1-Introduction
Fender systems are a key aspect in canal navigation, as they are the safety barrier for the security of navigation, operations, structures, vessels and people. Due to the many peculiarities of inland navigation, e.g. vessel beams adjusted to the very narrow canal/lock lanes, constant lateral frictions, shear loads, locks entrances, constant traffic and many other particularities, the performance of fender solutions depends on the designers understanding of how fender systems work and how solutions can be customized to canal characteristics.
Nowadays, it is impossible to successfully operate a canal without the correctly designed fender system. A wrong fender solution can cause many problems, increase the risk of accidents, delays or even interruptions in navigation. In some cases, like the Panama Canal, traffic interruptions can have a global impact in navigation and major economic losses.
Despite the importance of customized fender solutions for canals, the available international fender standards and norms typically lack in the requirements in canal navigation. The intent of the presentation is to summarize the guidelines about Fender Systems focusing on inland/canal navigation, explain the design challenges, and show a suitable approach to all these challenges.
2- Main challenges for inland navigation projects.
Currently, designers face many challenges when selecting Fender Systems for canal navigation:
- Canal expansions and vessel sizes increase. The continuing increase in vessel dimensions (size and displacement) together with the expansion of canal capacities – e.g. the Panama Canal expansion – allowing larger vessels to navigate through these infrastructures, makes traditional solutions unsuitable. Designers need to consider the expected vessels that will use the fenders during the complete life cycle, and we can assume that those vessels will be larger than today.
- Shear forces. Fender material must be able to support shear forces, since inland navigation through canals, results in constant traffic, flowing parallel to the fender surface. Shear forces are based on the reaction force of the fender system times the friction coefficient of the low friction material. Therefore, the designer needs to have a good understanding of fender materials and properties, to find a solution with low friction coefficient.
- Wear/abrasion. The continuous flow of traffic thru canals, results in constant wear and abrasion on the fender surfaces, which are more intense compared to fender wear/abrasion on typical pier berths. The use of special materials with low friction coefficient and abrasion index, such as UHMW-PE is essential to reduce wear and friction loads as well as fender deterioration. Also, it is essential to understand testing procedures to measure and control material resistance to abrasion and other properties which have an impact on material durability.
- Life cycle/traffic interruptions. Interruption of navigation along a canal caused by fender failure, maintenance or replacements has an important economic impact and can have consequences on global navigation in some cases. For that reason, fender solutions for canal application should have extended life cycle horizons, compared to standard fender systems.
3- Guidelines for a design approach
- The importance of designs. Fender System performance and a long life cycle will be the direct result of good fender design. An incorrect design will result in fender failure over a short term. Fender design requires a good knowledge and understanding of fender types, materials, standards/norms and solutions available in the industry. It is always recommended to look for advice of a reliable fender manufacturer to select and verify fender solutions.
- Fender Type selection. The analysis of which fender type is more suitable for canal applications depends on many different factors, and as in any other fender project, each case needs a customized solution. There are certain types of fenders which have suitable features for inland navigation:
- Arch/Square Fenders – Elastomeric rubber fenders with UHMW-PE pads. For this type of fenders, it is important to define how the UHMW-PE pads are fixed to the fender. Fixing the pads with bolts to the embedded steel plate inside the fender proves to be the much more robust solution than vulcanization, also in terms of maintenance cost
- Wheel/Roller Fenders – specially designed for lock entrances, and corners.
- Fender guidewall solutions for lock entrances – to provide guidance to vessels and support the correct approach into the usually narrow entrances. Guidewall solutions include the design of complete fender systems and the auxiliary structures to fix the guidewall, like pilings, etc.
- Fender material selection. Inland navigation applications need materials with special low friction coefficients and low abrasion index to reduce wear, especially these two materials should be carefully checked:
- Rubber, used as energy absorbing device, the properties recommended in PIANC Guidelines Appendix A – 7.3 are those that help to assure acceptable resistance to the effect of aging and environmental impact.
- UHMW-PE. Used as the contact surface between vessel and fenders, the use of polyethylene with ultra-high molecular weight not lower than 5 million g/mol and sand slurry test of approx. 15 based on ASTM 4020 (steel 0=100) is highly recommended.
- Test control. Marine fenders are an energy-absorbing device. Therefore, technical specifications for canal fender systems need to specify the procedure to determine and report performance of fenders. PIANC 2002 Guidelines, Appendix A provide a good procedure for testing fender performance under compression forces. However, for the special cases of canal fender systems which are subject to constant shear forces, it will be necessary to implement also a procedure to determine shear forces in combination with compression forces allowing only fenders tested and approved under compression-shear combination to be used for these applications.
4-Installation, operation and maintenance
Fenders are safety-critical systems which protect people, the environment, ships and structures from harm. To do this, fenders must be installed, used and maintained correctly. For the case of inland navigation canals, special attention should be put on the duration of installation and maintenance, since any of these activities will interfere daily operations and block traffic. Our presentation will provide guidelines and recommendations should be provided to assure that fender solutions are designed to minimize those interruptions.