Which depth is considered to be shallow water and what are the effects of shallow water on ships? This is one of the most common questions asked during the competency exams. So, today we will discuss both these questions in a simple manner.
First, let us see which depth is taken as shallow waters. Broadly speaking, answer for this question can differ depending upon the type of ship, it’s draft and other factors but generally speaking,
For manoeuvring purposes, the depth less than twice the draft of the vessel is considered to be shallow water.
Now, you must be wondering why so?
It is because at this depth, the seabed causes a drag on the vessel, which changes it’s manoeuvring characteristics.
Now, that we have understood what is shallow water, let us see and understand what are it’s effects on the ship:
- As the vessel enters shallow waters, the vibration throughout the ship increases. This is because the hull vibration almost matches with the engine vibrations.
- The bow waves increases, which increases the load on the engine. Hence the ship’s speed should be reduced.
- Appearance of muddy water at the stern part of the vessel.
- Vessel’s turning circle increases. It increases by as much as 3 times than in the deep waters.
- Directional stability of the vessel increases. Directional stability means the ability to maintain a single heading, i.e. it requires more helm to change the vessel’s heading.
- The steering of the vessel becomes sluggish as compared to that in deep waters.
- Pivot point of the vessel shifts a little bit aft, about 1/3rd of ship’s length from bow. This is the reason for vessel’s steering being sluggish.
- Squat increases. Squat is defined as reduction in UKC as the vessel moves through the water.
- Stopping distance increases when astern movement is given. Although propeller is moving astern but there is a void space in astern and there is not enough water for griping, hence resulting in increase of the stopping distance.
Hope, this article has simplified the shallow waters definition and has properly explained the shallow water effects on ship.
Have we missed any point? Feel free to share your views and opinions in the comments section.