View Full Version : how to calc speed of target?
Saw in one of the written tutorials, they time it takes for the ship to go bow to stern across your crosshair, similar to SH3. Then you take the time and divide by the length of the ship. Problem is, there's no length on the recognition ID????
magic452
07-24-10, 12:55 AM
The real recon manual had no ship lengths either.
Best bet is to use the three minute rule.
With map contacts on mark the position of the target and start the watch, wait three minutes and mark the new position again.
The distance between the marks will give you speed. 100 yards = 1 knot
500 yd = 5 kn. 1000 yd =10 Kn. For metric use 3' 15" 100 meters = 1 knot.
Do this three times and you will also get a very good course plot.
With no map contacts you'll need to plot the positions yourself.
See Rockin Robins Sub skippers bag of tricks thread for some useful Fleetboat stuff.
http://www.subsim.com/radioroom/showthread.php?t=146795
Magic
greyrider
07-24-10, 10:41 AM
here are recognition manuals for the us, uk, japan, germany and italy,
published in september, 1943.
clearly these show not only the length of the ships, but also the beam, height,and draft.
http://www.acepilots.com/ships/manual.html
speed IS the magic bullet when gathering info for the solution, and there are lots of ways to get it,
a search for target speed should bring up many techniques for obtaining speed here on the forums.
Position yourself alongside and keep the target on your 90/270 bearing while adjusting speed to match. If you do this long enough your own distance moved over time gives average speed of the target. You just have to keep the target unaware of you. Because they tend to adjust their course every now and then when they do notice you.
Armistead
07-25-10, 09:55 AM
The one thing to remember about speed is no matter what method you use, if they sense you after you figure speed, they'll slow down, zig, change speed. A common rookie mistake is to figure speed then get pinged by a escort and still use the speed they figured to shoot. Once they sense you they will zig and change speed, go in circles, ect. If this is happens you'll have to figure speed for each target on the fly. Most take a few stad measurements, guess, ect, moreso if you have escorts charging you. If they're changing courses, you have to really guess at where they're going to be when the torps get there and set up to shoot that way.
Sometimes it's best to head deep and wait it out. If you feel skilled enough you can start shooting at targets you feel you can best hit. Just remember the 3 minute rule, counting seconds through the scope, ect...only work if you get your shots off before they know you're there.
I also time a vessel crossing my crosshair to find speed. This little mod is just what the doctor ordered;) http://www.subsim.com/radioroom/showthread.php?t=166096&highlight=ship+lengths Just realised it's for RFB. Not sure if it would work in other applications though.
thank, found that post too, but the download doesn't work in that link. Any other place to get that file?
Thx for the info. I've been trying to let the TDC estimate speed by taking two or more range readings. So far it hasn't been that great. Sometimes ok, but more times wrong.
So if you're playing with no map contact updates, only other way is to time across the 0 bearing line, but need the length's for that. or use the active ping to get range and time the speed, problem is escorts could hear the ping.
Seems like most people play with no map contact updates, cuz without the 0 bearing rule (or active sonar), there's no other way to get speed.
Get two good bearing and range fixes, and use a slide rule to figure out AOB, speed, distance traveled.
http://www.subsim.com/radioroom/showthread.php?t=112765
I've used it with a regular slide rule and the speed omnimeter here: http://www.hnsa.org/doc/attackfinder/index.htm
It works rather nicely, and it's pretty quick. You poke the scope up a couple of times, instead of leaving it up to time the ship passing. No length needed, just range and bearing.
by range fixes, you mean with an active sonar ping? Doesn't that get the attention of the escorts?
by range fixes, you mean with an active sonar ping? Doesn't that get the attention of the escorts?
Radar, sonar, stadimeter, asking the crew for nearest visual contact.
I imagine the sonar would alert the escorts, but I've never used it, so I can't confirm.
Rockin Robbins
07-26-10, 04:15 AM
Keep in mind that timing the length of target across the crosshairs is not an authentic technique either for U-Boats or fleet boats. In practice, they did not know the length of the target, most of the time misidentifying tonnage and length by a factor of plus or minus 2 to even four. This would make any attempt to time length across the crosshair a comedy. It just wasn't done.
We cheat. Our recognition manual is perfect. It has the proper length for every target, and it contains every possible target on the surface of the seven seas! That is so far from the true state of affairs in any kind of WWII submarine that it renders our simulation into an arcade game.
If we want to run SH4 as a simulation, we have to use techniques that real sailors either used or could plausibly have used. Timing length across the wire doesn't satisfy either requirement.
greyrider
07-26-10, 07:43 AM
not to doubt ya rr, but i think i do, everyone hear forgets about the naval treaty of washington in the 1920's, and the treaty of london in the thirties.
the signatorie nations, japan uk, us france and italy, all agreed to limit specifications on ships, tonnage, length, gun sizes, the whole 9 yards.
alot of us ships had to be either converted, or dismantled to conform to the treaties, same with the other nations.
when the nations build new ships, they had to declare to the other signatory nations the new ships vital signs,
so ship lengths and weights and guns and all the other stuff had to be declared to the other nations.
i believe japan pulled out of the treaty in 1936, and then shorty after began building yamato, and her sister
its just like today treaties that the us has with russia, they know how many missiles we have, and we know what they have
its also obvious that ship length is in rec manuals,
joegrundman
07-26-10, 08:31 AM
Keep in mind that timing the length of target across the crosshairs is not an authentic technique either for U-Boats or fleet boats. In practice, they did not know the length of the target, most of the time misidentifying tonnage and length by a factor of plus or minus 2 to even four. This would make any attempt to time length across the crosshair a comedy. It just wasn't done.
what is your reason for saying this?
its also obvious that ship length is in rec manuals,
Knowing the correct length of the ship would involve having accurate data about the ship. The data you have may be incorrect from the beginning. The ship may have been modified after the data was collected. The ship may be painted in such a way to appear smaller than it actually is. You would need to make an accurate identification. If you look through the records, ships were quite often misidentified. Even if the Japanese were reporting accurate information about their heavy warships, you wouldn't be running across them that often. You would also need information about a large number of different merchant ships.
In the game, we can be sure of our identification and the accuracy of the data in the manual. During the war, you would have been using incomplete data, backed up by guesses, compiled with a lot of assumptions. You might get close enough to the actual speed to get a hit if you were close enough in, but you wouldn't be getting anywhere close to the accuracy you get in game.
Besides, watching the ship cross the wire involves leaving the scope exposed longer than needed. The longer the scope is up, the greater the chance it will be spotted. If you're at long range, leaving the scope up isn't as much of a problem, but the farther you are away, the less accurate your identification would be, therefore your speed estimate would be inaccurate.
Rockin Robbins
07-26-10, 12:42 PM
Joe, my reason for saying it is that it is the truth.
Yes, data on military vessels was marginally better than for merchies, on which there was very little information and much of that was wrong. But it is a fact that all nations cheated on the treaty and released inaccurate information to each other.
In addition, the real recognition manuals did not contain every ship on the ocean, or even a large fraction of them. Most of the time real skippers guessed, based on the closest fit to what they saw. Combatant nations also took pains to disguise their merchant and naval vessels to yield bad ranges, lengthening or shortening masts, painting them to make it difficult to determine the outline, even adding funnels in hopes of misidentification.
If we're interested in playing an arcade game, why not just use auto targeting? If we are playing SH4 as a simulation, the length by the wire method isn't on the menu.
that actually makes sense that they never knew length. Given the sheer number of vessels in the ocean. Maybe not so much for warships cuz they're probably known mostly i would think, but so many different types of merchant ships.
greyrider
07-27-10, 07:22 AM
Knowing the correct length of the ship would involve having accurate data about the ship. The data you have may be incorrect from the beginning. The ship may have been modified after the data was collected. The ship may be painted in such a way to appear smaller than it actually is. You would need to make an accurate identification. If you look through the records, ships were quite often misidentified. Even if the Japanese were reporting accurate information about their heavy warships, you wouldn't be running across them that often. You would also need information about a large number of different merchant ships.
In the game, we can be sure of our identification and the accuracy of the data in the manual. During the war, you would have been using incomplete data, backed up by guesses, compiled with a lot of assumptions. You might get close enough to the actual speed to get a hit if you were close enough in, but you wouldn't be getting anywhere close to the accuracy you get in game.
Besides, watching the ship cross the wire involves leaving the scope exposed longer than needed. The longer the scope is up, the greater the chance it will be spotted. If you're at long range, leaving the scope up isn't as much of a problem, but the farther you are away, the less accurate your identification would be, therefore your speed estimate would be inaccurate.
thats right, its called camouflage, often used military tactic.
but what does that have to do with a naval treaty?
a treaty is only good as long as nations have diplomatic ties, once nations are at war, its not worth the paper its printed on, and i would say null and void.
Besides, watching the ship cross the wire involves leaving the scope exposed longer than needed. The longer the scope is up, the greater the chance it will be spotted.
i know how to use a scope, do you? :) from your above statement, i dont think so.
one thing that drives me nuts here is that people state things as fact, but without showing proof,
wheres the beef? show us your proof. prove to us that what your saying is in fact true
i dont make any claim that ship length was the way to get speed, so i dont have to defend that point, if your saying that japan lied about its ships, i would say your wrong, because japan followed the treaty just like everyone else, until 1936, when they left it, and they left it because they thought it was unfair to them, as the us and the uk were permitted more ships then they were allowed to have.
you know, across the street from me sits a gold mine, that i cant get to as yet. my neighbor's father was a sonar operator on a us subchaser in ww2, and he has all his sonar manuals that he had used during the war and in training, maybe even turn count speed curves, and God only knows what else. im trying to get them from him, but hes real sentimental about his fathers things, he doesnt want to part with them, and i can understand that, he also needs a heart transplant.
but sitting across the street, in a damp celler is all the proof i need for all the things i worked on here at subsim with hydrophones, ill get it someday, and when i do, i will show all of you, its just a matter of time. :)
on a side note about merchants ships. most ocean going vessels in world war 2 were built in western powers shipyards, and thier built to be sold, and so to sell them, you have to advertise, when you advertise, you more than likely give your potential customers the complete run down on the specs and capabilities of the vessel, if you look in this game ships, say for instance a small merchant, all the combatant nations in sh4 have them, theres nothing unknown about them, because everyone has them.
if general electric makes a toaster, and sells it to new zealand, dont we know the specs of that toaster? same with ships sold to.
Stormflux
07-27-10, 12:24 PM
Here's what I do with no contact map updates, no external camera, and trying to stay reasonably true to life). First, take your initial range and bearing, start the stopwatch, then lower the scope and go draw it on the map.
Then, some time later, take another observation. A lot of people like to do this 3 minutes later, but you can use any number as long as it is easily divided into 60.
Say I've plotted a target traveling 5,000 yards in 10 minutes. This works out to 30,000 yards an hour, or 15 knots. (I used to tab out to Google to convert yards to knots, but then I realized it's 2:1 so there's no need.)
Of course my observations probably aren't perfect, but it's enough to plug into the TDC for now. You'll probably need to do it a few times as the target gets closer and your observations become better. If you do a good job, your plots will be evenly spaced and in a straight line. They never are, but that's the goal.
The other thing you can do, which they also did in real life, is leave the TDC running between observations. It will continually predict the bearing to target even with the scope down, which you can see by hovering over the TDC bearing indicator.
Each time you to to take an observation, raise your scope on this exact bearing and the target should be right in your crosshairs. If not, adjust your solution. By the time you're ready to fire, the TDC should be getting this right every time, that's how you know you've got an accurate shot.
Of course, if you're spotted, all bets are off. The target will begin to zig or alter speed, and you'll have to compensate on-the-fly. You may need to run alongside the target at close range waiting for a good shot, but that's ok. U.S. subs could shoot accurately at ridiculous gyro angles, unlike German subs which lacked this capability.
Rockin Robbins
07-27-10, 12:49 PM
if your saying that japan lied about its ships, i would say your wrong, because japan followed the treaty just like everyone else, until 1936, when they left it, and they left it because they thought it was unfair to them, as the us and the uk were permitted more ships then they were allowed to have.
... maybe even turn count speed curves...
on a side note about merchants ships. most ocean going vessels in world war 2 were built in western powers shipyards
Yikes! Talk about sweeping generalizations with no basis in truth! First of all, lying of the first degree takes place while under the treaty. Germany cheated, Japan cheated, England and the US cheated too, every chance we got! You don't think they invited inspectors to verify, do you? Where'd all those U-Boats come from? How about the military aircraft that weren't supposed to exist? Yup, cheating while diplomacy was still being practiced.
Then you casually mention turn count speed curves. The klaxon sounds! There WERE NONE in World War II. There were only a minority of enemy warships for which we had any data at all. For the merchant fleet we had almost nothing. Heck, we had so much data that the vast majority of merchant targets shot at during the war were misidentified. In practice, only our radar was responsible for half the sinkings.
That's not bad enough. The statement "most ocean going vessels in world war 2 were built in western powers shipyards" is the king of all fallacious unsupported statements. You are specifically claiming that most Japanese merchants were foreign made? Yikes! No response is possible without abuse.
I'm goin' down
07-28-10, 12:00 AM
nice to see ol' RR is mellowing with age (just like beer)
TwinStackPete379
08-03-10, 10:26 PM
Greyrider that recogniton manual is very cool. Ubi could use that to increase the realism of torp hits and such. Lotsa neat info in that manual!
green_abobo
08-03-10, 11:46 PM
1. :88) color me stupid here, but please tell me distance traveled divided by time was indeed an authentic determining factor for speed-in-knot guesstimates,as in a nomograph?
i wish i could plot their course and speed like a good dead-reckoning sailor from sonar,but i'm just not that skilled,and the above method works fairly accurately for merchants anyway.
for escorts it would have to be from sonar or long range radar,otherwise you risk too much attaining/maintaining visuals,and they just don't weigh enough to get depth charged, in my humble opinion.
2. off topic...RR,in another thread concerning convoy tactics,you mention your patented "end-around" maneuver. :hmmm: does this involve attacking from one side of the convoy with the forward tubes,diving deep as possible,and speeding across to the other side-go periscope depth and fire the sterns,thus evading the escorts,or did i misinterpret what you mean?
my question stems from usually attacking from inside the convoy, and usually after the forward torps go bang, i would then set up for a stern attack on the convoy line behind me @ a 180 degree bearing.sometimes it works no problem.
then the other times, it's pretty close because the escorts are already pinging me before i can get set up for the stern shots, so i figure it's better to just dive and then wait to come back up for the attack instead,if there's any leftovers by that time.
thanks again as always.
lenght of ship divided by time traveled with cross hairs on bow, time how long it takes cross hairs too clear stern, sub at zero speed . then multiply by 1.5 ,works pretty good from 90 to 45 bow angle . ship 270 meters 45sec through crosshairs times 1.5 = 9 knots. I shoot on manual TDC or paralell track manual set speed in knots.
lenght of ship divided by time traveled with cross hairs on bow, time how long it takes cross hairs too clear stern, sub at zero speed . then multiply by 1.5 ,works pretty good from 90 to 45 bow angle . ship 270 meters 45sec through crosshairs times 1.5 = 9 knots. I shoot on manual TDC or paralell track manual set speed in knots.Why 1.5? I'm pretty sure it's 1.94 knots per meter/second (= 3600s/1852m). Or 2 if you want to keep it simple. If the length is in yards then it is about 1.78 knots per yds/sec
the ship refernce gives the ship length in meters and we are living in a standard kind of world, miles, yards, ect, ect. got formula written down I'll double check it if I can find it, and get back with you, think I first found it in a earlier thread in this forum.
joegrundman
08-04-10, 07:20 AM
Joe, my reason for saying it is that it is the truth.
Yes, data on military vessels was marginally better than for merchies, on which there was very little information and much of that was wrong. But it is a fact that all nations cheated on the treaty and released inaccurate information to each other.
In addition, the real recognition manuals did not contain every ship on the ocean, or even a large fraction of them. Most of the time real skippers guessed, based on the closest fit to what they saw. Combatant nations also took pains to disguise their merchant and naval vessels to yield bad ranges, lengthening or shortening masts, painting them to make it difficult to determine the outline, even adding funnels in hopes of misidentification.
If we're interested in playing an arcade game, why not just use auto targeting? If we are playing SH4 as a simulation, the length by the wire method isn't on the menu.
Sorry I didn't notice you responded.
What are your sources for this claim?
The fixed wire method was of course not a USN technique. But there is good reason to believe it was a KM technique. Firstly, the reason it is called the fixed wire method is that the periscope head was fitted with a vertical wire that could be set to any azimuth and there it would remain. This was for the purpose of this technique.
After setting the azimuth with the fixed wire, the periscope was free to do as it pleased, including go back under the waves between the first and second measurement. Since neither SH3 nor SH5 have this feature, the scope crosshairs were used instead, but this meant the scope could not be used horizontally in the meantime.
It is true that accurate length data was not always available, but you are mistaken in assuming that that renders all guesses impossible.
Formulas were available just as the USN torpedo fire manual describes formulas for estimating mast height from counting number of decks, so estimates of length could be gained by appreciation that ship design followed certain plans and ratios and from such cues as counting number of cranes giving number of cargo bays (of typical volume), and thence dimensions.
In any case, the accuracy required is not as great as you might imagine.
Let's say we are just multiplying target length in m/time x2 to get knots, and we had 30 seconds.
If the length was
150m = 10 knots
125m = 8.3 knots
100m = 6.6 knots
75m = 5 knots
Well, you can see that getting length to the exact m is not important. The nearest 10 m is generally quite sufficient.
It is my opinion that a decent skipper ought to be able to look at a ship and guess it's length to approximately the nearest 10 m. Certainly you ought not to be easily confusing a 75m ship with a 150 m one.
And this is what i tend to do with SH3. The very large number of merchants added to SH3 makes using the recog manual unwieldy, and so i never use it anymore.
Besides the method is best used as a back up to for rapid confimation after obtaining your most detailed estimates through the overhaul maneuver, and other forms of plotting and approach, such as the constant bearing method.
a knot = 1.15 mile per hr http://en.wikipedia.org/wiki/Knot_(unit)
a knot = 1.15 mile per hr http://en.wikipedia.org/wiki/Knot_(unit)Yes, but even if you made a typo (1.5 versus 1.15), how did you come up with the speed derived to (statute) miles per hour?
Manual Plotting Hints and Tips
Determining Target Speed via Mark One Eyeball
don1reed on Subsim posted the following formula, which you can use to determine a target’s speed fairly accurately:
Ship's length past the vertical graticule / seconds x (3600/1852) = speed.
The bearing to your submarine from the targeted ship, your AOB, must be between 60 and 120 degrees. You should be at full stop for best results.
don1reed provided a quick example: i.e., T2 = 152.7m / 40 sec. x 1.94 = 7.4 kts.
Also see: Target speed calculation made easy (http://www.subsim.com/radioroom/showthread.php?t=108454)
Determining Target Course with Weapons Officer
Supplied by Gipodiablo on the Subsim forums.
If the target’s AoB is starboard, here’s the formula:
180 - AoB + Your Ship's Heading + Your Ship's Bearing to Target in Periscope
If the target’s AoB is port, here’s the formula:
AoB - 180 + Your Ship's Heading + Your Ship's Bearing to Target in Periscope
joegrundman
08-05-10, 03:32 AM
Yubba, dude, you are making life difficult for yourself.
Try looking in the subskipper's bag of tricks thread above.
Your main speed determination methods are:
plotting target course over time, using the 3 minute rule.
That is you take measurements every 3 minutes. Two is the minimum, more 3 minute measurements improves accuracy. The distance the target travels in 3 minutes, as shown on the nav map in 100yds= speed in knots. E.g it shows the target moved 900 yards = 9 knots.
You can take this plot using any of these methods:
radar (or using map contacts on, if you haven't the energy or skills to measure radar yourself, nor the enthusiasm to learn,)
watch officer report will give highly accurate range and bearing, if you feel happy doing this.
stadimeter is less accurate than radar, but not bad, esp if you have the essential ability to eyeball AOB. Most veterans from SH3 can use the stadimeter pretty well.
Pinging may alert defenders, but is accurate.
Other than plotting there are various other methods.
Matching course and speed
You try to maintain a constant relative position to the target. Once successful, you have the exact same course and speed. However must be done on the surface(and therefore at a distance) for targets faster than 9 knots, and underwater at 7 to 9 knots it uses up your batteries, and being noisy will alert enemy DDs. So for single merchants.
Using the Position Keeper
Generally this is my favourite method, since if you are practiced at getting AOB visually and loose speed and range estimates just by looking at the target, you get your solution without much work at all. Make your initial estimates and enter into PK and leave it on.
Observe using hydrophone/visual bearing to target how the target tracks compared to the PK. Take stadimeter readings every now and then anc compare with PK generated range. Every few minutes, if the target is not tracking well, adjust the PK with your new AOB, range and speed estimates. Typically after 3 or 4 adjustments your PK should be tracking well and all you need is final AOB, range and bearing data before shooting.
Collision Course.
If you can determine AOB then this method works. Set up a collision course and try to find a speed that holds the target on a constant relative bearing.
Now the formula for speed is :
Target speed = Submarine Speed x sin (bearing to target)/sin (AOB)
This operation is made much easier if you build yourself a replica of the wonderful, life-changing, ISWAS tool - files for download somewhere in this thread
http://www.subsim.com/radioroom/showthread.php?t=106923&highlight=iswas
Anyway, this list is not exhaustive. Learn plotting first!
Easy calulation 1ft per sec = 0.592483801295896 knot or round it off 0.6 knot. I sometimes put cross hairs on bow to first mast guess feet, time with stop watch. I 'm a lay and wait kind of guy this works well ,too many planes. http://www.calculateme.com/Speed/FeetperSecond/ToKnots.htm 1 meter per sec = 1.9438444 knot 1 knot = 0.514444444 meters per sec http://www.calculateme.com/Speed/index.htm hope this helps , good hunting. you have to be at 0 speed.
TwinStackPete379
08-08-10, 08:02 AM
The 3 minute rule + O'Kane fast 90 = lotsa wet Japanese shark bait. End of story.
Deephunter
08-08-10, 01:28 PM
If you're going to "guess feet", you might as well save yourself the trouble of doing the rest....Just guess speed right off the bat....
joegrundman
08-08-10, 02:00 PM
If you're going to "guess feet", you might as well save yourself the trouble of doing the rest....Just guess speed right off the bat....
sure that's an option, and it amounts to the same thing. It's just that unless you are practiced at estimating from bow waves etc. it's for some a better option to guesstimate length based on visual cues on the target (it's what everyone had to do for range without radar or pinging, after all) and use that to base your speed estimate instead of just guessing speed. Still, i think what you say is right, in real life, with skippers being people who spent a big percentage of their life watching ships going about, just looking at the target and guessing speed was a big part of it.
Has the advantage of being fast too.
I think it's tricky to do in the game environment, but i also do just guess speed quite often. Bow waves are particularly useful at low speeds, i find.
AFAIK, particularly British submariners depended heavily on Captain's eye for the data. Then again, their accuracy was none too special.
than a couple knots. I get good results with this method in manual targeting at the start of the war in a Sargo and that is about realistic as it gets ,it's a difference between putting torps on target or not. Can get speed in a matter of seconds.
Rockin Robbins
08-08-10, 04:01 PM
Ding! Ding! Ding! Ding! Joegrundman hits the nail on the head with the three minute rule (3 min 15 seconds if you use metric). That is the only unambiguous, authentic way to measure target speed. And accurate target speed is the Achilles heel of any targeting system. Enter an inaccurate AoB or range and you can get away with it. Small problems with target speed beget misses! The three minute rule is the best way because it eliminates target identification or guessing target length or performing mathematical gymnastics with constants carried out to ludicrously inappropriate numbers of significant figures. (the number of significant figures means something. Using them pretends that all your measurements are that accurate, a fallacy)
Eliminate or mitigate error. Error is unavoidable, therefore it must be a part of any targeting exercise. Failure to account for error is fatal.
Deephunter
08-09-10, 09:23 AM
I agree wit RR...Guesswork has no place in determining target speed. A couple of knots off can mean the difference between a hit and a miss, particularly for longer range shots.
joegrundman
08-09-10, 10:38 AM
I agree wit RR...Guesswork has no place in determining target speed. .
nonsense!:arrgh!:
Rockin Robbins
08-09-10, 01:22 PM
Guesswork is OK if you mitigate the error you know must be in the calculation. In the real war, they extended their spreads both ahead and behind the target, making a spread of more than 100% of the target length. They knew this guaranteed misses but they also knew they would get more hits by assuming there was some kind of error in their attack information.
This is one of the reasons we can sink so much more per cruise than they could. We have accurate enough information that we don't do much guessing. We send two torps toward a target and without laughing expect two hits.
They sent six toward the target hoping for one or two booms because guessing was a necessary part of the pre-radar attack plan.
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