Is SH5 A Good CelNav Practice And Test Bed?

[Sjizzle]

Originally Posted by Capt Codetrucker

Hi Folks,

The following discussion will probably seem like overkill since I am sure you have a clear understanding, but I wanted you to be able to get inside my "head" (thoughts) and follow my thinking. Years ago I had a clear understanding, but today I am not so sure. I think I need your help to realign my thought processes and/or methodology. Anyway, I hope you can because I must definitely be doing something wrong.

Here we go!

For the discussion below...
SHT = Silent Hunter game time
NST = The time displayed on YellowSubmarine's Sextant at time of shot.

For starters...
--- I have no idea if I am supposed to factor in Magnetic Declination and even if I did should I use the 1939 MagDec map or the one for the present day? Since I don't know I will ignore it for now.
--- I know I am in the Baltic Sea somewhere on a bearing of 315o from mouth of Memal Harbor.
--- I am E of Greenwich, so I will be somewhere in the E latitudes.
--- I have been traveling 315o bearing for 8 hrs. @ ~10kts. = ~80NM. Given I am traveling forty-five degrees (N headway equals W headway) we can assume I have traveled half the ~80NM north and half west.
--- Since the mouth to the Memal Harbor is roughly N55o 43'. Traveling 40NM to the N and 40NM to the W would place the sub at N56o 39' E019o 22' by DR.

Does the above make sense, or am I missing something?

Next, let's take a shot of Polaris...
--- Elevation - Polaris @ 56o 12.5'
--- Local Time - August 31, 1939 21:00 "A" Time zone (GMT+1).

Calculate our SHT position...
--- SHT GMT = August 31, 1939 20:00 (8:00 hrs past GMT Noon).
--- Since it is Polaris, the elevation equals latitude.
--- SHT Local = Noon GMT in Greenwich + 9:00 hrs. 9.0 Hrs x (360o/24 = 15o/Hr) = 9.0 x 15o = 135o W
So our present SHT position would be N56o 12.5' W135o 0'. This can't be correct. It is 3900+NM away from my DR position on a bearing of 344o. 7NM pff the coast of southern Alaska. What did I do wrong??

Calculate our NST position...
--- Polaris same as above.
--- NST Local = Unknown other than what can be calculated from NST GMT (presently 18:00) which would equal 19:00. So, Noon GMT in Greenwich + 6:00 hrs. 6.0 Hrs x (360o/24 = 15o/Hr) = 6.0 x 15o = 90o W.
So our present NST position would be N56o 12.5' W090o 0'. This also can't be correct. It is 3200+NM away from my DR position on a bearing of 319o. This is near the borders of the Canadian provinces of Manitoba and Ontario, just south of the Hudson Bay. This is driving me bats! What did I do wrong??

I hope this helps?

disable that mod it's inaccurate and doesn't work well... try to to thesame thing without the mod and report back pls !

Originally Posted by Sjizzle

disable that mod it's inaccurate and doesn't work well... try to to thesame thing without the mod and report back pls !

Thank you. I will try as you say. Does this mean my process and calculations are correct?

I really cannot remember HOW I used to reduce a shot, but if I am not oversimplifying, here is my process...

1. Shoot Polaris. Elevation = my latitude. No nautical almanac lookups necessary.
2. Record the time GMT.
3. Add/subtract the number of hours from last GMT Noon.
4. #Hrs x 15o = W longitude, if more than 180o, then 360o - W Longitude = E Longitude.

This is all I can remember. Is this correct?

[Sjizzle]

Originally Posted by Capt Codetrucker

I really cannot remember HOW I used to reduce a shot, but if I am not oversimplifying, here is my process...

1. Shoot Polaris. Elevation = my latitude. No nautical almanac lookups necessary.
2. Record the time GMT.
3. Add/subtract the number of hours from last GMT Noon.
4. #Hrs x 15o = W longitude, if more than 180o, then 360o - W Longitude = E Longitude.

This is all I can remember. Is this correct?

here we go example

If it is 18.00 GMT when it is 09.20 local time on the same day, then local time must be 8 hours and 40 minutes behind GMT. Therefore Long = – [(8 x 15o) + (40 ÷ 60 x 15o )] = – [120o + 10o] = -130o = 130o West

Originally Posted by Sjizzle

here we go example

If it is 18.00 GMT when it is 09.20 local time on the same day, then local time must be 8 hours and 40 minutes behind GMT. Therefore Long = – [(8 x 15o) + (40 ÷ 60 x 15o )] = – [120o + 10o] = -130o = 130o West

The above is for Local Time behind GMT. Please give me an example of 01.00 GMT and 02.00 Local where Local Time is ahead of GMT. When I tried it I got the following...

If it is 01.00 GMT when it is 02.00 local time on the same day, then local time must be 1 hours and 0 minutes *ahead* GMT. Therefore Long = - [(23 x 15o) + (0 ÷ 60 x 15o )] = – [345o + 0o] = -345o = 345o West = 015o E.

Plotting the above with the latitude of 56o 32' N which is on land.

FWIW - The SH5 GMT minutes are always the same as Local (Naut) minutes. This always produces a whole degree and 0 minutes difference.

[Sean C]

Or you could just subtract 1 from 2 to get 1 and multiply by 15.


Just remember that if local time is later than GMT, your longitude is East. If Local time is earlier than GMT, your longitude is West. The difference between the two times multiplied by 15 is your longitude.


Either way, a difference from GMT of +1 hr. is indeed at 15°E.

Originally Posted by Nathaniel B.

Or you could just subtract 1 from 2 to get 1 and multiply by 15.


Just remember that if local time is later than GMT, your longitude is East. If Local time is earlier than GMT, your longitude is West. The difference between the two times multiplied by 15 is your longitude.


Either way, a difference from GMT of +1 hr. is indeed at 15°E.

Yes indeed. Now go plot N56o32’ E015o00’ and you will see my conundrum. I am actually somewhere at N56o32’ E019o30’.

[Sean C]

Originally Posted by Capt Codetrucker

FWIW - The SH5 GMT minutes are always the same as Local (Naut) minutes. This always produces a whole degree and 0 minutes difference.

This makes me wonder if some type of zone time is being displayed instead of local time. In your example, if the zone time (at 15°00' E) is 0200, then the actual local time (at 19°30' E) would be 0218.


What do you mean by "local (Naut) minutes"?

Originally Posted by Nathaniel B.

...
What do you mean by "local (Naut) minutes"?

In SH5 if you click on the time it will toggle between "GMT" and "Naut." Presumably, "Naut" = Local.

Originally Posted by Nathaniel B.

This makes me wonder if some type of zone time is being displayed instead of local time. In your example, if the zone time (at 15°00' E) is 0200, then the actual local time (at 19°30' E) would be 0218.

Hmm...... is there a setting which will make the Naut/Local clock not be restricted to the start time of time zones? That would be really helpful. Here’s hoping!