Discover Dredging

Oldtimer Club at Damen: Dredges on the Road

Last week, we received the Oldtimer Club Nijkerk1 at our yard. Vehicles of every age and type gathered at the quayside next to our dredges and the club members were entertained in our office and factory on presentations and guided tours. I was happy to present part of my ‘History of Dredging’ story2. It was an engaging lecture for people that are actively involved in keeping rolling history alive. They were very excited to see how we have transported our dredges over time.

Transport of a single pontoon by Stoof Breda

When our predecessor company ‘De Groot’ started it’s business in Nijkerk, the idea was to be as close as possible to the emerging Zuiderzeewerken, the reclamation of the IJsselmeerpolders3. Most of the equipment could be launched from site and towed to the project site for mobilisation. Still, sometimes it was faster to deliver the equipment by truck, especially when it was small enough to fit on the loading bed.

Over time, the dredges increased in size, as did the trucks. And when the hull did not fit on the bed anymore, an (extendable) trailer could be utilised. Any additional equipment, spuds, pipeline, wires, etc. Could be loaded on separate trucks or later into containers for transport. As our products grew in size, this was the way we delivered the dredges. Also influenced by the constraint of the motorway bridge and the lock to the IJsselmeer. It has been a familiar sight to see trucks from the company ‘De Haan’ loading the dredges and bring them either to a port for shipment. Or sending directly to the client by road.

Suction dredge on transport by de Haan Transport

The modular design of our dredges has been a selling point for easy transport and quick mobilisation. This workaround turned out to be an advantage to our customers. The assembly at the destination can be done by local cranes. We can provide supervision and assistance on location. Even our biggest CSD’s have been road transported. e.g. The CSD650 was transported on 10 trucks and 7 containers. When you encounter this convoy on the road it is quite impressive.

Convoy of a dismounted CSD650 on 17 trucks

References

Ewout van Duursen 25 Years: Monitoring the Hopper Process

Ewout van Duursen (l) and colleague installing monitoring software on TSHD Tommy Norton

Regularly, I do write about the adventures of a student internship or graduation that I am involved in. And it really helps those young aspiring engineers to be in the limelight of attention. Today there is a different story on my website, the 25 year work anniversary of my esteemed colleague Ewout van Duursen1. A fitting opportunity to celebrate his achievements during his long career at Damen Dredging Equipment. Ewoud’s specialties are drive systems and programming. And especially in applications for trailing suction hopper dredges. One of the products he has been working on tirelessly are hopper process monitoring systems2.

Dredge master console with hopper process monitoring installed

A good TSHD monitoring system will show a number of processes for operating a trailing suction hopper dredge.

Trailing suction pipe visualisation
Pump performance monitoring
Hopper loading monitoring and draught measurement
Survey and positioning
Recording and reporting

One aspect I want to highlight is the hopper loading and draught measurement. There are some details that might be confusing at first.

Screen shot of a sample hopper loading process

Take for instance a nominally 1000 cube hopper. It may be rectangular 32 m long, 9 m wide and 4 m deep, without any obstructions for simplicity. The mathematical capacity would be 1152 m³. But you don’t want to have the cargo spilling over the coaming. The maximum water level might be 0.5 m below the coaming making the volume 1008 m³. The maximum height of the telescopic overflow may be 0.7 m below the coaming level, as the water draws down about 0.2 m from stagnation level to the rim of the overflow. This measurable volume is now 950 m³.

Diagram of various hopper loading volumes

And the cargo does not only have volume, it also has a mass. And as Archimedes already discovered, mass displaces its weight in volume of water. During design of the vessel and the hopper, the loaded sand is assumed to have a certain density, e.g. 1.6 ton/m³. But the density for the hopper may only be 1.5 ton/m³, as one has to accommodate for the transport water that also enters the hopper. So, you can’t fill the 950 m³ with 1521 ton of sand. The vessel can only carry 1426 ton of total cargo. This is 713 m³ sand of 1.6 ton/m³ and 237 m³ mixture of 1.2 ton/m³. It sounds disappointing when your 1000 cube hopper only carries 713 m³ of valuable sand. The 1.5 ton/m³ hopper density is rather low and the vessel is probably more intended for silt and mud with a lower in situ density. With mud of 1.5 ton/m³ density, you can load the hopper to the rim. And when you encounter heavier sand with e.g. a density of 1.8 ton/m³, don’t try to fill the hopper with this 713 m³ mentioned before. You’ll sink your ship. A good hopper loading monitoring system will enable you to monitor filling of the hopper to the maximum safe cargo capacity.

Heavy weather dredging (Retrieved from YouTube 18/10/2012, unknown source)

References

Young CEDA Evening: the Grabbing History of Dredging

Presenting my lecture on the history of dredging at Young CEDA

Last Tuesday, I gave a presentation for Young CEDA1. The topic was to be about the history of dredging2. And I happily accepted the invitation to educate the younger generation into the tradition of our craft. I consider myself somewhere in between. Not part of the old generation, but past the younger generation. Though I am old enough to have heard the old guys talk about their history and their knowledge of where our modern industry came from. In particular those stories came from the lectures by professor Jan de Koning3 I attended as a student. He really was able to put a perspective on the origins of processes and technologies. Some of those stories have been recounted on my website already4. The oldest dredging project5, the oldest rock cutting technology6 and the oldest dredge canal7 still in use. They were all there at the presentation that evening.

Traditional dredge scoops for peat dredging and waterway maintenance (Credit: Wikipedia)

Here I would like to focus on another development presented that evening, but new on my website. A well known tool in the industry was the dredge scoop8. It has been used for ages, until even recently. However, the working depth is limited to the length of the stick. Longer would make it hard and impractical to use efficiently. In ancient Persia, there were three Banū Mūsā brothers9. Three scholars in 9th century Baghdad, who worked on astronomy, mathematics and engineering. Ahmad Banū Mūsā published ‘The Book of Ingenious Devices’10 which described a tool to pick things up from underwater, specifically oysters.

Oyster grab invented by Ahmed Banu Musa (Credit: 1001 Inventions)

Ahmed Banū Mūsā described in detail the phases in the cycle: lowering, closing, lifting and opening. And it already looks very familiar to the grabs we are using today in the dredging industry known as a clam shell grab. Modern versions are constructed from steel and hydraulically operated. The capacity is usually a couple of cubic meters. But there are designs of up to 200 cubic meters11. The advantage of grab cranes is their simplicity and employability. Whether sand, clay or rock, special versions can adapt a crane to the requirements of your project. The disadvantage is that they can be messy and it is a discontinuous process. Usually involving multiple barges, making them labour intensive. Still, with the right experience and man power, this is the tool of choice for many countries.

Closing process of a clam shell grab under water (Credit: Sape Miedema)

One of the most important phases is the closing process of the clam shell grab. Here are the limitations on the power and operating speed, that are the most important in the calculation of the cycle time and equipment capacity. Sape Miedema has proposed a model for this phase in the grab cycle12. The rest of the cycle is just adding up the operating times and multiplying by your number of cycles.
Sometimes the grab crane is placed on the barge itself to reduce the total investment and running costs. When looking for such a vessel, it can also be interesting to consider adding a trailing suction pipe or a DOP pump to make the vessel even more adaptable to the project requirements.

Damen clam shell grab crane hopper with a trailing suction pipe

Oldtimer Club at Damen: Dredges on the Road

References

See also

Ewout van Duursen 25 Years: Monitoring the Hopper Process

References

See also

Young CEDA Evening: the Grabbing History of Dredging

References

See also