N7 Naval Gun Design and Research

[Kaiser Kirk]

During the creation of N7, Snip worked hard to trim the rules down and clear out the 'extra'.

The Gun Research rules remained, to allow us to have custom naval weapons or choose to use historical ones.

One thing that wound up deleted was the formula to convert the Muzzle Energy on the chart to Muzzle Velocity.

That formula is : MV = SQRT( ME * 2,000,000 / shell weight)

However, turning that formula into an estimate of how one's custom weapon performs is a little more difficult.

As a Player, I developed a spreadsheet to allow me to estimate the performance of the guns I was building into the Parthian Fleet. I also used BigGun and Logi's Ballistic calculator to figure penetration.

I took the attitude that the exact performance was the Moderator's problem or whoever adjudicated the battles... the battle part I volunteered to help with.

Then the 'mod hat' wound up on my brow, and I suddenly had to figure out how to run the Sino-Japanese war. So I turned to what had - a way to find MV and penetration, and SeeKrieg, and used that.  I screwed up some things - the MTBs should have been slower ~26kts for one, which would take a little more time to get down to 1000-2000 yards to launch...but overall it seemed to work out.

Pregame Snip Rulings :
Snip made the ruling that for a particular class of Gun, say 12", the ME applied to all guns in that size class. So a 12", 11, or 10.1" gun would all use the same ME, based on Tech year.

Snip made the ruling that Gun+Mount weight is the rotating weight one uses when refurbishing a warship and re-gunning.

Mod Calls I've made include :
- When fielding a gun of 41-45 caliber, use the ME for that range, even if your tech allows a longer gun.
- Turreted gun's magazine is what is meant by 'main battery magazine'.
- So long as bore & shell weight is equal or less, a mount and hoist can be replaced under 'basic refit'.
- Casements can be removed/changed under 'basic refit'.

and in relation to the Gun Research Chart
- When fielding a barrel shorter than the maximum, one gets a pro-rated ME. I.e. a 43caliber gets 43/45* ME.
- For bores under 10", the ME formula produced illogical results unless scaled for chamber size.

Additionally, if you break down the original chart by ME:Caliber, you discover some problems with the ratio going down as tech got better.

Example:
The basic chart for a 14" gun looks like this

                                                               

	14" Gun class (360mm to 311mm)
ME	Caliber	Ratio
3200	35	91.4
4200	40	105.0
4700	45	104.4
5100	50	102.0
5500	55	100.0
5900	60	98.3

As one can see, while ME overall climbs, the ME/Caliber actually declines.
Considering metalurgy and propellants were getting better,
this seems wrong.

I think it should be rationalized so the ratio does not decline.
In this case it would mean the peak 105 ME:Caliber ratio would then apply to the later calibers.

Naval Gun Spreadsheet

In what is intended to be a helpful tool for all,

I have created a new spreadsheet with just Naval Gun calcs meant to be easy to use and understand. 

The attached Spreadsheet therefore has 2 tabs.
-The first uses the chart as presented.
-The second uses the chart as rationalized.

Otherwise the two tabs are identical.

The gun currently modeled is the 1925, 215L47 firing an oversized shell the Parthians are finishing.
The MV is a little lower than I'd like, so I may adjust it to be a L48 or L49.
Or lower the shell weight to 175kg, which would boost MV to 760mps. 



Enter in your gun stats in the BLUE dialogue.

The Muzzle Velocity then calculates in the RED.

.

[Jefgte]

I have tested with 234mm gun (HMS Glatton)

Player Input   Step 1.   234   Proposed bore (mm)   
Player Input   Step 2.    51   Proposed caliber    
Player Input   Step 3.    190   Proposed shell weight (kg)   
            
   Step 4.    9,21   bore size in inches   
   Step 5.    418   shell weight in pounds   
            
Player Input   Step 5.    60   Maximum Caliber for Tech Year from chart   
Player Input   Step 6.    2800   Muzzle Energy for from Chart   
            
   Step 7.    2189,30   Adjusted Muzzle Energy for Bore   
   Step 8.    1860,90   Adjusted Muzzle Energy for Caliber   
      MV = SQRT( ME * 2,000,000 / shell weight)       
   RESULTS   910   Muzzle Velocity (meters per second)   
      2984   Muzzle Velocity (feet per second)   



From Naval Weapons:
"The original 24 cm (9.45") projectile would have weighed 419 lbs. (190 kg). Muzzle velocity was 2,900 fps (884 mps) using a 144 lbs. (65.3 kg) charge. These projectiles were required to be able to penetrate 8.75 in (22.2 cm) of Krupp cemented (face hardened) armor at 7,650 yards (7,000 m). CPC projectiles were to cost £15 each and the charges £11 each."

[Kaiser Kirk]

My first attempt at a reply did not work. Odd.


Jefgte's posted a good example, the Excel sheet gives a result +2.9% higher than "Real".
For Modeling, that is fairly good.

There is always the option to field the historical gun if desired.

The "Rules as Written" is just that Chart in Gun Research.
I do not know who created it, but when I joined at the end of N3*, it was there.
I believe the ME given are tied to British Dreadnaughts, with the rest probably estimates.
As the numbers are all even, they have obviously been rounded to the nearest 100s. 

The chart- as I showed in my 14" example, is inconsistent. Which is why I have 2 tabs.

The Chart ALSO would give ALL 10"< guns the same ME.
So a 3" would have the same ME as a 10"

Further, it had no provisions for fielding a 90/54 vs. a 90/55. The 54 caliber should have less ME.

So a 234mm/51 is an excellent example.

From Jefgte's results you can see it models a little higher MV, which is 910 vs 884, or +2.9%.

For a 51 caliber 10"< less gun, the Chart gives 2500ME (not the 2800 Jefgte used, that's 60calibers)

SO
Chart as presented : 1,054 MPS MV (+19.2%)
Chart with just Caliber Scaling (51/55) : 1,015 MPS MV (+14.8%)
Chart with just Volumetric Scaling : 932 MPS MV (+5.4%)
Chart with Caliber and Volumetric scaling (this version) : 910 MPS MV (+2.9%)

Prior to this, for Parthia I used Caliber and Cross-sectional scaling for the 10"<.
That was a reason for some of my L43 guns - I didn't NEED 50 calibers as the MV went too high
and I didn't want to be fielding guns with over 900mps, I wanted 800-850mps.

The volumetric scaling of this excel sheet seems more accurate, but would bring
my older guns down a touch. I am sticking with the MVs I modeled at the time, as Good Faith.



*N4,N5,N6 never got beyond planning

[Kaiser Kirk]

The End Goal here is :

1) Original Rule design of the chart was to : Ensure everyone can choose to design their naval guns so as to have the shell/MV combo they wish, as allowed by the tech

2) The current Gun Research rules don't allow that because
   a) the formula was accidentally omitted.
   b) without that you really can't derive the MV of a shell, so you may be building a gun
      with an unusable 950mps MV (strips rifling) or a very slow 680mps shell.
   c) the mod clarifications for this haven't been centralized or well presented, so putting them in one spot and incorporating them into spreadsheet makes it more accessible.

3) So the Excel sheet would again allow everyone - not just me- to model their guns.

Granted, I don't think anyone really wants that, but it's about equal access to the option.

4) I would like to append the Excel Sheet's Tab 2 - with the rationalized ME - to the Gun Research Rule for future reference.

That is in fact a rule change (mild), and so I wanted the player base to be able to chime in.