Berthing Operations and Fender Selection

A 100,000 DWT tanker arriving at a jetty at 0.12 m/s perpendicular to the berth carries roughly 1,200 kJ of kinetic energy at the moment of fender contact. That energy must be absorbed somewhere. The fender system absorbs it and converts it to elastic strain energy in rubber or compressed air, then returns most of it as a reaction force on the vessel and the berth structure. Get the fender selection wrong in either direction and the result is either a damaged hull and bent cargo arm from under-designed equipment, or a wildly over-engineered installation that costs three times what was needed. This article is the berthing-and-fendering leaf of the ports and terminals overview cluster: where that hub maps the port call end to end, this one carries the energy arithmetic and the fender-selection method behind it. The PIANC WG33 berthing energy calculator lets designers run these numbers interactively; the calculation method behind it is the subject of this article.

The berthing operation from first principles

Berthing is the controlled transfer of a vessel from open water to a secured-alongside position at a quay, jetty, or dolphin structure. The pilot boards well before arrival, typically 2 to 6 nautical miles off the port entrance, and takes conduct of the vessel from the master. Tugs are assigned based on vessel size, wind and current conditions, and the geometry of the berth. A VL tanker berthing at a single-point jetty in 20 knots of beam wind will typically use four to six tugs.

The approach breaks into three phases. In the stand-off phase, the vessel sits parallel to the berth at 50 to 150 meters off, engines slow or stopped, with tugs positioned to arrest lateral movement and correct yaw. In the approach phase, tug forces and remaining vessel momentum carry the ship laterally toward the berth at a controlled transverse velocity. In the contact phase, the vessel’s hull or its fender panel meets the berth fender system at the design berthing velocity. Mooring lines go out during and immediately after contact.

The critical number is the transverse (normal-to-berth) velocity at the instant of fender contact. All downstream engineering, from the energy absorbed by the rubber to the reaction force on the concrete dolphin, flows from that single figure.

Berthing velocity: the Brolsma curves and PIANC WG145 tables

J.U. Brolsma published the widely-used velocity guidance curves in a 1977 paper for the Rotterdam Port Authority. Those curves, reproduced and extended in PIANC WG33 and then revised in PIANC WG145 (2022, “Berthing Velocity Analysis of Seagoing Vessels over 30,000 DWT”), plot recommended design normal berthing velocity against vessel deadweight for five exposure classes: sheltered berths, easy berthing with good aids, easy berthing without aids, difficult berthing, and exposed open-sea berths.

The velocity recommendations are not theoretical maxima; they are the 95th-percentile observed velocities from field measurements at operating ports. Key reference values from PIANC WG145:

• 20,000 DWT vessel, sheltered berth with tugs and aids: 0.12 m/s design velocity
• 100,000 DWT tanker, sheltered berth: 0.10 m/s design, 0.15 m/s abnormal
• 200,000 DWT VLCC, sheltered berth: 0.08 m/s design, 0.12 m/s abnormal
• Any size vessel, exposed unprotected berth: 0.20 to 0.40 m/s depending on sea state

The inverse relationship between ship size and velocity arises from physics: a larger vessel has greater momentum at any given speed, and the consequences of collision with the structure are more severe. Operators and terminal designers therefore impose slower approach envelopes on larger vessels, backed up by real-time fendering status boards and berthing aids such as laser docking systems and Doppler berthing aids that display transverse velocity to the pilot.

The kinetic berthing energy formula

PIANC WG33 expresses the normal design berthing energy as:

Each coefficient carries a distinct physical meaning.

$C_m$: the added-mass coefficient. When a ship moves through water, it drags a body of water with it. When the ship decelerates at fender contact, that entrained water continues moving and adds to the effective impact mass. $C_m$ is the ratio of (ship mass + entrained water mass) to ship mass alone. For full-form vessels (block coefficient $C_b$ above 0.8) berthing broadside in open water, $C_m$ is typically 1.5 to 1.8. The Vasco Costa formula, cited in PIANC WG33, calculates $C_m$ as $1 + 2d/B$ where $d$ is the mean draft and $B$ the beam. The Ueda formula accounts for the berth proximity effect: in shallow water or close to a wall, the confined water reduces the entrained mass and $C_m$ can drop toward 1.3.

$C_e$: the eccentricity factor. A vessel doesn’t compress into a fender like a bead on a string; it pivots. When the contact point is offset from the vessel’s center of gravity, a portion of the kinetic energy goes into rotating the vessel rather than compressing the fender. $C_e$ is calculated from the geometry of the approach:

where $r$ is the radius of gyration of the vessel about its vertical axis (approximately 0.25 $L_{BP}$ for typical ship forms) and $l$ is the distance from the contact point to the vessel’s center of gravity projected along the berth. For a midship contact on a vessel with $r = 0.25 L_{BP}$, $C_e$ works out to 0.5 to 0.6. Contact at the bow or stern quarter point gives higher $C_e$ (less rotation benefit), typically 0.7 to 0.8.

$C_s$: the softness factor. This coefficient accounts for the elastic yielding of the hull plating during contact. A perfectly rigid hull meeting a perfectly rigid fender transfers 100% of the kinetic energy into compression. A soft fender system that starts deflecting before the hull has fully decelerated means the hull plates participate in absorbing energy. For hard rigid fenders $C_s = 1.0$. For pneumatic or very soft foam fenders $C_s = 0.9$. PIANC WG33 notes that the softness correction is small relative to the other factors and $C_s = 1.0$ is often used conservatively.

$C_c$: the berth configuration factor. In a closed berth (vessel berthing into a confined space with walls on three sides, such as a dry dock or enclosed dock), the water displaced by the hull can’t escape freely and a hydrodynamic cushioning effect reduces the effective impact velocity. $C_c = 0.8$ for closed berths. For an open berth (quayside with open water on all other sides) $C_c = 1.0$. Most tanker jetties and bulk terminals are open berths.

A worked example for a Suezmax tanker:

Ship: 160,000 DWT, displacement $M = 178,000$ t, $B = 50$ m, $d = 16$ m, $L_{BP} = 270$ m. Berthing: sheltered jetty, design velocity $v = 0.10$ m/s. Coefficients: $C_m = 1.64$ (Vasco Costa: $1 + 2 \times 16/50$), $C_e = 0.55$ (midship contact assumed), $C_s = 1.0$, $C_c = 1.0$.

This is the normal design energy. At abnormal velocity 0.15 m/s (applying the $v^2$ term), abnormal energy rises to $803 \times (0.15/0.10)^2 = 1,806$ kJ. The fender must absorb 803 kJ at normal and be checked against 1,806 kJ at abnormal without exceeding structural limits.

Safety factors and abnormal berthing

PIANC WG33 Section 4 applies safety factors to derive the fender design energy from the calculated normal energy. The normal factor is 1.5, giving a fender design energy of $1.5 \times E_{normal}$. The abnormal factor is applied separately: the abnormal vessel (the largest vessel realistically expected at the berth under any foreseeable circumstances, which may be substantially larger than the design vessel) is assessed at its own velocity from the PIANC tables, and the result multiplied by the abnormal safety factor (typically 1.25 to 1.5 depending on the consequence of damage). The governing case, normal design or abnormal, sets the fender specification.

OCIMF MEG4 for tanker terminals adds a further dimension: the terminal must be capable of absorbing a tug-assisted berthing where the tug propeller wash impinges on the hull at the moment of contact, adding an unpredictable lateral impulse. MEG4 recommends that tanker terminals assess berthing at 110% of the normal design velocity to capture these tug-interference scenarios.

The abnormal energy calculation is where many older fender designs fail when a terminal upgrades to handle larger vessels. A fender system designed in 1985 for Aframax tankers at 0.12 m/s may be presented twenty years later with VLCC calls. The energy jump is not proportional to deadweight; it scales with $M \times v^2$, so a VLCC with 2.5 times the displacement and the same velocity carries 2.5 times the energy. Operators who discover this mismatch late often resort to approach-speed restrictions, additional tug allocation, or temporary pneumatic fender augmentation while a redesign is tendered.

Fender types and selection criteria

The fender market produces dozens of configurations, but the engineering-practice choices reduce to five main types. Selection depends on energy demand, reaction force limit, tide range, vessel-size range, and whether the fender is on a permanent structure or deployed operationally.

Cell fenders are the workhorse of high-energy fixed installations. A large cell fender (roughly 1,400 mm height class) absorbs of the order of 1,500 kJ at its rated deflection near 72.5%, with a reaction force around 2,900 kN; the exact rated energy and reaction must be read from the manufacturer’s published performance datasheet for the specific unit and rubber grade. Trelleborg, Yokohama, and ShibataFenderTeam publish cells in this class with comparable specifications. The flat reaction curve is an advantage: the force on the hull increases gently across the deflection range, reaching its maximum only at full compression, which gives the mooring lines time to come taut and share the load.

Cone fenders have a progressive curve: the initial contact force is lower than at rated deflection, which is gentler on lighter vessels making first contact. The SuperCone geometry also allows angular deflection (the fender tilts rather than just compresses axially), accommodating the rotation of a vessel whose approach isn’t perfectly perpendicular. A large cone unit (roughly 1,250 mm height class) absorbs of the order of 950 kJ at about 55% deflection with around 1,800 kN reaction, with the precise figures again set by the manufacturer datasheet for the chosen unit and rubber grade.

Arch fenders are extruded V-section or D-section profiles bolted directly to the quay face. Energy absorption per meter runs 2 to 20 kJ/m depending on section size. They’re economical and quick to replace, which is why they persist on smaller ferry berths, fish quays, and as sacrificial contact surfaces on the sides of large mooring dolphins.

Pneumatic fenders classified under ISO 17357-1:2014 are tested at 80 kPa nominal inflation pressure. A standard 3,300 mm diameter by 6,500 mm long pneumatic fender at the 50 kPa initial-pressure rating absorbs on the order of 1,340 kJ at 60% deflection with around 1,480 kN reaction; the catalogued value depends on the rated initial pressure, and the manufacturer datasheet gives the figure for each pressure class. They float at the waterline and self-adjust to tidal changes, which is their principal advantage over fixed fenders for STS operations. The disadvantage is maintenance: valves leak, skins abrade on rough hull coatings, and a deflated pneumatic fender in mid-STS operation is an emergency. ISO 17357-1 mandates burst pressure testing to 200% of rated inflation pressure for each unit at manufacture.

Foam-filled fenders solve the deflation problem by using closed-cell polyethylene or polyurethane foam inside the rubber skin. They can’t deflate catastrophically, but they also can’t be serviced by re-inflation. After severe compression, the foam core creeps over time and the rated energy absorption declines. Manufacturers typically warrant rated performance for five years and recommend replacement after ten.

The fender performance curve and hull-pressure limit

Every fender sold for port use has a published performance curve: a graph of reaction force (kN) and energy absorption (kJ) against deflection (%), derived from manufacturer testing at 23°C with a 0.1 m/s deflection rate per the test method in PIANC WG33 Annex A. The curve is the primary selection tool.

The fender selection process, per PIANC WG33, runs as follows. Calculate the design berthing energy $E_d = 1.5 \times E_{normal}$. From the candidate fender’s performance curve, find the deflection at which absorbed energy equals $E_d$. Read off the reaction force $R$ at that deflection. Calculate the hull contact pressure: $p = R / A_{panel}$ where $A_{panel}$ is the face area of the fender panel. Check that $p$ does not exceed the hull-pressure allowable for the design vessel.

Hull-pressure allowables aren’t published by ship classification societies as a single universal figure. The governing document is the owner’s or operator’s specification derived from the vessel’s structural analysis. PIANC WG33 Annex C gives typical guidance ranges: 200 to 400 kPa for cargo ships and tankers with conventional single-skin plating, and lower values, 150 to 250 kPa, for vessels with thinner plating such as gas carriers, product tankers, and RoRo vessels. A fender design that generates 600 kPa on the hull of a product tanker will dent the shell plating below the waterline on repeated contacts, leading to classification society findings at the next survey.

Panel sizing is therefore as important as rubber specification. A fender with 2,000 kJ absorption and 2,500 kN peak reaction needs a panel with at least $2,500,000 / 200,000 = 12.5$ m$^2$ face area to stay within 200 kPa on a tanker. In practice, panel dimensions are also constrained by the vessel’s frame spacing, the operating tide range (the panel must stay within the parallel midbody at all tidal stages), and the structural capacity of the dolphin to which the fender is mounted.

The fender reaction at deflection calculator lets designers check reaction force against a given fender’s rated data without hand-interpolating the performance curve.

Temperature and velocity corrections to rated performance

Rubber stiffness changes with temperature and loading rate. PIANC WG33 publishes correction factors: natural rubber fenders tested at 23°C will be approximately 10% stiffer (higher reaction at the same deflection) at 0°C and about 7% softer at 40°C. The loading-rate correction matters more for operational berthing: the 0.1 m/s standard test rate is representative of normal berthing, but an emergency contact at 0.3 m/s generates approximately 15 to 25% higher reaction than the catalogued value. This is why abnormal berthing analysis uses the uncorrected catalogue data as a lower bound and the temperature-velocity-corrected upper bound to bracket the structural design.

Foam-filled fenders show larger temperature sensitivity than solid rubber; at -20°C their stiffness can increase by 30%, a significant consideration for Arctic or northern Baltic terminal designs.

OCIMF MEG4 practice for tanker terminals

Oil terminals load and discharge at high flow rates to vessels carrying flammable or toxic cargoes. The consequence of a berthing impact that damages the cargo manifold or disconnects a loading arm is an oil spill or fire. OCIMF MEG4, the 4th edition published in 2018, is the terminal industry’s primary reference for mooring and fendering at tanker berths and extends PIANC WG33 with tanker-specific guidance.

MEG4 organizes tanker berths by the maximum vessel the berth is designed to handle, expressed in DWT. For each tier it sets minimum fender specifications, maximum design berthing velocities, minimum number of mooring lines by direction (head, stern, breast, spring), and the maximum wind and current limits for berthing, mooring, and cargo operations.

For a dedicated VLCC jetty (maximum design vessel 320,000 DWT), MEG4 guidance leads to:

• Minimum two breasting dolphins on each side, each capable of resisting the full design berthing energy
• Fender panels spanning a minimum of 12 m vertical to accommodate spring tides
• Maximum approach velocity 0.08 m/s normal to berth with tug assistance
• Environmental limits: cease operations above Beaufort 6 (approximately 14 m/s) for berths with limited shelter

Dolphin-based designs separate the berthing function (breasting dolphins carry the fenders and take the berthing impact) from the mooring function (separate mooring dolphins forward and aft of the breasting line carry the head, stern, breast, and spring lines). This separation means the mooring dolphins can be placed at the optimal geometry for line leads without compromising fender positioning for berthing loads. The jetty platform between them carries the cargo arms and utilities without needing to be designed for full vessel berthing impact.

Mooring geometry, line elasticity, and dynamic loads

Once the vessel is alongside and moored, the fender system transitions from an energy absorber to a compression element in the mooring system. Wind, current, and passing-ship effects generate continuous lateral forces that must be resisted by the combination of fender reaction and mooring line tension. This connects directly to the topics covered in mooring forces and station keeping.

OCIMF MEG4 is explicit about line elasticity matching. A mooring arrangement that mixes steel wire ropes with synthetic polyester tails in the same function (say, two breast lines with wire and two with polyester) will have the wire ropes carry essentially all the lateral load until they reach their limit, because steel wire spring constant is 10 to 20 times higher than polyester at the same length and diameter. When the wire parts, the polyester lines suddenly see the full load and may be at 80% of MBL with no warning. OCIMF MEG4 Table 5 and associated guidance specify that all lines in the same direction should be the same material and construction, or synthetic tails of matched elasticity fitted to wire drums.

The standard working load for synthetic mooring lines is 50% of the minimum breaking load (MBL), and for wire rope 55% of MBL, per MEG4. Safety factor for the bollard or bitts holding the line is typically 1.25 on those line loads. The mooring line safety factor calculator runs the MBL check against calculated line tension.

Environmental forces: wind, current, and seiches

Berthing velocity is the primary input to the energy calculation, but environmental forces during the moored condition determine whether the vessel stays safely alongside. For tanker berths, OCIMF publishes wind force coefficient tables (longitudinal and transverse coefficients by heading angle) for VLCCs, Aframax, and Suezmax tankers. These coefficients multiplied by $\tfrac{1}{2} \rho V_{wind}^2 \times A_{projected}$ give longitudinal and transverse wind forces in kN. A laden 160,000 DWT Suezmax presents approximately 2,800 m$^2$ of transverse area; at 20 m/s wind speed (Beaufort 8), the transverse wind force is roughly 490 kN, requiring substantial mooring capacity to hold position.

Currents add a drag force proportional to $V_{current}^2$. At berths on tidal rivers or in channels with significant through-flow (Rotterdam, the Delaware River, the Mississippi), currents of 2 to 3 knots normal to the berth can add 200 to 400 kN of lateral force on a laden VLCC, pushing the vessel into the fenders and loading the offshore mooring lines.

Seiches are periodic oscillations of water in enclosed or semi-enclosed basins (harbors, fjords, large bays) triggered by wind, atmospheric pressure gradients, or tsunamis. A harbor seiche with a period near the natural period of the moored vessel can cause resonant surging and swaying loads that far exceed the steady-state design envelope. Rotterdam’s Maasvlakte 2 container terminal experienced seiche-induced surging forces well in excess of mooring design loads in 2014 and 2015, requiring mooring-line tension monitoring and adaptive load-shedding procedures. Design codes increasingly require a seiche and long-wave analysis as part of the berth environmental assessment.

Tidal range effects on fender design

A fender panel must stay in contact with the vessel hull across the full tidal range. At a port with a 6 m spring tide (roughly the range at Southampton, UK or Baltimore, US), the contact point on the hull moves up and down by 6 m over a 12.4-hour tidal cycle. If the fender panel is only 3 m tall, it will be out of contact at half-tide and the hull will bear directly on the panel frame at the extremes, concentrating forces on narrow structural elements.

Standard practice for high-tidal-range berths is to specify tall panel fenders (6 to 10 m vertical span), stacked fender arrangements with overlapping vertical coverage, or floating fender pontoons that ride the tide. BS 6349-4 Section 7 covers tidal adjustment in detail and requires that the design verify contact geometry at mean high water springs, mean low water springs, and at the 200-year extreme water levels.

Rubber vs pneumatic: the selection decision

For a permanent berth designed around a specific vessel class, rubber cell or cone fenders on fixed mounting frames are the standard choice. They require little maintenance, tolerate rough contact from steel-hulled vessels, and their catalogued performance is stable over a 20-year service life (with periodic inspection and replacement of abrasion-resistant facing panels). The mounting hardware is bolted to the quay face or dolphin front plate and the whole assembly is accessible for inspection from the quay deck.

Pneumatic fenders suit four scenarios: STS operations where both vessels are moving and a fixed fender can’t be positioned; temporary augmentation of an undersized berth during an unplanned large-vessel call; ice-prone locations where a fixed rubber fender would be damaged by ice pressure or differential thermal expansion; and ports where the vessel range is so wide that no single fixed rubber unit spans the energy and hull-pressure envelope.

The decision crossover point: where the required energy absorption exceeds about 3,000 kJ at a permanent berth, the largest rubber fenders (one or two units per dolphin face) begin to compete on cost with two or three pneumatic units hanging on the vessel’s side. Above 4,000 kJ, pneumatic fenders are often the better economic choice for low-frequency-use berths such as dry-docking facilities and occasional deep-draft import terminals.

Dolphin structures and fender mounting

A breasting dolphin is a piled structure that extends above the waterline to carry the fender panel, provide the hard point for the vessel to push against, and transfer the berthing load to the seabed through a pile group. The dolphin’s structural design is driven by the fender reaction force: at full deflection the fender pushes back with, for example, 3,500 kN on a large cell fender, and the dolphin must transmit that horizontal shear to the pile group.

Dolphin pile groups are typically battered (angled from vertical) in alternate pairs so that the horizontal component of the berthing force is carried partly in axial pile compression and partly in axial tension of the battered piles on the far side. A vertical-only pile group under a large dolphin would need very large pile diameters to resist horizontal loads in bending alone. The dolphin deck elevation is set to suit the range of vessels, typically at the height of the loaded vessel’s waterline plus fender panel height plus a working margin; the idle vessel (empty or partly laden) will ride higher but is lighter and carries less berthing energy.

Mooring dolphins are separate smaller structures forward and aft of the breasting dolphin line. They carry the bollards for head, stern, breast, and spring lines but are not designed for berthing impact. Placing bollards on the breasting dolphin itself is avoided because the berthing impact transmits vibration and dynamic shock loads to the mooring hardware; separate dolphin structures decouple these loads.

Breakaway forces and emergency departure

A breakaway occurs when wind, current, or wave forces exceed the combined capacity of the mooring lines, either through a sudden gusts or an accumulation of environmental loads over the watch. The consequence at a tanker berth is usually simultaneous hose or loading-arm disconnection, with the possibility of oil release and fire.

MEG4 Chapter 7 requires tanker terminals to maintain a documented breakaway force analysis. For each mooring arrangement (typically 6 to 16 lines in various configurations), the analysis calculates the algebraic sum of line breaking loads in the longitudinal and transverse directions and compares this with the maximum environmental forces expected during normal port operations. Where the environmental forces could exceed 75% of the total breaking load capacity in any direction, the terminal must implement operational wind-speed cut-offs, additional lines, or tug standby requirements.

The Emergency Towing-Off Pennant (ETOP) is a pre-rigged wire pennant on the tanker’s bow and stern that allows a tug to get a line to the vessel rapidly in an emergency without approaching the manifold area. OCIMF recommendations require ETOP deployment at all tanker berths, with the pennant secured to a quick-release hook on the dolphin, ready for immediate tug connection. ETOP minimum breaking strength is matched to the total bollard pull of the designated emergency tug.

Fender maintenance and inspection intervals

Rubber fenders degrade through three mechanisms: fatigue cracking from repeated compression cycles, ozone attack on the exposed surface, and mechanical damage from vessel contact and ice. PIANC WG33 Annex B recommends formal inspection at 12-month intervals, with records of visual condition, any cracks at the rubber-steel bond zone, and the condition of abrasion-resistant facing panels (the UHMW-PE or rubber face plates that take the direct hull contact). A cell fender showing cracks longer than 10% of the fender circumference at the base steel ring should be replaced; cracking at this point indicates the compression fatigue life is approaching its limit.

Abrasion-resistant facing panels have a shorter service life than the rubber body. UHMW-PE panels on a busy container terminal handling two or three vessels per week may need replacement after three to five years. Bolt-on UHMW-PE panels are typically 30 to 80 mm thick; when worn below 20 mm the rubber face behind them begins to contact hull coatings, transferring abrasion damage to the vessel. Replacement is straightforward because the panels bolt directly to the fender panel steel frame.

Pneumatic fenders require quarterly pressure checks and annual submersion testing. ISO 17357-1 Annex C details the inspection protocol: check inflation pressure (nominal 80 kPa; replace if retention drops below 75 kPa within 24 hours of inflation to rated pressure), inspect valve bodies for corrosion, and check the net for missing or fractured rope strands. Chain stoppers and shackles connecting the fender to the vessel or quay are checked for wear and corrosion at the same interval.

Mooring-line condition monitoring

Synthetic fiber mooring lines (polyester, HMPE / Dyneema, nylon) degrade through fatigue, UV exposure, contamination, and mechanical abrasion on bitts. A line that was 100-tonne MBL when new may be at 60-tonne MBL after five years of port service. Visual inspection detects external damage (cut yarns, abrasion) but not internal fatigue or contamination. OCIMF MEG4 requires records of each line’s service history (date of service entry, total high-load cycles, repairs) and mandates retirement after a specified number of high-load cycles or years in service, whichever comes first.

Mooring tension monitoring (MTM) systems fitted at the bollard with load cells provide real-time line tension data to the terminal control room. They’re now required by several port authorities for large tanker terminals and liquefied natural gas (LNG) terminals as a condition of terminal acceptance. When a line load exceeds 50% MBL (the working limit), an alarm goes to the master and terminal operator. When it exceeds 70% MBL, cargo operations typically halt under the terminal’s emergency procedures.

Limitations of the PIANC kinetic energy method

The PIANC WG33 kinetic energy method is a practical engineering tool, not a precise physical simulation of berthing impact. Several limitations apply.

The method treats the vessel as a rigid body and the fender as a lump-spring, ignoring hull flexibility. For a modern double-hull VLCC with closely-spaced transverse frames, the hull deflects locally at the fender contact point by 20 to 50 mm before the fender has compressed by any measurable amount. This hull deflection absorbs a small amount of additional energy and slightly reduces peak reaction force. The correction is small for conventional steel hulls but can be relevant for aluminium vessel superstructures or very thin-plated vessels.

The eccentricity factor $C_e$ assumes a specific contact geometry that may not hold for angled approaches. When a vessel approaches at 15 to 20 degrees to the berth face (a common situation at open anchorages), the geometry of the contact point relative to the center of gravity changes during the approach itself, and the simple $C_e$ formula becomes approximate. PIANC WG145 discusses this and recommends dynamic simulation for berths where oblique approaches are common.

The velocity input is the dominant source of uncertainty. The Brolsma curves are statistical summaries; individual berthing velocities can be 2 to 3 times the design value if a tug loses power at a critical moment, if the pilot misjudges the last 20 meters, or if a sudden squall hits just before contact. Berthing aid systems such as the Dockmaster (Trelleborg) or BAS system (Cavotec) that display continuous approach velocity and angle in real time on a vessel-mounted console and on a shore display cut the tail of the velocity distribution substantially, reducing the frequency of contacts above 0.20 m/s at monitored berths.

The method also doesn’t account for successive contacts. In moderate swell at an exposed berth, the vessel may contact the fender, rebound, and contact again within 10 to 30 seconds. Each contact adds strain cycles to the rubber. Most fender design standards assume single-contact sizing and rely on general fatigue allowances in the rubber specification. At truly exposed berths, the fatigue life of the fender can be the governing design parameter rather than single-contact energy capacity.

A final limitation is that the standard reaction-force figure is the rated value from a type-test at a controlled temperature and a single compression speed, whereas the fender in service meets the hull at the ambient temperature and the actual approach speed. Rubber stiffens as temperature falls and as the strain rate rises, so a fender rated at 23 degrees Celsius and the standard test speed can return a reaction force 15 to 25 percent higher on a cold morning under a fast approach, and a correspondingly lower force in tropical heat. ISO 17357-1 for pneumatic fenders and the manufacturer performance sheets for solid rubber units publish velocity-factor and temperature-factor curves for exactly this reason, and the designer applies both factors to the rated curve before checking the hull-pressure limit. Ignoring them can leave the hull plating exposed to a peak reaction the bare catalogue figure does not predict.

For operational guidance on the approach procedure itself and pilot-master coordination during berthing, see pilotage operations. For the full treatment of mooring line loads, environmental force analysis, and the moored condition, see mooring forces and station keeping. For tug force requirements during approach, see tug operations and bollard pull, and for the towage charge that those tug movements attract on the port bill, see port dues and disbursements. The hardware on the vessel side of the connection, mooring winches, bitts, and fairleads, is covered in marine mooring equipment and winches. The berth particulars these fender systems are sized against, channel depth, tidal range, and maximum design vessel, are tabulated port by port in world port profiles, and the approach waterways feeding those berths are covered in canals and straits.

See also

Calculators:

• Berthing Energy (PIANC) – kinetic energy with Cm, Ce, Cs, Cc coefficients
• Berthing Energy – Fender Impact – simplified fender-sizing energy
• Fender Reaction at Deflection – reaction force from fender performance curve
• Mooring Line Safety Factor – MBL check against calculated tension

Related wiki articles:

• Ports and Terminals Overview: the cluster hub that maps the full port call, from pilotage through berthing to cargo and departure.
• Mooring Forces and Station Keeping: wind, current, and passing-ship loads on the moored vessel and the line-tension arithmetic.
• Pilotage Operations: the pilot’s conduct of the approach and the master-pilot exchange before contact.
• Tug Operations and Bollard Pull: the tug force that controls the transverse approach velocity at the berth.
• Marine Mooring Equipment and Winches: the vessel-side hardware, winches, bitts, and fairleads, that the lines run through.
• Port Dues and Disbursements: the towage, pilotage, and berth charges the call attracts on the port bill.
• World Port Profiles: the per-port channel depth, tidal range, and maximum design vessel that fender systems are sized against.
• Canals and Straits: the chokepoints and approach waterways that feed the berths these fenders protect.
• Towage and Salvage Operations: the contractual and operational frame for tug assistance and emergency response.