Who's good at math to calculate ..

[robj250]

.. a night time attack on a convoy. Here is the situation: it is presently 1952 hrs. I just received a message that there is a convoy doing 8 kts NNE. My course is 268°. Now if I stay on my course, it will probably end up as a daylight attack because their course will cross my course if I continue on 268°. Now in all my past encounters with reported convoys, the convoy has never changed course. I have no idea what course to take with my upgraded VIIB at ahead flank to intercept them during the night. If I wait for them to cross my course they would have to travel about 263 km and I would only have to travel 100.7 km. Oh, the weather is clear and the seas are calm so I should be able to do 18 kts. Is this enough information? Is it possible for me to change to a certian course to make a night-time attack? I have no idea whether it is possible or not.

[don1reed]

More input, please. What grid are you in, and what grid is the convoy in?

[robj250]

More input, please. What grid are you in, and what grid is the convoy in?
I am in grid BE69, they are on the edge at BE94 and BE95. It is Jan 4, 1943, so SR 0805 Universal time Jan 5

[moselgott]

hi, can you prepare a little sketch?? i.e. with all distances (sub-convoy;shortes way from sub-imaginary cours of the convoy[->right ankle];convoy-point where sub will cross the cours at its shortest way), ankles, bearing of sub and convoy...would be helpful. i think it would be the best if you mark all these information in your F5-map and make a sreenshot.

[robj250]

hi, can you prepare a little sketch?? i.e. with all distances (sub-convoy;shortes way from sub-imaginary cours of the convoy[->right ankle];convoy-point where sub will cross the cours at its shortest way), ankles, bearing of sub and convoy...would be helpful. i think it would be the best if you mark all these information in your F5-map and make a sreenshot.
Sure, I made a snap of the map. I have to reduce it and host it on imageshack first.
http://img137.imageshack.us/img137/2126/snap7vc.jpg

[don1reed]

The way I see it, Rob, if you both continue on and reach the point of interdiction, i.e., 263km @ 8kn., it would take the convoy--

D = S x T, or transposing,
T = D/S = 142 nm / 8 kn. = 17hr and 45 min.

You, on the other hand, have 17:45 to travel 100.7 km (54.4 nm) to meet the convoy. Then,

S = D/T = 54.4 nm / 17:45 = 3 knots. <---Your speed.

You said the time was 19:52...plus the 17:45 = 13:37 the next day.

If you travelled at 5 kn. you'd get there a little earlier ... to set up your ambush, or, stay off enough to shadow them 'til dark, then move in to attack.

[robj250]

The way I see it, Rob, if you both continue on and reach the point of interdiction, i.e., 263km @ 8kn., it would take the convoy--

D = S x T, or transposing,
T = D/S = 142 nm / 8 kn. = 17hr and 45 min.

You, on the other hand, have 17:45 to travel 100.7 km (54.4 nm) to meet the convoy. Then,

S = D/T = 54.4 nm / 17:45 = 3 knots. <---Your speed.

You said the time was 19:52...plus the 17:45 = 13:37 the next day.

If you travelled at 5 kn. you'd get there a little earlier ... to set up your ambush, or, stay off enough to shadow them 'til dark, then move in to attack.

Thank you. I don't wanna seen stupid, but how do I calculate nm from km? Reason being, I would like to design a spreadsheet to do the calculations for me. Did you use .54 to get nm?

[Ula Jolly]

One nm = 1852 m = 1,852 km
To go from km to nm, take 100.7 km and divide it on 1,852 - equals just short of 54.4 nm
From nm to km, take 54,4 nm and multiply with 1,852 - equals just under 100,75 km, or 100 750 m :)

[don1reed]

You're not stupid, Rob, the fault lies with the Devs for not including nautical miles with a nautical sim...

km x .54 = nm

btw: If you don't want to wait 17:45 to link up with the enemy...you can meet them half way in between their starting point to the interdiction site. Instead of them travelling 142 nm, how about 80 nm or 148 km?
You'd have to change course to about 234° and travel about 97 nm. Use the same Distance = Speed x Time formula to figure your speed to arrive at that point when they do.

All the best,

[robj250]

You're not stupid, Rob, the fault lies with the Devs for not including nautical miles with a nautical sim...

km x .54 = nm

btw: If you don't want to wait 17:45 to link up with the enemy...you can meet them half way in between their starting point to the interdiction site. Instead of them travelling 142 nm, how about 80 nm or 148 km?
You'd have to change course to about 234° and travel about 97 nm. Use the same Distance = Speed x Time formula to figure your speed to arrive at that point when they do.

All the best,

Thank you very much don1reed. I hope I can design a spread sheet to do all this for me. It seemed so easy for you, even to be able to figure out what course I would have to change to.

[Threadfin]

Ya know, you've already essentially drawn the interception. It doesn't have to be so complicated. In this case you should straighten out the line representing the target's course so it's more accurate. Then sail to that line as indicated by the line representing your boat's course. So far, just as you've drawn it. Then sail the target's reciprocal. Just sail right along the line the target is travelling along in the opposite direction. No math, guaranteed intercept.

[Ula Jolly]

It is indeed rather easy, I personally think you would benefit greatly from not making a spreadsheet, but doing loose estimates in your head each time - it doesn't hurt in any way, and only serves to back up your sense of practical maths.

Seeing as he knows at which direction the convoy is going, he can draw a line that makes it's course. Very nice line, you should always drag lines. :D
Since he knows the convoy's speed and what time it currently is, he knows for how many hours he would like the convoy to travel before the sub meets up with it. He can use the SHIII ruler to measure the distance ON the distance line, and this will be the spot most convenient to meet the convoy. Then you just adjust your own ship's direction until it's poking at the point.

But wait a m......
are the distances in SHIII in KILOMETERS? :doh:

[robj250]

But wait a m......
are the distances in SHIII in KILOMETERS? :doh:
Ah, no. I made a snap of the positions, printed it out, then used a mm ruler to calculate the distances. I already have a spread sheet that will then calculate the km. Then a college friend of mine put in an intercept time, but that doesn't work, however, the 3 knots (being my speed) to reach their crossing path was correct, but my friend has been unable to provide a formula which will tell me when we meet at that point. If I could get that to come out correctly it would be great.
Anyway, thanks a whole lot everyone for helping me. :up:
I just have to decide whether I want to wait for them and then follow them until nightfall or go on the course of 234° for 97 nm.

[Ula Jolly]

A mathematical formula should rely on vectors.

And... you printed it out? BWAHAHAHAHAHAHAa, that is so pioneer and cool! I used to create flight plans for Flight Simulator 98 by measuring up distances on not even half-accurate maps. :rotfl:
See, the point is.... up in your right corner, you have a set of tools, one being a ruler. Just put the cursor to the edge of the map. Experiment with these, please - YOU'LL BENEFIT. :rotfl:

[Cpt.Thorne]

There is also a mod that has a lines on the right edge of the map where you can (using the rluer, drawing a line into the scale) easily see the speed in kts to km/minute to km/h or sumfink like that. I cannot remember how it is and cannot check it as I am not amongst my command room computer :doh: but I use it and it works quite well.
Prost!

[Ula Jolly]

Saw it, never actually found it. Could you link it if you know where it is?

[KeybdFlyer]

I'm almost afraid to throw my hat into this high-level discussion! :lol: I've read several people's ideas on plotting an intercept course and in the end gave-up and play it by ear most of the time. I've found so far (from a whole 2 weeks playing experience, lol) that the map icon gives a pretty fair indication of the potential target's course, so I use the ruler to extend a line as accurately as I can to a point just beyond my own position (assuming I'm ahead of its course as in this example). I use a high-end speed for each description - say 7kts for slow and 13kts for medium, then mark how far it would be along that line for each hour of travel (using 1.852 as a factor for km-nm). I underestimate my own speed very slightly - say 1knt less than I might be able to make - then use the compasses to check my own hourly distances. Somewhere, the two will coincide approximately, but that's close enough and I head off on the indicated heading, making sure that I will end up ahead of the target. Whilst chugging along, I then use the ruler to mark two lines parallel to the target's course, 4,500 mts either side, and another two 1,000mts either side. Upon reaching the intercept (invariably I'm early) I then zig-zag between the outermost limits back towards the target, submerging for the hydrophones when between the two 1000mt lines. The width of the "lane" allows for any inaccuracy in the estimation of the target's course and unless you're unlucky, you should get a contact pretty quickly allowing time to position yourself. Anyway - it works for me, lol. Now if only I could get a hang of getting the torp to pass nicely just below the keel instead of either a couple of mts below or glancing off the curve of the hull. Very annoying and very wasteful. Practice, practice, practice :)

[robj250]

I'm almost afraid to throw my hat into this high-level discussion! :lol: I've read several people's ideas on plotting an intercept course and in the end gave-up and play it by ear most of the time. I've found so far (from a whole 2 weeks playing experience, lol) that the map icon gives a pretty fair indication of the potential target's course, so I use the ruler to extend a line as accurately as I can to a point just beyond my own position (assuming I'm ahead of its course as in this example). I use a high-end speed for each description - say 7kts for slow and 13kts for medium, then mark how far it would be along that line for each hour of travel (using 1.852 as a factor for km-nm). I underestimate my own speed very slightly - say 1knt less than I might be able to make - then use the compasses to check my own hourly distances. Somewhere, the two will coincide approximately, but that's close enough and I head off on the indicated heading, making sure that I will end up ahead of the target. Whilst chugging along, I then use the ruler to mark two lines parallel to the target's course, 4,500 mts either side, and another two 1,000mts either side. Upon reaching the intercept (invariably I'm early) I then zig-zag between the outermost limits back towards the target, submerging for the hydrophones when between the two 1000mt lines. The width of the "lane" allows for any inaccuracy in the estimation of the target's course and unless you're unlucky, you should get a contact pretty quickly allowing time to position yourself. Anyway - it works for me, lol. Now if only I could get a hang of getting the torp to pass nicely just below the keel instead of either a couple of mts below or glancing off the curve of the hull. Very annoying and very wasteful. Practice, practice, practice :)

Thanks, I'll keep that one in mind as well.

[robj250]

I'll let you all know how I made out as I'm going to try and make the intercept today. :D

[robj250]

Hit the nail right on the head. I altered course to 230° and ahead flank until 0151 and stopped and waited. Warship spotted 0217. Now waiting at periscope depth. 4 warship contacts and I don't know how many merchants. Also I received a BdU radio message that there is another convoy coming, Yippie!!! :rotfl:
Thanks a bunch guys, really appreciated the help.
Don1reed, how did you know that 234 was about the right angle?

[Cpt.Thorne]

Saw it, never actually found it. Could you link it if you know where it is?
IIRC found it from here http://u-boot.realsimulation.com/ SH3 downloads-> general section and it was this Time Distance Speed Chart mod or some other chart mod. Hope you find a goodone.
Prost!

[Alyebard]

Try this "distance traveled"

http://www.communitymanuals.com/shiii/index.php?title=Distance_Traveled

and a good article "intercepting targets"

http://www.communitymanuals.com/shiii/index.php?title=Intercepting_Targets

[robj250]

Thanks Alyebard.
I'll try that table and calculations, but I already have the intercepting one but had problems understanding.