Change In Station

[XLjedi]

Originally Posted by Kirby_TFS

I guess one question would be can you set up an intercept between 2 contacts and not use the ownship? I see now that doing a change of station requires the ship that does the actual change of station to be the ownship. I though I knew where the ships were going, but couldn't get the MoBo to give me a simple answer. .

Yes, MoBo is very flexible in that regard. The way the intercept feature works is that it always gives an intercept based on the connecting line. If there is no connecting line, the intercept is displayed in relation to OwnShip. But if you connect a contact to another contact it will plot intercept between contacts.

Actually, MoBo is designed to be usable for relative motion problems without even having a background image of a maneuvering board. I could've easily plotted the same solution with a blank background, or a nav map screen print.

Here's the same answer with OwnShip as the Flagship.

Notice above the connecting line between "Port Beam Station" and "Cruiser A" allows the "Port Beam Intercept" to be plotted for "Cruiser A" rather than "Flagship". That connecting line is also known as the DRM line (Direction of Relative Motion). CH11_Prob1_Rev.DAT

Originally Posted by Kirby_TFS

When I was looking at the answers on the paper manuevering board I couldn't understand why they were putting a parallel line to the DRM line at the end of the vector for the flagships speed. That part was really throwing me.

If I have time maybe I'll post an example as-if MoBo was merely a piece of paper and do a longhand intercept calculation.

Originally Posted by Kirby_TFS

Thanks for the answers, and if you want to post any other pratical solutions I would love to put them in my notebook collection.

If you have some specific examples you'd like to see plotted or a screen print of a nav map, post em.

[XLjedi]

The longer manual solution would look like this...


Now here you can see the parallel line drawn from the "r" position. In this case we're using the actual maneuvering board graphic to represent the speed vector. The "r" is on the 6th ring which in 2:1 would represent 12kts.

A parallel line to the DRM is drawn from the "r" position to the 9th ring which represents 18kts.

With that line you can plot point m1 which intersects the parallel line at the speed ring for 18kts. Notice now how the line plotted from the center of the board to m1 is pointing to the 262° bearing. So for an 18kt speed, "Cruiser A" must take course 262° to intercept the M2 station.

I don't recommend you actually use MoBo like this, just because it's faster to use the intercept tool; but you certainly can if you want to. Incidentally, this same plot example appears on page 11-16.

[Kirby_TFS]

Arronblood,
I was working through the examples and trying to get in my mind why we do each step in using the MoBo. I can see the intercept, get the actual course and speed, find distance, etc., and enjoy the MoBo program. I'm not interested in using it as a paper solution as that does take too much time. But when working through problem #3 in change of station it is not making any sense. I know that the CPA is going to be after the ship crosses the ownship's path. Could you possibly work this one out and publish the how's and why's for each step? Also are there any general rules to follow in getting solutions? I enjoy working these problems, but don't always know why I'm getting the answers. If the answers were not posted I would have worked several of these wrong.

[XLjedi]

Problem 3... lemme go take a look...

Some of these things are just too painful simple in MoBo to figure out. So when you read Chapter 11 it can be confusing as heck when they explain a bunch of steps that you don't need in MoBo.

[XLjedi]

Ewww... yeah that's a tricky one.

So seldomly am I concerned about calculating a CPA that I sorta didn't build any shortcut methods for auto-plotting a DRM line given two ship locations from a DRT plot.

Usually the DRM is observed based on M1 and M2 and you just connect the line and the CPA forms a right triangle to the DRM line. In this case they're just telling us we're gonna be coming by your area and we only know the M1 position. We have to determine the DRM line. I don't have any handy tools for doing that automagically... at least not yet.

Here's one way to plot the DRM so you can determine the CPA...


Shoot, I wouldn't of figured out that one without reading their steps and looking at their example plot on page 11-19. So don't feel too bad...

[Sockeye]

Very helpful discussion here!

Last year I had been working through a similiar question from one of the Radar Operator Handbooks. I'll have to find the battle problem to be absolutely sure, but I recall their procedure describing how own-ship becomes the (maneuvering) target vessel while the actual target remains stationary on the board. My brain groaned!

For some reason though, using the "match" function and multiple contact criteria to plot steerpoints never occured to me. I had been using a more cumbersome approach of nodes and time intervals, something like a table of values until I found time values that jibed with each other.

After reading this, everything is much more streamlined