Quote:
Originally Posted by PL_Cmd_Jacek
Thank you for your promt response, this material looks very interesting. I have to try it.
I also has a question regarding your 3-bearingAOBfinder from your filefront page. I do not understand, what exactly means "angle on relative motion"
Edit: and also what mean: DRM, MRM and SRM (from the example)
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Good question. I knew someone would eventually want to challenge me on that. To understand what I mean with "angle on relative motion" those other 3 abbreviations need to be understood. It is very wel explained in "The Radar Navigation and Maneuvering Board Manual",
specifically chapter 3. Here is the link to the full pack of pdf files:
http://www.nga.mil/MSISiteContent/St...NM/pub1310.zip
The file I uploaded to my filefront page (the link I gave in my previous post) are 2 pages from chapter 6, which has excercises and problems you can try to solve.
But I'll try to summ it up here.
DRM = "direction of relative movement". (refferenced to north)
SRM = "speed of relative movement", knots
MRM = "miles of relative movement", or basically just the distance the target moved in a relative plot.
If both you and your target are moving at the same speed and the same course, then you two do not move relative to one another. He wil keep being at the same range from you and at the same bearing. The speed vectors are identical. Same length and same direction. There is no space between the heads of the vectors (when you draw them from the same origin).
If the both of you had for example a course due north, but he is faster and behind you, then he would come closing up on you. Both speed vectors are still pointing in the same direction (north), but his vector is longer.The space between these arrowheads is the relative motion vector. In this case the relative motion is also pointing north. The relative motion vector starts at your speed's arrowhead, and ends at his speed's arrowhead. (vectors can be drawn anywhere in a drawing, as long as their length and direction is the same. so don't take their placement too literal)
In this case the speed of relative motion is easy to compute. Because the vectors are aligned and in the same direction it's the difference in length. But if your course and speed is completely different from his course and speed you need to make a drawing of them and measure the space between it. The 2 vectors start at a common point, and the relative motion vector closes the triangle, starting at the arrow head of your speed vector. Also this space between the arrow heads has a direction, hence the 'direction of relative motion', which is measured as an angle to north.
'miles of relative motion' is really the distance between plots you make i.e with your periscope. Except!, on a maneuvering board you do not plot the target position from your current location as you move along the map. (like it is shown in most tutorials here) On a maneuvering board each plot of the target is done from the center of the circular board. This makes it very easy to see how the target moves relative around you. You are allways in the center. (well, not always, but I'll let the maneuvering board manul explain when not)
So what is that 'angle on relative motion'? Well it looks a bit like 'angle on the bow', but cannot rely on a visual picture of the bow orientation. Angle on the bow is the angle between the line of sight (or bearing) and the course(heading) of the target. If the viewer through the periscope or on the bridge isn't moving then target is the sole cause of the relative motion. And the 'direction of relative motion' is the same as his course, and the 'speed of relative motion' is his speed. If you can accurately guesstimate the angle, you can derive the target course based on the viewing angle and own course. But if the viewing ship is also moving, then the 'direction of relative motion', aswel as the 'speed of relative motion' changes from the motionless situation. Then there is no direct link anymore between the angle or view on the bow, and his relative motion. And my tool cannot be used anymore to provide AOB as it was explained in those steps. Well, it can, but that would be too complicated to explain now, if this is all new to you. I'm not even sure I was clear enough with this explanation.
I really should have named it 'angle on direction of relative movement'. Or 'angle on DRM'. That would have been a more propper term. But probably made even less sense. I don't know. I just think like a mad professor.
