BY ANNA TOWNSHEND
While dredges still need operators for monitoring and emergencies automated dredge operations are increasing efficiency by minimizing operator error and adjusting systems in real-time. To better understand automation systems for dredges IDR spoke with Jay Wise of Kruse Integration about many of the tools options and consideration for its automation products.
Kruse Integration is a system integrator. The company specializes in automation and factory controls design and programming using programmable logic controllers (PLCs). The article will first discuss Global Positioning System (GPS) which is essential for other types of dredge automation systems.
The installation and equipment needed for GPS varies significantly depending on the type of dredge. Wise said a cutter suction dredge with a swinging ladder has three important coordinates – x y and z – the ladder in relation to the hull; how close the cutter gets to the trunnion; and the depth respectively.
“The y would be straight out parallel to the hull of the dredge “ Wise said. “As the ladder descends the x is coming into the trunnion. The z the depth will be going down. As the ladder descends z increases and x decreases.” Monitoring those offsets can all be done with an inclinometer (ladder depth angle) and encoder (ladder swing angle). If the ladder doesn’t swing a single inclinometer is all that is need to calculate the x and z.
The GPS system should be RTK which will give elevation. If the GPS is not RTK equipped then the dredge needs a tide gauge and a draft gauge for automation. “The tide gauge will give you where the water elevation is and the draft gauge will give you the trunnion level relative to the water level” Wise said. “You need both for real elevation. The draft will change based on how much fuel and weight you have on the dredge.” Instead RTK will provide all that and the exact location of the trunnion in one.
For smaller cutter suction dredges which move around more compared to larger dredges automation systems also need pitch and roll sensors.
Automation on an excavator requires a few more steps and equipment. The system needs inclinometers on the bucket the stick and the boom. The system also requires RTK GPS which gives heading and position. The system also needs GPS on the barge so it can track the excavator relative to the barge and a wireless radio from the barge GPS to the excavator. Excavators with rotating buckets need an encoder to pick up the rotation of the bucket.
The equipment requirements for automating cranes can be even more complicated than excavators. Like an excavator the system needs an inclinometer for the boom. It also needs a GPS antenna at the tip of the boom to give the position of the boom and a GPS antenna on the cab of the crane to get the position of the trunnion on the boom. “In order to get payout for the crane you need z (depth) and you need to be able to calculate the rotation. You need an encoder on the payout drum” Wise said. Alternately there are several industrial pulley rotation monitor transmitters on the market that can be installed on the boom tip to indicate cable payout.
Wise said putting GPS on a dredge for the sand and gravel industry was a very hard sell until about the mid 1990s whereas dredge contractors have longer had a need for GPS systems because the U.S. Army Corps of Engineers requires them to log data and locations on projects. It took the sand and gravel industry longer to realize the benefits Wise said but the industry soon got very reliant on it.
Even with automation the dredges are not completely unmanned and the operator should be monitoring all the systems. Position software (like those from HYPACK or Teledyne) can superimpose borders and lines from AutoCAD. Management can create locations and assign lines data and names to certain projects in the office and import that into the software package on the dredge. It becomes an easy way for the dredge operator and office management or inland managers to communicate about project locations digs and project progression.
“To have a fully automated dredge you need to have a GPS system. Kruse systems send info and receive info from the GPS system so it can make automatic decisions via the PLC in the code” Wise said. GPS is essential for automation but only the first step in automation capabilities. The following outlines many of the automation options designed by Kruse Integration and how the systems work with the dredge’s GPS and the dredge operator.
AUTO SWING SPEED
This system monitors the slurry production in a pipeline. To operate the winches and swing the dredge from one side to the other manually the operator is controlling the swing cables out front attached to anchors off to the side. One winch hauls in and the other pays out the cables tighten to one side and the dredge swings in that direction. As an operator swings he’s typically looking at his vacuum in the pipeline Wise said. The more vacuum the more material that can be picked up.
“Operators typically swing at a comfortable speed to maintain cable tension” Wise said. “But if you hit a sweet spot with a lot of material the operator will often swing right through it too quickly.” With an automated system the operator sets the desired vacuum. If the system detects a lot of material the dredge swing will slow or even stop to collect the extra sediment until the vacuum drops off.
AUTO CAVE-IN DETECTION
This feature is much more applicable for the sand and gravel industry because they are digging so deep. On most cutter suction dredges an automated suction relief valve will open near the pump if needed. If there is a deep enough cave in and the material has covered the valve and the pump the pump starts to cavitate. When the pump is starved of flow and vacuum increases beyond 29 inHg the water vaporizes at the pump vanes and the violent eruption of the vapors can pit and destroy a pump as it cavitates Wise said. “To avoid that you put in a suction relief valve prior to the pump” Wise said. “But if cave ins are large enough it will cover the suction relief valve” he said.
The automation system can detect that the vacuum has been too high for too long (the operator sets that value) and that the pump is cavitating. The system will stop the swinging motion and alert the operator that it’s taking over. The automation will then reverse the dredge to pull it out of the cave in.
Wise noted that it’s also important to monitor the pitch of the dredge and the float on the bow of the dredge. If the bow pitches down too much the dredge will sink. The automation has interlocks to not allow this condition.
AUTO SWING TENSION CONTROL
As the ladder swings to the right one winch is hauling in and the other is paying out to maintain the cable taught. “We’re always monitoring the payout tension of the opposing winch the opposite side you’re swinging to so that the cutter doesn’t walk up over the swing cable” Wise said. Operators can monitor tension controls and gauges to keep the cable adequately tight but not as efficiently as an automated system.
Through AutoCAD a project manager can develop a profile for a project which it uploads into the dredge positioning software for the operator on-board. “You design a profile that you want to cut too certain slopes and angles” Wise said. “The automation will control the swing ladder and advancement to make the cutter follow the design profile.”
AUTO SPUDDING AND REVERSE SWING CONTROL
Upon operator entry the automation will step up the dredge a certain distance after a complete swing. “At the end of each swing the dredge will begin to step ahead at the end of the swing as it reverses swing directions. It’s something the operator can’t accurately do. Typically it’s stepping ahead the size of the cutter” Wise said.
For environmental work often on smaller dredges there is a section at the end of the ladder which allows articulation of the cutter. The automation maintains the desired angle of the knuckle regardless of the ladder angle to keep the cutter at optimum angle.
Booster Pump Control – Many projects use multiple boosters and the problems that come with them can be multiplied as boosters are added Wise said. Manual operations need someone to watch the diesel engine control its speed and watch the gauges on the booster pump. The operation needs to maintain a certain pump pressure. The ideal pressure based on the size of the pump should be designated by the pump manufacturer. An operator on land or on a barge is watching all the information and gauges and speeding it up and down and radioing with the dredge. With automation the PLC on the booster pump can monitor the intake and discharge transmitter on the pump and wireless radio can communicate with the dredge. The automation will control the pump speed to maintain the desired positive intake pressure. “The dredge operator will now be able to see all the information from the diesel engine” Wise said. “But more so we’re showing him the intake and discharge pressure of the booster pump itself.”
Worse case scenario: if the dredge starts to slow down with the booster pump still running the pump will cavitate and shake. If the pressure gets too high the automated system needs to increase the speed. This type of automation is very popular. Wise said “I do more of that than I do even full dredge automation.”
MOVING TO AUTOMATION
The step to automate a dredge can be a big one and contractors need a qualified systems integrator for the project. “The dredging industry is very specific and under supported for automation” Wise said in his blog (visit at blog.kruseintegration.com). His advice in selecting the right contractor for an automation project: find someone familiar with the dredging industry and ask for examples of their work; ask the right questions about your project and data needs; avoid any system integrator that uses proprietary hardware or software and make sure you own the code licenses and documentation when the project is complete.