So, now I am going to having now established that, I have no choice in starting manoeuvring, but to establish an equation of motion. First thing, I have to do is to write down a frame, coordinate frame etcetera, define various parameters. So, that I can write equation of motion, so that is what we will do today the rest of this this time see here. Remember we are talking at a lower level, now I am talking of only a ship manoeuvring in calm water. Therefore, I am concerned only at z equal to 0 planes. This piece of paper z equal to 0, this this piece of paper, if my sea surface.
So, I have here (Refer Slide Time: 33:27), now I want to track the position. So, what I should do, first of all let me just draw this properly. Then, we will know arbitrary motion of the ship is there. We need to draw obviously, actually somewhere here (No audio from 33:53 to 34:07). Let us say, let me first draw this see here. We I need to define various parameters.
Now, in order to track the ship, how do I know its position where it is located, I must have some coordinate system. So, I am going to have an, what is called an inertial coordinate system, initially O here X 0, Y 0 or small X 0, we can call it small, because there too many symbols will come. So, this is small X 0, small Y 0 inertial coordinates system. Now, I must fix a point on the hull.
Now, you you know, just like in in seakeeping the position of that is fully fixed, but with respect to a fixed point on the hull and the rotation of that. So, first of all we here just like in seakeeping, we will define another, so called body coordinate system. Let us see this body coordinate system will look like, will call it this way and this way in this case.
And this point is we call this say some point. Typically, centre of gravity the trace of the central gravity actually it need not be central gravity. But we are taking here central gravity the trace of that, this this this line, this blue line is the trace of the central gravity. That means, this is what the path it is taking, say this this line is the path at g is following this. That is my path.
So, obviously, the two coordinate that is X 0 G and Y 0 G tells me, the location of that. So, it I know the location of the G and also I need to know the orientation of that. So, you see here what would happen is that, I have a spaced fixed coordinate system o X 0 Y 0. So, it is inertial coordinate system I may call (No audio from 36:18 to 36:39). Now, I
will have G X Y a body, this is my vector v, the fluid velocity vector v (No audio from 37:00 to 37:15).