Speed number--figuring out ships speed

[Leoz]

(Important: This idea is not new or original. Others have provided similar lists/charts. It is just a reminder for new people (like myself). Anything that makes producing a firing solution quicker is good.)

This is useful if you don't happen to have the wonderful Ujag timepiece on your boat.

Scenario: calculating a ships speed by how many seconds it takes to travel its own length.

Typically it is done by ships length in meters, divided by the seconds you observe, then multiply by 1.85 to get a ship's speed in knots.

The list below takes out an extra step.

Pick the "speed number"* (made up the term) for the length of ship you are tracking. For example: "144" for a ship that is 78 meters long. Divide it by the time in seconds it takes for the ship to travel its own length. For example: 30 seconds and you come up with the following.

144/30=4.8 knots.** Your ship that is 78 meters long, is moving at a speed of 4.8 knots.

Ship length: 78 meters long. Speed number: 144
Ship length: 94 meters long. Speed number: 174
Ship length: 140 meters long. Speed number: 259
Ship length: 150 meters long. Speed number: 278
Ship length: 160 meters long. Speed number: 296
Ship length: 170 meters long. Speed number: 315
Ship length: 180 meters long. Speed number: 333
Ship length: 190 meters long. Speed number: 352


*Rounded to nearest number.

** Note: as I rounded out the speed number for simplicity, the actual speed number for a 78 meter long ship is 144.3. Thus the ship would be moving 4.81 knots for this scenario.

[Leoz]

This may be of use to have next to your periscope and UZO things...






Time it takes for this 78 meter long ship to cover it's own length....

[Zosimus]

Do you really do that? Does it work?

I mean, normally when I am chasing a ship, I already know it's speed because it's part of a convoy that I found when the game announced a nearby convoy complete with its speed.

If not, I'm probably just shooting at it with my deck gun.

Otherwise, if I think it's big enough to justify a salvo, I'll just chase it for 32 minutes. A ship going 7 knots will cover 7 km in 32.4 minutes. That gives me lots of time to set up a shot. You'll know its course spot on, its speed, and be able to set up for an easy shot with time to spare.

[3catcircus]

Originally Posted by Zosimus

Do you really do that? Does it work?

I mean, normally when I am chasing a ship, I already know it's speed because it's part of a convoy that I found when the game announced a nearby convoy complete with its speed.

If not, I'm probably just shooting at it with my deck gun.

Otherwise, if I think it's big enough to justify a salvo, I'll just chase it for 32 minutes. A ship going 7 knots will cover 7 km in 32.4 minutes. That gives me lots of time to set up a shot. You'll know its course spot on, its speed, and be able to set up for an easy shot with time to spare.

You're joking, right? Chasing it for 32 mins? One can easily calculate speed. Take a range/bearing and plot it. Do it again 3 minutes and 15 seconds later. Measure the distance it has traveled and divide by 100. That's its speed in knots. You can also calculate based on start/stop of the stopwatch as its bow and stern cross the wire, knowing ship length.

[Zosimus]

Originally Posted by 3catcircus

You're joking, right? Chasing it for 32 mins? One can easily calculate speed. Take a range/bearing and plot it. Do it again 3 minutes and 15 seconds later. Measure the distance it has traveled and divide by 100. That's its speed in knots. You can also calculate based on start/stop of the stopwatch as its bow and stern cross the wire, knowing ship length.

No, I'm not joking.

Oh, and I think the number you're looking for 3 minutes 14.4 seconds. That is exactly 3.24 minutes. In fact, if you multiply that number by 10, you'll get the 32.4 minutes that I mentioned above.

But no, I don't measure ship speed over 3m15s because it isn't accurate. You see, even if you have map contacts on, it will surely take you at least a half a second to click the x on the screen and then turn the stopwatch on. Even then, you'll notice that that x is not exactly in the middle of that box. And the problem only gets worse if you zoom in or out. Suddenly the x isn't even near the box.

In fact, a lot of times you'll watch the ship for 6m29s only to find that it appears to have covered 1.3 km. Really? The ship speed is 6.5 knots? I find that hard to believe. Maybe we should watch it out to 9m43s to be certain whether it's speed is closer to 6 or to 7. I suppose you propose to do all that underwater, scope up while the ship is moving away from you. Brilliant.

Or what if you're hunting by hydrophone? How exactly do you determine the ship length from 25m under water at 14 km away? Do you use your psychic abilities?

Or are you one of the types who fires a few torpedoes off and, if they miss, you just reload your last save and try again?

[3catcircus]

Originally Posted by Zosimus

No, I'm not joking.

Oh, and I think the number you're looking for 3 minutes 14.4 seconds. That is exactly 3.24 minutes. In fact, if you multiply that number by 10, you'll get the 32.4 minutes that I mentioned above.

But no, I don't measure ship speed over 3m15s because it isn't accurate. You see, even if you have map contacts on, it will surely take you at least a half a second to click the x on the screen and then turn the stopwatch on. Even then, you'll notice that that x is not exactly in the middle of that box. And the problem only gets worse if you zoom in or out. Suddenly the x isn't even near the box.

In fact, a lot of times you'll watch the ship for 6m29s only to find that it appears to have covered 1.3 km. Really? The ship speed is 6.5 knots? I find that hard to believe. Maybe we should watch it out to 9m43s to be certain whether it's speed is closer to 6 or to 7. I suppose you propose to do all that underwater, scope up while the ship is moving away from you. Brilliant.

Or what if you're hunting by hydrophone? How exactly do you determine the ship length from 25m under water at 14 km away? Do you use your psychic abilities?

Or are you one of the types who fires a few torpedoes off and, if they miss, you just reload your last save and try again?

I'll assume you meant no offense since tone can't be implied from your text.

I've done real time/bearing and geoplots as part of a Section Tracking Party in a former life. For purposes of the game, the pause key is the equivalent to that Section Tracking Party made up of multiple people. The minimal amount of tine necessary to switch to the nav map and hit pause is actually a lot less than people doing a real plot. How *I* do it in the game with map contacts off is get a range, note the bearing, go to nav map, pause, plot a mark, go back, hit the stopwatch, and wait. Get the new range/bearing at 3:15, go back, pause plot, get the course and speef from the plot, and do it again. Do that over the span of the 10 minutes spent on your final leg and you've got an adequate solution. I don't bother with the plot if I'm doing an overhaul maneuver once I've established his course.

[Leoz]

I use just about all methods mentioned depending on the situation. I use the final stopwatch check usually before a submerged attack.

Back when playing NYGM, I had the *perception* from observing a variety of attacks that target ships would change speed more often and my previous estimations could be off. Again: perception as I don't know the game programming efforts.

Have never really observed that much with GWX.

[BigWalleye]

Some observations:

1. We are at an advantage over our RL counterparts. We know that AI ships only move at speeds in integer knots. Check in the campaign.xxx files. Or turn on the God's eye view so you can get exact data. You'll see what I mean.

2. Knowing the target's speed to better than the nearest integer is not necessary for a successful firing solution. The target is BIG. At 1000 meters, optimum firing range as recommended by KM doctrine, a 140 meter long ship will subtend 8 degrees. The lead angle for a 90 degree shot is 14.5 degrees for a target moving at 10 knots. So if you aim for the center of the target, you can have a speed error of 27% at 1000 meters and still hit. At 2000 meters, quite a long shot, the allowable error drops to 14%. That's 8.5 kts, instead of 10kts. It is not difficult to distinguish between 8.5 and 10 kts.

3. Submarine commanders were warriors, not engineers and certainly not accountants. If you read the first-person accounts, they didn't attempt to determine target parameters with great accuracy, just enough to get the torpedo on the target with a good probability of success. Better to fire two fish, hit, and retire than to try for the perfect shot, get detected, and have to abort the attack. I don't recall ever having read of an RL sub skipper who regarded the attack as a math problem. That's for staff officers.

Remember that the torpedo is a big, powerful weapon. Any hit will do a lot of damage. A heart shot is not needed.

[Zosimus]

Well, there are lots of ways to skin a cat. For example, let's suppose that you don't know how to use a three-bearing method to determine the ship's course. No problem. Here's an easy and infallible way to determine the ship's course, range, and speed.

Assuming that the ship is either moving away or constant distance, simply steer directly toward the ship on the surface. It won't be long till you will be directly astern of the ship and following the ship on exact same course as the ship.

Then you can easily pace the ship to determine its exact speed.

Let's assume, for example, that the ship is going 22º at 7 knots. Just locate the ship and draw a circle around that ship with a radius of either 7 or 14 km. The ship will be on the 7 km circle in 32.4 minutes and the 14 km circle in 64.8 minutes. So as long as the ship doesn't change course (ships do that sometimes) you'll know exactly where that ship will be at a specific future time.

Then conduct an end around attack. I'm assuming pretty much anyone can do that. Since you know the target's course, speed, and location at a set future time, you can easily move out to 10 km distance (assuming normal, imperfect weather) and race around the target at full speed without being seen. Move in submerged, set up for the attack, and hit it with a two-torpedo salvo at 1 km distance.

All of this can be done without identifying the ship, knowing its draft, or knowing its beam. In fact, the entire operation can be conducted periscope down till the last second when you go up just long enough to take the shot and send it to the bottom.

[Leoz]

Originally Posted by BigWalleye

Some observations:

1. We are at an advantage over our RL counterparts. We know that AI ships only move at speeds in integer knots. Check in the campaign.xxx files. Or turn on the God's eye view so you can get exact data. You'll see what I mean.

2. Knowing the target's speed to better than the nearest integer is not necessary for a successful firing solution. The target is BIG. At 1000 meters, optimum firing range as recommended by KM doctrine, a 140 meter long ship will subtend 8 degrees. The lead angle for a 90 degree shot is 14.5 degrees for a target moving at 10 knots. So if you aim for the center of the target, you can have a speed error of 27% at 1000 meters and still hit. At 2000 meters, quite a long shot, the allowable error drops to 14%. That's 8.5 kts, instead of 10kts. It is not difficult to distinguish between 8.5 and 10 kts.

3. Submarine commanders were warriors, not engineers and certainly not accountants. If you read the first-person accounts, they didn't attempt to determine target parameters with great accuracy, just enough to get the torpedo on the target with a good probability of success. Better to fire two fish, hit, and retire than to try for the perfect shot, get detected, and have to abort the attack. I don't recall ever having read of an RL sub skipper who regarded the attack as a math problem. That's for staff officers.

Remember that the torpedo is a big, powerful weapon. Any hit will do a lot of damage. A heart shot is not needed.

Great read! Thanks.

[BigWalleye]

BTW, LGN1 has made a easy-to-use chart for finding speed by the wire-crossing method. You can download it here: http://www.2shared.com/file/qIEMFogN/lgn1fixedwire.html
Sorry, no pic.

[bstanko6]

Whatever method you use... be consistent. It will fare better with every attack you make.

[Zosimus]

Originally Posted by Leoz

Great read! Thanks.

Originally Posted by BigWalleye

Some observations:

1. We are at an advantage over our RL counterparts. We know that AI ships only move at speeds in integer knots. Check in the campaign.xxx files. Or turn on the God's eye view so you can get exact data. You'll see what I mean.

2. Knowing the target's speed to better than the nearest integer is not necessary for a successful firing solution. The target is BIG. At 1000 meters, optimum firing range as recommended by KM doctrine, a 140 meter long ship will subtend 8 degrees. The lead angle for a 90 degree shot is 14.5 degrees for a target moving at 10 knots. So if you aim for the center of the target, you can have a speed error of 27% at 1000 meters and still hit. At 2000 meters, quite a long shot, the allowable error drops to 14%. That's 8.5 kts, instead of 10kts. It is not difficult to distinguish between 8.5 and 10 kts.

3. Submarine commanders were warriors, not engineers and certainly not accountants. If you read the first-person accounts, they didn't attempt to determine target parameters with great accuracy, just enough to get the torpedo on the target with a good probability of success. Better to fire two fish, hit, and retire than to try for the perfect shot, get detected, and have to abort the attack. I don't recall ever having read of an RL sub skipper who regarded the attack as a math problem. That's for staff officers.

Remember that the torpedo is a big, powerful weapon. Any hit will do a lot of damage. A heart shot is not needed.

Your argument relies on a lot of bad assumptions.

Let's run with your example. The target covers 8º and we are firing not a center shot but a salvo shot (that's what KM recommended, isn't it?) with a 4º salvo angle that we can control when we switch to salvo mode.

For ease of understanding, we will label the boat thus:

3 2 1 0 1 2 3 (0 is dead center).

So your torpedoes are aimed at -2 and +2

Suddenly your 27% permissible error rate goes out the window. The acceptable error rate must surely fall to 13% or less.

Additionally, you are assuming that the ship is going 10 knots. Most of the convoys I attack are going about 7 or 8 knots. If we re-calculate with 7 knots, and 13% error that means +/- 0.91 knots. That means that if you think the ship is going 7 but it's really going 8, then one of your torpedoes is going to miss.

Furthermore, there's another possible error involved. The speed setting is analog. You cannot digitally enter 7.0 knots. You are moving the dial and it looks like it's 7, but maybe you actually set for 6.9 and you didn't know. Or maybe you tried to set the AOB for 90º at the moment of the shot, but because of inaccuracies, it's actually set to 88º

Finally, perhaps you're right that your average u-boat commander didn't care about the exact math involved. However, if we look at the list of the top 50 u-boat commanders at https://en.wikipedia.org/wiki/List_o...oat_commanders and arbitrarily pick 26 and 27 (about the middle of the most successful pack) we see that they are sinking about 3 ships per patrol and #29 drops to fewer than 2 ships per patrol.

So, basically, your average u-boat captain sucked. And if you do things the way he did, you'll suck too.

[BigWalleye]

Originally Posted by Zosimus

Your argument relies on a lot of bad assumptions.

Let's run with your example. The target covers 8º and we are firing not a center shot but a salvo shot (that's what KM recommended, isn't it?) with a 4º salvo angle that we can control when we switch to salvo mode.

For ease of understanding, we will label the boat thus:

3 2 1 0 1 2 3 (0 is dead center).

So your torpedoes are aimed at -2 and +2

Suddenly your 27% permissible error rate goes out the window. The acceptable error rate must surely fall to 13% or less.

Additionally, you are assuming that the ship is going 10 knots. Most of the convoys I attack are going about 7 or 8 knots. If we re-calculate with 7 knots, and 13% error that means +/- 0.91 knots. That means that if you think the ship is going 7 but it's really going 8, then one of your torpedoes is going to miss.

Let's go back and read the Submarine Commander's Handbook, Kriegsmarine publication number 1643, edition of 1943.

172.) If the range is over 1,000 m, or if there is uncertainty as regards the aiming data (high

speed of the enemy, several torpedoes (2, 3, or 4) should be released on the "fan" pattern. The

idea is to make sure of

one hit. It is better to score only one hit than to miss the target with each of several consecutive shots.

The target should therefore be covered by aiming at the boundaries a the area of dispersion on

the target; i.e., the shots should be spread by the width of the dispersion area in relation to one

shot aimed on the basis of the estimated data (if 2 or 4 shots are fired, in relation to an

imaginary middle shot).

So, according to the KM manual, the purpose of the salvo is not to hit with all torpedoes, but to ensure that at least one hits the target. By firing the 4-degree spread, our tolerable speed error increases from 27% to a whopping 45%.

Finally, perhaps you're right that your average u-boat commander didn't care about the exact math involved. However, if we look at the list of the top 50 u-boat commanders at https://en.wikipedia.org/wiki/List_o...oat_commanders and arbitrarily pick 26 and 27 (about the middle of the most successful pack) we see that they are sinking about 3 ships per patrol and #29 drops to fewer than 2 ships per patrol.

So, basically, your average u-boat captain sucked. And if you do things the way he did, you'll suck too.

So where is Kretschmer's treatise on the mathematics of the submerged approach? Where did Topp earn his PhD in Toppology? And what is your basis for claiming that what you do is any closer to Kretschmer's technique than to Rosenstiel's? Evidence, please.

Let's look at some of these commanders who you say "sucked." Because the names are familiar to anyone who knows the history of the U-boat war. Jenisch (26) sank 17 vessels in 6 patrols. Zapp (27) sank 16 in 5 patrols. Endrass (23) sank a "mere" 22 vessesl in 10 patrols. These were brave, seasoned, experienced naval commanders. Do not denigrate their performance just because you and I can achieve higher scores in a game which is a trivialization of the environment they fought in.

Now, you spent good money for your copy of the game, and you can play it any way you want. You can turn it into your high school science project in trigonometry if you wish. Or you can play at 27% realism (sic) and sink the entire British Navy every patrol. Whatever floats your (U-) boat.

But if I can use historically attested tactics and methods in this little game, and get results as good as Hardegen (rank 24, 22 ships in 5 patrols for 115, 656 tons), then I am having fun. If Hardegen sucked, and if Endrass and Jenisch and Zapp sucked, then well, I guess I suck too. It could be worse.

YMMV

Who said that SH3 was a simulation ?

No. SH3 is a game based on the German submarines of WWII, but it's far from a real simulation. Very far !