Easy way to plot intercept course?

[JohnCarterOfMars]

I've been using my own home-grown (for me, but others may have previously posted the same) technique for gathering the intercept information that doesn't involve racing in front of the ship to watch the masts line up or approximate the angle on bow.

It's also good because you can do it immediately while traveling towards the sighted ship.

1. Order your Watch Officer to the bridge. You will need him.
2. Have your Watch Officer give you a reading of the sighted ship.
3. Start a 5-minute timer.
4. Draw a line from your boat to the sighted ship following the bearing and reported distance.
5. Wait 5 minutes.
6. After 5 minutes, have your Watch Officer give you another reading.
7. Draw a second line from your boat to the new bearing and distance of the ship.
8. Measure the distance between the two sighted ship positions.
9. Look up this distance on the M/Min table on the 5-minute column and note the corresponding speed. This is the speed that the sighted ship is traveling.
10. Repeat this process two more times and then measure the distance from the original position to the most recent reading. Look this distance up on the 15 minute column to find the corresponding speed to verify.
11. Take one more reading in 5 minutes, measure the distance from the original reading to this last one and add the distances on the 5-minute and 15 minute columns for the previously determined speed, and see if it matches the distance between the original reading and the latest reading.
12. After the second reading you should know the general direction of travel of the sighted ship. You can now turn the boat towards that direction.
13. After the 20-minute reading, you should have enough plots to approximate the true direction of the sighted ship.
14. You now have the speed and direction of travel of the sighted ship. Plot the intercept course from this information.
15. I usually add 2 degrees to the intercept angle to get ahead of the ship.
16. Then I draw a perpendicular line of 1.5 Km from the intercept point to find my actual destination, and then turn 90 degrees towards the intercept point to wait for the ship.
17. While I am traveling to the intercept point, I will enter my 90 degree angle attack data into the TDC.
18. You can take additional periodic readings just to ensure that the sighted ship is still on its course and that you are ahead of it. You can take an additional 5-minute reading to ensure that the ship hasn't changed speed, too.

I find this approach to be good enough for the TDC, which is 1940s technology. I don't need perfect precision for it to work, and I don't need to waste fuel, time, or exposure risk chasing ahead of the ship just to find it's perfect course.