SUBSIM Radio Room Forums - cacluating ship speed manually

Page 1 of 2

Show 20 post(s) from this thread on one page

SUBSIM Radio Room Forums (https://www.subsim.com/radioroom/index.php)

- Silent Hunter 4: Wolves of the Pacific (https://www.subsim.com/radioroom/forumdisplay.php?f=202)

- - cacluating ship speed manually (https://www.subsim.com/radioroom/showthread.php?t=182954)

I'm goin' down

04-24-11 04:56 PM

cacluating ship speed manually

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

04-24-11 05:51 PM

3600 seconds in an hour
1852 meters in a nautical mile

.

TorpX

04-25-11 04:30 PM

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

04-25-11 04:51 PM

I guess....:O:

TorpX

04-25-11 05:11 PM

Quote:

Originally Posted by Armistead (Post 1650818)

I guess....:O:

I guess not everybody likes math. :haha:

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

I'm goin' down

04-25-11 05:28 PM

armistead

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

04-25-11 05:52 PM

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

04-25-11 06:07 PM

Quote:

Originally Posted by TorpX (Post 1650798)

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.

Quote:

Originally Posted by Armistead (Post 1650818)

I guess....:O:

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

04-25-11 06:24 PM

Quote:

Originally Posted by Pisces (Post 1650857)

This will work too. :)

I'm goin' down

04-25-11 08:30 PM

Quote:

Originally Posted by Pisces (Post 1650857)

Quote:

Originally Posted by TorpX (Post 1650881)

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. :D. This I have got see! (...er, read.):hmmm:

TorpX

04-25-11 11:32 PM

Quote:

Originally Posted by I'm goin' down (Post 1650940)

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

04-26-11 12:59 AM

Quote:

Originally Posted by I'm goin' down (Post 1650940)

Quote:

Originally Posted by TorpX (Post 1650991)

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!:yeah::yeah: (Communicating in English is not easy, especially in technical matters. I see where I was confused.)

Pisces

04-26-11 07:34 AM

Quote:

Originally Posted by TorpX (Post 1650991)

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} :up:

Fish40

04-26-11 07:58 AM

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:hmmm:. The method does work though, provided the ship lengths are accurate.

Wilcke

04-26-11 10:26 AM

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.

Daniel Prates

04-26-11 04:07 PM

Great thread guys, excellent info! Let's all rate it so this is easily found in the future.

TorpX

04-26-11 11:09 PM

Quote:

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:hmmm:. The method does work though, provided the ship lengths are accurate.

I toyed with this method when I played SHCE, but went back to plotting, since I had to plot anyway, to get the course and plan the attack. But there is no reason why it can't be used. Another reason I don't use it now is, as you touch on, the rec. manual is lacking in this sort of data (in RFB at least).

Quote:

TorpeX MADE MY DAY!:yeah::yeah:

:shucks: Pleased to help.

If I ever figure out how to post graphics here, I have some really nifty technical nuggets to share.

makman94

04-28-11 12:09 PM

Quote:

Originally Posted by TorpX (Post 1650798)

.......
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.

Hi TorpX,

....:hmmm:...i believe that this formula is wrong for getting target's speed,TorpX !

the problem is not so simple for been solved by this simple formula.
where did you find this formula written ? before i proceed and explain why this formula is not correct i would like you to explain it more detailed (for example write the formula more clearer or show with a little example how you are using it and getting speed)) becuase ,maybe, i am missing something at the way you have written this formula.

ps: if you can prove the above formula...would be even better.

sorry for being the 'Doupting Thomas' here but this formula is not working, TorpX. and there is no way to make it work becuase you are not considering the target's course (relative to your own course) factor which is a very important factor ! this factor has equal importance with your boat's speed factor (which you are correctly considering) and has ,also, equal importance with the bearing to target factor (which,also, you are correctly considering).

as i said ,is not so easy problem . a good tool that help in situations like this is the back side of attack disc (in case that we don't want to use digital-modern-calculators)

ps: @TorpX : don't feel offended ...i will be huppy if ,at the end, prooved to be me on the wrong side.

Pisces

04-28-11 02:44 PM

Quote:

Originally Posted by makman94 (Post 1652646)

I agree, somehow the AOB should be worked into this too. I don't know how exactly though.

TorpX

04-28-11 09:25 PM

@ makman94 and Pisces:

No offense taken.
You may be right. I dug the formula out of my old papers and have not used it in a long time. I will play around with it and check before I report back. I should have done this anyway.

All times are GMT -5. The time now is 09:00 PM.

Page 1 of 2

Show 20 post(s) from this thread on one page