Last week we had another of our training courses for service engineers and field service engineers1. The interaction with people actually working with our products is quite refreshing and every time I understand their issues better. One of those issues is that they have to discuss with the client are spares for the wear parts. In a planned maintenance context, wear parts are a little odd. Sometimes, they are worn away or break down unexpectedly. And that is the moment customers call for spares. We do have a lot of spares on stock, but sometimes even we run out of stock or we advise to use a special execution of the concerned part for the specific operation of the client. And then we have to inform the service people and the client that there is a long lead time. Several times, they are filled with disbelief and under such circumstances it is very difficult to explain the reasons behind it. So, that is why I developed this little game to experience the waiting time for special wear parts.
It is based on the old board game of ‘Snakes and Ladders’2. All it takes are the board, one dice and as much tokens as players. All start at the first position. The places are all phases in the manufacturing of the wear parts and each have their specific issues.
Each pattern is used multiple times and wears down, itself. Also, some patterns have to be configured for the specific application, execution or material of the wear part.
Moulding: the pattern is placed in a casting box and filled with sand.
Sometimes there are more casting boxes needed and they have to be stacked carefully. Depending on the configuration, this step might be very short. Then you go directly from 2 to 4.
Part of the casting system is already in the sand box with the pattern, but it has to be finished as the last part of the preparation.
The material is melted in the furnace. This can take some time, depending on the size of the cast.
The actual casting is done in minutes. Fifteen, at the most.
But the cooling in the casting box takes weeks. Wait one turn.
Sometimes the casting has not gone properly and the cast have to be done again. Back to square one.
Satisfied with the cast, then it has to be touched up at the fettling station.
A special heat treatment brings the final hardness and toughness to the product.
The fitting surfaces of the wear parts have to be machined.
Rotating parts have to be balanced. For non-rotating parts, this can be skipped.
Then there is the bottle neck: quality control. If there is a deviation that can n ot be mitigated, you have to go back to square one.
Depending on the location, transport can take weeks.
Don’t start me about customs handling. Your anticipated spares are in bonded storage and customs is missing a document, wait some weeks or skip a turn.
Finally, you’ve made it! Installation on the dredge.
Message of the game: keep your warehouse well stocked with wear parts3,4, or your dredge will be idle for months, before you can work again. Have fun!
As promised, I still have several stories for you and this is another one. As you may remember, we’ve visited China for attending the WODCON in Shanghai1 and afterwards travelled to Beijing for sightseeing. A must see destination in Beijing is the Forbidden City. The epicentre of ancient Chinese power, the seat of the emperor. Once the exclusive domain of the supreme ruler, now a tourist attraction for the general public. The Forbidden City was mainly build in the Yongle era of the Ming dynasty2 between 1407 and 1420. It comprises numerous courtyards and halls and temples. All the buildings are surrounded by thick walls and a moat.
This moat is an impressive 6 meters deep and 52 meters wide. That is a big moat. But remember it is long: 3.5km around3. So, it is an impressive moat. Now consider this moat is dug in the fifteenth century. It has been dug by hand! Imagine, thousands of labourers digging, carrying and removing the soil from the moat. That is quite an operation.
To put this in perspective. The moat has a volume of 6x52x3,532m=1,101,984m³. Yes, that is over a million cubic meters. Even for a modern dredging project it is a serious volume. And digging a hole at one place is the first step. Where do you dispose it? At a dredging project, there is a reclamation area. As this was dry land, there was no reclamation area. So, what do you do with such a volume? If you pile it up, you can store a volume of V=1/3 pi r² h in a cone. Assume a slope of one third of the height to the radius, the height of the pile can be calculated and will be around 49 meter. And that is exactly what the ancient engineers did: they created the hill of Jingshan Park4. With its five peaks, it is not exactly a cone, but the estimated height was quite close!
The engineers had probably carefully planned how they constructed this hill and planned the delivery of the material accordingly. Nowadays, with the much higher production rates and shorter project delivery times, it is highly inadvisable to build a reclamation area with this height. There are several reasons why not to do it like that. First, it would take time to drain the pore water away from the core of the hill. Loading more on top quickly would make it very instable. Sometimes with disastrous results5. Another is when you create high banks, it will be easier for shear planes to form and collapse the structure that way. Lastly, a lower reclamation area will also have a larger surface area and more choice to select multiple locations to evenly distribute the material in volume and composition. A well designed reclamation area requires good knowledge of the deposited material and a skillful team that operates the equipment to manage the deposition.
Based on the exposed rocks sometimes seen on the sides of the Jingshang Park hill, the core is probably consisting of bigger rocks as a kind of backbone. But not every rock found in the moat ended up in the hill throughout the area. Several decorative rocks can be found that have a typical size that could just be handled by manual labour. Just another tribute to the perseverance of those classic engineers.
In the past intermezzo, a lot of blog ideas past my mind. In due time, I will share some of them with you. Others already arrive by themselves naturally. e.g. Lately we’ve had another CEDA Dredging Management Commission meeting1. In preparation for the upcoming CEDA Dredging Days2, we discussed some publications that will be presented there3. Next to the meeting, we also did a site visit to a prestigious project. The Monaco extension project ‘Anse du Portier’ certainly demanded some serious management skills for the dredging works.
The extension project had already received a lot of attention in the press and in the dredging community. It certainly is a remarkable project, where a lot of disciplines are coming together. I would like to refer you from the excellent video on the Anse du Portier project itself4:
Extension en mer de Monaco – Techniques de construction (Credit: Anse du Portier Project)
Or, if you can hold your breath, to the presentation of Camille Kapella at the CEDA Dredging Days5, where she will elaborate on all the difficult challenges in the project. At the moment of our visit, the last caisson had just been placed in the construction6.
Caissons are a demanding construction in terms of dredging. Of course, there are examples, where location and placement were not so important, but usually the requirements are much stricter and the conditions much harsher. Caissons have to be placed next to each other in the first place. And joining them all together might end up in a big deviation as errors propagate through each misplacement. This has been recognised already for a long time. Even one of the first tunnels built of sunken caissons, the Maastunnel7, had specifications that are still in use today. So, how did they do this? There is a nice historic video available from the old Polygoon Journaal.
Building of the Maas Tunnel (Credit Polygoon Journaal)
In the case of the Maastunnel, they employed wires driving huge dials and sight line beacons. Under perfect conditions, enough time and an enormous amount of manpower, the objectives can be achieved. Nowadays, this approach would be too costly or can’t be used as the local circumstances prevent them. Waves, tides, difficult location or other factors are the edges of the envelope for modern caisson placement and all were present here in Monaco. Specifically, the challenges at the Anse du Portier site were the steep bedrock, the open coastline vulnerable to waves and environmental concerns. For each, of the challenges, appropriate solutions were chosen to manage the project.
The construction of the caissons to withstand the wave action during the lifetime is remarkable. The top of the caissons are equipped with so called patented Jarlan chambers8. This is a design concept known in the offshore construction to temper the wave action. Waves enter the construction through slots in the walls and enter a chamber with more columns for further dissipation of the wave energy. A similar approach is already discovered by nature itself: coastal mangrove forests.