Real Navigation with SH4

[Minimax]

one more test:

start at 30°00'S 105°00'E
1. Jan 44 delay to Vans alamac: - 5 Minutes SR
I went once around the world:
same position
11 Mar 1944 delay to Vans alamac: - 3 Minutes SR


second test:

start at 30°00'S 105°00'E
1. Jan 44 delay to Vans alamac: - 5 Minutes SR
23. Jan 44 delay to Vans alamac: - 4 Minutes SR

If there are rules, they're not easy to work out...

[don1reed]

I'm currently @ 30-13.9N 133-41E, 4 APR 42, just 168nm SSE of Japanese Island of Shikoku. Although the clock is showing 0953, real local time for my location is 0553 GMT = 2053. Dawn just broke (red light just went out at center of sun on horizon.

The clock in game is showing 0953 ( +11 (X Ray timezone)) (using WWII phonetic alphabet)
Sun Rise for my location is 0553 ( -9 (Item timezone))
GMT 2053

Van's sun Almanac shows SR for 30°N for 4APR as 0546. I missed it by 7 minutes. Those 7 min. puts me ~106nm South of my known position.

[kv29]

EDITED:

Im so full of sh*t, how could I post something like that?? I couldn´t reproduce my own formula, lol....

[Minimax]

I couldn´t reproduce my own formula, lol....

take it easy - you're not alone

[don1reed]

EPHIFFANY MOMENT !!!

Dang....How could I be so stupid!!!!

....all along I've been using van's Sun Almanac to figure my LATITUDE

Where, all along, I should have been using it for determing my LONGITUDE!!!


In my example above, (Post #47), I give my known position as:

30-13.9N 133-41E

my on board clock shows 0953 for sunrise for timezone XRay +11, (0953 +11 = 2053 GMT) but, I'm in time zone ITEM -9...this makes the time at my location (2053 -9 = 0553)(note: going from GMT to Time zone reverses the sign (-9) to a +9, then, 2053 +9 = 0553).

Van's chart shows SR for 30-N = 0546.

.0553
-0546
......7 min. My SR occurs 7 min. after van's almanac, this means I'm 7 min. further west, my Longitude will get smaller.

The middle of time zone (-9) = 135°E.

Time to Arc conversion: 7 min. converts to ~1° 30'.

...134° 60' (same as 135°)
.....-1° 30'
...133° 30' This is my computed Longitude, however, I know I'm really located just 11 nm east, at 133-41E.

11 nm is really doable!!! On a good, sunny,
clear day, you can see that far from the tower!!! (22,000 yds) Landfall and harbor lights can be found)



-...-


Soberness returns.....

That takes care of Longitude....now, to narrow down on Latitude.

That only leaves the star Polaris at night and the Sun at noon as accurate navigational bodies...unless you guys have another solution (???)

[kv29]

don, take a few more reading at very distant position one from another.
I had another theory to calculate local time, which worked quite good on small/middle distances but was full of garbage at longer ones.

btw, if you calculate total time between SR and SS and divide it by 2, that gives you real noon to SR and noon to SS, or perhaps not?

[don1reed]

BTW:

If you have a old or current issue of the "Nautical Almanac" lying about, you can also use the right-hand daily pages for sunrise/sunset, moonrise/set, and time of meridian passage. These tables do not change from year to year, so they're still valid.

edit: Let me check on your findings...I doubled with your posting and didn't get a chance to read it before I pushed the save button...

also, be aware that I still have my sub icon visible so that accuracy can be found and compared.

[kv29]

How are you supposed to know you are at "Xray" (?) +11 and gmt -9, if your sub does not show up in the map?

[don1reed]

How are you supposed to know you are at "Xray" (?) +11 and gmt -9, if your sub does not show up in the map?

I started from Oahu, H.I. timezone +10 http://www.epm.com/zonemap.jpg I'll post a timezone chart later today for GMT conversion.

I refitted at Midway Island. timezone +11.

A view of a timezone chart shows that almost all of Japan is in timezone (-9), my destination.

Navigation can also be accomplished by D'ed Reckoning (DR), that is:

Distance = Speed (in knots) x Time (in hours). You can reasonably calculate and predict where you're going to be in x amount of hours at y speed.

This is why the sim is easier than RL because there's no Set/Drift/Tide/Current/Deviation or Variation to contend with. Even with all of these obstacles eliminated, it will still add new dimensions and complexity to the game. You won't be able to kick back and relax, because now as navigator you'll be keeping a "sailor's eye" always peeled at the clock.

In response to your request: Base time and destination time are 6 timezones apart.

I left 30-14N 133-41E (near Japan heading back to homeport) at 0953 internal clock time (real time for the location = 0553 4 Apr 42).

Course 092T Speed 11kn. As luck would have it...it stayed overcast for 3 days when I spied a break in the clouds and took a moonsight.

Doing DR, it was 41 hours and 33 min. since my last known fix. D=SxT

D = 11kn x 41.55 = 457 nm. divided by 60 tells me I travelled 7° 37'.

133° 41'E + 7° 37' = assumed longitude of 141° 18'E which is still in time zone (-9).

The center of timezone (-9) is 135°E, it extends 7° 30' East and West. It extends from 127° 30'E to 142° 30'E

For testing purposes I still have the sub icon displayed. My real location was: 140° 24'E. There is a 54nm difference; however, using the observation scope I measured the moon's altitude as ~3° 30'. Using my navigation pgm I computed that the moon's intercept crossed my course line at 140° 33'...that's only 9nm from my true position. Thats totally satisfactory.

Not everyone has or can afford a celnav pgm on their cpu, so we've got to devise a sure-fire, less complicated method where anyone could get Lat/Long fixes without too much effort that'll scare 'em away.

[kv29]

Very good explanation
but as good as it is, is a quite daunting task to do as you say.
btw, something is a bit screwed about SR and SS in this game. Does the red light thing show what is "supposed" to be the SS/SR point? (even though is visually innacurate). sunrise is quite accurate, but sunset is not.

[don1reed]

The Sun Almanac shows SunSet for 30°N for 4 Apr as: 18:19
5 Apr as 18:20
6 Apr as 18:21.

Now...

Compare that with daily pages I copied from 1999 and 2007 Nautical Almanacs:



As you can see, there is very little difference between the times. The Nautical Almanac, however, uses just one time for three (3) days. Also, note that the Meridian Passage (Noon) is already figured on the bottom of the Nautical Almanac.

...and you are right, about the Red Light showing the actual SRSS. The trick of the navigational problem for us is to:

Summary:

1] Convert Base time to GMT, then, to find real location time for srss wherever we are, we:

2] Convert GMT back to location time. (Whenever we convert GMT to Zonetime, we must ALWAYS change the sign of the zone then do the math., i.e., if the zonetime = (-9), we must change it to +9...and visa versa) The Zone Description (ZD) (- / + ) is on the bottom of van's Sun Almanac pages.

[don1reed]

As promised, here is GMT conversion chart. Copy it or make one yourself.

Simple to use:

Find base time, follow across to GMT or Zebra in the middle, then on to Zone time for your location.

[kv29]

a big thanks .
btw, is there a mod to disable the sub location? no, Im not going to use it the first time at sea trying to do celnav, Im not that crazy....

[Minimax]

@don1reed

Thank you for your explanation - but there is still a delay up to 7 minutes. That's a long time for positioning on a longitude

I'm afraid, we have to make our own table for every starting position.
Am I right or wrong?

is there a mod to disable the sub location?

yes - i made one and can give you a link this evening (gmt-2) - I've just to part it from my mod-sampler.

I'm stuck in making the sextant click- and moveable.

[Minimax]

here's the mod: http://www.wamotec.de/tmp/MM_Einstei...alNav_beta.rar (7,6 MB)

- the sub location (sub icon) is disabled
- some bug-hunting-mods are integrated (including the start position for P.H. at 179°E)
- bettered radar, upgraded hud
- no gamebalance changes
- no visual goodies or anything else



With [ctrl+left_click] you will get back a small sub icon at your position - if you want to see it, you have to zoom in.