i) U-69 has a top speed of 17knts.
ii) U-69 gets a report of a convoy/taskforce/lone ship. In this case its a task force at 14knts.
iii) Draw a line along the target's heading.
iv) Draw a line from the target to U-69
v) Make a mark 14km* along the target's path. If the target was going at 7knts then the mark would only be 7km along the targets path. 8knts would equal 8km etc. etc.
*(The mark can be 1.4km or 140km, it matter as long as you keep to the same scale with all other distances)
vi) Now use the compass tool draw a circle starting from the marker you just made. The radius of the circle should be equal to U-69's to speed. In this case the circle has a radius of 17km because U-69 can go 17knts.
vii) Now draw a line from the middle of the circle to the point on the circumference of the circle that circumference intersects the line from U-69 to the target. In the diagram this line is labeled "(3)".
ix) Now measure the angle between the new line and the line from U-69 to the target. We will call this
"ANGLE A" it is about 35deg.
x) I have cleared up some lines we don't need any more.
xi) Finally use the protractor tool.
Make the first click on the convoy.
Make the second click on U-69.
Measure the angle so it is the same as
"ANGLE A".
xii) If you follow this new line you will arrive exactly at the same time the target does. If you want time to prepare for the target, then add a few degrees to
"ANGLE A".
The advantage of this method is that it gives you the shortest, fastest target intercept.
*edit* sorry, my spell checker went wild.
*edit#2* Sorry if I have made mistakes, geomotory is not my strong point