Digging deep

05 May 2017
Multi-talented: the hybrid tug will be configured for a variety of roles. Credit: Damen

Multi-talented: the hybrid tug will be configured for a variety of roles. Credit: Damen

Two disparate innovations in dredging could have ramifications for ports. Barry Cross investigates

The solidly dependable dredging sector has recently announced two major innovations that ports could benefit from. First, a combined tug-dredger has been developed for markets where owning individuals tugs and dredgers cannot be financially justified, and second a new dredged materials centre is planned for North America to look into innovative ways of disposing of dredged material.

For the first, it is international shipyard Damen that has been tasked with building two special-purpose tug-dredgers. The client is De Boer Remorquage SARL, a subsidiary of Baggerbedrijf De Boer (Dutch Dredging).

These unique vessels will incorporate maintenance dredging capabilities and be deployed in French Guyana on behalf of the Grand Port Maritime de Guyane as part of a ten-year contract covering the ports of Cayenne and Kourou.

According to Hugo van de Graaf of Dutch Dredging, the vessels' primary function will be to assist vessels entering and leaving port, as well as deployment on emergency tasks, most notably fire-fighting. However, not to be dismissed is their secondary role, which will see them used to assist with maintenance dredging operations in both ports.

Special purpose

Of the two vessels, the larger, the WID 2915, is to be configured for a variety of roles, including dredging using the Air and Water Injection Dredging (AIRSET) method. The smaller vessel, the ASD 2310 SD, which requires a shallower draft, will be fitted out to operate the equipment needed for bed-levelling, as well as having the capability to carry out surveying activities. Significantly, the two tugs will be the only support vessels available in either port, so will also be required to transport equipment and cargo, which could be up to container-sized loads.

“These are the first two combined tug-dredgers that we have ordered,” says Mr van de Graaf, who notes that, technically, it was not easy to combine these two features in one vessel. The difficulty, he explains, is that different parameters come into play when designing a tug compared with a dredger. For example, the width of dredging pipe has to be offset against the need to manoeuvre the tug, while the on-board engines have to produce maximum propulsion power when towing compared with lower speed and power requirements when used for dredging duties.

“It's true that the overall dredging element that the vessels will be asked to undertake could probably be done more efficiently by a dedicated dredger. However, it is not envisaged that either vessels will be fully occupied in their roles of either dredger or tug. It is therefore for this specific contract much more economically interesting to build a vessel that combines both functions,” says Mr van de Graaf.

Asked whether there isn't a danger that Damen is actually being asked to build a bad tug and a bad dredger, Mr van de Graaf concedes: “This risk indeed existed, but the team came up with a design that makes it possible for the vessels to undertake both activities in a more than acceptable fashion. But there had to be a compromise, since, as I mentioned previously, the opportunities for these vessels to be fully employed as either tugs or dredgers is strictly limited, so combining the two functions makes good financial sense.”

Guyane needs

Much of the impetus for the new vessel actually came from Grand Port Maritime de Guyane, which asked bidders to make a competitive proposal based on a combined vessel, he notes.

“Given this specific situation, it appeared to make sense to bid with [hybrid] vessels, since had we offered a dedicated dredger and a dedicated tug, we would have been more expensive.”

In respect of return on investment, Mr van de Graaf stresses that, in the shipping business, ROI has to be viewed in terms of years, which is why the vessels were designed with a specific minimum working age of at least ten years. Indeed, ROI will be considerably enhanced simply due to the fact that Dutch Dredging will effectively be “sweating an asset”, rather than having individual tugs or dredgers tied up in harbour for want of anything better to do.

“Interestingly, we calculate that while they can perform either task, we expect them to be deployed more as dredgers than tugs,” he says.

Quizzed as to whether he saw more opportunities to place orders for similar vessels, or whether this would be a one-off order, Mr van de Graaf says it depends on the needs of the client and on the port.

“In the case of a smaller port where there are both limited towing and limited dredging activities, it makes sense to deploy combined vessels, since these are the ideal solution.”
The WID 2915 is scheduled for delivery in November 2017, and the ASD 2310 SD in March 2018.

A new purpose

The other significant development in the dredging sector is to be found on the other side of the Atlantic, where Toledo-Lucas County Port Authority has received a $2.5m grant to design and construct the Great Lakes Dredged Material Center for Innovation, at the Riverside CDF in north Toledo.

“This project will help local leaders evaluate dredged material placement, de-watering, use of interim cover crops, soil amendments, and other testing, operations and maintenance activities necessary to plan for the full-scale implementation of the beneficial use of dredged materials for agricultural and blended soil product purposes,” notes Joe Cappel, vice president of business development at Toledo-Lucas County Port Authority.

Asked whether the aim of the project is turn a cost (dredging) into a profit by selling the sediment that is dredged up, Mr Cappel says: “We would love for an entrepreneur to discover a way to create value in the material that exceeds the cost of transportation and processing the material. Due to the fact that the material is mostly fine silt and clay, the costs of transportation and processing exceeds the value that can be derived from beneficial uses of the material in this region, which therefore presents a real challenge.”

To replace open lake placement of dredged materials with upland placement, the main headache will be to find enough land where the material can be utilised.

“The cost involved with drying the material, possibly blending it with other materials, and transporting it via truck, rail or pipe will be much more expensive than open lake placement. Indeed, any cost for dredged material placement and disposal that exceeds the cost of the US Army Corps of Engineers' Federal Standard of open lake placement will need to be covered by a non-federal project sponsor,” he says.

“Our hope is that we can find uses for the material that will benefit the community and region and reduce the amount of material that is deposited in Lake Erie each year. We hope that the benefits the material provides will be break even with the cost of delivering suitable material for each project.”

Who’s buying?

In respect of potential customers for dredged material, Mr Cappel says that the Dredged Material Center of Innovation hopes to collect data that will be useful to the agricultural community in the hope that farmers will consider allowing material to be placed on their fields on a larger scale than the initial pilot project can accommodate.

“There may be others who are interested in blending dredged material with other products to meet specifications for fill material and other uses,” he notes, pointing out that the material could also be used in landscape applications, to construct wetlands, or to create finished products like lightweight aggregate or even compressed into bricks. “There are many possibilities for this material and the port and our partners at the State of Ohio and the US Army Corps of Engineers stand ready to assist anyone interested with further exploration of various opportunities to beneficially use this material from Toledo Harbor.”

However, although the harbour material is mostly silt and clay, it is not considered to be “contaminated” per the Clean Water Act, which currently allows the U.S. Army Corps to place it in Lake Erie. The material does contain some nutrients, which is both the main concern and driver for placing the material upland after it is dredged instead of back into the lake. Material that was previously placed into the main Confined Disposal Facility (CDF) in Toledo has already been tested and analysed with hopes that someone will mine the material for a project which would create new capacity in the CDF for material that would otherwise go into Lake Erie.