How to dress your dredge pump for success

C. de Groot Double walled dredge pump, 1970

Sometimes, we are just reinventing the wheel. In 1970, when we were still this company ‘C. de Groot’, we delivered a dry soil transfer pumping station ‘GP6’ to Volker Stevin. Special requirement of the client, was to have a double walled dredge pump installed. Because of the pressurised outer cover, the cast inner pump wall had less stress and lasted longer. Even more, in case the inner wall became damaged, it leaked into the gap between inner and outer wall. No mixture spilled into the pump room. Double walled pumps were already around in the ‘60s, but always in cast material. C. de Groot was the first to build one from steel plates. In effect, we were the inventor of the double walled dredge pump. Since 1970, a lot of high performance or safety demanding pumps have been built this way. Not only by us, but later by many other manufacturers1 also.

Now, we might upturn history again, as we developed a new outer cover for dredge pumps2. This time, the outer cover can be literally tailored to your pump. It is of woven flexible material, that can be zipped around any new or existing pump. Well, it involves some modifications of the steel pump doors, but it should fit on any size or design. It will withstand the pressures occurring during a pump burst, when the cast casing is worn through.

We went through several interesting design and test cycles, before we finally had a solution, that ticked all the marks:

  • Light weight
  • Easy access
  • Water tight
  • Safe and reliable
  • Durable
  • Retrofit

Added advantages are: less weight on the dredge pump is more cargo in the hopper. And as fabric can be slid through the gap between lowest point of the pump and the bottom plate of the hull, the pump will stay at the lowest possible location, favouring a good NPSHa.

Ewout van Duursen will explain more about how we achieved confidence in this concept, on the CEDA Dredging Days3. We did a lot of practical tests and thereby gained operational experience on handling a real life DynaCover. We discovered that the handling is much easier than a steel cover, indeed. As for the experiments: stay tuned, because the presentation will involve some Mythbuster style research, rather than academic experiments. In a way, fitting between the other interesting more scientific presentations of the Friday morning session of 11:00.

In line with the practical nature of this research, we have a sample of a DynaCover with us, for you to judge yourself4. It will provide you a tangible glimpse of the future, where double walled dredge pumps look like this:

Damen DynaCover double walled dredge pump, 2017


  1. Double walled dredge pump for longer life, Ports & Dredging #73, p13, IHC, 1971
  2. Innovative outer pump cover zipped on
  3. Presentation session Ewout van Duursen
  4. Damen booth

See also

CEDA Dredging Days

Hopper Loading: What Happens Beneath the Surface

Hopper loading in the sunset

Above is a typical view from the bridge of a trailing suction hopper dredge. I had to visit this dredge, because the operator had problems loading the hopper. As the valuable cargo of sand is always covered beneath a layer of water, they had no idea what the problem exactly was. Although the waterline was dangerously high, the delivered pile of sand on the quay was relatively small. After a couple of dredge cycles, measuring the loading curve and sounding the surface of the sand beneath the water layer, it dawned to me, there were in fact two problems. One, the dredged sediment was much heavier than the hopper density would allow. Two, the distribution in the hopper was not very efficient and on the return trip home, most of the sediment was washed out again. The first problem took some time to convince the owner, but finally the argument came through. The last problem was very difficult to imagine for them and as I had no proof or calculations to show them, they could not visualize the faulty loading process. Luckily, they accepted the proposed modifications and could make some profit again.

Ever since that incident, we were looking for some way to model the hopper loading more credibly with better visual reporting. Simultaneously, this could also improve our design and layout of our hopper dredgers. One of the best models we could use, were those by Van Rhee1, or by Miedema and Vlasblom2. As we have close contact with the Delft University of Technology, we asked them for a graduation project to improve these calculations. Eventually, Ben Sloof applied for the assignment and proposed a very interesting approach to solve this mystery.

Whereas the existing models rely on analytical models with at most a few well defined areas, Ben indicated, that there was also the possibility to address this with a regular CFD solver. He would have to modify the various components to work with particles in the fluid, but he was convinced he could pull it off. As this implies a lot of coding and knowledge of fluid dynamics, this was a tall order and certainly took some time. Now, he is almost ready to graduate. As this is a very interesting topic for everyone, he will take part in the Young CEDA pitch talks3 at the CEDA Dredging Days. His presentation on a ‘Re-engineered model to optimize the settling of material in the hopper’ will certainly be interesting to attend.

Concentration and Velocity


  1. Van Rhee hopper loading model
  2. Miedema & Vlasblom
  3. Young CEDA pitch talks

See also

Damen Standard TSHD

Damen MAD

Countdown to the CEDA Dredging Days 2017

Audience at CEDA Dredging Days 2015 (Credit: CEDA 2015)

One week from now, the CEDA Dredging Days 2017 will be held in Rotterdam1. This is THE event for the dredging industry to share the latest developments on a technical level. So far I’ve attended every single Dredging Days since 1993. None of them have been a disappointment. There is always something new to discover. Either a presentation with a novel development, or new people to meet or old acquaintances that share a new story on the latest work.

As this is the place to be for discoveries in dredging, I will start of my first serious posts with this event. It is for you to discover whether my personal interests will be exciting enough to read. I do hope you will be fascinated enough, that I may serve you as your personal reporter on site.

There are a lot of exciting items on the program and I can’t cover them all, but most interesting to me are:

  1. Technical visit to the Prinses Beatrix Lock expansion project2
  2. The presentation of the Checklist for Successful Dredging Management3
  3. Presentation Klaas Slager, A novel approach to determine dredge pump NPSHr in field conditions
  4. Presentation Ewout van Duursen, New approach of a double walled pump house
  5. Young CEDA Pitch Talk by Ben Sloof, CFD in hopper loading calculations
  6. Damen Booth at the Dredging Exhibition4

Each of them have a personal interest to me, one way or the other. As there is a lot to discuss about these items, I will cover them in their own posts over the course of the next weeks. Maybe interspersed with reports of noteworthy events as they happen.

So, I hope to see you on the CEDA Dredging Days, I will be at the Damen booth #15 on the Dredging Exhibition. Or you can come back and read my reports here.

Receiving a visitor at the Dredging Exhibition 2015 (Credit: CEDA 2015)


  1. CEDA Dredging Days 2017
  2. Technical visit
  3. Checklist for Successful Dredging Management
  4. Damen Booth at the Dredging Exhibition

See also