Convoy interception tutorial #1 (pic heavy)

I don't consider myself the definitive expert of convoy interceptions, but I thought I'd show how I calculate mine. This is the first of four tutorials which are divided into the following:

1. radio contact plotted with you ahead of the contact,
2. radio contact plotted with you behind the contact,
3. visual spotted with you ahead of the contact, and,
4. visual spotted with you behind the contact.

At the moment I've only the first two done. Assuming there is interest in the second set of two I'll do those as well.

This tutorial covers instances where you receive a radio contact report of a convoy and you find yourself in reasonably positioned in front of them. This is the easiest of the four, unless the contact is so close that reaching an intercept position has you in their visual range before you reach your interception point. If that should be the case then your best bet is to treat it as if you were behind the contact, and follow the guidelines for that method of interception.

Your basic radio contact plotted with you ahead of the contact will look like the following:



As you can see, there should be no difficulty for you to catch up and meet with the enemy convoy. The trick is to do it without being seen or spotted, and without getting so far ahead you risk losing contact due to convoy course changes or from being off a little on your convoy course estimation.

The method I use for plotting convoy course is to place the tip of the compass tool at the far end of the convoy heading 'tail' then draw the circle radius straight through the center marking of the convoy plot. Zoom in if you wish and tweak the exact position of the circle for more precision. Next I use the ruler tool and set one end at the convoy center, drawing outwards along the convoy path the compass tool marked out. The exact distance to mark often needs to be tweaked, as you'll see in a moment. In this example I marked a course 100km long:



The next step is to calculate your best approach route. In this case I used the compass tool; the ruler would work as well. Simply place the end of either tool at your position then extend it to the endpoint of the convoy route you've marked.



As plotted, it will take you 133 km to reach the same position the convoy will after traveling 100km. But will you reach there before, after, or at the same time? That's the question, as it'll do you no good at all to reach that point after the convoy is passed, or worse, as it arrives at the same time and the escorts catch you with your pants down!

As the convoy is traveling at 7 knots, and your flank speed is (hopefully!) higher than twice that, a basic 'cheat' way I use to estimate things is to double or halve things. In this instance, if the convoy is traveling 100km at 7 knots, I should be able to travel 200km at 14 knots. As I only need to travel 133 I'll certainly get there far ahead of them. But all that extra time I wait is time things can go wrong, too. Much better is to get there ahead of them, in time to position myself before they can detect me but with a minimum of time to wait for them to show up.

In the following image I've shortened the convoy distance to 70km, and adjusted my course to intercept. Now I'm traveling 143km to their 70, which is almost exactly twice. As my speed will be more than twice this means I've got a pretty decent calculated course to position myself.



I like the convenience of the nomograph I have for more closely calculating speeds/distances/times. Sometimes, though, even there you have to tweak a bit.

The last two images show me verifying the speeds/distances/times of the convoy and myself. In the first one, you'll see that if I try and determine the time to travel 70 km at 7 knots I wind up off the scale for the time bar. In the second one what I've done is divide the distances by 10.





Instead of determining the convoy travel time for 70km at 7 knots I've used 7km at 7 knots. And did the same for my travel time calculation: instead of 140 km at 14 knots I've used 14km at 14 knots. As you can see, the result shows an arrival time of virtually the same. However, as I'll be moving at flank speed --which is faster than 14 knots-- I'll actually arrive in plenty of time to set myself up for the attack!

I hope you all find this helpful.

[Letum]

I think there is a better way.....I'll draw some diagrams and post them asap....

[Letum]

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

[Fangschuss]

Thanks Kaleuns

Both interception calculations works great for me

Gute Jagd und Fette Beute

[Jimbuna]

Well written/explained sir and so very succinct and to the point
This will surely be of immense benefit to a lot of fledgling kaleuns out there

[Mooncatt]

well here is what i do.......
guess!!!! i usually find im right and usually arrive before they do and have ample chance to get myself into a perfect attack position

[mookiemookie]

Originally Posted by mooncatt

well here is what i do.......
guess!!!! i usually find im right and usually arrive before they do and have ample chance to get myself into a perfect attack position

That certainly can work too, but why not make it exact when it's so easy to do?

Thanks for the tips, guys.

[Mooncatt]

well this is the problem im not very mathematicly minded and find it difficult to do.
i did a while ago saw on here a very simple way to do it, and it looked really easy but when i tried to do it it didnt work

[Metl]

anyone have a quick and easy for a firing solution?

[Capa]

Nice work, this will probably help me a lot. The previously available guide (guide to the hunt) was a bit confusing and seemed bizarrely off, the way I read it. No disrespect to that author though.

[Canovaro]

Albrecht I like your fast plotting.
I made something like Letum's some time ago:

[seafarer]

So, nobody else uses MoBo?

[Pisces]

Canovaro:

And an easy way to plot that parallel (Uboot) course line is to temporarily mark the intersection of the circle and target-Uboot-line with the pencil tool. Then grab the end of the circle's arrow and extend the circle radius through that pencil mark until the Uboot is inside the circle. Then drag the center of the circle along the targets course line until the circle-radius overlays your Uboot. Now the circle radius (towards the center) is your course line to the interceptpoint.

[Captain Nemo]

Very interesting, thanks for posting these. Personally when I receive a radio contact of a convoy, I use the ruler to draw a line from the contact in the direction given in the contacts details. Using the tail gives a more accurate course but remember when GWX 1.04 comes out, if you use GWX that is, these will no longer be shown. Anyway, once I've drawn the line with the ruler on the map along the predicted course of the convoy, I ask my navigator to plot a course that ends at a point on the predicted course line. At my current speed setting this waypoint will show how long it will take for me to arrive at that point. I then calculate using pre-printed tables how far the convoy would have travelled in that time. If the result of my calculation puts me ahead of the convoy, all well and good, if the convoy would have passed my interception point then I'll need to increase speed and or move the waypoint. I find this method quick and easy and very reliable.

Nemo

[Keelbuster]

Originally Posted by Captain Nemo

Using the tail gives a more accurate course but remember when GWX 1.04 comes out, if you use GWX that is, these will no longer be shown.
Nemo

Yea - i always wondered about the realism of those course tails. I used to play RuB and they left the tail out, so you were left searching a 45 degree quadrant where you expected the convoy to be.

Basically, here's what i do (and sorry to barf all over the tutorials): My strategy relies on getting to the intercept location as early as possible. That gives me time to hide and update my knowledge of their course. The above methods, while precise, appear to land you within visual range of the lead escorts before you can get into firing position. My strat tries to get you there first, and is also approximate.

1. The radio report gives me an exact location fix. I plot it.

2. Draw a guess line from that starting point. The guess line is where I think they're going. Convoys don't travel at random (unless they're zigging, which makes all of this insanely hard) and you can usually guess fairly well what they're course is (especially in the med ).

3. If it's a contact that goes faster than me (e.g., TF), plot the 90 degree intercept course to the guess line and go there asap. If their distance to the intercept point is longer than mine, it might not be worth it, but then again, for a BB, i'd take a long shot. If the contact is going slower than me, i bend my approach course in (towards them), or out (away from them), in order to avoid getting there too early or late respectively. This is done by eye. When in doubt, I get there early.

4. When I get near the intercept point, I start taking sound checks. When I hear them, i draw line down that bearing to intersect with my first one, to guess their position along their expected course. I adjust my course according to the rules in 3., and continue to approach.

4b. If I get to the intercept point before them, I start to move down their bearing at PD. I wait till I can hear them, and decide if my guess on their course was off to one side or the other and correct a bit, move to new intercept, dive to PD, check to see if I'm moving straight down their bearing or not. This can give me a damn good course estimate.

5. If I make visual contact, I plot it with a guess range (knowing that my boys tend to spot them at 15km in good weather, 8 km in light fog). Then I connect my original contact with my new data, and voila - course. As you approach, you can also get a feel for the accuracy of your course estimate by eye - the convoy lanes draw a nice smoke-stack line that betrays the AoB. Then I get into firing position, and when they get close, start taking stad readings and get a really good course and speed estimate. Then I sink the bastards.

On the whole, this system works pretty darn well, and relies on very little explicit math.