resistance. The key is that an improvement of the properties is tied to the right use of the material.
Rubber Blend - why choosing a blend of natural and synthetic rubber is advantageous for high-quality rubber fenders
Typically, rubber fenders are made from a blend of polymers. Most common polymers are natural rubber (NR), which is sourced in the form of latex from rubber trees and styrene-butadiene rubber (SBR), a synthetic rubber which is derived from petroleum byproducts. Using NR- and SBR-only compounds is not recommended.
Thermogravimetric Analysis (TGA) - Two facts why a TGA for rubber compounds is useful.
TGA is a method of thermal analysis in which a sample of a rubber fender is continuously weighed during controlled heating. By performing a TGA, you are able to:
① Verify chemical composition of the rubber compound - As different components burn off at different temperatures, the loss in weight provides an indication of the sample’s composition.
② Verify traceability between rubber test sheet and final product - TGA results of both should be similar but can deviate to some degree due to laboratory conditions.