cacluating ship speed manually

[I'm goin' down]

I do not want to use the 3 minute rule. Plus, I am playing OM and using meters to calculate distances. I found this online, posted by our very own donreed1. I want to calculate speed by timing the target as it passes the perpendicular line on the scope. Will it work?

Ship's length past the vertical graticule / seconds x (3600/1852) = speed.

The bearing to your submarine from the targeted ship, your AOB, must be between 60 and 120 degrees. You should be at full stop for best results.

don1reed provided a quick example: i.e., T2 = 152.7m / 40 sec. x 1.94 = 7.4 kts.

Is this acciurate? Why 3600/1852?

[Diopos]

3600 seconds in an hour
1852 meters in a nautical mile

.

[TorpX]

The formula quoted is accurate as far as it goes, but does not take into account your subs movement. If you want to estimate speed while moving you must account for both your own speed and the relative bearing.


I used to use the following formula:

speed (kts.) = .59 target length (ft.) / time(sec.) + sub speed(kts.) * sin target bearing

if your sub and target are going in opposite directions then the last term sub speed(kts.) * sin target bearing is subtracted.

[Armistead]

I guess....

[TorpX]

Originally Posted by Armistead

I guess....

I guess not everybody likes math.


Actually, I decided that the best way was to just plot it out like they did in real life.

[I'm goin' down]

in OM you can calculate speed using the Kiub interface, but you still have time the target as it passes the perpendicular line on the scope. Using donreed1's method if you are stopped skips the step with the interface. Also, in OM, the U-Boat's don't pick up the target map contact at great distance. If the target is close, saving time in the Kiub set up for manual targeting can be invaluable, especially if the target is moving at a high rate of speed.

[Pisces]

Just keeping the periscope at 0 or 180 degrees and turning the sub with the bow or aft right in front of the target also corrects for own motion completely. Don't turn while you take the time though, or twist the periscope. Make sure the compass is steady. But other than that you could go at flank (forward or backwards) if you wish.

[I'm goin' down]

Originally Posted by TorpX

The formula quoted is accurate as far as it goes, but does not take into account your subs movement. If you want to estimate speed while moving you must account for both your own speed and the relative bearing.


I used to use the following formula:

speed (kts.) = .59 target length (ft.) / time(sec.) + sub speed(kts.) * sin target bearing

if your sub and target are going in opposite directions then the last term sub speed(kts.) * sin target bearing is subtracted.

Originally Posted by Armistead

I guess....

These math guys are taking over the world. Next thing you know, they will invent computers to use in every day life, connect them together, and start usikng computers to send messages, prepare business plans, solve problems, and heaven forbid, play chess and challenge Bobby Fischer. They may even try using them to send a man to the moon, can you believe that? It's totally nuts!

[TorpX]

Originally Posted by Pisces

Just keeping the periscope at 0 or 180 degrees and turning the sub with the bow or aft right in front of the target also corrects for own motion completely. Don't turn while you take the time though, or twist the periscope. Make sure the compass is steady. But other than that you could go at flank (forward or backwards) if you wish.

This will work too.

[I'm goin' down]

Originally Posted by Pisces

Just keeping the periscope at 0 or 180 degrees and turning the sub with the bow or aft right in front of the target also corrects for own motion completely. Don't turn while you take the time though, or twist the periscope. Make sure the compass is steady. But other than that you could go at flank (forward or backwards) if you wish.

Originally Posted by TorpX

This will work too.

Huh? Huh? (one for each post.)

How do you keep periscope at 0 or 180 degrees and just in front of the bow of the target without turning your boat or "twisting" the periscope. I assume "twisting" does not mean bending the periscope, but refers the act of of rotating or swiviliing iit. Just for fun, let's assume the target is a big, fat Yamato BB, plodding along at a meager 24 kts. . This I have got see! (...er, read.)

[TorpX]

Originally Posted by I'm goin' down

Huh? Huh? (one for each post.)

How do you keep periscope at 0 or 180 degrees and just in front of the bow of the target without turning your boat or "twisting" the periscope. I assume "twisting" does not mean bending the periscope, but refers the act of of rotating or swiviliing iit. Just for fun, let's assume the target is a big, fat Yamato BB, plodding along at a meager 24 kts. . This I have got see! (...er, read.)

What he means is you would turn your boat so your bow is just in front of the target, you then have the periscope at 0 deg. (ahead), then you time the transit of the target past the wire, while holding the course and periscope steady. You can turn the boat and periscope before you start timing, but not while you are timing. The same goes for 180 deg. periscope view, because in either case the plane of the wire isn't moving relative to the target's course. If you are viewing the target at some bearing other than 0 or 180 deg., the plane of the wire is moving in relation to the target's course and must be acounted for to get accurate results. I hope this explains it better.

[I'm goin' down]

Originally Posted by I'm goin' down

Huh? Huh? (one for each post.)

How do you keep periscope at 0 or 180 degrees and just in front of the bow of the target without turning your boat or "twisting" the periscope. I assume "twisting" does not mean bending the periscope, but refers the act of of rotating or swiviliing iit. Just for fun, let's assume the target is a big, fat Yamato BB, plodding along at a meager 24 kts. . This I have got see! (...er, read.)

Originally Posted by TorpX

What he means is you would turn your boat so your bow is just in front of the target, you then have the periscope at 0 deg. (ahead), then you time the transit of the target past the wire, while holding the course and periscope steady. You can turn the boat and periscope before you start timing, but not while you are timing. The same goes for 180 deg. periscope view, because in either case the plane of the wire isn't moving relative to the target's course. If you are viewing the target at some bearing other than 0 or 180 deg., the plane of the wire is moving in relation to the target's course and must be acounted for to get accurate results. I hope this explains it better.

TorpeX MADE MY DAY! (Communicating in English is not easy, especially in technical matters. I see where I was confused.)

[Pisces]

Originally Posted by TorpX

What he means is you would turn your boat so your bow is just in front of the target, you then have the periscope at 0 deg. (ahead), then you time the transit of the target past the wire, while holding the course and periscope steady. You can turn the boat and periscope before you start timing, but not while you are timing. The same goes for 180 deg. periscope view, because in either case the plane of the wire isn't moving relative to the target's course. If you are viewing the target at some bearing other than 0 or 180 deg., the plane of the wire is moving in relation to the target's course and must be acounted for to get accurate results. I hope this explains it better.

{places stamp of approval}

[Fish40]

I used this method with great success in both SH3 and 4. As for the latter, I was told that this wasn't practiced much in reality since the info on Japanese merchant ships was spotty at best, and true ship length was difficult to accertain. Not certain how true this was in the Atlantic. The method does work though, provided the ship lengths are accurate.

[Wilcke]

Be aware that with OM, your crew watch and hydrophone station will report speeds; slow, medium, fast and in the documentation you have a range of speeds for all those different calls. To add to the fun the targets in OM also like to change their speeds at the most opportune times, namely just before you fire a torpedo.

It just adds to the fun and fog of war.