Case Study – Increasing CSD production for channel dredging

Recently Strategic Dredging executed a consultancy project for one of our clients. The consultancy resulted in a 10% production increase and further improvements to be made soon.
Read below to find out what and how.

The situation

The project consisted of dredging an existing channel of about 11 km long. Luckily te discharge area was roughly in the middle, so that the discharge distance was a maximum of 6 km. Still a long distance, but manageable.

The project was tendered for with an expected progress of 120-150 m of channel per day of 12 hours. When they called us in they dredged a stretch of 70-80 m per day.

For a typical cross section of the channel during our visit, see the below figure.

The challenges

This project had several challenges, which weren’t identified during the estimating phase.

Gas in the soil

Some of the softer soil contained concentrations of gas. This was not anticipated and in fact the contractor was already in discussion with the client, because this has caused weeks of delays due to a needed modification of the vessel and reduced productions. By the time we arrived the issue was solved.

Slope dredging

As shown in the figure a slope of 1 in 4 needed to be dredged on either side of the channel. The dredger had manual controls, so the operator had to manually dredge these slopes. Technically not a problem, but it does cost production as you can’t swing as fast. This latter fact was not incorporated in the initial estimation.

Dense compacted fine sand on port side

Counter to many people’s expectation Fine Sand is more difficult to dredge than coarser sand. In this case the Fine Sand was quite densely packed, resulting in frequent stalling of the cutterhead if care wasn’t given to this area. The swingspeed was greatly reduced in this area.

The combination of dredging a slope and dredging of the dense fine sand resulted in a lower average swingspeed, which in turn resulted in less progress in the channel.

The improvements

After assessing the situation several improvements were made or suggested.

Larger step-size

Initially the CSD was making steps of 0.5 m, or 6 steps in a spudwagon. We tested making steps of 0.6 m. Because of this it was even harder to get through the Dense Fine Sand and that took more time. But the remainder of the swing where there was less soil we could still swing at full speed. Since we now only needed 5 swings per wagon the total result was less time needed to complete a spudwagon. This change alone resulted in a 10% production increase.

Increasing the maximum swing speed

The maximum speed of the side winches was 15 m/min. The maximum swingspeed was thus limited to about 15 m/min. Since this was a smaller CSD this wouldn’t be an issue under normal circumstances. But for this project a higher maximum swingspeed would result in less time needed during a large part of the swing, thereby increasing the overall production.

Slope dredging automation

The CSD is of a standardized variant, so changes are that the manufacturer has developed automation for this dredger. A slope dredging automation, technically a design dredging automation, will allow you to put the design into the CSD’s computer. Subsequently it will automatically operate the side winches and ladder winches to follow the design. It can do this more accurate than a human operator and in the case of this project it would mean the operator could focus more on dredging the Dense Fine Sand, which overall would reduce the amount of stalling of the cutterhead and thus time lost.

Hire professional production estimators

This is the first CSD for this client. Although the company employs experienced commercial estimators, they didn’t have experience with estimating productions of a CSD. Although hiring professional production estimators wouldn’t solve their current problems, it would have prevented many of the commercial challenges they now face.

For instance, dredging a stretch of 120 m per day was really at the maximum technical capabilities of the CSD. With the smallest problem the production would be less.

Having a realistic production estimate would either have resulted in an achievable planning and pricing or in the choice to not participate in this project. The latter would have saved the contractor thousands of euro’s as the project is now taking longer than planned, without compensation.

 

Our visit resulted in 10% higher productions and even further possible improvements after implementing our suggestions. This directly resulted in thousands of euro’s in reduced costs as they could complete the project faster.

What do you think of the client’s situation? Did you experience something similar? Please let us know in the below comment box.

To your success,
Timon Vinke

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