Real Navigation with SH4

I have found that the center of the sun both in rises and sets corrosponds pretty good with the almanac values from various programs. That is - RL rise value (upper limb) corrosponds with game center sun value - and - RL set value (lower limb) corrosponds with game center sun value.

If you take your pictures you will see that the center of the sun is set at about 17:16:00 witch corrosponds pretty well with the almanac data for 3-Jan 1943 between 320 and 20 deg. north with a weight to the 30ish time.

Originally Posted by don1reed

@Kv29: Closest I could get was a quick mission of 17 JAN 44 but from the same location: 21-14N 157-59W. My real life nav pgm for that date and year shows 18:02:40 for sunset, Azimuth 246° true.
The Sun tables of van shows 17:42
When the red light came on 17:08

My StarCalc proggy shows 17:40:00 for the sunset at 21deg14min N and 157deg 59 min W with Azimuth at some 248deg true

[don1reed]

I understand, Mav, but real life mariners don't use, StarCalc to navigate as it doesn't provide for:

IC (index corrections) of sextant
HE (height of eye above ocean)
Course/Speed
Choice of Limb
Temp/Pressure
Magnetic Variation
Altitude Correction
Dip
Nautical Almanac (ephemeris daily pages)

whereas commercial pgms such as, "Navigator"; "Celestnav" (for Palm); Tamaya NC-2100E celestial computer; Starpilot by Starpath; etc., do, plus much more.

I guess I'm trying to put too fine an edge on the navigational possibilities of of SH3/4 with it's non-linear visuals which cause distortion if not viewed exactly centered in the screen without the baseline "horizon" as reference.

In real life I've never been > than 3nm off, and at sea thats only 6,000 yds. Not bad with just a sextant. If I were searching for a one-man liferaft, 6k might as well be on the moon; but, for making landfall, it's practically right-on-the-money.

The trick of navigation with SH4 is consistancy. To have the sunrise-sunset be within 1° (60nm) Latitude of where you think you are I guess is good enough. If this is the case, then I suppose one doesn't have to get the virtual sextant to work either...all you need for sunrise/sunset is the Observation scope to see around the superstructure of the tower.

When the sun's azimuth is 000/180° (true)(depending on which hemisphere you are) you'll have both Lat & Long providing you have the wherewithal to perform a sight reduction.

You may or may not have heard of, Josuha Slocum, who in 1895 at age 51 single-handed around the globe using nothing more than a windup alarm clock for a chronometer...he however was an expert navigator/seaman and knew how to clear Lunars to determine GMT. There not much call for that these days, pity.

-...-

When SH1 hit the market, some of us tried to use celnav and/or ded reckoning nav to wing our way around the sea. If you remeber in SH1 all you had to do was click on the sub's icon to get your Lat/Long, so what we did was zoom way in so as not to be able to see any of the surrounding land mass or spawned shipping. Really reduced the tonnage. I found out that then that the non-linear and mismarked Lat/Long lines in the sim were way off, mathematically, i.e.,

In Real Life this formula will tell you what Great Circle course to follow for long distances:

Posit: 28N, 177E Destination: 33N, 139E

Course = arctan [ sin DLo / (cos L1 tan L2) - (sin L1 cos DLo)]

Distance = arccos [(sin L1 sin L2) + (cos L1 cos L2 cos DLo)]

Well, doing the math proved to me that the charts in SH1, 2, 3, & 4 are nothing like real charts...they give the player a sense of movement and position within the game nothing more, because having done the math and followed the course provided always ran me aground if you TC greater than 128.

Still, we try to navigate...I have to admit that SH3 & 4 seems more realistic.

[kv29]

mav and don, with the info available about sh4 capabilities, is there a "way" we can try to navigate?

Minimax, I have downloaded the 3 mod packs and I couldn´t find what part of them is supposed to "fix" the dateline. would you be kind enough to start a new career at perth and post your sunset&sunrise results? thanks

[don1reed]

Perth it is.


...er...What time frame?

later

[don1reed]

Posit: 32-13N 114-54E
Zone Time: (-8)
C 274 / S 0
Sun Almanac:
Sunrise: 0502 interpolated for location 0456
Sunset: 1904 interpolated for location 1900

Starpath:
SR: 05:17:22 Az: 118
SS: 19:30:38 Az: 242

Star Calc:
SR: 0517
SS: 1930

SH4:
SR: 0522 when red light went out.
SS: 1922 when red light came on.

-...-

BTW!!!

Looking at the #1 scope, aka observation scope...did you know....

1. It rotates to ~90° elevation.
2. It can read angles up to 32° above horizon when bottom of lens is poised on horizon.
3. It can read angles from 90° down to 58° when fully rotated upwards to it's upper stop.

This means that only 26° (between 58 & 32) cannot be referenced to the horizon for measuring altitudes of celestial bodies.

So...If I take a sight on Polaris and I have to swing the scope up to it's upper stop, all I have to do is count # of degrees down from the top of the scope (90°) to the body, then subtract that number from 90 to find it's altitude.

That missing 26° however, contains a lot of stars...but it still might work. The scope must be kept in low magnification however.

Yea Don - lots of math that dont really fit into SH4 at all. But then again im not going to try the mathamatical part of celestial navigation - Waaaaaay to complicated for me.

What i wanted was using SR and SS's and star fixes with my sextant.

--

Now that example you have in your last post

What did the times for the sun rise and set show on upper limb, center and lower limb? witch one of them corrosponded with the red light.

From my testings it was not the red light that should be used, but rather sun center on horizon.

[don1reed]

SH4:
SR: 0522 when red light went out.
SS: 1922 when red light came on.

Starpath & StarCalc deal with reality and give times for the real geographical coordinate occurrance of SR/SS. I only use them for reference when playing SH4...to get an idea when sr/ss might occur in SH4.

SH4 is a game and as such shows SR/SS when the sun is half out of the water (Center), when the red light turns on/off.

As I tried to explain earlier, the geo coordinates in the charts of SH1 thru SH4 are mathematically incorrect. They were made to suit the game engine, not to memic how the real earth is laid out as a real nautical chart would.

Here's a pic to show you what I mean:


The charts in SH1 thru SH4 are set up to represent a Mercator chart. In real life it's impossible to sail a straight line course over long distances using just a Mercator chart, because in actuality it would be a curve with many smaller rhumblines, so that you would have to change course every 200 to 300 nm to get from point A to point B. On the Gnomonic chart which makes exception for the curvature of the earth, a straight line course (great circle course) can be drawn and followed. The difference is striking, don't you think?

note: pic from Bowditch.

To further illustrate what I'm talking about, I've had numerous occasions in the past to plot my "game" coordinates on a real chart...
I was disappointed to find out that they were nowhere close to each other, nor could I follow the same course lines in the "game" compared to the real chart...say sailing through the San Bernadino Str., for example.

So, to devise a "game" method to navigate is where we stand now. The eye candy is great but how do we simulate celestial navigation in a "game" without mathematics? The easy answer, is do what we've been doing all along I'm afraid.

ohhh - so you say it does not work either in SH-3 ? bummer

I was hoping for a simple sunset longitude coupled with a polaris fix for lattitude. But i gues its in vain.

[don1reed]

I'm of the opinion that any simularity to navigation is purely accidental.

Someday, it will happen, hopefully.

[Minimax]

OK - SH4 doesn't use mercator-projection - no new information
and we can't use great circle navigation....

But mayby, we can use the sun to locate our position:

It seems that the clock is allright, if your starting position is at a longitude for a full hour.
We can't change the projection, we can't change the clock or sun, but we can change our starting position!

The clock starts allways at a full hour - usually that doesn't correspond to the starting position longitude. What's about starting at a full 15° position and use Vans almanac ?

[don1reed]

I'm of the opinion that any simularity to navigation is purely accidental.

I'm sure if the Devs would have meant celnav to be a feature within the sim(s), they would have waved it in front of our noses. They would have put bright lights around that accomplishment.

I'll give credit where credit is due, however, van's nav mod is a pretty good attempt getting to where we need to be, but 60nm doesn't happen with any consistancy or accruacy, and there's still a gulf between latitude and longitude. In Uboats: you'd never find the milkcow if you can only get within 60nm. I've yet to hear anyone extolling the celnav accuracy in SH3. Occasionally a "blind hog" finds an acorn.

Like it's been said, timing is everthing.

I've mentioned this before in another thread: When celnav was still being taught at the USNaval Academy, their standard for accuracy was 0.5nm.

cheers,

[kv29]

minimax, the clock only shows you local time IF you are at 179°E. as don said, is based on the international date line. If you start at another point in the grid, lets say 145°e, the clock still shows 179° time (I proved that with my star calc proggy). If we don´t have a working sextant, we need another clock with real local time to calculate longitude! Now I think the devs took out the second clock (real local time) on purpose.

[Minimax]

the clock only shows you local time IF you are at 179°E.

I see - my thought was: If there is a way to calculate the SR/SS, we could develop our own SR/SS - Table. Maybe one for each starting position...

The red light turns on off according to rules - we have to calculate these rules. Same with Solaris.

But if there's no rule to applay...


I hope, my English isn't too bad to understand my ideas.

[kv29]

I was wrong! I think I found a way!
doing more tests right now. Will come back later.....