(Refer Slide Time: 34:35)
See if you no it is very interesting as you say, if you take a, if you are standing here, if it you know, if it pitches, the pitch has much more this thing because, why happen the the the the z value is z is heave plus x into pitch,
So, you see, x is a large number in order of length therefore, this has a large inference. So, normally, the pitching contributes to large of, you know, this thing and if you do; obviously, dot dot this omega square will come, then this contribution is larger. But if you have (( )) of mid shape, maybe it is not. So, if you are in a somewhat in.
Nowadays accommodation, see nowadays your accommodation is at the end. If your accommodation is at centre, may be it is not that bad for pitching. But, see most modern ships, you probably have gone you have been at the, (( )) most likely mid ship accommodation is almost obsolete.
Therefore, your (( )) is larger therefore, obviously, it is pitch that causes more, (( )) that is obvious you know, and pitch also is more dominant. See, even though it is pitching 2 degrees if the ship is say, 200 meter long, it is 100 into 2 degree.
So, you can you can imagine that hundred into 2 degree means you know, in radian if you make 2 into what by 57 say 57 types. So, it is almost 4 meter of you know, like if it is going down 2 degree at a distance hundred meter, it is basically going down 4 meter
what a lot and in fact, heaving may not be 4 meter, heaving may be 1 meter. So, pitch contribution is normally more, that is the fact.
(Refer Slide Time: 36:24)
Now, at the very beginning, having done all this, there is something called polar plots and Operability criteria. I just that is the last we will do. Operability polar plots, see what happens for almost all (( )) you have got number of index. See, I have got slamming deck wetness motion sickness index maximum, say, roll may be maximum pitch like that.
Many ship owners would actually tell you, will give you a criteria. They will give you a criteria saying that, look my ship cannot operate if slamming is more than so and so numbers; deck wetness is more than so and so number; M.S.I is more than so and so numbers, etcetera. etcetera
They can give you a number of criteria. All are actually Derived Responses or direct Response you may call, and they will give you a set of criteria. For example, people will say that maximum pitch should be less than 3 degree, maximum roll should be less than 10 degree for the vessel to operate, for suppose it is doing some operation motion, sickness should be less than so and so, deck wetness should be less than 1 per so many hours, etcetera. etcetera
Now, you have done all this calculation, there is a set of criteria given. What we can do in a polar plot is something like that.
See, you draw a diagram here, where there is heading angles are here, this is all heading angles you know, this various angles.
(Refer Slide Time: 37:46)
This is say, say theta equal to 0 degree like that, 90 degree 1 8y degree, you have got speed lines here. This is v equal to say, 2 knot v equal to 4 knot v equal to say, 6 knot, etcetera. So, you make a diagram like that.
Now, you find out, let me say, slamming, my slamming should be less than so and so; that is my criteria.
Now, I find out that at this particular speed, that exactly slamming becomes so and so, provided, it is at this speed, at this you know, at this heading angle, at this speed, my slamming is just like that, and this speed at this heading angle, my slamming is just like that. Like that, you that you have the boundary in this graph.
Then what happened? I will just very briefly tell you you can actually join them, you find out that look, if the ship is operating in this zone, this combination of heading and speed, then my slamming is going to be more than what is stipulated.
In other words, see, I have found out slamming. This will be for a particular sea state number equal to 4 say, some given sea state slamming as a function of angle heading angle and speed. Obviously, it depends on this 2 criteria for a given sea state.
Now, I have I have I have to determine, see now I do a long elaborate calculation. I do a calculation of all this Derived Response, for all possible speeds of the ship and all angles, all sea states.
Now, for a given sea state, I will find out which combination of theta and v, my slamming exceeds the limit.
So, I will say that if the ship is within this range, my ship is now going to not meet the slamming criteria. So, this is my operation zone.
In other words, I can operate in sea state 4 from the slamming point of view, provided my v and mu are within this range. This is the simple polar plot, what is called because, you would like to know this. is I will give you another example, probably better in terms of roll.
(Refer Slide Time: 40:06)
See, this roll may be better. See, this sea states another sea state, this is again 90 degree, the normally you will find out that 90 degree roll is very high.
So, you will find out that the ship at very high speed and 90 degree, it may be something like that. What does it mean?
See, this is, lets us say, this is 2 knots, this is 4 knots, see this is 0, this is 2 knot, this is 4 knot, this is say, 8 knots, like that. What it means it is that, at 90 degree heading angle, any speed more than 2 knots, the ship is going to roll. More than 10 degree means it is not going to meet the criteria.