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Underwater excavation is called dredging. A dredge is a machine that scoops or suctions sediment from the bottom of the waterways or is used to mine materials underwater. While the instrumentation of modern dredges is computer assisted, the basic excavation methods of dredges have remained the same since the late 1800s. The two main types of dredges Local 25 members work aboard are mechanical dredges and hydrhydraulic dredges.
Mechanical dredges remove material by scooping it from the bottom and then placing it onto a waiting barge or a disposal area. The two most common types of mechanical dredges are dipper dredges and clamshell dredges. These names refer to the type of scooping buckets they employ. The dredge is mounted on a large barge and is usually towed to the dredge site and secured in by anchors or anchor pilings, called spuds. Disposal barges, called dump scows, are used in conjunction with the mechanical dredge.
Hydraulic dredges work by sucking a mixture of dredged material and water from the channel bottom. The amount of water sucked up with the material is controlled to make the best mixture. Pipeline and hopper dredges are the two main types of hydraulic dredges.
Pipeline dredges suck dredged material through one end and push it out the discharge pipeline directly into the disposal site. Most pipeline dredges have a cutterhead on the suction end. A cutterhead is a mechanical device that has rotating blades or teeth to break up or loosen the bottom material so that it can be sucked through the dredge. Pipeline dredges are mounted to barges and usually not self-powered, but are towed to the dredging site and secured in place by anchor piling, called spuds.
Hopper dredges are ships with large hoppers, or containment areas, inside. The dredge suctions dredged material from the channel bottom through long intake pipes and stores it in the hoppers. When the hoppers are full, the dredged material is either pumped off through a pipeline or the ship travels to an in-water disposal site, where the dredged material is discharged through the bottom of the ship.
Disposal site selection for dredged material is one of the most important and challenging parts of planning a dredging project. The most common disposal methods are beach renourishment, ocean placement and confined disposal facilities.
Beach renourishment is the placement of dredged material on or near the beach through a pipeline, usually to replenish an eroding beach or protect an eroding wetland. This is the most visible dredging project to the public. The dredged material is generally sand coming from inlets, coastal entrance bars, or main offshore waterways. Both hopper dredges and pipeline dredges can use beach renourishment sites. Once the dredged material is on the beach, heavy equipment operators help control the placement and direction of the sand.
What’s the Difference Between a Suction Hose and a Discharge Hose?
A suction hose does just that, it’s a pump, pulls, vacuums, or sucks the material or liquid through the hose. They can also be referred to as Delivery Hoses. Typically, suction hoses can be used for both suction and discharge. Each hose is different, double-check with Atlanta Rubber & Hydraulics if you are unsure or if you are considering a specialty hose.
Suction hoses are constructed to maintain their round shape and not collapse when used under the hose’s normal use. Note that using a hose other than its unintended use will damage the hose.
There is also no such thing as a hose that a vehicle can run over. No matter what, a vehicle driving over a hose will destroy it.
What is a Discharge Hose?
A discharge hose is also referred to as a lay-flat hose. Most discharge hoses are made to handle water and mild chemicals.
Only use discharge hoses with the flow of gravity. Discharge hoses are not meant to discharge liquid against gravity. (Yes, this must be stated and we won’t further elaborate.)
Discharge hoses take up less space than suction hoses, hence the name lay flat. They can be made from different materials and take up less space.
Atlanta Rubber & Hydraulics is a solutions provider of industrial hose, rubber, and hydraulics for a wide variety of industrial markets. We offer custom assemblies as well as industry-standard hose assemblies. Some of our markets include – Rental, Construction, Liquid Waste, Agriculture, Manufacturing and Plant Facilities, Hydraulics, OEM, and Environmental Businesses.
Atlanta Rubber is centrally located in Marietta, GA with 2 satellite locations in Gainesville, GA, and Stallings, NC.
Fenders are buffers between vessels and the wharf. The principal function of a fendering system is to provide protection for both wharf and vessel by absorbing the vessel's berthing energy thus reducing the forces on both the wharf structure and vessel. The used of fender allow a reduction of wharf construction costs and provides ship owners with a satisfactory system for ship protection.
Fender systems vary from quite complicated arrangements to virtually no fendering. The simpler the better. Most usual form of modern fendering is rubber in various shapes, an improvement of the old rubber tire or steel flexible piles.
Preparation of rubber compound
Preparation of steel plates
Application of bonding agent
Compression moulding according to the shape of the fender
Types of Chain Grades
Industrial chains consist of linked segments of durable metal, such as stainless steel, galvanized steel, and brass. They are available in a wide range of sizes and strengths to lift and transport materials across a diverse set of applications.
The tensile strength of the base material—i.e., the ultimate breaking strength—determines the rating and grade given to the particular chain. The greater the breaking strength, the higher the grade, and vice versa. The grade indicated for a chain helps industry professionals identify the types of applications for which it is appropriate. For example, the strength of galvanized chains relies on the amount of carbon present in the metal; as grade 30 chain has less carbon, it is weaker than grade 40 chain and suitable for service duty applications rather than heavy-duty applications.
At Armstrong / Alar Chain Corporation, we pride ourselves on our extensive knowledge and experience with metal chains, hooks, fasteners, wire rope, and accessories. Our experts understand the uses and limitations of chains and can offer advice on the types and attachments suitable for virtually any application.
When selecting a chain for an application, it is important to consider its grade. Each chain grade demonstrates different properties that make it suitable for some applications, but not for others. An analysis of the working load limit (WLL) of the chain— generally one-third the weight of the break strength—can help industry professionals determine its strengths and weaknesses. Below we outline some of the most common chain grades and their properties and uses.
How do Mooring Systems Work?
A mooring system is made up of a mooring line, anchor and connectors, and is used for station keeping of a ship or floating platform in all water depths. A mooring line connects an anchor on the seafloor to a floating structure. We will focus on mooring Mobile Offshore Drilling Units and Floating Production Systems.
The mooring line can be made up of synthetic fiber rope, wire and chain or a combination of the three. Environmental factors - wind, waves and currents - determine which materials make up the mooring system.
Chain is the most common choice for permanent moorings in shallow water up o 100 m, whereas steel wire rope is lighter weight and has a higher elasticity than chain, which is a better choice in water depths greater than 300 m. However, synthetic fiber rope is the lightest weight of all three. Configurations include all chain, chain and wire rope (conventional mooring line to 2,000 m), chain and synthetic fiber rope, and chain, wire rope and synthetic fiber rope combinations are used in ultra-deepwater (greater than 2,000 m).
The mooring system relies on the strength of the anchors. The holding capacity of anchors depends on the digging depth and the soil properties. The mooring lines run from the vessel to the anchors on the seafloor. Anchor types include: drag embedment, suction and vertical load.
A drag embedment anchor (DEA) is the most utilized anchor for mooring floating MODUs in the Gulf of Mexico. The drag anchor is dragged along the seabed until it reaches the required depth. As it penetrates the seabed, it uses soil resistance to hold the anchor in place. The drag embedment anchor is mainly used for catenary moorings, where the mooring line arrives on the seabed horizontally. It does not perform well under vertical forces.
Suction piles are the predominant mooring and foundation system used for deepwater development projects worldwide. Tubular piles are driven into the seabed and a pump sucks out the water from the top of the tubular, which pulls the pile further into the seabed. Suction piles can be used in sand, clay and mud soils, but not gravel, as water can flow through the ground during installation, making suction difficult. Once the pile is in position, the friction between the pile and the soil holds it in place. It can resist both vertical and horizontal forces.
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