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Zosimus · 08-04-15, 10:06 AM

Here's some advice for what good it may do you.

I assume that you are tracking a convoy. The first step to tracking a convoy is to determine its heading. This is hard when you cannot get a visual on the cargo ships. The escorts change course all the time and although you can (eventually) get the course by watching escorts, it can take much longer and is quite hard to do in the rain.

There is, however, a simple, safe, and foolproof way to determine the convoy's heading. The key is to look for stragglers. Behind any convoy, there is almost always a tramp steamer (or two) that has fallen behind the others and is struggling to catch up. The key is that its heading is the same as that of the convoy. You can safely intercept this straggler to determine its heading or use the three-bearing method (hydrophone) to determine its course.

Once that's done, you can draw a course line through the target (you can use the hydrophone distance... it doesn't matter really) and then extend this line as far as you can. You can just hold the mouse open drawing the line and use the arrow keys to move the screen till you get to a conveniently long distance.

Now catch up to the convoy. If you can hear the convoy by hydrophone, then it must be less than 20 km away. If you cannot hear the convoy, just draw a 20.0 circle and race in the direction of the convoy until you hit the 20 km mark and go to 25m under to listen again. Sooner or later, you'll find that convoy and hear one of the cargo ships.

Pay attention to the speed. If the merchant speed is "slow" then it must be moving at 7 or fewer knots. If the speed says "medium" then it must be at 8 or more knots.

Draw a circle centered where that merchant's hydrophone line intercepts the line you've drawn. The radius of the circle should be 13.6 for slow (7 knots) or 15.6 for medium (8 knots) and note down the time one hour from now on a separate sheet of paper. That's where the ship should be in one hour assuming that the heading and speed are accurate.

Then surface and move to intercept. Assuming you are behind the convoy, your heading should be about 30-50 degrees off of the convoy's heading. Initially, 40 is a good number. You'll want to go about 5 km and then go to 25 meters for another listen. If it seems that you're not catching up to the convoy, then go to 30º off of its course. If it seems that you're catching up too quickly then go to 50º off of its course.

Then cruise on out until you are 18 km off of the projected course or until the hour is up. Listen to the convoy every hour. Does it seem to be on the course you have projected? Does it seem to have covered the right amount of distance? If not, you may have to adjust your speed or heading assumptions. It may take several hours to overtake the convoy, and you will have plenty of time to refine your assumptions.

Once you're 18 km out, simply parallel the convoy (or maybe 0-5º angled toward it) until you have passed the convoy. Then angle in maybe 20-30º until you intercept the line you've drawn. Don't forget to listen for the convoy every hour and to keep drawing circles showing where you think the convoy will be in one hour's time.

Good luck!

08-04-15, 10:06 AM	#5
Zosimus XO Join Date: Jun 2014 Location: Chorrillos, Lima, Peru Posts: 401 Downloads: 3 Uploads: 0	Here's some advice for what good it may do you. I assume that you are tracking a convoy. The first step to tracking a convoy is to determine its heading. This is hard when you cannot get a visual on the cargo ships. The escorts change course all the time and although you can (eventually) get the course by watching escorts, it can take much longer and is quite hard to do in the rain. There is, however, a simple, safe, and foolproof way to determine the convoy's heading. The key is to look for stragglers. Behind any convoy, there is almost always a tramp steamer (or two) that has fallen behind the others and is struggling to catch up. The key is that its heading is the same as that of the convoy. You can safely intercept this straggler to determine its heading or use the three-bearing method (hydrophone) to determine its course. Once that's done, you can draw a course line through the target (you can use the hydrophone distance... it doesn't matter really) and then extend this line as far as you can. You can just hold the mouse open drawing the line and use the arrow keys to move the screen till you get to a conveniently long distance. Now catch up to the convoy. If you can hear the convoy by hydrophone, then it must be less than 20 km away. If you cannot hear the convoy, just draw a 20.0 circle and race in the direction of the convoy until you hit the 20 km mark and go to 25m under to listen again. Sooner or later, you'll find that convoy and hear one of the cargo ships. Pay attention to the speed. If the merchant speed is "slow" then it must be moving at 7 or fewer knots. If the speed says "medium" then it must be at 8 or more knots. Draw a circle centered where that merchant's hydrophone line intercepts the line you've drawn. The radius of the circle should be 13.6 for slow (7 knots) or 15.6 for medium (8 knots) and note down the time one hour from now on a separate sheet of paper. That's where the ship should be in one hour assuming that the heading and speed are accurate. Then surface and move to intercept. Assuming you are behind the convoy, your heading should be about 30-50 degrees off of the convoy's heading. Initially, 40 is a good number. You'll want to go about 5 km and then go to 25 meters for another listen. If it seems that you're not catching up to the convoy, then go to 30º off of its course. If it seems that you're catching up too quickly then go to 50º off of its course. Then cruise on out until you are 18 km off of the projected course or until the hour is up. Listen to the convoy every hour. Does it seem to be on the course you have projected? Does it seem to have covered the right amount of distance? If not, you may have to adjust your speed or heading assumptions. It may take several hours to overtake the convoy, and you will have plenty of time to refine your assumptions. Once you're 18 km out, simply parallel the convoy (or maybe 0-5º angled toward it) until you have passed the convoy. Then angle in maybe 20-30º until you intercept the line you've drawn. Don't forget to listen for the convoy every hour and to keep drawing circles showing where you think the convoy will be in one hour's time. Good luck!