HOW DOES CABLE DRIVE PROPULSION WORK AND WHAT OPTIONS DO I HAVE FOR ANCHOR POINTS?


Most conventional dredges run on cables whether it is a spud dredge with swing wires and underwater anchors or an auger cutter head dredge like the Mud Cat.  Cable drive systems are ideal when working in lined lagoons or smaller bodies of water that are under 1,000 ft. (305m) long.          

Auger dredges with horizontal shrouded cutterheads using a 4-point cable drive system are the lowest turbidity dredge system in the world and the preferred method for hydraulic dredging of contaminated sediments.

When working in a lined lagoon we can outfit the cutterhead with the optional gauge wheels to protect the polyethylene or cement liner from the cutterhead.  Damaging a polyethylene liner in a contaminated or toxic lagoon can result in material from the lagoon entering the ground water supply.  High profile cases around the world where equipment has damaged liners have caused millions in damage and repairs as well as massive fines to the lagoon operator.  Most of the time the simple addition of gauge wheels to a cutterhead can press the liner down as it is cleaned and prevents costly damage and environmental issues.  Hanging pump dredges should not be used in lined lagoons as they can suck up the plastic liner and damage it, costing millions of dollars in damage and requiring a lagoon to be relined.

Set-Up: The above cable drive schematic shows the most common set-up for a 4-point cable drive travel system.  You have four shore anchor points: two at the front shore and two at the opposite rear shore.  The anchor plates are easy to install with a common sledgehammer.  Once you have your 4-anchor plates installed you connect the front right and front left with the front anchor line which consists of two cable tensioners.  Then you connect your rear right and rear left with the rear anchor line.  Position both anchor line “triangles” on the far left or far right (depending on what side of the lagoon you start on) and run the travel cable from the front anchor line triangle, through the dredge to tensioner attached to the rear anchor line triangle, then tension the travel cable.  Once the cable system is anchored and the travel cable is spooled through the dredges windlass and connected to the front and rear anchor lines you are ready to dredge.

Cutting Method: The dredge cuts a precise path that is 7.5 ft.-12 ft. (2.3-3.6m) wide depending on the dredge model that you are using.  The cut will typically be around 2-3 ft. (0.6-0.91m) deep.  Once you get to the end of the cut you can reverse the dredge back to the starting position and take another uniform layer out or ratchet over your anchor lines to the next cut.  The cutting method is very precise unlike hanging pump dredges that drag an excavator type pump on the bottom of the lagoon.  Hanging pump dredges either drag through the material creating large ridges and a very un-uniform bottom or they cut holes into consolidated materials and create a Swiss cheese moon scape on the bottom of the lagoon.  Additionally, the auger cutter pattern is very straight, so it acts as a rudimentary positioning system since the cuts can be measured by the cutterhead length and they are all parallel.

Target Stops: The yellow target stops shown at the front and back of the travel line are for use with radio remote control dredges which come standard on Mud Cat E-Series dredges.  This proprietary technology called Auto SenseTM prevents the dredge from going past the end of the cut and damaging the lagoon liner or wall.  If an operator is not paying attention, then when the dredge gets to the end of the cut a limit switch recognizes the target and automatically stops it and returns it to the home position at the rear anchor line yellow target stop and then waits for the next cut.

A. Cable Span: As mentioned earlier, the total length of the travel cable should be limited to 1,000 ft. with an auger dredge for weight and positioning purposes.  Keep in mind the longer the travel cable the more wind can impact the straightness of the cut.  The MudCat 4-point anchor system allows for up to 65 ft. of lateral movement before the anchors must be repositioned.  Once all the cuts have been made for the current anchor position, you need to leapfrog the furthest anchor point (from front and rear) right or left anchors as needed to continue to cut across the pond and re-install them in the next position to get ready for the next set of cuts.  Additionally, it is important to note that there is a significant bank height at the edge of the pond as there may be some additional requirements for proper cable drive set-up.

B. Models: Cable drive is standard on all MudCat E-Series and D-Series models.  

C. Alternative Anchor Points: There are cases where using the stakes and anchor plates is not possible or there are just other alternatives.  In this discussion we will review these other options: 

1. Cement Blocks: Cement blocks can be poured locally into a square form with a reinforced center anchor point.  This inexpensive and easy solution allows an anchor point to be set in place of the standard anchor plates due to loose soil or gravel that will not hold the anchor plates in place.

 

2. Jersey Barriers: Another option is 10 ft. long Jersey barriers.  They are approximately 4,000 lbs. each and when laid on their side, or slightly dug in, can be an effective anchor point.

3. Tractors / Excavators / Skid Steers: If available then just hook up the travel cable to an appropriately sized tractor, excavator, or skid steer on one side of the pond and then on the other.  After each cut move forward in parallel and you have eliminated the need to reset the anchor plates.  Make sure to follow appropriate safety practices when anchoring to equipment (choking, brakes, load rating, etc.).  Also, make sure that any lateral movement is done at very slow speeds and while monitoring the dredge and cable for any snags or obstacles.

4. Trees or Pilings: If you are working on a lake or in a marina then chances are there will be trees or pilings.  Simply use heavy duty industrial nylon straps positioned as low as possible instead of anchor plates.

5. Buried Cement Blocks w/ Eyelet: When soil is too loose for standard 4-stake anchor plates then buried cement blocks are a good alternative.  Set your eyelet and post in your concrete form.

6. Permanent Posts: If you are working in the same pond or lagoon on a regular basis or for annual maintenance, then installing permanent posts is a great way to reduce labor costs and increase efficiency.  Space the posts up to 65 ft. apart (19.8m).  Simply leapfrog the come along and anchor hook-up to the next post and you are on to the next set of cuts.

7. Drop Down Anchors: When working with high seawalls, canal walls, lagoon walls or seawater intake walls, drop down anchors with pullies can be utilized.  The primary anchor is bolted to the top of the wall while the drop down anchor pully is located further down the wall to create a suitable connection point that is not too high for the traverse / travel line to connect to.

8. Heavy Duty Work Truck Lateral Movement Points: Work trucks can be used in pairs or in combination with a standard anchor point.  This allows for quicker anchor resetting.  Make sure to follow appropriate safety practices when anchoring to a vehicle (choking, brakes, load rating, etc.)  Make sure that any lateral movement is done at very slow speeds and while monitoring the dredge and cable for any snags or obstacles.

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