[I'm goin' down]

i have been playing with map contact disabled. This means you have nothing on the map to help you calculate speed. Here is what to do in that situation, still using the 3 minute rule. Stop your boat.

To calculate speed in yards, I wait until the target is closing. If it is going to cross the bow of your boat, wait until it is between 270 deg. and 60 deg. on the scope for an accurate measurement. (Again, your boat should not be moving when you calculate speed using this method.)

1. Measure the time in seconds it takes the target to cross the line (ie. the wire) in the center of the periscope if the target is closing on the bow of your boat.
2. Divide the ship's length by the nummber of seconds to derive the speed per second in feet.
3. Divide feet per second by 3 to convert feet to yds.
4. Mulitply speed in terms of yards per second x 180 seconds and you have calculated distance over a 3 minute time span.
5. Convert distance over 3 minutes to knots using the 3 minute rule. See example below.

Example:

Target is 100 feet in length per identification manual (target length in feet is provided in the ship's manual for the OTC mod).
1. It takes 10 seconds for the target to cross the wire.
2. 100 ft./10 seconds = speed is 10 feet per second.
3. 10 ft. per second/3 ft. = speed is 3.33 yds. per second.
4. 3.33 yds. per second x 180 seconds (i.e. 3 minutes) = 584 yds. travelled over the course of 3 minutes.
5. Distance travelled over 3 minutes coverted to knots = 584 yds. translates into 5.84 kts. using the three minute rule.

Why measure speed between 270 deg. and 60 deg.? Because, according to Karamozonev (spell?) in a post in the ATO forum dealing with his Kiub (Kreigsmarine Interface for U-Boats) mod, speed calcuations based upon the time it takes a target to cross the wire are most accurate when the readings are between those bearings on the scope. It has worked like a charm for me, so I use it.

If measuring speed when the closing target will cross the stern of your boat rather than its bow, take the speed readings when the target is between 120 degrees and 240 degrees on the scope. Otherwise, the steps above are same as nos. 1 -5 above.

Between plotting course manually, calculating speed manually, and setting up to fire torpedoes, plan on spending a LONG time. You are going to miss dinner, the movie you were going to see, and your date will be pissed.