I had worked out the technique years ago when I was still playing SHCE. I thought, at the time, it was a brilliant idea and that it would be a great help to me. I soon stopped using it. Why? Not because it was ahistorical, but because I didn't see any advantage to it.
If the target is abeam, one must 'add' the sub's speed to the target's. If the target is ahead this is not neccessary, but then your already lost your window of opportunity. If the target is far away, it will be hull down and you can't use it. If the Aob is small, you can't really tell when the stern passes the wire. When you put your boat on a normal approach course, frequently, the target will be moving very little, relative to the wire, making the technique unusable. In any case, I would still have to make a plot to obtain the course and range, so I would use it for the speed also. The timing target length, or whatever you want to call it, will not give you any information that you can't get form a good plot.
That said, I don't see anything wrong with using it. It may be ahistorical, but it is not implausible. Certainly, at least some of the IJN warships were distinctive and would permit its use.
