[musikerz]

Thx, badaboom, i will check it out, and Fincuan 2. And to RR, so u actually mean it's not possible to do that in SH4? Then i don't get it, some article i read in the internet did mention this "propeller method", even the documentary "silent service" said that.

quote from http://jtmcdaniel.com/periscope.html

Target speed

The final factor needed is the target's speed. There are several methods of obtaining this, though none can really be called 100% accurate.

First, periscope observation. The periscope optics are marked in degrees in both the vertical and horizontal axes. If the distance to the target is known, it is possible to determine speed by timing the elapsed time required for it to travel a given number of degrees. The problem with this method is, of course, that it is dependent upon an accurate range, since you are measuring the length of time the target takes to traverse a known number of degrees, and it also means exposing the periscope while you do it, which is potentially dangerous if the enemy spots it. (Japanese merchantmen not only carried deck guns, frequently with gun crews who actually knew what they were doing, but also depth charges, and didn't hesitate to use them.)

Second, general knowledge. Some types of vessels are known to routinely travel at certain speeds. This will usually be the most economical cruising speed. However, since the target's captain may be in a hurry, or may be moving slower than usual, this will tend to be the least accurate method of determining speed. An experienced captain can often make a fairly accurate guess at a target's speed by the appearance of the bow wave.

Third, counting revolutions. The sonar operator can listen to the sound of the target's propellers and determine the number of revolutions per minute. If the submarine's captain knows the pitch (the distance travelled in one revolutiion) of the target's propellers, he can make a fairly accurate estimate of speed. For instance, a screw with a 24-foot pitch should move the ship forward 24 feet for each revolution. One hundred revolutions per minute should, therefore, move the ship forward 2,400 feet, or 800 yards. This would give a rough distance travelled of 1 nautical mile (2,025 yards) every 2-1/2 minutes, or a speed of about 23.7 knots. This sort of speed would generally indicate a large warship or liner. Freighters were usually slower, with the fastest generally limited to about 16 knots. (Fuel economy was the major factor—fast ships use a lot of fuel, so high speed was mostly found in passenger ships, where the line could charge extra for a fast passage, specialised freighters like banana boats, which had to deliver their cargo before it spoiled, and warships, where cost wasn't a major consideration. In any case, if screw pitch is known, and an accurate count obtained, this can give a fairly accurate speed estimate. Also a ship's screws are far from being 100% efficient—the only vessels that manage this are submarines at a considerable depth, where the great sea pressure suppresses wake and cavitation.)

Well, i know this is a little 2 crazy for a gamer to listen to the hydrophone and count the rotations, and have to look up a TPK table for each ship which are not provided in the game, but it seems to me, without the map update this is the best and easiest way to find out how fast the target is, for the sonar operator at least, especially in the darkness.