Quote:
Originally Posted by suitednate
Thanks everyone. Appreciate your responses. I know what you are saying is true in that you don’t need range to have a good solution (at least on the German boats) but I was wondering why this is the case? It seems to go against logic.....
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In the general case you need range, but you don't need range when using certain targeting methods. For example the Dick O'Kane method, wherein you are waiting for the enemy ship perpendicularly to her course, and plan that your torpedo will hit her when she is at 0 Bearing (straight ahead from you; you are going to shoot before she is straight ahead, of course).
In such a scenario, range doesn't matter. You only need the speed of target, which will allow you to calculate at what bearing to shoot. This can be proven with trigonometry (range cancels out and plays no role), but I 'll spare you. Here is another way to think about it:
In scenario A for a large range, suppose it turns out that you have to shoot when enemy is at Bearing 350, so that the torpedo hits when the enemy is at Bearing 0. This requires some calculation (which is what the firing solution is), but let's say that's what turns out. You shoot when she is at 350, both the enemy and the torpedo travel for a while, and they meet at Bearing 0. Right ahead of you.
In Scenario B, everything is exactly the same as before (course and speed of target are the same, you are again waiting perpendicularly), but this time you are much closer to her course. When do you have to shoot? Again, when she is at Bearing 350! The range is shorter now and the torpedo will travel for less time to reach the enemy's course, but the enemy will also travel for less time to get right in front of you! They will again meet at Bearing 0 as in Scenario A.
Therefore, it turns out (and can be proven rigorously with trigonometry) that in scenarios such as the above, range doesn't matter. You only need to know at what Bearing you have to shoot, which you can calculate if you know the speed of the torpedo (which you do know) and the speed of the enemy (which you have to measure).
I just described the Dick O'Kane method of manual targeting. For a different speed of target you have to calculate a new bearing for shooting, but for most merchant speeds you are going to be OK if you shoot when she is at 350 (if coming from the left) or 10 (if coming from the right). It won't land exactly where you thought it would land, but close enough.
However, note this method doesn't work any more if some of the specifics of the situation change (eg, if you are not perpendicular to the enemy's course).