[RingoCalamity]

So now we know which way our guy is headed, and where we expect him to be in 12 minutes. We're going to spend that 12 minutes, if we are going for a shot, running a parallel course at our best speed. The more separation we can get from our initial position, the more accurate our speed and range data will be - however, the longer we wait, the more magnified any course errors we've made will become.

PART V

While we're under way, we're going to plot a line on our chart. It stretches from our initial position to -and through - the expected target position at 12 minutes.

At 12 minutes, we take another bearing to target. It is very, very unlikely that he will be where we thought he would. This is okay, the 11 knot speed was always just an estimate. Now we have his actual range and speed.

Let's draw a line along our new bearing to target, the 12 minute bearing. At some point, it is going to intersect with the line we drew in the first paragraph of PART V above, his expected position. This intersection between his expected and actual bearing will be his actual position.

We can now do two things - estimate his speed with a good degree of accuracy, or determine it exactly.

For the estimate, we use the range between the 11 knot expected track, and our own parallel track. If he is halfway between the two, his speed will be about 5.5 knots. Closer to us means he's going slower. Closer to the estimated track means he's going faster. Outside of the estimated 11 knot track means he's going even faster than our 11 knot estimate.

Calculating the speed exactly is easy. We measure the distance, along the same heading as the 11 knot path but now starting from the expected/actual intersection, back to the first bearing we took of his boat, which would have been 18 minutes prior (12 minutes + 6 minutes for the first set of timed bearings). You could calculate his speed from his actual position to any of the actual bearings, just match the times. I'm using the first because I believe the data will be more accurate with the larger sample.

For example - range between his expected/actual intersection, and the first timed bearing, is 4500m. He covered 4500m in 18 minutes, for a speed of 250 metres per minute. Times 60, that's 15 kilometres/hour. Multiplying by 0.54 gives a conversion of 8.1 knots.

So, now we have our target's speed, position, and heading. From here we should be able to move into position, swing our bow around to face the target, and plot a good solution for a Dick O'Kane type attack, although like I said initially, I think repeating the initial timed bearings a few times would be valuable to refine our data. I won't repeat the details of setting up the O'Kane shot here as it's been covered elsewhere and I think most are comfortable at this point with that technique.

Due to our slow speed submerged and the fact that this technique takes a significant amount of time to develop, it is clearly not applicable to all situations. Still, I think there's something here and in some situations it could be valuable.