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Post by oldpop2000 on Oct 4, 2018 21:06:29 GMT -6
Director:
First, remember that a weapons system requirement generally comes from some sort of war game, be it table top or actual physical games. They can be just an update to an older system. For the Japanese, the rational for the super-battleships, conceived in the early 1930’s was valid. The Japanese could not compete with the US in a race for quantity of warships, so they had to turn to the alternative- superior quality. Remember that the threats to warships by aircraft had not manifested itself yet. The flimsy aircraft of the time frame that the Yamato’s were conceived in, were not felt to be a real threat to these super-battleships. The Japanese designers did not have any idea that aircraft technology would move as fast as it did. Most navy’s during this time period had no idea that the carrier and its airwing would become as potent as it did. The most important failure of the concept of the Yamato’s was the expenditure of limited resources on such large, expensive ships. Had they just upgraded the design of the Nagato’s, they might have been able to build more of these ships providing them with higher speed and longer range. Many people do not understand the reason for the Yamato’s not participating in the Guadalcanal actions at night was due to their limited range. They could not steam at full speed from Truk to arrive at night to do the bombardments. Only the Kongo’s could do that. They might have been able to use an upgrade Nagato to perform such operations.
We have to admit that it took well over 300 aircraft with 2000 lbs. bombs and torpedoes to sink both of these ships. So, they were built to take punishment and did so. However, their lighter 25mm AA guns were very poor and they did not consider our development during the war of heavier torpedoes and the fact that we realized that the best method of sinking them was to torpedo one side of the ship, not both. By torpedoing one side, we overwhelmed their torpedo bulkheads and transfer systems, designed to move water from one side to the other to stabilize the ship. There was also a defective joint in their armor which contributed to their problems.
The bottom line was, in my opinion, to try to build more improved Nagato’s which might have left more funding for advancements in carriers and other ships along with releasing some shipyards to preform more updates and upgrades. I’ve always felt that the Japanese Navy felt these were the epitome of the strength, a symbol of a strong nation. I will say that much of the criticism after the war by historians and Japanese officers is 20-20 hindsight, the clearest vision in the world.
In answer to your question, yes, a lighter shell is more affected by atmospherics than a heavier shell. How much I would have to research, it’s been a while.
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Post by aeson on Oct 4, 2018 21:30:50 GMT -6
In general, yes, a lighter shell will tend to be more affected by wind affects and aerodynamic drag than a heavier shell.
What you're doing wrong with that calculation is that you're modeling number of guns as the dominant factor in probability of scoring hits. It isn't; probability of putting a salvo on target is the dominant factor in probability of scoring hits. You put a salvo on target, and you've got pretty good odds of scoring at least one and decent odds of scoring a couple hits, and at least some of the other shells probably at least come close; you fail to put a salvo on target, and you probably don't score any hits at all.
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Post by oldpop2000 on Oct 4, 2018 22:10:01 GMT -6
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foarp
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Post by foarp on Oct 5, 2018 5:57:15 GMT -6
Okay, so I'm a bored physicist and thought I might be able to work this one out. Newton's approximation for penetrators is a good place to start. en.wikipedia.org/wiki/Impact_depth#Newton's_approximation_for_the_impact_depth Assuming an armour-piercing shell of approximately the same density as the armour it's striking, the maximum penetration of a shell is roughly its length. By eye the length of the AP shells used for the Japanese 18" gun were roughly 2.5m long, so that's about the thickness of armour you would need at close range. It might be surprising that the length of the shell is the deciding factor in this approximation, but it basically comes down to how much weight is behind the penetrating end of the shell. Calibre is important at least in part because it increases the amount of propellant that is placed behind the shell to drive it faster and keep it at speeds where Newton's approximation works. This gives us a rough ball-park maximum figure. However, Newton's approximation only really works for very high-speed penetrators. Even high-velocity shells don't typically achieve the necessary speeds (i.e., where the armour literally flows like liquid under the impact). Here's a calculator for working out penetration using Krupp's approximation, which is more suitable.. tankarchives.blogspot.com/p/demarre-calculator.htmlUsing 20" = 508 mm. The stats for the 18" naval gun ( en.wikipedia.org/wiki/40_cm/45_Type_94_naval_gun ) give a velocity at close range of 690 m/s - we can assume that a 20" shell would have at least this velocity. The weight of the 18" AP shell is 1,460 kg, but we need to know its density to know how to scale up this weight for an 20" shell, as the relationship between mass and calibre is not linear. The shell appears to be half a cylinder and half a cone - for simplicity's sake let's say that each part is the same length (by eye, looking at the photo of the AP shell on Wiki, this is roughly true). The mass of a cylinder = density x pi x r-squared x h. The mass of a cone = density x pi x r-squared x h/3. assuming both parts have equal density, height, length, radius it looks like the weight of the cone is 1/3rd that of the weight of the cylinder section. This means that of the 1,460 kg of the 18" shell, the cone only contributes 25% of the mass (365kg) with the cylinder making up 1095kg. So the density of the shell = 1095/pi x 0.4585-squared x 1.25 = 1326 kg/m-squared. With that I can now work out what the weight of a 20" shell having the same density as the 18" shell, and being 2.5 metres long, and comprising a cylinder section and a cone section of equal length is. It's 1.25 x 1326 x pi x 0.508-squared x 2.5 = 3359 kg Plugging these figures into the calculator gives a close-range penetration of 739 mm, or 29 inches of armour. At long range (30000 metres), with a velocity of 475 m/s, penetration drops to 509mm, or 20 inches of armour. However these figures look like they're in the right ballpark but still don't look realistic enough - I'll try and give this some more attention when I get time.
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Post by bcoopactual on Oct 5, 2018 8:48:01 GMT -6
Okay, so I'm a bored physicist and thought I might be able to work this one out. Newton's approximation for penetrators is a good place to start. en.wikipedia.org/wiki/Impact_depth#Newton's_approximation_for_the_impact_depth Assuming an armour-piercing shell of approximately the same density as the armour it's striking, the maximum penetration of a shell is roughly its length. By eye the length of the AP shells used for the Japanese 18" gun were roughly 2.5m long, so that's about the thickness of armour you would need at close range. It might be surprising that the length of the shell is the deciding factor in this approximation, but it basically comes down to how much weight is behind the penetrating end of the shell. Calibre is important at least in part because it increases the amount of propellant that is placed behind the shell to drive it faster and keep it at speeds where Newton's approximation works. This gives us a rough ball-park maximum figure. However, Newton's approximation only really works for very high-speed penetrators. Even high-velocity shells don't typically achieve the necessary speeds (i.e., where the armour literally flows like liquid under the impact). Here's a calculator for working out penetration using Krupp's approximation, which is more suitable.. tankarchives.blogspot.com/p/demarre-calculator.htmlUsing 20" = 508 mm. The stats for the 18" naval gun ( en.wikipedia.org/wiki/40_cm/45_Type_94_naval_gun ) give a velocity at close range of 690 m/s - we can assume that a 20" shell would have at least this velocity. The weight of the 18" AP shell is 1,460 kg, but we need to know its density to know how to scale up this weight for an 20" shell, as the relationship between mass and calibre is not linear. The shell appears to be half a cylinder and half a cone - for simplicity's sake let's say that each part is the same length (by eye, looking at the photo of the AP shell on Wiki, this is roughly true). The mass of a cylinder = density x pi x r-squared x h. The mass of a cone = density x pi x r-squared x h/3. assuming both parts have equal density, height, length, radius it looks like the weight of the cone is 1/3rd that of the weight of the cylinder section. This means that of the 1,460 kg of the 18" shell, the cone only contributes 25% of the mass (365kg) with the cylinder making up 1095kg. So the density of the shell = 1095/pi x 0.4585-squared x 1.25 = 1326 kg/m-squared. With that I can now work out what the weight of a 20" shell having the same density as the 18" shell, and being 2.5 metres long, and comprising a cylinder section and a cone section of equal length is. It's 1.25 x 1326 x pi x 0.508-squared x 2.5 = 3359 kg Plugging these figures into the calculator gives a close-range penetration of 739 mm, or 29 inches of armour. At long range (30000 metres), with a velocity of 475 m/s, penetration drops to 509mm, or 20 inches of armour. However these figures look like they're in the right ballpark but still don't look realistic enough - I'll try and give this some more attention when I get time. Welcome to the forum and thanks for the input. Assuming your ballpark numbers work out close to what you get when you get a chance to refine them it looks like 20 inch guns are going to have similar problems to 18 inch guns in RTW1. It's going to be hard to build a balanced ship that carries 20 inch guns because of displacement limits and armor thickness limits in the ship design program. I wonder if there is another way to make them more useful by making monitors a part of the game. Have monitors give a bonus to invasions or create unrest by bombarding home areas if in Northern Europe, etc. Maybe create missions around defending or sinking them. Not a priority by any means or even necessarily a good idea, it's just a thought.
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Post by alexbrunius on Oct 5, 2018 9:17:50 GMT -6
Okay, so I'm a bored physicist and thought I might be able to work this one out. .... The weight of the 18" AP shell is 1,460 kg, but we need to know its density to know how to scale up this weight for an 20" shell, as the relationship between mass and calibre is not linear. I'm by no means a physicist or mathematician but I do remember how volume scale works from high school. This means that assuming all the dimensions are scaled up equally and we have the same density distribution it's trivial to calculate the mass because it's a function of volume = cubic relationship. 20/18.1 = 1.105 scale factor 1.11^3 = 1.349 mass factor So if our initial 18" shell have a weight of 1460 kg a 20" shell will have a weight of 1970 kg ( 1.349 * 1460 ). This is reasonably close enough to the actual known weight of these shells as given by Wikipedia: "The armor-piercing shells would have weighed 1,950 kg (4,300 lb).[13]" [Remark removed by moderators - you should attack the person's argument, not the person -thanks.]
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Post by oldpop2000 on Oct 5, 2018 9:37:24 GMT -6
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Post by ccip on Oct 5, 2018 10:55:25 GMT -6
Director: First, remember that a weapons system requirement generally comes from some sort of war game, be it table top or actual physical games. They can be just an update to an older system. For the Japanese, the rational for the super-battleships, conceived in the early 1930’s was valid. The Japanese could not compete with the US in a race for quantity of warships, so they had to turn to the alternative- superior quality. Remember that the threats to warships by aircraft had not manifested itself yet. The flimsy aircraft of the time frame that the Yamato’s were conceived in, were not felt to be a real threat to these super-battleships. The Japanese designers did not have any idea that aircraft technology would move as fast as it did. Most navy’s during this time period had no idea that the carrier and its airwing would become as potent as it did. The most important failure of the concept of the Yamato’s was the expenditure of limited resources on such large, expensive ships. Had they just upgraded the design of the Nagato’s, they might have been able to build more of these ships providing them with higher speed and longer range. Many people do not understand the reason for the Yamato’s not participating in the Guadalcanal actions at night was due to their limited range. They could not steam at full speed from Truk to arrive at night to do the bombardments. Only the Kongo’s could do that. They might have been able to use an upgrade Nagato to perform such operations. We have to admit that it took well over 300 aircraft with 2000 lbs. bombs and torpedoes to sink both of these ships. So, they were built to take punishment and did so. However, their lighter 25mm AA guns were very poor and they did not consider our development during the war of heavier torpedoes and the fact that we realized that the best method of sinking them was to torpedo one side of the ship, not both. By torpedoing one side, we overwhelmed their torpedo bulkheads and transfer systems, designed to move water from one side to the other to stabilize the ship. There was also a defective joint in their armor which contributed to their problems. The bottom line was, in my opinion, to try to build more improved Nagato’s which might have left more funding for advancements in carriers and other ships along with releasing some shipyards to preform more updates and upgrades. I’ve always felt that the Japanese Navy felt these were the epitome of the strength, a symbol of a strong nation. I will say that much of the criticism after the war by historians and Japanese officers is 20-20 hindsight, the clearest vision in the world. In answer to your question, yes, a lighter shell is more affected by atmospherics than a heavier shell. How much I would have to research, it’s been a while. Can I just say that being able to actually game out the "More Nagatos vs. the super-ship" and other such scenarios is the reason why I'm so excited for RTW/RTW 2?
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Post by director on Oct 5, 2018 20:26:11 GMT -6
ccip - can I just say that I share your excitement? I'm running a 'USAvCSA' game now and I plan to test the 'quantity over quality' theory by sticking to a house limit of 35-40k tons for capital ships and then copying that in the American Xerox-machine shipyards. We'll see how that goes.
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Post by oldpop2000 on Oct 5, 2018 20:40:15 GMT -6
I wanted to share a set of specifications generated by Vice-Admiral Dr. Yuzuru Hiraga in 1928 as a replacement for the Kongo class battlecruiser. I find it interesting because it had 10 x 16 inch guns, and it was estimated that it could do about 26.3 knots.
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foarp
New Member
Posts: 7
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Post by foarp on Oct 6, 2018 2:18:41 GMT -6
Okay, so I'm a bored physicist and thought I might be able to work this one out. .... The weight of the 18" AP shell is 1,460 kg, but we need to know its density to know how to scale up this weight for an 20" shell, as the relationship between mass and calibre is not linear. I'm by no means a physicist or mathematician but I do remember how volume scale works from high school. This means that assuming all the dimensions are scaled up equally and we have the same density distribution it's trivial to calculate the mass because it's a function of volume = cubic relationship. 20/18.1 = 1.105 scale factor 1.11^3 = 1.349 mass factor So if our initial 18" shell have a weight of 1460 kg a 20" shell will have a weight of 1970 kg ( 1.349 * 1460 ). This is reasonably close enough to the actual known weight of these shells as given by Wikipedia: "The armor-piercing shells would have weighed 1,950 kg (4,300 lb).[13]" [Remark removed by moderators - you should attack the person's argument, not the person -thanks.]Everything in this comment is helpful, except the last bit. [Remarks by the original poster have been removed by the moderators and the poster has been spoken to. Thanks.]Welcome to the forum and thanks for the input. Assuming your ballpark numbers work out close to what you get when you get a chance to refine them it looks like 20 inch guns are going to have similar problems to 18 inch guns in RTW1. It's going to be hard to build a balanced ship that carries 20 inch guns because of displacement limits and armor thickness limits in the ship design program. I wonder if there is another way to make them more useful by making monitors a part of the game. Have monitors give a bonus to invasions or create unrest by bombarding home areas if in Northern Europe, etc. Maybe create missions around defending or sinking them. Not a priority by any means or even necessarily a good idea, it's just a thought. Yup, even with the lower shell-mass discussed above we're talking very heavy shells, guns, etc.
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