Rob hi
I can understand your frustration with convoys. My rate of success in getting them is about 30-40% of the time. They do change direction frequently and that's making things difficult (as it was in reality). Since you're not using the hunt technique I would suggest the following.
Use the ruler to plot the approximate convoy (or target it's the same thing) direction. Now that you have a line on the map with their course draw a line (using the ruler) connecting your sub with a position on the course of the target. Where the two lines intersect depends on the your relative position to the target. Usually I tend to arrange it in such way so that I have to travel the same (more or less) distance as the target to the interception point. I do this in order to make sure that the target will not pass me by. Now depending on the target's speed you arrange yours but I usually go ahead flak and reach the interception point early. Then I just wait. In this don't forget that since the ploting of the course is not accurate the target might be a few Km further away from where you're expecting it, so you might need to make further adjustments. In any case I'll try to make a very quick tutorial and PM it to you. It will probably be later on today or tomorrow though as I'm at work now and things over here are a bit busy.
In the mean time good luck and good shooting
