Celestial Navigation in SH4

[don1reed]

Roger that, TorpX.

An easy way to test, at least, it's what I did with SH3 was use the "in game" ruler tool to measure the distance between Meridians and also between Parallels. It doesn't stack up to a real Mercator projection chart.

So most of the time I make my own (Paper) 2° x 2° charts to annotate my progress using Mary Blewitt's instructive book, CELESTIAL NAVIGATION for YACHTSMEN.(about $13.00 US) (Still Avail via Amazon via Subsim). I highly recommend her book. During WWII she taught many Navy and Airmen how to nav.

[6SJ7GT]

Like a lot of Sh4 navigators, I did not know a lot about celestial navigation when I started this project. Here are a few links that helped me understand the process.

Celestial Navigation Net - Lots of info here. The Theory and Practice pages are especially helpful.

Ed Falk's tutorial on a leg of the silicon sea cruise is one of the best basic tutorials I have found.

Universal plotting sheet for 81/2 X 11 paper (pdf)
To use this one, draw your longitude lines by using the degree scale. if you are at 21d latitude, your verticle (long) lines will be thru the 21d marks above and below the middle latitude line. draw a light diagonal line up and to the right in the bottom right lat-long box. A divider held horizontal from the respective latitude minute marking to the diagonal will give the respective minute of longitude for measuring.

Graph paper printer - mercator paper is under scientififc types. A real find, this program is useful for almost any type of graph paper you need.

Here is a method of using lined paper to construct a plot sheet:
Use lined paper, college ruled, Turn the paper 90d, so the lines are vertical.
Ruled lines are used for longitude. Every sixth or twelfth line is darkened to
represent a whole degree of longitude. (depending on the scale desired).

Lines of latitude are added by construction, starting with the lowest latitude
desired. Whole degrees are 60 miles.

From your lowest Latitude line, at the most R/H longitude line, draw a line at
an angle up from the Latitude of your lowest latitude line plus a
0.5d(i.e. 28.5d). For ten miles to each vertical line use 6 lines; for 5 miles
to the line use 12 vertical lines. Where the angled line crosses your 6th and/or
12th line swing an arc until it touches your R/H vertical longitude line. This
is the point of the next latitude line. Draw a line perpendicular to the
longitude across the page. Repeat the process with each higher latitude (29.5d),
etc.

The bottom angle line, where it crosses the intermediate vertical longitude
lines, is the distance interval. 10 miles each line for 6 line spacing. 5 miles
each line for 12 line spacing. This forms a handy scale of miles or minutes of
latitude.

The accuracy is within the tolerance of your #2 pencil point.

I have also found that the game map has the tools needed to plot your position, but you need to do this on paper until you get the hang of celnav.

Note that when using Stellarium to take star sights you don't need any altitude or sextant corrections, simplifies things a little in comparison to the above tutorial.

[6SJ7GT]

Forgot to mention some tools you will need for starters:
A ruler
Dividers
Protractor
later you may want a parallel ruler.

You can download the maritime or aviation sight reduction tables here.

And when you are thoroughly confused by celnav you can get the Maneuvering board manual and start on that.

Mike 6sj7gt

[TorpX]

This dead reckoning business has proved to be harder than I anticipated. I have been playing around with the school mission to try to see what might be done about it.

• First, as measured by the in-game ruler, the degrees of lat. are 64.7nm. The deg. of lon. are also 64.7nm. The meridians do not converge at all, end of story. In other words the earth is flat. At least, this is consistant.
• The speeds given by the HUD knotmeter are too high. In a S-18 class boat going standard gives a reading of ~10.4 when you are moving 10.0 kt. Figures for other speeds were similer. This includes submerged movement. While not entirely consistant, I would suggest multiplying the displayed speed by .95. I did not use the helm position knotmeter as it gives even higher values: At std, the helm dial would be about 10.7 or 10.8, the HUD dial would be about 10.4, and the actual speed 10.0.
• The HUD compass is very hard to read, and in my set up, at least, seemed to be off a good 2 degrees. The heading, as stated by the crew, seemed to be accurate to within a degree. I experimented with three ways to get the most accurate heading. None of them were very satisfactory. Using the HUD dial was terrible, using short waypoint lines did not work well, even putting the boat on a grid line and using the permanent protractor (a RFB thing, I guess) gave uneven results ( and would be extremely impractical anyway). All things considered, going by the crew statements, seems the best. A heading within .5 deg. is about the best you can hope for with the game as it is now.

Though few using cel-nav will be using the waypoints, I happened to observe some things that might be of interest. I found that the helmsman does not steer a constant heading between waypoints. If, for example, you put two wp's a long distance apart on the equator, say 120 or 240nm, go to high TC, then slow down to zoom in, you can find yourself 1 or 2 nm off course. As you near the next wp, increasing corrections would be made to the heading to reach it. This becomes more obvious, if you place a distant wp, then, after the rudder has reached 0, order the crew to steer a constant course, go to high TC, and see how far off you are as you pass by the wp. Evidently, the game designers didn't contemplate any need for precision here.

I should point out here, that I tabulated these figures in calm conditions. There were no wind or weather factors involved. Rough seas are bound to make speed estimates much harder.

All and all, I think the in game compass and nav tools leave a lot to be desired, but would like to hear from others. I presume Sh3 captains are, excuse the pun, in the same boat. I have some other ideas, but want to use all of this in the game some more.

[don1reed]

Chalk it up to drift and/or set.

Actually 2nm (4000 yds.) isn't that bad for DR navigation. If your bridge is 20' asl you can see the horizon out to 5.2nm (according to Bowditch). So, if your trying to make landfall, 4000 yds. is in the ball park. If it's dark, layoff, till twilight, then make your approach.

Alas, with SH1, raising the scope (high-scope) 60', you could see over the horizon, out to 9.1nm.

If you dissect, Mike's brilliant script for Python, you'll notice that the formula for determining your true game Lat/Long, located in SH4...\Save games, are numbers divided by 120,000. This is what converts the numbers generated by the game's engine into Lat/Long that are usable for navigation purposes.

Every time you do a "Save" your true location will be updated. Real Live navigation is accomplished on Mercator Projection Charts. The games navigation is modeled on something the Dev's invented to fit the F5 chart on the player's screen.

I do most of my chart work on plotting sheets. I annotate the F5 screen with "X's" wherever my "fixes" allow. Usually my fixes and where the game shows me to be are pretty dang close. Admittedly, DR in the game leaves an awful lot to be desired; but, taken on the whole, I'm very entertained with the Silent Hunter franchise.

Happy New Year.

[TorpX]

Don Reed,
I think you misunderstood my post. I was only holding to within 1 or 2 nm by using the in-game waypoints, a major cheat really. This was just to check actual speeds vs. indicated speeds. I agree 1 or 2 nm at the end of a long day of cruising going by DR would be great. But with the lack of precision in the compass or knotmeter, I doubt I will get anything like that 'in play'.

Since you're here let me ask you, if you were starting from a known position and cruised for 24 hrs at 10kt with only, lets say a few course changes, how far off would you expect your DR position to be?

I was considering printing some maps out, and maybe I will, but would prefer to keep the extra "paperwork" to a minimum.

I don't mean to sound negative though, Sh4 is the best game I know of. Otherwise, I wouldn't be making the effort to do this.

Happy New Year!

[don1reed]

Yes, I misunderstood your post.

In real life, D = S x T. 10kn x 24hrs = 240 nm


In the game, 240nm x cos (Lat) = _____

what Lat are you in?

If you're on the Equator, then, 240nm.

@ 1 degree Lat, then 239.9nm,
@ 30 degree Lat, then 207.8nm,
@ 45 degree Lat, then 169.7nm,
@ 60 degree Lat, then 120nm.

Distance x cos (Lat) is what I use in SH3...and it keeps me in the ball park.

I play time x1 and I take 5 sights per day and connect the dots (fixes). I use the measurement tool with compass to set my course between fixes and waypoints, in order to keep my boat headed for points on the ocean that the game understands.

In real life you could use the "Great Circle" formula to set your course between point A and B. On a Mercator Projection chart, a Great Circle course is a curved line. On a Gnomonic Projection chart, a Great Circle course is a straight line. If you have a desk globe and a piece of string, you can put one end at San Francisco, as example, and the other end on Japan. When viewed top-dead-center, the string appears as a straight line, and a curved chord from a side view.

What is happening in the game, is the curving of the course line which is transparent to the player.

To expand on the Gnomonic chart a bit further, absent a Navigational computer, mariners would use a Gnomonic chart to fashion a straight line course, paying sharp attention to where the course intersects with major latitudes and longitudes. These course Lat/Long crossings are then transferred to a Mercator Projection chart. Once layout is complete, it can be seen the course is curved and where course changes will occur on the Mercator chart as separate, short legs. A succession of straight, connecting courses, called Rhumb lines. (almost like calculus ) The overall effect appears as a curved course. I have not tried it yet, lacking a desk globe, but, I don't see why it wouldn't work for our purposes in the game. At least, you'd be able to see why the course changes between your waypoints.

[6SJ7GT]

Interesting discussion.

When I researched the game, I found that the devs measured E/W, then N/S in yards from 0d north and 0d west. They also used 2000 yds as a Nautical Mile. Thus the 120000 figure for a degree of latitude or longitude at the equator. Since an actual nautical mile is 6076 feet this might explain some of the errors vs real life in long distance navigation.

By moving first along the equator then N/S, you can translate your position to a flat map, it would create problems measuring E/W at places other than the equator, though.

Mike 6sj7gt

[TorpX]

If anybody is still checking into this thread, I'd like to know how many people are using this or how many have tried it. This goes for both Sh3 and Sh4. I would be interested in hearing about their experiences.

Anybody?

[don1reed]

I've been using it ever since, Mike, first posted it for SH4 and later converted it for use with SH3.

Sadly, I have not yet found a way to use with SH5.

A lot of folks have problems with SH3 due to the "drifting" and/or "sleepy helmsman" and probably don't use it that much on that game. Since I play TC x1 primarily, that gives me time to "whack" him when he falls asleep, to keep him on course.

Biggest problem is with the F5 screen Chart, particularly with DR in latitudes N and S where longitude degrees are significantly narrower than 60nm.

Lately I've only been using three star fixes obtained with pre-dawn and sunset twilight. Running fixes (RFix) using the Sun requires a DR more equivalent to one that could be obtained in real life. This results in an "UNSAT" RFix.

Using the Three star Fix usually puts me right on the money.

[Armistead]

I did for awhile, but it takes sometime and in itself can become the focus of the game. The coming in and out to use the program is a task. You eventually become so wrapped up in it you forget fighting. The only issue I had is my sub icon faded in and out some, instead of being totally gone.

[I'm goin' down]

you made it further than me. I cannot figure how to navigate. I need a video or an ELEMENTARY tutorial.

[TorpX]

Originally Posted by Armistead

I did for awhile, but it takes sometime and in itself can become the focus of the game. The coming in and out to use the program is a task. You eventually become so wrapped up in it you forget fighting.

This is pretty much my view of it. I did it for a little while, but found it absorbed a lot of time and energy. I would like to be able to play through a week or so, if things are quiet. As it was, after a day or two, I didn't really want to find a contact.

I do like the concept though. If there were better in-game tools or, put another way, fewer obstacles in Sh4, I think it could be a viable proposition. As it is, it's a tough row to hoe.

In any case, a have a few ideas in case there are modders who would like to develop the approach further:

1. Create some kind of dead reckoning indicator in the game. With the game as it is now, you have a choice between knowing exactly where you are (I don't need celestial navigation), and having no idea where you are (I'm hoplessly lost). Trying to account for every course change, speed change, evasive maneuver or weather effect is too much work load, IMO. Also, the player needs this to make an in-game tactical plot when the time comes.
2. Have a "navigator" in the game, where your position could be calculated automatically, with a reasonable degree of error (say 3 to 5 nm, weather permitting), so the player does not have to do it every single day.
3. Mod the charts/terrain so that prominent mountains and landmarks could be used to a greater extent. If mtn peaks were accurately marked on the charts (both location and elevation), they would be useful. Same for lighthouses (and maybe a few distinctive features here and there). The Sh4 generic land, in the game doesn't help the cause.

Of these, I consider no. 1, to be the most important, but I'm guessing, also the most difficult (or perhaps impossible). When I was using this approach, I found I could do the star fixes (tho it took more time that I wanted), but the dead reckoning business was torture. Definitely, its the worst part.

[don1reed]

At least, for those who have tried it for the first time in their lives, it gives one an appreciation of the state of the art of navigation in the 1940's. It demands a lot more than -- point and click.

Yes, it takes the focus away from the point of the "game" if you must rely on volumes of Tables (HO Pub 211, 229, or 249) or the ephemeris provided by Mike's almanac for the war years. I breeze through the calcs, admittedly, as I use professional computer programs for navigation, who's database covers two centuries. For me it's a simple matter of just entering date, time, Ho, Assumed Position, and selecting the appropriate body. The program(s) spit out the correct Lat/Long every time.

I agree, Torp, that the DR in all series of Silent Hunter "game" is hosed...fubar.

My dream would be able to use a virtual sextant (a second use for the Observation periscope, perhaps).

[TorpX]

Originally Posted by don1reed

At least, for those who have tried it for the first time in their lives, it gives one an appreciation of the state of the art of navigation in the 1940's. It demands a lot more than -- point and click.

Yeah, I admit I'm a little lazy.

Originally Posted by don1reed

Yes, it takes the focus away from the point of the "game" if you must rely on volumes of Tables (HO Pub 211, 229, or 249) or the ephemeris provided by Mike's almanac for the war years. I breeze through the calcs, admittedly, as I use professional computer programs for navigation, who's database covers two centuries. For me it's a simple matter of just entering date, time, Ho, Assumed Position, and selecting the appropriate body. The program(s) spit out the correct Lat/Long every time.

Ahhhhhhh.......... That would help.

Originally Posted by don1reed

I agree, Torp, that the DR in all series of Silent Hunter "game" is hosed...fubar.

Yes, but I do admit it has one BIG advantage over my earlier fav, SHCE; I can actually sail accross the Pacific. I really didn't like being confined to a virtual aquarium.

Originally Posted by don1reed

My dream would be able to use a virtual sextant (a second use for the Observation periscope, perhaps).

Maybe there will be a Silent Hunter VI.