Talk:USS Portsmouth (CL-102)

legacy

I have no references, someone else may be able to find them, but when CL-102 was broken up ~1971, the mothballed forward engineroom was disassembled, shipped up to upstate New York, and reassembled to provide a steam load for a research reactor, GE's "MARF" plant. When I was there in 1979, MARF had a WW2-era engineroom attached to a brand-new research reactor, and a picture of USS Portsmouth on the engineroom wall. The staff had the story, but I don't know how we can prove it for Wikipedia. SandyJax (talk) 09:47, 23 July 2023 (UTC)

These sorts of things are fairly common (off the top of my head, some machinery from the turrets of HMS Royal Sovereign (05) were used in the Lovell telescope), but they're also fairly hard to track down. The closest thing I've been able to dig up on this is this book that states that the "engine room from a decommissioned cruiser..." but it, A, doesn't mention Portsmouth by name, and B, is self-published. Parsecboy (talk) 10:34, 23 July 2023 (UTC)

Well, of course! If you're building an observatory, you need training and elevation gear, and it has to be massive enough to hold the telescope steady while it tracks the star, planet, etc as it moves across the sky. Pulling from an old warship's turrets sounds like a great idea. As long as it's smooth enough to keep the telescope from shaking...

For MARF, though, they were trying to keep the boilerwater chemistry clean for this brand new reactor, and they ran the steam and condensate through a 40-year-old rusty engineroom. We got boilerwater samples in every color of the rainbow EXCEPT 'clear'. SandyJax (talk) 15:35, 24 July 2023 (UTC)

Yeah, that doesn't make a lot of sense!

Unfortunate that I still haven't been able to track anything down - would have been nice to be able to include in the article. Parsecboy (talk) 12:12, 26 July 2023 (UTC)

On Rifling:

(The following doesn't belong here in the "USS Portsmouth" page, but I didn't see where it should go.)
   The 'Notes' section has an incorrect definition. It says "/47 refers to the length of the gun in terms of calibers. A /47 gun is 47 times long as it is in bore diameter."
   Consider two guns, both with 5' rifled barrels. One is a .22-caliber squirrel gun. The other is a 16" cannon. The 16" shell will do far more damage wherever it hits, but the .22 will hit its target. When the 16" shell leaves that 5' barrel, it has turned less than four times its diameter, and it isn't quite centered yet. It's still bouncing around some. The .22, on the other hand, by the time it leaves its 5' barrel it has spun almost 300 times, is perfectly centered in the barrel, and if the barrel is straight it will hit what it was aimed at.
   Thus, it isn't raw barrel length that we compare, it's the ratio of rifled barrel length to projectile diameter. In the last century, the US Navy has commonly used a 5"/25 (Pre-WW2 AA), a 5"/38 (General purpose everywhere in WW2), and a 5"/54 (Cold-War destroyers). Just looking at the numbers, it should be clear that the newer guns were far more accurate than the older ones, even before looking at technical advances, because they had longer barrels.
   And, of course, the overall length of the entire gun has nothing to do with it. I tried to replace 'gun' with 'length of the rifled barrel' but apparently the actual note is somewhere else and I didn't see where. Perhaps another editor with better wiki-fu can do this for me. SandyJax (talk) 15:26, 24 July 2023 (UTC)

No, the note is right - but it also isn't exactly specific about the definition of the measurement. If you look at the Navweaps page for the 6"/47, you'll see that the Navy does use the full length of the gun in its caliber designation, not just the rifled length (which would actually be just about 39.7 calibers). There are other navies that use different measurement lengths (off the top of my head, the Germans at least in WWII also included the breech, so they referred to the 38cm SK C/34 as a 52-caliber gun, whereas the US and UK called it a 47-caliber gun) but that's sort of beside the point.

But that's also not how it works; the barrel only needs to sufficiently stabilize the round, which the 25-caliber gun is perfectly capable of doing (and the length of the barrel is not directly related to the number of revolutions of the projectile - that has much more to do with the twist rate of the rifling - for example, the .300 AAC Blackout is optimized for a 1-in-8 twist rate, fired from an 9" barrel, meaning that it makes a single revolution before exiting the muzzle, which is plenty to stabilize the bullet). The difference barrel length makes is velocity, in that the expanding propellant gasses have that much longer to impart energy to the projectile. The faster the projectile, the flatter its trajectory, the longer its range, and the greater the impact velocity (and thus penetration) when it hits something.

Flatter trajectories of course make it easier to aim at and hit a target, but then we've moved beyond considerations of the mechanical accuracy of the barrel itself. Where barrel length can actually affect accuracy is at extreme ranges, where the round loses enough velocity to enter the transonic range, since the forces affecting the projectile change markedly and can cause it to diverge from its original flight path (see External_ballistics#Transonic_problem for a better explanation - but in other words, if two snipers are firing at targets a thousand yards away, with identical rifles firing identical ammunition, but one of them has a 10-inch barrel and the other has a 30-inch barrel, the rounds fired by the longer-barrel gun will still be supersonic, but those from the short barrel won't, and so the former has a much better chance of hitting the target than the latter). At practical battle ranges, assuming the mounts, fire control systems, etc. are identical, the /25, /38, and /54 are all more or less equally accurate. Parsecboy (talk) 12:42, 26 July 2023 (UTC)