VOSTA LMG dragheads are designed in a modular setup so that the main body can be fitted with different types of visor. This means that the draghead can easily be converted into the required type for the soil that needs to be dredged, without the need for an entirely new unit.
VOSTA LMG standard dragheads are available as Universal draghead, California type draghead and Turbulence visor draghead. Universal dragheads are best suited for general use in varying soil types, a California draghead is recommended for compact and firmly packed soil types, turbulence visor dragheads offer superior performance in soft and free flowing soil.
The drag head mainly consists of a visor carrier and a movable visor, connected by heavy duty hinges. Wear parts are made of highly wear resistant material and can be easily replaced. The position of the visor is self-adjusted by gravity, enabling optimised contact with the ground. The visor is equipped with a water flap at the top (California and Turbulence visor type) or at the aft end (Universal type) of the visor, which is adjusted mechanically. The water flap opening can be adjusted to the soil properties and to the suction head of the dredge pump.
The soil is loosened by pressure water jets and by cutting teeth (California and Universal type), both arranged over the whole width of the visor. The visor carrier includes a jet water connection to the side suction pipe. Jet water nozzles are arranged in a replaceable steel beam which is mounted below the hinge line. The effect of the pressure water can be adjusted to the dredging conditions by using different sets of nozzles.
Enquiries: components@vostalmg.com
Universal draghead type UJ
The Universal Draghead mainly consists of a visor carrier, flange-mounted to the suction pipe and a pivoting mounted self-adjusting visor. The soil to be dredged is loosened by cutting teeth at the visor and the effect of pressure water supply through special nozzles. The visor is equipped with a mechanically adjustable water flap for supply of additional transport of water when dredging in soft grounds.
VOSTA LMG Universal Dragheads offer a combination of high excavation capabilities for loosening the soil and optimised hydraulic properties for mixture transportation. High mixture concentrations are possible in many kinds of soil. Concentrations are more constant even in more compact soils, where the water flap is blocked in an optimised position. Optimal position depends on specific soil properties and dredging depth. Production can be optimised by controlling the contact force of the draghead to the ground through a swell compensator system.
Universal Dragheads are welded constructions made of structural steel. Cutting teeth of abrasion resistant cast steel and jet water nozzles are arranged over the whole width of the visor. Jet water nozzles are arranged in a replaceable steel beam and equipped with wearing bushes. Visor carrier and visor are connected by heavy duty hinges with wearing bushes. The visor is equipped with side wear pieces of highly wear resistant material. Wear pieces as well as cutting teeth can be easily replaced.
A grid is provided to avoid suction of big stones or blocks. Strong rubber fenders prevent damage when the draghead touches the ship's hull. A safety joint and shear bolts can optionally be provided to safeguard draghead from excessive trailing forces.
California draghead type CJ
The California draghead mainly consists of a visor carrier, fixed to the side suction pipe and a pivot mounted self-adjusting visor. A self-adjustable visor with an optimised shape forms an enclosed space directly above the ground. The visor is equipped with knives and ripping teeth to loosen compact soils. Pressure water is used for fluidization of the ground. Wide dragheads are equipped with two independent visors, so that the whole suction area is in close contact to the ground even on uneven ground. The California visor has mechanically adjustable water inlets on top, allowing supply of additional transport water in soft grounds.
This type of draghead is particular suitable for dredging firmly packed and strongly binding types of soil. Due to the modular design a VOSTA LMG California draghead can easily be converted to a VOSTA LMG draghead with a Turbulence visor or a Universal visor.
The California draghead is a welded construction made of structural steel. Knives and teeth can be easily replaced. Wearing parts are made of highly wear resistant material and can be exchanged or armoured by built-up welds. Strong rubber fenders are provided to avoid damage to the ship's hull. A safety joint and shear bolts can optionally be provided to safeguard the draghead from excessive trailing forces.
The California draghead is a welded construction made of structural steel. Knives and teeth can be easily replaced. Wearing parts are made of highly wear resistant material and can be exchanged or armoured by built-up welds. Strong rubber fenders are provided to avoid damage to the ship's hull. A safety joint and shear bolts can optionally be provided to safeguard the draghead from excessive trailing forces.
Turbulance Visor draghead type TJ
The self-adjusting visor of the Turbulence Visor draghead has an optimised shape and forms a closed space directly above the ground, so that the suction capability of the dredge pump is concentrated in the enclosed area. Wide dragheads are equipped with two independent visors to achieve a close contact even on uneven grounds. Adjustable sliding shoes at the visor end may be used to set the gap between ground and visor for the supply of transport water. More compact soils are loosened by jet water nozzles in front of the visor carrier. The Turbulence Visor also has mechanically adjustable water inlets on top, allowing supply of additional transport water in soft grounds.
This type of draghead enables high concentrations in various kinds of soil. Special advantages are the low weight and low trailing forces, especially when a suitable swell compensator system is used.
The draghead is a welded construction made of structural steel. Wearing parts are made of highly wear resistant material and can be easily replaced or armoured by built-up welds. Strong rubber fenders are provided to avoid damage to the ship's hull. If required, a safety joint and shear bolts can be provided to protect the draghead from excessive trailing forces caused by collision with large obstacles on the ground.
This type of draghead enables high concentrations in various kinds of soil. Special advantages are the low weight and low trailing forces, especially when a suitable swell compensator system is used.
The draghead is a welded construction made of structural steel. Wearing parts are made of highly wear resistant material and can be easily replaced or armoured by built-up welds. Strong rubber fenders are provided to avoid damage to the ship's hull. If required, a safety joint and shear bolts can be provided to protect the draghead from excessive trailing forces caused by collision with large obstacles on the ground.
Special types
Active dragheads type UJA
Active Dragheads offer the highest production rates possible, even in compact soils and at varying dredging depths. Special attention is given to an optimised pressure water injection. The pressure nozzles can be arranged at the visor carrier and / or at the visor itself according to customers' preferences.
The hydraulic power pack can be installed on deck or as an integrated part of the draghead. It is designed as a plug-in unit and consists of a submersible, electrically powered pump unit with all necessary control elements and a hydraulic oil tank with a buffer for pressure compensation. There is no need for hydraulic pipes on the trailing suction pipe, only power and signal cables are required. Hydraulic cylinders are equipped with a continuous position measuring system.
Various control systems are available from VOSTA LMG, enabling efficient use of the active draghead. The basic version of the control system includes continuous position indicators and switches for bridge desk mounting. Advanced dredge control and automation systems adjust the visor position and water flap automatically. Visor position can be controlled for instance with constant position, pre-selected grab depth or cylinder force and water flap position according to suction pressure at draghead. In case of upgrading an existing dredge VOSTA LMG provides necessary support to adapt or replace the dredge control system.
Dragheads for environmental dredging type KDT
This type of draghead is part of a special loading technology developed by VOSTA LMG. The transport water runs in a closed circuit and is not conveyed through the overflow ducts to the outside of the dredge, reducing the intake of contaminated particles. Transport water is fed back to the draghead and used again, so that only a small amount of transport water is sucked from the outside of the draghead.
Dragheads of type KDT are equipped with a self-adjustable visor and jet water supply at the visor carrier, similar to dragheads with a turbulence visor. Transport water is supplied via an additional connection between the side suction pipe and the visor of the draghead and fed into the suction area towards the suction mouth. Flow rate of transport water can be controlled by a flap.
The draghead and the system as a whole have demonstrated their functionality and efficiency in extensive model studies and field tests.
To meet a wide range of dredging requirements, a range of standard options for the dragheads is available. Other options are available on request.
- Safety joint - prevents excessive trailing forces in case of underwater collision
- Domite wearplates, minimum hardness 700 Brinell, weldable
- Different size of jet nozzles
- Turtle deflector
The modular design of the dragheads allows the unit to be easily adapted to different types of soil. The visor can be changed without replacing the whole draghead. This will increase flexibility of the hopper dredge, while decreasing stock on board.
