VESSEL REVIEW | Versatile river clearance dredger for Philippine public works agency

The Department of Public Works and Highways (DPWH), the Philippine government agency responsible for engineering and construction, recently took delivery of a new dredger from IMS Dredges of New Richmond, Wisconsin. The new dredger will be deployed in Pampanga province north of Manila, where it will clear the Tulaoc River of sediment and vegetation.

The DPWH dredger is equipped with IMS’ proprietary cutterhead designed for cutting up and pumping vegetation such as water hyacinth several hundred metres away to a remote discharge area. This allows the vessel to effectively clear dense aquatic vegetation in urban environments without needing to rehandle it with multiple excavators or transport boats. Successful clearance means there will be no vegetation rapidly growing, trapping debris, and obstructing water flow, thus reducing the risk of flooding.

“We opted for this vessel because it is capable of clearing water hyacinths as well as dredging the Tulaoc River to increase its capacity,” the DPWH told Baird Maritime. “Water hyacinths can potentially block the flow of water, so it is important to clear the river of vegetation before proceeding with dredging operations.”

Designed for clearing vegetation

The dredger was designed as a dual-function, one-truck transportable, self-propelled vessel. It has two convertible attachments: one for dredging and another for clearing water hyacinth. The discharge pipes are also easier to installed compared to other dredgers of similar capability.

The standard cutterhead is used for hydraulic dredging down to a maximum depth of 6.7 metres (22 feet), thus creating an even bottom profile as it takes out uniform, parallel layers of material with minimum suspended solids. The cutter utilises a shrouded environmental auger design that allows for a higher percentage of solids to be pumped compared to similar sized basket-type cutter dredgers.

The hull itself utilises a catamaran design with steel construction and skeleton-frame reinforcement. The 316 hydraulic fittings and hardware are made from stainless steel for improved resistance to corrosion.

“The main concern influencing the selection of the vessel was the need to mitigate flooding by reducing the volume of water hyacinth floating on the rivers,” the DPWH said. “It is also important that the weeds be cut and dissolved, since these can be also used as fertiliser.”

The use of the dredger will directly benefit the Pampanga municipality of San Simon, which is also a catch basin and is therefore prone to flooding and damage during the rainy season. The vessel can also help reduce pollution by ensuring the dredged materials can be repurposed for other applications. Lastly, with the river free of obstructions, residents will have more opportunities for fishing.

The weed-specific cutterhead will be used for non-stop shredding and hydraulically pumping vegetation up to one kilometre (0.6 mile) away to the discharge area. IMS said this makes the dredger the only vessel of its kind in the world that can hydraulically extract both sediment and vegetation through a single pipeline.

A weed rake is attached to the front gantry of the dredger and provides a constant feed of dense hyacinths to the cutterhead. The cutterhead rotates hundreds of rpm with hundreds of serrated razor-sharp agricultural teeth passing through static rows of razor teeth to prevent clogging of the dredge pump. The low-turbidity shroud, along with the centrifugal dredge pump, creates a powerful vacuum that sends the chopped vegetation at a velocity of up to three metres (10 feet) per second to the discharge area where the vegetation can be collected and rapidly dewatered due to particle size and weight.

The cutterhead power unit also has locking security doors and a full shroud. These features provide protection from the elements, ensuring a longer service life.

Adaptable propulsion for various water environments

“The propulsion system utilises a specialised drive, which is individually operated for high manoeuvrability and performance,” the DPWH told Baird Maritime. “It also comes with a standard cable and traverse drive.”

The patented 280kW (380hp) paddle wheel propulsion drive developed by IMS allows the dredger to move under its own power without causing turbidity and without the need for bulky cables and spuds. This capability makes the vessel suitable for work in inland waterways, especially those where the use of anchors or spuds is prohibited.

The paddle wheels can be used on the surface in large cement- or polyethylene-lined lagoons where cable rigging is not possible due to larger dimensions of the ponds. The paddle wheels can also be lowered past the waterline to propel the vessel in areas with mud or sediment. The wheels are also more reliable compared to conventional propellers as they are not likely to become clogged by debris or aquatic vegetation, enabling continuous use of the dredger in areas containing these obstructions.

The operator sits in a climate-controlled cabin. In this area are electronic-over-hydraulic joystick controls for ease of operation of the vessel and its equipment, a monitor showing a closed-loop video feed of the discharge, oversized backlit analog gauges, an adjustable chair, a sound system, a horn, and dual bi-folding doors with port and starboard access.

The superstructure and the hull are sandblasted and painted with two coats of marine epoxy suitable for saltwater service. The hull is also fitted with zinc anodes. The deck is free of obstructions, ensuring clear pathways from fore and aft and from port to starboard as well as easy access to the various components for maintenance and repairs.

Following its work on the Tulaoc River, the new DPWH dredger will be deployed to serve a new project in November. By then, it will be equipped with a cutterhead optimised for hydraulically dredging sand, silt, and organics.