The WID does not “scoop”. But it does “bring up” – not outside but within the water. A totally out-of-box concept from a Dutch Naval Architect, unexplored in India till this vessel.
Oxford dictionary definition of “dredge”
- clear the bed of (a harbour, river, or other area of water) by scooping out mud, weeds, and rubbish with a dredge
- an apparatus for bringing up objects or mud from a river or seabed by scooping or dragging
The WID does not “scoop“. But it does “bring up” – not outside but within the water.
Background: Concept of WID
In ports which are tidal, there is often deposit of very loose soil on the hard bed. It keeps on accumulating. A normal echo-sounder of a ship displays the navigable depth up to top of this soil layer. The soil is soft and will not damage to a ship or its propeller. But the master will adhere to the depth displayed in the echo-sounder and refuse to enter the port.
The WID removes the soft soil – efficiently and economically. Without a WID, the only option is a TSHD which is quite ludicrous and extremely expensive as you will be dredging a large amount of water with an insignificant amount of loose soil.
Conventional dredgers (TSHDs, CSDs, etc) have been around for a very long time. But the WID is a relatively new concept, just around 50 years or so. A totally out-of-box concept from a Dutch Naval Architect who could somehow convince his friend, the owner, to give it a shot. (The owner also owns one of the world’s largest dredging companies.) They built two – both are in operation even today.
My involvement with a WID
My client, an owner of several ports, wanted to build and own a new WID, to replace one that was on hire. (Incidentally this was one of the two WIDs built 50 years back!)
At that point I was not even aware that WID was an acronym for a Water Injection Dredger. There is very little historical and empirical data available on WIDs. Few full feature WIDs are in existence because of the specialised nature of operation and requirement in very few ports.
One had to start learning from basics. I worked with several reputed designers of Holland, hydraulic experts in India and dredger masters with hands on experience. The result was Shanti Sagar 15, operating successfully for over 7 years.
How does a WID work
Using high volume, low pressure pumps, water is injected through an injection ladder with an injection bar (see picture). The injection bar can be lowered or raised to position it slightly above the loose soil. The injection bar is fitted with a series of nozzles and the bar can be rotated to ensure that the injection is almost perpendicular to the soil layer. The gentle injection “brings up” and this layer of water with the soil moves with the WID wake as it starts dredging, moving out of the port during the ebb tide and carrying back the soil to open sea from where it came.
This is a very simplified explanation. There is much more to it – dual frequency echo sounder, real time display of soil bed and its movement, a real time kinetics to ensure that correct dredging is done for a particular tide.