Fender (boating)

Fender protecting the side of a sailing vessel as it heads into port

In boating, a fender is a bumper used to absorb the kinetic energy of a boat or vessel berthing against a jetty, quay wall or other vessel. Fenders, used on all types of vessels, from cargo ships to cruise ships, ferries and personal yachts, prevent damage to vessels and berthing structures. To do this, fenders have high energy absorption and low reaction force. Fenders are typically manufactured out of rubber, foam elastomer or plastic. Rubber fenders are either extruded or made in a mold. The type of fender that is most suitable for an application depends on many variables, including dimensions and displacement of the vessel, maximum allowable stand-off, berthing structure, tidal variations and other berth-specific conditions. The size of the fender unit is based on the berthing energy of the vessel which is related to the square of the berthing velocity.

Historically, fenders were woven from rope in a variety of patterns. Fenders of woven rope are still used today by historic boat owners.

Yachts, small leisure craft and support vessels typically have mobile fenders which are placed between the boat and the dock as the boat approaches the dock. Docks and other marine structures, such as canal entrances and bases of bridges, have permanent fenders placed to avoid damage from boats. Old tires are often used as fenders in such places.

Fendering is also used on ports and berths as well. The fendering systems act as elastic buffer devices that are used to slow ships down and prevent damage to the ship or dock structure in the mooring process.

Types

Ship to Berth (STB) Fendering

A cylindrical fender in a harbour in Italy

Marine fenders are used at ports and docks on quay walls and other berthing structures. They absorb the kinetic energy of a berthing vessel and thus prevent damage to the vessel or the berthing structure. There are 2 major categories of fenders for port applications: Fixed and Floating. Fixed fenders are mounted to the berth structure and compose of buckling fenders such as cell fenders, V-type fenders, and non-buckling fenders such as cylindrical fenders. Floating fenders are placed between the berth structure and ship, and include pneumatic fenders and foam-filled fenders.

Fender spacing should be determined by the smallest ship using the berth, as well as the design ships' hull radius of curvature. To ensure all ships can be accommodated at the berth, fender spacing should be about 5–10% of the ship's length for vessels up to 20,000 dwt. Berths handling larger ships can should have a fender spacing of about 25–50% of the ship's length.

Design life of port fenders will vary by ship type, berthing frequency, temperature, saltwater content, and other environmental factors. Fender manufacturers recommend a design life of 5–15 years on berths accepting general cargo, while 10–20 years for more specialized berths such as those accepting tanker ships.

Damaged fendering equipment is the responsibility of either the port owner or ship owner. Port owner responsibility includes damages by ordinary wear and tear by ships, weathering, faulty mounting, incorrect fender type, etc. Ship owner responsibility includes any damages to the fendering system caused by the ship, such as crashing into the berth structure during berthing.

Ship to Ship (STS) Fendering

A Yokohama fender

For bunkering operations between two vessels, floating fenders such as pneumatic or foam elastomer fenders are typically used.

Fender shape, function and application

Cylindrical fenders

Cylindrical fenders are commonly used fenders which ensure a safe and linear berthing for different kinds of vessels. Cylindrical (extruded) fenders are an economical solution to protect most berthing structures, and offer ease of installation. In France, professional mariners call them "bougnafles".

Arch fenders

Arch fenders were introduced to improve upon the performance of Cylindrical fenders. Arch fenders have a better Energy / Reaction force ratio and recommended for all types of applications. The shape of these fenders helps to dissipate the stresses evenly. These extruded fenders are very easy to install and are maintenance free. Generally preferred for small to medium range vessels.

Cell fenders

A very basic wooden fender

Cell fenders are best employed for small or large vessels where reaction force is an important criterion. Among all types of fenders, cell fenders offer minimum reaction per ton-meter energy absorbed. The very geometric shape gives it sturdiness, shear resistance, compact structure and the capacity to absorb energy equally from all directions. The Cylindrical buckling column absorbs axial loads effectively and buckles radially. This results in multi-directional dispersion of energy. Cell fenders are the most durable rubber fenders available and are currently the largest moulded fenders made. 2000–2500 mm high cell fenders are typically used for LNG berths. In order to distribute the reaction force, cell fenders are typically supplied with large fender panels, which keeps the hull pressure low.

Cone fenders

Cone fenders are an improved version of Cell type Fender recently introduced and recommended for all types of applications including high tidal variation sites. This advanced feature of lesser height of fenders improves material handling capabilities of Deck / Vessel Cranes which reduces overall cost of the project. Due to the geometrical shape of the fenders it can deflect more and it can absorb more energy from any direction. Maintaining reaction force, but doubling energy absorption, can be achieved by using two identical cone fenders in a back-to-back arrangement. In order to distribute the reaction force, cone fenders are typically supplied with large fender panels, which keeps the hull pressure low.

Pneumatic fenders

These fenders are extensively used for ship to ship transfers at mid seas, double banking operations, and as vessel-to-berth at dock/jetties. The special property of a pneumatic fender is its low reaction force at low deflection. This property of pneumatic fenders makes them the most suitable fender for liquid cargo vessels and defense vessels with very sensitive equipment. These fenders have excellent energy absorption characteristics and linear load deflection characteristics. Pneumatic fenders should comply to the ISO 17357 standard. The pneumatic fender is also known as the Yokohama fender or floating fender. There are four basic types of pneumatic fenders that comply with the international standard: Type I (Chain&Tyre Net Type), Type II (Sling Type), Type III (Rib Type) and Type IV (Rope Net Type). It has become an ideal ship protection medium used extensively by large tankers, LPG vessels, ocean platforms etc. The most appropriate type will depend on its application and the requirements of the equipment.

Hydro-pneumatic fenders

The submarine hydro-pneumatic fender (SHPF), first developed in the 1980s, is a unique fender system designed to provide minimal hull pressure loads and soft compression during berthing and a large stand-off to accommodate the large bulbous shape of the submarine. Its pneumatic fenders body is stronger than standard pneumatic fenders and is equipped with a specially designed counter weight to keep the fender vertical in water. Each SHPF system is customised specially for each type or class of submarine, depending on its water-air ratio, shape of the hull, berthing-type, energy absorption and jetty design.

Foam elastomer fenders

These fenders are typically made of a closed-cell Polyethylene foam core, which is encapsulated in a nylon or Kevlar reinforced Polyurethane skin. The performance of foam elastomer fenders is comparable to that of a pneumatic fender, but the fenders will not lose their function in case the skin gets punctured. Foam elastomer fenders cannot deflate.

D fenders

D-type fenders are commonly used on vessels as well as small jetties. They are compression-moulded with steel inserts if required.

Square fenders

Square fenders are commonly used on vessels as well as small jetties. They are compression-moulded fenders generally used on tugs, boats and ships.

 Do have excellent sea water resistance and resistance to ozone ageing and ultra violet rays.

Keyhole fenders

Keyhole fenders are the most versatile bow, stem fenders used on tugboats and small port craft/ferries. They offer maximum protection to tugs/ferries with their typical profile and load-absorbing capabilities.

Tugboat fenders

File:Tug Red Cloud YTB-268.jpg

Red Cloud (foreground), a type V2-ME-A1 tug, alongside USNS David C. Shanks, at the Golden Gate at San Francisco, California, 1950s. On the bow is a tugboat fender, also call beards or bow pudding, which are rope padding to protect the bow.

Tugboat fenders are made of high-abrasion-resistance rubber with good resilience properties. They are very popular with small port craft owners and tug owners. These fenders are compression moulded in high-pressure thermic-fluid-heated moulds and have excellent seawater resistance. Tugboat fenders are also call beards or bow pudding. In the past they were made of rope for padding to protect the bow.

Solid rubber fender

Solid rubber fenders have a long history and come in a wide range of anti-collision equipment. They operate by managing shear, rotation and compression forces depending on the fender structure. Designs include D type, cone type, drum type, fan-shaped, rectangular and cylindrical. Solid rubber fenders have high energy absorption and reaction force, are low cost, have a long service life, and are easy to install and maintain. In addition to their use on vessels, they are often found protecting docks as well.

Floating rubber fender

Floating rubber fenders made of solid rubber are a newer protective shipboard equipment. They feature large compressive deformation energy absorption, low reaction force, ability to float and easy installation. They can adapt to changes in tide for dockside installations.

Fender design

There are a number of different standards used worldwide to design fender systems. The most commonly used one, is the PIANC "Guidelines for the design of fender systems, 2002", which is the update of its predessecor from 1984. In Japan the Japanese Industrial Standards (JIS) are commonly used, whereas in the United Kingdom and the United States of America, the British Standard BS 6349:part 4 still used quite regularly.

Designing a fender system basically is determining what the berthing energy of a vessel or range of vessels will be, then determine what capacity the fender needs to have to absorb that kinetic energy and finally how to find a way to avoid the reaction force creating too much hull pressure. In principle, a berthing energy calculation is a simple kinetic energy calculation, adjusted for specific behaviour of a berthing vessel or the specific characteristics of the berthing location or structure.