Dredger of the Month: TSHD Lesse 

Lesse. Credit: Baggerbedrijf De Boer - Dutch Dredging

DPC considers how the Royal IHC and Dutch Dredging-designed TSHD Lesse can be deployed to shallow regions

Trailing suction hopper dredger (TSHD) Lesse is the ninth such dredger in Dutch Dredging’s fleet of vessels. Launched in Varna, Bulgaria, it stands out as the Netherlands-based company’s most sophisticated vessel to date. Its design is based on the earlier Royal IHC-built TSHDs Albatros and Mahury, with each model an improvement on the last.

Both these vessels, along with Lesse, were designed by Dutch Dredging and Royal IHC, said Robin Mansour, Dutch Dredging’s project manager for the Caribbean. He noted, “There are a lot of improvements on Lesse. One of them is the smooth bow. Because of this Lesse can reach higher speeds.”

Dutch Dredging was involved in the design and construction of the vessel and a lot of attention was given to making it as easy to use as possible, maximising its ‘up-time’, as well as incorporating wear-resistant parts and maintenance-free equipment.

Hugo van de Graaf, vice-president of Dutch Dredging, said, “Mahury and Albatros are both versatile dredgers with high levels of productivity.

“We are glad to have made the decision to invest in new IHC-built TSHD once again. Because of the further-improved design that has been developed in co-operation with our crew, this vessel is even more efficient and can be deployed worldwide.”

Dutch Dredging characterizes Lesse by its small draught, which allows for easy transport and reduces restrictions as to where and at what time of year it can be deployed.

The vessel is designed to maintain sea channels and inland waterways, as well as perform land reclamation. It is equipped with the latest electronic system to improve positioning, sounding, and execution of dredging work.

Go with the flow

The impact of sediment plumes created from dredging and reclamation activities continue to be reviewed, and dredging companies are making concerted efforts to minimise their impact. Royal IHC’s solution is an upgraded version of its telescopic overflow system, known as the Plumigator, which has been installed on Lesse.

The Plumigator significantly reduces the sludge cloud around the ship that is known to harm marine life, said Royal IHC. It also tackles issues caused by the overflow process such as air pockets underneath the ship.
Lesse’soverflow system is designed to optimise the efficiency of the dredging process by draining excess water and leaving more weight available for the payload. At the same time it also limits the amount of turbulence in the hopper.

The mixture will then have as much time as possible to settle, which in turn maximises the retention of solids. Lesse’s telescopic system allows the overflow to be set at different levels, optimising the loading process depending on the dredged material.

The ability to control the level of the overflow is paramount in ensuring an optimal, non-turbulent flow inside the hopper.

“As a family business, Dutch Dredging is happy to invest in sustainable relationships,” says CEO Kees van de Graaf Jr. “We’ve enjoyed the co-operation with IHC and Dolphin Shipyard in Bulgaria so far and are proud of our construction team, which conducted the local supervision.”

Lesse at work

Lesse’s first job following its November 2018 launch was in French Guiana “on our 12-year maintenance contract for the Grand Port Maritime de la Guyana in Cayenne. We started there in September 2019 with Lesse for two weeks”, said Mansour.

Its most recent project, which ended in January 2020, was at Queens Wharf and Caricom Wharf, for the Port Authority of Trinidad and Tobago at the Port of Port of Spain. “This was her first major dredging project,” said Mansour.

Capital dredging activity at the site enabled access to an additional two meters of berth and a new jetty. According to the Trinidad and Tobago Minister of Works and Transport, Senator Rohan Sinanan, it has been 14 years since the last dredging took place and it was considered long overdue.

Lesse was chosen for this particular project “because it’s a shallow draught dredger, with an empty draught of 2.5 m and a fully loaded draught of 4.5 m”, explained Mansour. “Because it’s so shallow, we could be very efficient on that particular project due to being able to dredge in any of the project’s locations.”

The vessel has a larger hopper than Albatros and Mahury and the capacity of the dredging equipment has been increased accordingly. Lesse has a dredging depth of 30 m below the waterline and a hopper capacity of 2,300 m³.

The project saw it dredge up and dispose of about 700,000 m³ of silt and sandy clay over four months at the Trinidad and Tobago site.

Growing environmental awareness and social challenges such as air quality have resulted in dredgers becoming eco-friendlier. Lesse operates on marine gas, is IMO Tier II compliant with NOx emission limits, and has a ‘Green Passport’ notation, complying with the strictest international emission requirements.

With numerous improvements made to each vessel commissioned by Dutch Dredging, the next in line will no doubt be an interesting piece of engineering.