What is, what what is this angle? Before before, I come to this angle or rather we can call them also. This angle, what is this angle this is angle of attack of the of the hull, because you remember the at this point the vessel is moving this side. This is my v, whereas this is my direction of the longitude of axis. So, that means, this is my angle of attack because fluid is coming this way. If I sit here on the hull fluid comes this way.
So, this angle, it is the angle of attack with from aerodynamicist nomenclature. Here, we normally call this a drift angle. (No audio from 38:14 to 38:22) This is actually same as angle of attack (No audio from 38:25 to 38:34). Why I am saying is that if you think this ship to be a lifting surface, which of course, how it behaves eventually at a low. You know very low efficiency lifting surface, then this becomes my angle of attack, but typically in in our nomenclature. It is referred to as drift angle.
Now, if I measured this angle also with respect to this line. How do I put this line again, Say no, I think I will put another (No audio from 39:13 to 39:36). Say here drift angle is the angle between the velocity vector and X axis that makes sense. Let us take it slowly the drift angle is the angle between the velocity vector and X axis. Whereas, heading angle or yaw angle is the angle that it is making from it is original heading to this. That is, what the the heading it make with respect to X axis, the X 0 axis.
See heading or yaw, see initially it is coming this side. Now, you are measuring the yaw angle or heading angle with respect to that. See for example, if I say it is going a 0 degree. Now, it is yawing 40 means, basically instead of going along this line is it it is heading with 40 angle. So, this is what we call basically the in the ship’s heading angle or yaw angle.
See, yaw angle, once again is measure of the ship’s heading with respect to a fixed reference line. See, when I say the ship is heading 180 degree with respect to some line which means with respect to line it is head is 180 degree or 10 degree or whatever. So, heading is always measured with respect to a fixed reference line. In this case the reference line is an inertial O X 0 line.