SUBSIM Radio Room Forums - Estimating speed in less than 1min.

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- - Estimating speed in less than 1min. (https://www.subsim.com/radioroom/showthread.php?t=157305)

Tonnage_Ace

10-15-09 01:52 PM

Estimating speed in less than 1min.

Just started playing SH3 again and I forget the method I used to quickly judge speed peering through the scope.

I used to get a rough heading of the target ship/convoy along with a rough speed est. but I fine tuned it with this speed calculation where I would sit off the ship's expected path at 90* and time how long it took the ship to cross my vertical reticule. This should be REALLY helpful for any newbies because your range and AOB can be off but speed is the killer. If the ship passes your reticule at 340* you can get a good speed estimate for the -5/+5 gyro shot.

Anyone remember that formula? I used to tap it into my phone from memory:doh:

I know the values were ship's length, time, ???, speed in knots.

http://img381.imageshack.us/img381/1766/gtg.jpg

Picked up a new toy, Germans make good cars too:arrgh!:

psykopatsak

10-15-09 02:54 PM

HAH, God 'ole "Spit-log" from a distance? never thought of that!

the spitlog formula is (2xboat length in meters)/(time in seconds)=speed in knots. the time is that for a stationary object in the water to go from very boats prow to stern.

if you have a calculator you could use 1.852 x boat length instead.

Snestorm

10-30-09 07:37 PM

Quote:

Originally Posted by psykopatsak (Post 1189814)

Thanks psykopatsak!
This should greatly improve my ability to gather information while submerged.
As I'm into oktober 1943, spending too much time on the surface is not a good idé.

psykopatsak

10-31-09 11:22 AM

now, the odd thing i have herd is that you should mutliply with 1.94? why is that?

Sonoboy

10-31-09 11:47 AM

the way you come to multiply by 1.94 is as follows:

speed in knots = (length in meters)/(time in seconds)*(3600 to convert seconds to hours)/(1000 to convert meters to kilometers)*(0.54 to convert kilometers to nautical miles)

if you simplify it, it becomes:

speed in knots = (length in meters)/(time in seconds)*1.944

Pisces

10-31-09 05:54 PM

We want the speed to be in knots, or nautical miles per hour. But we have only the distance in meters, and the time in seconds, so it needs some conversion factors.

ship length in nautical miles= length/1852m

time in hours = time in seconds/3600s

Speed = length /time

Code:

Speed (in knots, nautical miles/hour) = length         seconds

                                        --------  / -------------

                                           1852          3600



Speed (in knots, nautical miles/hour) = length       3600

                                          -------  * --------

                                          1852        seconds



Speed (in knots, nautical miles/hour)  = (3600/1852) * length/seconds



3600/1852 = 1.94...

psykopatsak

10-31-09 06:59 PM

oh, yeah, that explains how. advanced math :/

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