Methode used to sink a lot of ships

[Bilge_Rat]

Good summary Stoianm, but if I can add a few additional pointers:

Originally Posted by stoianm

1) lock the target
2) identify the target
3) put your vertical line of the scope in the front of the target and start the clock (cronometer)
4) stop the clock when the ship just pased your vertical line of the periscope

Open the SOAN and check the lenght of the ship: we supose the lenght of the ship is 149 metters and the clock show us 19 sec

We aplie the math: speed of the ship = lenght of the ship/time*1.94

speed = 149/19*1.94=15.21 knots - we will consider 15 knots

This is an acurate method to find the speed! (in my opinion) - for best result i recommand a distance around 3000 meters and an angle not to far from 90 degrees (20 degree less or more) - if not maybe you will mistake around 0.5 knots

so, untill now we know the speed = 15 knots

As you point out, this method is only really accurate if the target is at an AOB of around 90 degrees to your sub. The rest of the time, it will not give you an accurate speed reading.

Another method which is independent of AOB is the map plot method, namely:

1) determine Range, Bearing, plot on TAI/NAV map(Mark #1);
2) run chrono for a fixed time period;
3) determine Range, Bearing, plot on TAI/NAV map(Mark #2);
4) draw a line from Mark #1 to Mark #2, measure distance with ruler.

You can then determine speed with the following formula:

-distance measured on map x (factor to convert to distance travelled over an hour, for example if you ran chrono for 1 min, you would multiply by 60) divided by 1852;or

-if you run the chrono for 3min 15 seconds, you can just drop the last 2 digits from the distance measured to get the speed in knots.

5) use the stadimeter and find the distance from the ship.

we supouse that we have distance=3000 metters

If you have one of the realistic periscope mods (I use Arclight's mod), you can also measure range by eye as follows:

1) identify target and determine mast height;
2) measure mast height in number of Horizontal Bars on the scope;

you can then measure the range based on a formula, for example with Arclight's MRP, the formula is:

1.5x - MastHeight x 100 / horizontal bars = Range

6x - MastHeight x 400 / horizontal bars = Range

for example, a Liberty Ship has a mast height of 27.1 meters, if the measured height is 4 bars at 6x, the range would be 2,710 meters.

i.e. 27.1 x 400= 10,840 divided by 4= 2,710 meters.

This thread can also be of interest. The 1st post by Hitman links to a document of German U-boat periscopes.

http://www.subsim.com/radioroom/showthread.php?t=166280

6) now we will find the AOB using a methode called ,,AOB aproaces zero'' - wich is the most acurate metode to find the AOB of a ship.

AOB=degrees(asin(ARobserved/ARreference))

AR= aspect ratio

How this is working:

ARreference= lenght of the ship/mast hight of the ship

if you using the map plot method, you will also have the accurate course of the target on the map. You can then easily determine the AOB by using the protactor to measure it.

You now have Range, Bearing, Speed and AOB which can plug into the TDC. Best of all, you just need the scope, map and a calculator.