Hey guys! I was innocently stalking another thread on authentic methods of speed measurement in a pre-radar submarine. Someone popped up with the time the length across the wire method, which for some reason is very popular on Subsim. I'm afraid I blasted that great method as completely historically bogus.
So we talked about using bow wave and then stern wave to estimate speed. That works well, and in the game it's very reliable with experience. It was also used during the war.
But I was looking for a more analytical method, because that's my personal character defect
, and ended up looking through the Submarine Torpedo Fire Control Manual from 1946 (link later). It was so great that it belongs here in your bag of tricks! It's amazing what happens when you look at what the real submariners did. There sure weren't stupid!
Quote:
However, the stern wave is tremendously influenced by the hull shape, and of course there is a wide variety of hull shapes. You can also judge speed by the spacing between the bow wave and the quarter wave, which is further away from the bow wave with increasing speed.
Of all the methods, however, the bow wave is the most uniform between different ships.
Now this is all about the real thing and I don't know how closely the game reflects reality in this area.
Now here's an even better method stolen from the Submarine Torpedo Fire Control Manual of 1946. It relies only on achieving a collision course with your target. This can be done at just about any own speed, and even submerged if need be. How do you know you are on a collision course? Your target's bearing doesn't change with time. Your target is traveling from right to left. So let's say you take a target bearing of 15 degrees. Two minutes later it's 20 degrees (sorry, the alt-0186 shortcut for the degree sign doesn't work in Linux and I don't want to chase down the equivalent right now.). This means that the target is lagging behind. Either change course slightly toward the target or slow down. Take another measurement two minutes later. If you're still at 20 degrees, you have achieved a collision course. Make minute adjustments over time until you hold the same bearing for over three minutes. Collision course achieved! It's chart time:
All right, in official Navy terms Ab is angle on the bow. You understand that. LA is the lead angle, that's the angle between the bearing line to the target and your bow. S sub T is target speed and S sub O is Own Speed. These abbreviations are used uniformly throughout official submarine attack procedures. So, reading the formula there, Target Speed equals your own speed times the sine of the lead angle divided by the sin of the angle on the bow. The real guys would work that out in seconds on a slide rule, so you may authentically use a calculator.
Now you have with perfect authenticity calculated the speed and can derive the exact course of your adversary. Is it too much for some game players? Sure it is. Is it possible to do within the game? Absolutely. It's what I will do next time I'm caught in a boat without radar! If I can. The eyeball methods are better for quickly developing situations where you either shoot quickly or not at all. Guess this post ends up in the Sub Skipper's Bag of Tricks thread now...
And as a bonus, I found something else. You can put your target abeam and eyeball a relatively parallel course, right? You don't have to be accurate: 25 degrees off one way or another still yields pretty good results. Some idea of range is necessary too. But for what it's worth:
OK, that means that you're on a parallel course with your target. Your courses are the same, but of course, your speeds are different. We'll just say he's a mile, 2000 yards, away. Taking a series of bearings, his bearing is decreasing, he's falling back of 2 degrees per minute and you're going 10 knots. So he's traveling two knots slower than you are! Peg that guy at 8 knots.
Now get on a collision course and do the other calc. This will confirm and give you a reliable range at the same time when you diagram it out at the plotting table!
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