The Present Situation and Development Trend of Ship Fender
With the upsizing of ships and the needs of berthing docks, the ship’s fender equipment has gone through several stages, from the solid rubber fender made of brown rope to the floating inflatable rubber fender. Floating inflatable rubber fender has many advantages such as angular compression, high energy absorption, low pressure on hull and good motion with waves, so it is widely used. According to the international standard, there are two types of floating inflatable rubber fenders: high pressure type and low pressure type. Among them, the low-pressure type is a new addition to the inflatable fender standard of the 2014 edition, which reflects the new demand and development trend of inflatable fender internationally. The new fender varieties include water injection fender, yacht fender, polyurethane solid fender, etc. The air tightness, elastic deformation, compression recovery, parallel compression, angular compression and durability of fender are briefly introduced. The application and installation method of inflatable rubber fender in ship to ship and wharf protection are introduced. The appropriate size of fender can be selected economically and reasonably by calculating the impact energy.
1. Ship fender
With the increase of tonnage of ships, the collision energy of berthing docks increases exponentially. Old fender equipment needs to be updated because it cannot meet the needs of protection. In the past, when a riverboat docked at the dock, the crew would place a ball made of brown rope on the dock to cushion it. The side of the ship with a rubber strap tied into the strip, commonly known as the “handle”, to protect the ship’s side. Lots of old car tyres will be tied to the docks. These devices are called fenders. Later, old car tires were gradually replaced by solid rubber brain protectors, which used the compression of rubber to absorb impact energy. However, the completely solid rubber block has limited deformation ability, little energy absorption and easy damage in contact extrusion. Therefore, it developed hollow structure of the rubber fender, such as cylindrical rubber fender, cone rubber fender, cell rubber fender, etc.
If the cell rubber fender is subjected to only positive pressure, its length will change and it will swell and deform. However, in the process of berthing, the ship will not only be subjected to positive pressure but also be subjected to the action of tangential force, so it will cause the displacement and deformation of the cell rubber fender, forming a curved shape. This kind of fender, which absorbs energy by compression deformation of solid rubber, is suitable for protecting wharves and serving as the head and tail of tugboats in some ports. Since it’s massive, it absorbs relatively little energy, it puts a lot of pressure on the ship when it hits, and it’s hard to adapt to the changing draft.
Floating inflatable rubber fender is a Yokohama innovation. According to the company’s data, the company first made the floating inflatable rubber fender in 1958, which was originally intended to be used for the berthing of whaling vessels on the water, and then mainly used as shock absorbers for the berthing of whale processing vessels, oil tankers and transport vessels. Later, the floating inflatable rubber fender was widely used as a fender for dock structures and between ships. Due to its excellent performance, the product is in great demand in the fields of oil, mining, offshore engineering and drilling, fishing, and shipbuilding.
In April 2000, in order to welcome the visit of the Australian naval fleet to China, a number of 1.5m diameter floating inflatable rubber fenders with sheaths were ordered by the PLA navy Shanghai base to hang beside the dock, providing a guarantee for the safe and stable berthing of Australian naval vessels. This move ended the history of using used tires and solid rubber pads as fender equipment at the port.
For large ships berthing to each other at sea, floating inflatable fender is the best choice, because it is good with waves, can adapt to frequent bumps and collisions with waves, and absorb energy. The hull of the back pressure is small, with fender and shock absorption function. The large ball surfaces are covered with sheaths made from old car tyres.
2. Floating pneumatic rubber fender
2.1 Advantages of floating inflatable rubber fender
2.1.1 Feasibility of angular compression
No matter ship to ship or ship berthing dock, it is first angular contact and then gradually parallel berthing. When compressed by spherical angle, the internal air flow and surface pressure are the same, good deformation ability can adapt to the change of Angle, which is incomparable to the non-inflatable fender.
2.1.2 High absorption energy
Energy absorption is the main index of fender performance, which depends on the working pressure of fender and the travel of compression deformation. In general, the longer the compression travel, the greater the energy absorption. The inflatable rubber fender can usually be compressed to more than 60% of the diameter. If the diameter is 3.3m, the compression line can reach about 2m. When the compression capacity of 3.3m ×4.5m type 80 relies on the fender reaches 60%, the absorption energy can reach 1640 kJ, which is difficult to be achieved by general solid rubber fenders.
2.1.3 The hull is subjected to little pressure
When the ship is close to the ship or the wharf, the damage degree of the hull plate depends on the pressure intensity transmitted to the shell plate by the fender, that is, the pressure per unit area. When the ship touches the solid rubber fender beside the dock, the solid fender will act like a spring. With the increase of compression, the backpressure on the hull plate increases in proportion to the increase of pressure. If the pressure reaches the yield limit of the plate frame, the hull plate will be permanently deformed. The scars on the hulls of old ships docked at the docks are a case in point.
When inflatable rubber fender is pressed against the ball, the contact area expands rapidly and the reaction force increases rapidly with the increase of compression amount. While the fender absorbs energy, it also stops the movement of the ship, but the internal pressure does not change significantly, nor does the pressure intensity of the hull plate. Compared with the solid rubber fender, the hull is subjected to much less pressure per unit area, so it will not be damaged.
2.1.4 Good movement with the waves
Whether the boat is berthing at the dock or docking side by side, the boat will follow the waves. As the tide rises and falls, waves and currents cause the boat to sway and move back and forth. When the inflatable ball is suspended by the dock or the side of the ship, despite the rope, it floats on the water with the ball and is good with the ship. It can also rotate and move freely, and always stays near the waterline. Therefore, no matter the tide rises and falls, the influence of the ship movement caused by the wave will be greatly reduced.
The solid rubber fender is fixed at the dock side, and the rigid friction between the ship sports caused by waves and the fender will lead to the paint damage of the hull board and the wear of the fender surface. When the inflatable rubber is used to touch the fender, the rigid friction will become flexible friction, greatly reducing the damage to the hull surface.
3. The yacht fender
Yacht is to point to the light boat with lesser dimensions commonly, wait like houseboat, travel boat and room boat. These boats are usually docked at the marina and can be docked at public docks or alongside other boats when traveling. Yachts of all sizes are usually equipped with a fender.
The yacht depends on the fender form each different, the color profusion, roughly may divide into the shape of ball and the cylinder. Yachts rely on the weight of the ball is lighter, so it relies on the ball surface is generally made of PVC plastic or polyurea materials, filled with air inside. The surface of the yacht depends on the ball to be smooth, soft and resistant to impact. At present, this kind relies on the ball to have not unified standard, is generally by the experience disposition.
4. Solid polyurethane floating fender
In recent years, the polyurethane floating fender has come to the surface. Since it does not need to be inflated, there is no inflation leakage problem. The range of use is similar to that of floating inflatable rubber ball, and the maintenance is simple, which can be used for 10 to 15 years.
Polyurethane floating fender is also a kind of compressible fender, which is covered with polyurethane foam or plastic foam as buffer medium. In the process of use, the collision energy is absorbed through its compression deformation to reduce the damage to the wharf and the ship. According to customer requirements, this kind of fender can also be fitted with various types of sheaths.