Background
Fender selection is the engineering exercise that determines what equipment is installed at the berth to absorb berthing energy and limit hull pressure. The selection must consider the design vessel, the realistic abnormal vessel (often substantially larger than the original design), the approach speed envelope, the geometry of the berth, the tide range, and the consequences of failure. Modern fender selection is governed primarily by the PIANC Working Group reports and, for tanker terminals, the OCIMF Mooring Equipment Guidelines, both of which provide structured methodologies that are generally accepted by port authorities and terminal designers.
This article describes the kinetic energy approach to berthing, the principal fender types and their performance characteristics, the PIANC and OCIMF design frameworks, the influence of wind, current, and tide, the layout of mooring lines and the role of dolphins and breasting structures, abnormal berthing scenarios, and the calculation of breakaway forces for emergency departure.
Berthing Fundamentals
A berthing operation begins when the vessel reaches the berth approach line, typically 200-300 metres off the quay, and ends when all mooring lines are made fast and the vessel is in the design alongside position. The vessel is normally under the conduct of a pilot with tug assistance, using a combination of own engine, thrusters, and tug forces to control approach velocity, alignment, and final positioning.
The approach is conventionally divided into stand-off (vessel parallel to berth at 30-60 metres off), approach (lateral movement towards berth), and contact (initial fender contact and energy absorption). The lateral velocity at contact, often called the berthing velocity or transverse approach velocity, is the critical parameter that determines berthing energy. Recommended berthing velocities are tabulated in PIANC WG33 and depend on vessel size, environmental conditions, and ease of berth approach.
Kinetic Energy of Berthing
The fundamental berthing energy equation, used in PIANC and OCIMF methodologies, is:
E = 0.5 * M * V^2 * Cm * Ce * Cc * Cs
Where E is the berthing energy in kilojoules, M is the displacement of the vessel in tonnes, V is the berthing velocity perpendicular to the berth in metres per second, Cm is the added mass coefficient (typically 1.5-2.0 for displacement vessels), Ce is the eccentricity coefficient (accounting for rotation), Cc is the configuration coefficient (1.0 for an open berth, less for confined berths where water cushioning helps), and Cs is the softness coefficient (1.0 for hard fenders, 0.9 for soft fenders that deflect with the hull).
The added mass coefficient Cm accounts for the water that moves with the vessel during berthing. For full-form vessels berthing broadside, Cm typically ranges from 1.5 to 1.8. For finer hull forms it may be lower. The Vasco Costa formula and the Ueda formula are alternative methods of calculating Cm and are referenced in PIANC.
The eccentricity coefficient Ce accounts for the rotation of the vessel about her vertical axis during berthing. For a typical approach where the vessel pivots about a point near amidships and the contact is at a quarter point, Ce is around 0.5-0.7, meaning that 50-70% of the kinetic energy is absorbed by the fender, with the remainder dissipated in rotation.
For a 100,000 DWT tanker (displacement around 130,000 tonnes) berthing at 0.15 m/s perpendicular velocity:
- Kinetic energy = 0.5 * 130,000 * 0.15^2 = 1,463 kJ
- With Cm = 1.7 and Ce = 0.6, Cc = 1.0, Cs = 1.0: E = 1,463 * 1.7 * 0.6 = 1,492 kJ
- This is the energy that must be absorbed by the fenders at first contact.
Fender Types and Performance
Modern fenders fall into four principal categories.
Cell fenders (sometimes called cylindrical or Super Cell) are vertical cylindrical rubber units fixed to the quay face with a frontal panel that distributes the load to the hull. Cell fenders provide high energy absorption per unit volume of rubber and a relatively flat reaction force-deflection curve. They are widely used at container, bulk, and tanker terminals. Energy absorption ranges from a few hundred kJ for small units to 2,500 kJ or more for the largest single units.
Cone fenders (Super Cone, ShibataCone equivalents) are conical rubber units with similar mounting and panel arrangements to cell fenders but with a more progressive reaction curve. They are commonly used where a softer initial contact is desired and where the design vessel range is wide.
Arch fenders (V-fenders) are extruded rubber profiles attached to the quay face. They are simpler and less expensive than cell or cone units but absorb less energy per unit length. They are used at smaller berths, on the inner side of dolphins, and for tug fender applications.
Pneumatic (Yokohama) fenders are floating rubber bladders inflated with air, used principally as ship-to-ship transfer fenders and as portable berth fenders for vessels larger than the original berth design. The trapped air provides a very soft and progressive reaction curve, making them suitable for STS operations between a moored vessel and a coming-alongside service ship. Pneumatic fender sizes are standardised in ISO 17357.
Foam-filled fenders are an alternative to pneumatic fenders for STS and emergency applications. They use closed-cell foam in a reinforced rubber skin and are non-deflatable. Their performance is similar to pneumatic at the cost of greater weight per unit.
Each fender’s published performance is given in a Catalogue Performance curve showing reaction force and energy absorption against deflection. The fender is selected by matching its rated energy absorption (RPD, Rated Performance Data) to the calculated berthing energy with appropriate factors.
PIANC Guidelines
The Permanent International Association of Navigation Congresses (PIANC) Working Group reports are the authoritative reference for fender selection. PIANC WG33 (2002), titled Guidelines for the Design of Fender Systems, sets out the structured methodology adopted internationally. PIANC WG145 (2018), Berthing Velocities and Fender Design, updated the velocity recommendations and the energy calculation framework.
The PIANC methodology requires the designer to define:
- The design vessel range, including the abnormal vessel (the largest vessel that may use the berth in unusual circumstances).
- The berthing velocity envelope, drawn from PIANC tables based on vessel size, exposure, and ease of berthing.
- The energy at normal and abnormal conditions, with safety factors typically 1.5 for design and 2.0 for abnormal.
- The maximum allowable hull pressure, typically 200-400 kPa for tankers and bulk carriers, lower for ships with thinner shell plating.
- The reaction force on the structure, used to design the quay and dolphins.
The fender is then selected from manufacturer catalogues to provide the required energy absorption at deflection without exceeding the hull pressure or the structural reaction limit. Multiple fenders along the berth share the load with rotation effects considered.
OCIMF Guidelines
The Oil Companies International Marine Forum (OCIMF) Mooring Equipment Guidelines, currently in the 4th edition (MEG4, 2018), is the leading reference for tanker terminal mooring and fendering. OCIMF specifies fender selection particularly for tanker berths exposed to wind and current, and provides standardised approach methodologies for calculating environmental forces, the resulting mooring line tensions, and the breakaway forces in emergencies.
OCIMF tanker berth fendering normally uses cell or cone fenders mounted on breasting dolphins (separate vertical structures connected to the quay by walkways) rather than continuous fenders along a quay face. This design accommodates the wide range of tanker sizes that may use a single berth and provides a defined contact point for berthing.
Abnormal Berthing
Abnormal berthing refers to berthing under conditions that exceed the design envelope: a vessel larger than design, an approach speed higher than expected, an unfavourable wind or current, or a tug failure. Modern berths are designed to absorb abnormal berthing energy, typically 1.5-2.0 times the normal design energy, without permanent damage but with controlled deflection of fenders into their full compression range.
Abnormal berthing analysis requires:
- A defined abnormal vessel (e.g. an Aframax at a Panamax-design berth).
- An abnormal velocity, typically the 95th-percentile velocity from PIANC tables applied to the abnormal vessel.
- A check that the fender absorbs the abnormal energy without exceeding its catalogue maximum compression and without transmitting force above the structural design limit.
Tidal and Wind Effects
Tide range affects berthing in three ways. First, the vertical movement of the vessel relative to the berth changes the contact point on the fender, with potential for the fender to be pushed under the bottom of the vessel at low tide or above the deck at high tide. Modern designs use deep, vertically tall fenders or stacked fender arrangements to maintain contact across the tide range.
Second, the tide creates lateral and vertical loads on mooring lines. As the tide falls, vertical forces in the lines increase; as it rises, the line angles change. Mooring tension monitoring is increasingly used at modern tanker berths to detect dangerous loads.
Third, tidal currents may make berthing impossible at certain states. Many tanker berths operate berthing windows tied to slack water, with arrival times planned to coincide.
Wind effect on berthing is calculated using OCIMF wind force coefficients, which give the longitudinal and transverse force on a vessel as a function of wind speed, wind direction, and exposed area. A laden tanker presents around 1,800 m² of side area; a containership in ballast may present 6,000-8,000 m² due to the deck stack. A 20 m/s beam wind on a containership in light condition can require multiple tugs and may exceed the safe berthing envelope.
Mooring Layout
The mooring layout describes the arrangement of mooring lines from the vessel to the berth structure. A standard arrangement uses a combination of head lines, breast lines, fore springs, aft springs, and stern lines. OCIMF MEG4 sets out preferred arrangements for tankers, typically using:
- 4 head lines from the bow leading forward and outward
- 2 forward breast lines from amidships forward leading perpendicular
- 2 forward springs leading aft from forward
- Equivalent arrangement at the stern
- All lines of similar elasticity to share loads equally
Mixed line types (steel wire and synthetic) should not be used in the same direction because they have different elasticity and the steel wire bears all the load until it breaks, after which the synthetic suddenly loads. This is a common cause of mooring equipment failures.
Dolphins and Breasting Structures
A breasting dolphin is a separate vertical structure standing in the water in line with the berthing face, designed to take the full berthing reaction force and transfer it to the seabed through piles. Breasting dolphins typically carry the principal cell or cone fenders. Mooring dolphins, smaller structures positioned forward and aft of the breasting line, carry the head and stern lines.
Dolphin-based berths are economical for tanker berths because the cargo arms are mounted on a smaller jetty platform and only the breasting and mooring dolphins need to be designed for environmental loads. This allows a single berth to handle a wide range of vessel sizes by varying the contact dolphins used.
Breakaway Forces
A breakaway is the failure of one or more mooring lines under load, typically caused by environmental forces exceeding the line breaking strength or by inadequate line distribution. A complete breakaway results in the vessel parting from the berth, often with cargo arms still connected; the consequences include cargo arm rupture, oil spill, and possible collision with structures or other vessels.
Breakaway force analysis under OCIMF MEG4 calculates the maximum environmental forces (wind, current, passing ship effects) and compares them with the available line capacity, with a safety factor on minimum breaking load of typically 1.82 (line working load 55% of MBL). Where the calculated force exceeds available capacity, additional lines, larger lines, or cessation of operations is required.
The Emergency Towing Off Pennant (ETOP) is a mandatory feature on tanker berths, allowing a tug to take the vessel off the berth in emergencies (fire on shore, breakaway risk, collision threat). ETOP requirements are set in OCIMF guidance.
Related Wiki Articles
- Pilotage Operations
- Tug Operations and Bollard Pull
- Marine Mooring Equipment and Winches
- Marine Anchor and Anchor Handling Equipment
- Marine Bridge Equipment and Integrated Bridge Systems
- Marine Cargo Securing and Lashing Systems
- SOLAS Convention
- Towage and Salvage Operations
See also
Calculators
- Berthing Energy - Fender Impact
- Berthing Energy (PIANC)
- Fender Reaction at Deflection
- Mooring Line Safety Factor
Related wiki articles
References
- PIANC Working Group 33, Guidelines for the Design of Fender Systems, 2002
- PIANC Working Group 145, Berthing Velocities and Fender Design, 2018
- PIANC Working Group 153, Recommendations for the Design and Assessment of Marine Oil and Petrochemical Terminals, 2016
- OCIMF Mooring Equipment Guidelines (MEG4), 4th Edition, 2018
- OCIMF Recommendations for Equipment Employed in the Bow Mooring of Conventional Tankers at Single Point Moorings (5th Edition)
- OCIMF Wind and Current Force Coefficients for VLCCs, current edition
- ISO 17357, Ships and Marine Technology, High Pressure Floating Pneumatic Rubber Fenders
- BS 6349-4, Maritime Works, Design of Fendering and Mooring Systems
- EAU 2012 (German Recommendations for Waterfront Structures)
- ICS Bridge Procedures Guide, current edition
- INTERTANKO and INTERCARGO terminal interface guidance