how to re-set the tdc

[jazman]

Originally Posted by Joe S

Jazman,

forget about the range, it means nothing. The reason is, once you know the amount of lead, the angle of lead stays the same no matter what the range. I normally set the range with the rangefinder, but I use averages for the type of ship. for example, I enter 98 feet for the mastheight of all large freighters. Then I estimate the range with the split image, etc, but I do it mainly to replicate what the original captain or fire control officer did. Since most of my shooting is done under 1500 yds, I manually adjust the range once the target gets in close so that I get an accurate representation of the setup on the attack map to confirm the solution. If range is your main problem, you are in good shape. I hope you find this helpful. Joe S

Thanks for the advice, I have the O'Kane method down cold. And I worked the trigonometry so I understand why the range doesn't matter. It's when I use the PK for non-O'Kane shooting that I have problems with range.

[Joe S]

Jazman:

Range doesn't matter with either method. If you want, you can pre-set the range for the distance to the target's track at the point of firing. If you are off by a little or a lot it makes no difference. Test the theory in the training mission and let me know what you find. Joe

[Joe S]

Jazman,

If you are having problems with manual tdc it is NOT because of the range estimation. It is more likely error in the speed estimation. a small error in speed estimation will result in a miss except at extemely close range. If you want to improve the stadimeter range finding method, determine the height of the smokestack, which is easier to see than the top of the mast. The top of the mast often dissappears making it impossible to get an accurate fix. If you use the smokestack heigh you should see a big improvement. Joe

[jazman]

Originally Posted by Joe S

Jazman,

If you are having problems with manual tdc it is NOT because of the range estimation. It is more likely error in the speed estimation. a small error in speed estimation will result in a miss except at extemely close range. If you want to improve the stadimeter range finding method, determine the height of the smokestack, which is easier to see than the top of the mast. The top of the mast often dissappears making it impossible to get an accurate fix. If you use the smokestack heigh you should see a big improvement. Joe

OK, I spent some time working out the trig on a non-90 AoB solution. If we know the AOB, and the target speed, and the torpedo speed, and the range, there are two unknowns to solve: the time of the run, and the gyro angle. We need two equations. The ones that come to mind are the law of sines and the law of cosines. The law of cosines, unfortunately, seems to depend on the range. If the range is an unknown we're hosed because we need a third equation, am I missing something? Surely there are computational methods to solving this? That would be why you need a _computer_, right?

For the 90-deg AoB, the time of the run is an unknown, but cancels out nicely, and you need only one equation, because only the gyro angle is unknown. A basic trig equation works.

[Joe S]

Jazman,

I had a rough time with high school algebra. All I can say is that range is the least important component of a firing solution, no matter what method you are using(with some exceptions that probably dont apply here.). At any rate, on the nav map, draw a line representing the target's course. Pick a spot that marks the approximate location of the target where you plan on torpedoing it. Measure the range from that spot on the target track to your sub and enter it manually into the TDc. If you have an accurate speed estimate and your range is under 1500 yds you should be getting hits. I hope this helps. Someone with better math skills than me is going to have to explain the mathematical reason why range is not important. Joe

[jazman]

Originally Posted by Joe S

Jazman,

I had a rough time with high school algebra. All I can say is that range is the least important component of a firing solution, no matter what method you are using(with some exceptions that probably dont apply here.). At any rate, on the nav map, draw a line representing the target's course. Pick a spot that marks the approximate location of the target where you plan on torpedoing it. Measure the range from that spot on the target track to your sub and enter it manually into the TDc. If you have an accurate speed estimate and your range is under 1500 yds you should be getting hits. I hope this helps. Someone with better math skills than me is going to have to explain the mathematical reason why range is not important. Joe

It's probably that in the exact mathematics it matters, but for practical purposes (here come the engineers!) it's a wash. I guess all the focus on range is because the lower the range, the greater the margin of error and still get hits.

[XLjedi]

Originally Posted by jazman

It's probably that in the exact mathematics it matters, but for practical purposes (here come the engineers!) it's a wash. I guess all the focus on range is because the lower the range, the greater the margin of error and still get hits.

Well... not an engineer... but here comes the finance/programmer guy.

If target speed and course are constant, and intercept speed and course are constant, there's a trig solution that gives the third side of the triangle and thus calculate the intercept course. The three angles of the triangle never change as the torpedo approaches its target. The bearing to the target remains constant (you may have heard of the Constant Bearing Formula?) right up until impact. Since this solution never changes as the two objects converge you could infinitely expand the distance between the two and still score hits on a perfect 2D plane.

Likewise if you're running the bridge of a ship and you have a radar bearing on another ship and you notice that as you track that ship for 30 mins the range is steadily decreasing but the bearing is not changing what might that be telling you? (you're on a collision course)

There is one variable that does throw a wrench into the sub targeting though. The torpedo advance. The range doesn't matter commentaries relate only to low gyro angle shots. If you are shooting with more than a 3-5° gyro then your solution will be influenced by error in range estimation. If you typically shoot within the 1000-2000 meter range then set the TDC for 1500 and you don't have to worry too much about it if you keep your angles low.

Incidentally, I always thought it would be cool to drive a train. Then people could ask me what I do and I'd say, "I'm an Engineer"... and they'd say something like, "Oh, really? Mechanical or Electrical?" and I'd say, "Trains".