American militarism pre-WW2 and the Ultimate Battleship

[T. A. Gardner]

At 40kn, that's ~970 yards traveled.

Oh, that's right I forgot USS Behemoth is also capable of 40 knots and is inertialess. Never mind.

So it uses captured German die Glocke technology does it?



Well, at least there'd be room for it...

[TheMarcksPlan]

At 40kn, that's ~970 yards traveled.

Oh, that's right I forgot USS Behemoth is also capable of 40 knots and is inertialess. Never mind.

So it uses captured German die Glocke technology does it?

Awwe, I understand guys. Yesterday's formula-based discussion tired you out and you need to rest and fall back to "man on the street" intuition. That's okay, yesterday was fun and you've earned a mental respite.

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For anybody who wants to dig into a fundamentals-based discussion on propulsion/speed of a very large WW2-era ship, discussion is back in this post.

One thing I haven't mentioned so far: Maneuverability, including reverse-steaming potential.

Electric propulsion enables rapid distribution of the ship's HP to its various propellers. While steaming in battle and at optimal range, we wouldn't need to maintain speed faster than the enemy battle line - else we're shortly out of optimal range.

Instead of slowing down all the propellers to match, say, 27kn enemy speed, we'd run only ~half propellers on the centerline and shut down those in the the wings. It's less fuel-efficient but negligible given a battle's duration. Why do this? Because with the wing propellers inert they can be rapidly spooled up for maneuver: For a quick turn to port, go full throttle forward on the starboard engines and full reverse port. This should provide an excellent turning radius for a large ship. Here the ship's high B:L ratio helps - the outer props have a large moment arm for creating rotational torque.

------------------------------------------

Reverse

The ship probably also has a few relatively small forward propellers that would only be used for reverse and maneuver. These would be, say, 15ft diameter and therefore a small contribution to the ship's friction drag. In normal times they'd windmill and most of their additional friction would be captured by using their electric motors as dynamos to feed the ship.

By putting these smaller propellers at maximum depth (tips 95ft below waterline) they'd operate in ambient water pressure ~4.8x higher than at 20ft.

The cavitation limit for these 15ft propellers would be ~570 RPM (taking ~625k HP). Thus 4 small propellers could use nearly all the ship's horsepower rapidly to stop it or - in conjunction with the normal propellers - to drive it reverse. Of course these propellers could also help with maneuver via asymmetric thrust. Again the small propellers have low propulsive efficiency but we're not using them for long-range cruise.

As the ship can do at least 35kn in reverse, our tactic while engaging an enemy fleet broadside would be to use reverse instead of turning about when required. This allows the battery to fire continuously, something a maneuvering ship typically can't do.

Reverse also enables more possibilities for runway configuration.

[T. A. Gardner]

Awwe, I understand guys. Yesterday's formula-based discussion tired you out and you need to rest and fall back to "man on the street" intuition. That's okay, yesterday was fun and you've earned a mental respite.

No, I just enjoy tossing in a bit of snark and sarcasm from time to time. It lightens the mood when the conversation starts getting ugly.

[TheMarcksPlan]

No, I just enjoy tossing in a bit of snark and sarcasm from time to time.

Well snark on. Perhaps you can see why it's easy to read that as "there's no way this ship could do 40kn on 3mil HP" but as that wasn't your intent...

[TheMarcksPlan]

Re the threat of high-level superbombs from superbombers...

Main response, already stated, is that nobody but U.S. (maybe UK) can build enough superbombers to pose a credible threat to 36in of mild steel.

I should emphasize more clearly that the underlying physics favors the megaship, however. Per the already-quoted studies, armor/steel penetration escalates linearly with diameter for a given shell/bomb form and striking velocity. So if you want to double armor penetration, your superbomber and shell/bomb have to be ~8x larger.

By contrast, a ship of sufficient size/firepower need protect only its vitals from unlikely superbomb hits, an area that remains basically constant. If we need to increase armor thickness linearly over a given area, the compensatory non-citadel delta to displacement and attendant propulsion delta are insignificant, given extremely favorable displacement/HP ratios for a megaship.

To put hard numbers on it: To protect against a B-36's max payload (86k lbs) in a single air-dropped shell/bomb would require ~51in of high-tensile construction steel. Over the same 2000x350ft citadel under discussion, that requires 191k tons more than 36in deck armor or 5% greater displacement, which would require ~3% higher HP for a given speed.

...that doesn't answer the question whether its feasible to build a megaship, but it does answer the question whether, within the megaship domain, escalating (non-nuclear) airpower reactions are feasible.

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But the heavy bomber's threat to megaship is only half the question; megaship's threat to heavy bombers is at least symmetrical.

A megaship with 1,000 high-elevation 18in guns at 5/min RoF - feel free to quibble whether that's possible on the particular megaship I've sketched but it's feasible for a massive ship - puts up the AA weight of ~50,000 88mm flak guns. For comparison, the heaviest anti-HB flak concentration I can think of was around Leuna with ~1,700 heavy AA guns. Germany built 21,000 88mm guns during the entire war.

Per Westerman's Flak, the German 88mm Flak 41 shot down a heavy bomber for every 5k rounds fired. With a megaship firing 5k 18in rounds/min and each shell worth ~142 88mm shells, that's 35 18in shells/bomber or >140 HB's/min.

...but that's based on German fire control practices and no VT fuses. With Allied fire control and VT fuses, 10 shells/HB is a conservative estimate (again per Westerman's Flak, a late-war copy of Allied gun-laying radar tech - "Kulmbach" - reduced kills to 300 rds/kill or by a factor of >16).

Even with a probably-conservative 10 18in shells/HB, the megaship could kill 500 HB's per minute. That makes feasible destroying a 1,500-bomber force during its ~3min run at the megaship (and 3min assumes no evasive maneuvers by the megaship that force reassembly and go-arounds under megaship fire). Unless we're talking basically Kamikaze Japanese pilots of that massive bomber fleet (an economically implausible projection), the suicidal odds are going to cause skyrocketing "creepback" and ineffective attacks against the megaship.

For another AA scale comparison, consider an Iowa/SoDak/Juneau-class ship firing 12 5in/38's at 15 rds/min. The megaship main battery's weight of fire is alone 1,320x as great (leaving aside secondary/tertiary guns for now). Attacks against any of those ships were guaranteed to lose at least a few planes OTL. It's likely the megaship could shoot down thousands of closer-flying carrier AC or other non-HB aircraft, were it possible to assemble so many AC for an attack.

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The requirement to be functionally invulnerable to air attack is why my fun little sketch places DP main batteries at its center. It costs a lot to make a giant turret rotate at speeds sufficient for medium/long range AA fire, however. I estimate that the 15-20k ton rotating main battery turrets would each require ~30k HP to move adequately. That's feasible on the megaship because - unlike normal BB's, the rotating machinery isn't confined to a barbette and to the "electric deck" below the gunhouse. As the armored deck is flush with topside, turret-rotating machinery fits easily outside the rotating structure rather than within.

As we'll need additional HP to ram quickly projectiles at the ~45-degree loading angle, and to hoist ~10,000t/min of shells and powder, I budget 1mil HP for total auxiliary machinery power. That raises the megaship's total to 4mil HP, still <20x an Iowa for 400x the surface firepower and >1,000x the AA punch.

And, btw, with electric drive the auxiliary generating capacity - functionally indistinguishable from main generator plant - can feed the props (which are well short of their cavitation limits). So a megaship making an operational dash to attain favorable tactical position (i.e. when it doesn't need to rotate/load the main battery) can do 43-44kn.

[Terry Duncan]

So, the latest wonder to be achieved by this curious proposal is an 18" gun with a RoF of in excess of 10rpm and multiple degree per second training as well as all angle loading and at least 70 degree elevation too? A draught of 95ft when suited, a high length to bean ratio resulting in not only a high speed but great maneuverability too, plus presumably variable sized propellors?

[TheMarcksPlan]

18" gun with a RoF of in excess of 10rpm

No:

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

----------------------------------------

A draught of 95ft when suited

No:

I've set maximum battle-draft at 110ft.

----------------------------------------

a high length to beam ratio

No:

Length:beam ratio of 6:1, beam=550ft.

----------------------------------------------

plus presumably variable sized propellors?

No:

Reverse

The ship probably also has a few relatively small forward propellers that would only be used for reverse and maneuver. These would be, say, 15ft diameter and therefore a small contribution to the ship's friction drag. In normal times they'd windmill and most of their additional friction would be captured by using their electric motors as dynamos to feed the ship.

By putting these smaller propellers at maximum depth (tips 95ft below waterline) they'd operate in ambient water pressure ~4.8x higher than at 20ft.

The cavitation limit for these 15ft propellers would be ~570 RPM (taking ~625k HP). Thus 4 small propellers could use nearly all the ship's horsepower rapidly to stop it or - in conjunction with the normal propellers - to drive it reverse. Of course these propellers could also help with maneuver via asymmetric thrust. Again the small propellers have low propulsive efficiency but we're not using them for long-range cruise.

Electric propulsion enables rapid distribution of the ship's HP to its various propellers. While steaming in battle and at optimal range, we wouldn't need to maintain speed faster than the enemy battle line - else we're shortly out of optimal range.

Instead of slowing down all the propellers to match, say, 27kn enemy speed, we'd run only ~half propellers on the centerline and shut down those in the the wings. It's less fuel-efficient but negligible given a battle's duration. Why do this? Because with the wing propellers inert they can be rapidly spooled up for maneuver: For a quick turn to port, go full throttle forward on the starboard engines and full reverse port. This should provide an excellent turning radius for a large ship. Here the ship's high B:L ratio helps - the outer props have a large moment arm for creating rotational torque.

As the above posts make clear, use of propellers at different critical points based on distribution of electrical generating capacity. Not the remotest suggestion that propellers change size/pitch. Where'd you get that?

[Sid Guttridge]

Hi T A Gardner,

I like your photo, but I think it might have been photo-shopped.

I thought the crack in the Liberty Bell made it functionally useless?

Cheers,

Sid

[Terry Duncan]

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

So, pre-proximity fused AA functionally useless, rather like the supposedly AA capable 18.1" on Yamato.

A draught of 95ft when suited

No:

I've set maximum battle-draft at 110ft.

Deeper than many seas where a ship will possibly be needed.

a high length to beam ratio

No:

Length:beam ratio of 6:1, beam=550ft.

With that length to beam ratio a high speed is very difficult to obtain, which is why the Iowa's had such a long thin bow and such a high power plant output, and even then didnt make 33kts yet alone 40kts.

----------------------------------------------

plus presumably variable sized propellors?

No:

Reverse

The ship probably also has a few relatively small forward propellers that would only be used for reverse and maneuver. These would be, say, 15ft diameter and therefore a small contribution to the ship's friction drag. In normal times they'd windmill and most of their additional friction would be captured by using their electric motors as dynamos to feed the ship.

By putting these smaller propellers at maximum depth (tips 95ft below waterline) they'd operate in ambient water pressure ~4.8x higher than at 20ft.

The cavitation limit for these 15ft propellers would be ~570 RPM (taking ~625k HP). Thus 4 small propellers could use nearly all the ship's horsepower rapidly to stop it or - in conjunction with the normal propellers - to drive it reverse. Of course these propellers could also help with maneuver via asymmetric thrust. Again the small propellers have low propulsive efficiency but we're not using them for long-range cruise.

Electric propulsion enables rapid distribution of the ship's HP to its various propellers. While steaming in battle and at optimal range, we wouldn't need to maintain speed faster than the enemy battle line - else we're shortly out of optimal range.

Instead of slowing down all the propellers to match, say, 27kn enemy speed, we'd run only ~half propellers on the centerline and shut down those in the the wings. It's less fuel-efficient but negligible given a battle's duration. Why do this? Because with the wing propellers inert they can be rapidly spooled up for maneuver: For a quick turn to port, go full throttle forward on the starboard engines and full reverse port. This should provide an excellent turning radius for a large ship. Here the ship's high B:L ratio helps - the outer props have a large moment arm for creating rotational torque.

As the above posts make clear, use of propellers at different critical points based on distribution of electrical generating capacity. Not the remotest suggestion that propellers change size/pitch. Where'd you get that?

I has just curious as such a massively variable draught hull and massive speed ambitions presumably isnt relying on 15ft propellors for actual general movement?

This interesting comment;

Here the ship's high B:L ratio helps

6 - 1 is not a high B:L ratio, it is roughly that of a WWI dreadnought and nothing like the roughly 10:1 the Japanese needed for their cruisers to reach 35kts pre-WWII. Most navies found 7:1 or 8:1 the minimum needed for obtaining high speeds. Once you drop below this, and certain hull forms, you need vastly more power to just move the ship. It is almost impossible to achieve both high speed and high maneuverability as the two require different hull forms and ratios.

Have you ever tried to use any of the ship design programs out there to create what you are proposing?

[Terry Duncan]

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

So, pre-proximity fused AA functionally useless, rather like the supposedly AA capable 18.1" on Yamato.

A draught of 95ft when suited

No:

I've set maximum battle-draft at 110ft.

Deeper than many seas where a ship will possibly be needed.

a high length to beam ratio

No:

Length:beam ratio of 6:1, beam=550ft.

With that length to beam ratio a high speed is very difficult to obtain, which is why the Iowa's had such a long thin bow and such a high power plant output, and even then didnt make 33kts yet alone 40kts.

----------------------------------------------

plus presumably variable sized propellors?

No:

Reverse

The ship probably also has a few relatively small forward propellers that would only be used for reverse and maneuver. These would be, say, 15ft diameter and therefore a small contribution to the ship's friction drag. In normal times they'd windmill and most of their additional friction would be captured by using their electric motors as dynamos to feed the ship.

By putting these smaller propellers at maximum depth (tips 95ft below waterline) they'd operate in ambient water pressure ~4.8x higher than at 20ft.

The cavitation limit for these 15ft propellers would be ~570 RPM (taking ~625k HP). Thus 4 small propellers could use nearly all the ship's horsepower rapidly to stop it or - in conjunction with the normal propellers - to drive it reverse. Of course these propellers could also help with maneuver via asymmetric thrust. Again the small propellers have low propulsive efficiency but we're not using them for long-range cruise.

Electric propulsion enables rapid distribution of the ship's HP to its various propellers. While steaming in battle and at optimal range, we wouldn't need to maintain speed faster than the enemy battle line - else we're shortly out of optimal range.

Instead of slowing down all the propellers to match, say, 27kn enemy speed, we'd run only ~half propellers on the centerline and shut down those in the the wings. It's less fuel-efficient but negligible given a battle's duration. Why do this? Because with the wing propellers inert they can be rapidly spooled up for maneuver: For a quick turn to port, go full throttle forward on the starboard engines and full reverse port. This should provide an excellent turning radius for a large ship. Here the ship's high B:L ratio helps - the outer props have a large moment arm for creating rotational torque.

As the above posts make clear, use of propellers at different critical points based on distribution of electrical generating capacity. Not the remotest suggestion that propellers change size/pitch. Where'd you get that?

I am just curious as such a massively variable draught hull and massive speed ambitions presumably isnt relying on 15ft propellors for actual general movement?

This interesting comment;

Here the ship's high B:L ratio helps

6 - 1 is not a high B:L ratio, it is roughly that of a WWI dreadnought and nothing like the roughly 10:1 the Japanese needed for their cruisers to reach 35kts pre-WWII. Most navies found 7:1 or 8:1 the minimum needed for obtaining high speeds. Once you drop below this, and certain hull forms, you need vastly more power to just move the ship. It is almost impossible to achieve both high speed and high maneuverability as the two require different hull forms and ratios.

Have you ever tried to use any of the ship design programs out there to create what you are proposing?

[Terry Duncan]

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

So, pre-proximity fused AA functionally useless, rather like the supposedly AA capable 18.1" on Yamato.

A draught of 95ft when suited

No:

I've set maximum battle-draft at 110ft.

Deeper than many seas where a ship will possibly be needed.

a high length to beam ratio

No:

Length:beam ratio of 6:1, beam=550ft.

With that length to beam ratio a high speed is very difficult to obtain, which is why the Iowa's had such a long thin bow and such a high power plant output, and even then didnt make 33kts yet alone 40kts.

----------------------------------------------

plus presumably variable sized propellors?

No:

Reverse

The ship probably also has a few relatively small forward propellers that would only be used for reverse and maneuver. These would be, say, 15ft diameter and therefore a small contribution to the ship's friction drag. In normal times they'd windmill and most of their additional friction would be captured by using their electric motors as dynamos to feed the ship.

By putting these smaller propellers at maximum depth (tips 95ft below waterline) they'd operate in ambient water pressure ~4.8x higher than at 20ft.

The cavitation limit for these 15ft propellers would be ~570 RPM (taking ~625k HP). Thus 4 small propellers could use nearly all the ship's horsepower rapidly to stop it or - in conjunction with the normal propellers - to drive it reverse. Of course these propellers could also help with maneuver via asymmetric thrust. Again the small propellers have low propulsive efficiency but we're not using them for long-range cruise.

Electric propulsion enables rapid distribution of the ship's HP to its various propellers. While steaming in battle and at optimal range, we wouldn't need to maintain speed faster than the enemy battle line - else we're shortly out of optimal range.

Instead of slowing down all the propellers to match, say, 27kn enemy speed, we'd run only ~half propellers on the centerline and shut down those in the the wings. It's less fuel-efficient but negligible given a battle's duration. Why do this? Because with the wing propellers inert they can be rapidly spooled up for maneuver: For a quick turn to port, go full throttle forward on the starboard engines and full reverse port. This should provide an excellent turning radius for a large ship. Here the ship's high B:L ratio helps - the outer props have a large moment arm for creating rotational torque.

As the above posts make clear, use of propellers at different critical points based on distribution of electrical generating capacity. Not the remotest suggestion that propellers change size/pitch. Where'd you get that?

I am just curious as such a massively variable draught hull and massive speed ambitions presumably isnt relying on 15ft propellors for actual general movement?

This interesting comment;

Here the ship's high B:L ratio helps

6 - 1 is not a high B:L ratio, it is roughly that of a WWI dreadnought and nothing like the roughly 10:1 the Japanese needed for their cruisers to reach 35kts pre-WWII. Most navies found 7:1 or 8:1 the minimum needed for obtaining high speeds. Once you drop below this, and certain hull forms, you need vastly more power to just move the ship. It is almost impossible to achieve both high speed and high maneuverability as the two require different hull forms and ratios.

Have you ever tried to use any of the ship design programs out there to create what you are proposing?

[Richard Anderson]

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

So, pre-proximity fused AA functionally useless, rather like the supposedly AA capable 18.1" on Yamato.

A firing cycle of 20 seconds at "high-elevation" for an "18in gun"?

[Tom from Cornwall]

A firing cycle of 20 seconds at "high-elevation" for an "18in gun"?

Would need a very large magazine! And some very large gunners.

Regards

Tom

[T. A. Gardner]

6 - 1 is not a high B:L ratio, it is roughly that of a WWI dreadnought and nothing like the roughly 10:1 the Japanese needed for their cruisers to reach 35kts pre-WWII. Most navies found 7:1 or 8:1 the minimum needed for obtaining high speeds. Once you drop below this, and certain hull forms, you need vastly more power to just move the ship. It is almost impossible to achieve both high speed and high maneuverability as the two require different hull forms and ratios.

Have you ever tried to use any of the ship design programs out there to create what you are proposing?

Then there's the moment of inertia to overcome when maneuvering. You'd need a lot of rudder(s) to change course simply because of the moving mass of the ship. Same goes for acceleration and deceleration.

[Takao]

A megaship with 1,000 high-elevation 18in guns at 5/min RoF

So, pre-proximity fused AA functionally useless, rather like the supposedly AA capable 18.1" on Yamato.

A firing cycle of 20 seconds at "high-elevation" for an "18in gun"?

A firing cycle of 12 seconds....

After all, the guns are manned by alien space bats