Finding the range the hard way.

[Telemon]

Thanks every one, for your comments particularly Rockin Robbins. This is a very interesting subject.

A point Rockin. You suggested, I think, that the formula is invalidated, or is dependant upon a particular screen resolutuion "...because the angle subtended by one division is dependent on your screen resolution". But surely screen resolution is irrelevant. If one knows the angular value of each division of the reticule then the angle subtended will always be the same.

My practice is to use the tangent rather than the cosec, this gives the range to the target at the waterline rather than to the masthead. My reasoning is that although, at longer ranges, the difference is small and can be accepted at shorter ranges i.e below 1000yds the error can be significant. I like to get in to c750 yds.

Joe S. I agree with you that trying to get a range using the stadimeter especially with 'no stabilised view' selected is a nightmare. Howver, why shouldn't you use the stack! If you look at the manual it is possible to estimate the height of the stack or any other part of the target, bridge, derrick et al. then do the trig calculation to get the range. Be aware though that because you are using a smaller height the error in range will be greater. On a pitch black night with rain though, it might be better than nothing.

Incidently I use an old Thorton PP221 slide rule fo my calculations.

[Hitman]

The short answer is no because the angle subtended by one division is dependent on your screen resolution. Last I knew Capn Scurvy was working on that and had a solution in the works.

IIRC there is a problem with one specific resolution, but in all others the image is correctly scaled.

The thread is here, for anyone interested in further reading: http://www.subsim.com/radioroom/showthread.php?t=175729

[Rockin Robbins]

There's a natural tendency to want to pick an easy to see aspect of the target: stack, cabin height, flight deck, but you probably wonder why the real guys liked to use the masthead height. By the way, their recognition manuals tended to give heights for stacks, masthead, cabin top and deck of most targets. Real sub skippers could pick whatever they wanted for their stadimeter range measurements.

But the accuracy of your distance calculation depends on three factors. The closer the target is, the more accurate your determination will be of course. The more accurate your stadimeter angle measurement is the more accurate your distance will be.

But also the higher the measurement point is on the target, the more accurate your distance determination will be. Your error for a masthead height of 50' will be half that of a distance determination based on a stack height of 25' for instance. Your accuracy is directly proportional to the height of the aspect being measured. So whenever they could the real sub skippers used masthead heights, the tallest part of any target.

Stadimeters are nasty inaccurate enough without you handicapping yourself!

[Joe S]

Thanks for the explanation about the potential for error. Would it not be true, however, that in a situation like ours, where there is a tendency for the image of the mastheight to be corrupted due to screen graphics issues, that the stack would be a more reliable measurement to use even though it might be theoretically less accurate? Joe S

[Rockin Robbins]

I don't know about graphics corruption issues. I don't have any. I'd have to say the jury is out on that one. However, if the mast is twice as tall as the stack, then your error tolerance is doubled: you can have twice the error using the mast and still have the same distance error resulting. It's difficult for me to imagine that you could have twice the error sighting on the masthead. You might get a little more error, but it would still result in a more accurate distance measurement.

It can be difficult to resolve the masthead at extreme range. However, at that range, small errors make huge differences in your result, so range measurements that far out should be viewed as exercises in futility anyway. They just give you a starting number that you know will be very different before you shoot, no matter what aspect of the target you are measuring.

[Joe S]

In my experience with this sim, the image of the mast is often times very inconsistent. It will apprear to be a certain height and then the next second its only about 2/3 as tall, which I always assumed was due to the inabilitly of the computer to clearly display the image. With a more substantial object such as a smokestack, this image on the screen remains stable, and it would seem to me that you would get a more reliable result for that reason. I havent tested this idea, but it makes sense, at least in theory. Joe S

[Rockin Robbins]

That's interesting. I've never seen that effect. I wonder which video cards are affected?

[TorpX]

Originally Posted by Joe S

In my experience with this sim, the image of the mast is often times very inconsistent. It will apprear to be a certain height and then the next second its only about 2/3 as tall, which I always assumed was due to the inabilitly of the computer to clearly display the image. With a more substantial object such as a smokestack, this image on the screen remains stable, and it would seem to me that you would get a more reliable result for that reason. I havent tested this idea, but it makes sense, at least in theory. Joe S

I've noticed the same thing. I assumed this was from the software simulating haze, mirage or any RL visibility factors. It definately makes accurate range estimates a lot harder.

However, as RR points out, the main purpose of long range plotting is to allow you to con the boat and reach a favorable attack position. There is no need to compute a final torpedo firing solution when the target is at long range, at least not ordinarily.