VMI Introduces New Self-Propelled Horizontal Dredge MD-822-SP (USA)
VMI is proud to announce the introduction of its new self-propelled horizontal dredge; the MD-822-SP. The MD-822-SP uses a unique patent-pending auger drive system to maneuver and position the dredge during operation.
The auger drive system is mounted directly behind the horizontal cutter head to provide thrust and steer the dredge while digging. By placing the auger drive system directly behind the cutter head it allows a better transfer of force to the point of resistance than placing the drives further away. The cutter head can require a significant amount of force to be applied while digging into tough material. The amount of force applied can have a significant impact on the dredge production rate depending on the material and conditions. By placing the drives directly behind the cutter head it limits the distance the two opposing forces have against one another and also enables the dredge to steer better while digging.
Dredges typically need significant force while dredging but at a controllable low speed. Auger drives were incorporated due to the large amount of thrust they can generate at low speeds. Augers are also capable of producing force in a single direction while rotating. Propellers can generate large amounts of thrust, but require higher rotation speeds. The added benefit of the auger drive system is the ability to spin across the bottom surface. This adds more controllability while positioning the dredge. The augers are capable of being raised and lowered behind the cutter head allowing the operator to use either plain water or the combination of the bottom surface and water to propel the dredge. The dredge operator may raise the augers up, so that the cutter head protrudes further down and spin the augers in water to provide thrust. The dredge operator may also lower the augers against the bottom surface or in some cases submerge the augers into the bottom material to provide additional thrust and stability to the dredge.
The augers are driven by two-speed hydraulic motors capable of shifting speeds on the fly. Control of the auger drives is handled by a single joystick with a high/low button to change between speeds. The augers travel along with the cutter head as the boom is raised and lowered, but stay at their horizontal position while moving up and down. The tilt of the augers is adjustable through use of an adjustable linkage. This allows the operator to adjust the desired tilt of the augers to be maintained. The augers counter rotate one another when driving forward or backward to help counterbalance each other and maintain straight line stability. On fairly stable bottom surfaces the augers are capable of spinning the dredge around by walking along the bottom surface similar to a wheel on the road. The augers’ elevations are independent of one another enabling the ability to travel over uneven terrain. One auger is capable of rising up over a hump while the other lowers down.
A steerable, rear mounted propeller is included to help guide the dredge by providing thrust to the rear of the machine. The propeller is controlled through a single joystick mounted next to the operator’s seat on the opposite side as the auger drive joystick. The rear propeller can be used independently to help steer the dredge or provide additional thrust during operation and traveling.
The MD-822-SP also allows the ability to use to cable as the means of propulsion. An onboard traverse winch common to VMI horizontal dredges comes standard. Once the cable is connected to the dredge a flip of a switch and one lever is all that is required to convert the dredge from auger drive to cable propulsion. An added bonus to the dredge is the ability to display video inside the operator’s cabin. Operators may relay video from cameras on or off the dredge to a display screen inside the cab.
Source: VMI, May 11, 2011