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Old 05-20-2019, 02:03 AM   #121
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Default Re: GRUMEC and the Invisible Residents

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Originally Posted by lwcamp View Post
One idea would be to focus high intensity sonar beams on suspected biological targets. This could cause significant injury. The most significant injury is likely to occur at interfaces between materials of different density or elastic properties - such as occurs where muscle meets bone or where gas is present inside the body, such as at lungs or swim bladders. Sound is about the only thing that goes well through water, allowing stand-off strikes against incoming fish-men with a rapidly re-directable beam.

Luke
That's awesome!

Can you use the standard sonar arrays of the Brazilian SSKs, like the CSU-83/1 from Atlas Elektronik, to do this?

Or do you need special modifications?
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Old 05-20-2019, 07:58 AM   #122
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Default Re: GRUMEC and the Invisible Residents

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Originally Posted by Icelander View Post
That's awesome!

Can you use the standard sonar arrays of the Brazilian SSKs, like the CSU-83/1 from Atlas Elektronik, to do this?

Or do you need special modifications?
My understanding is that active sonar is enough of a danger that the U.S. Navy doesn't use it when divers are in the water. This is one of those areas where more data would be helpful. Nonetheless (https://en.wikipedia.org/wiki/Sonic_weapon)
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Researchers found that low frequency sonar exposure could result in significant cavitations, hypothermia, and tissue shearing. No follow up experiments were recommended. Tests performed on mice show the threshold for both lung and liver damage occurs at about 184 dB. Damage increases rapidly as intensity is increased.
- and military sonars get up to about 235 dB, around 100,000 times higher intensity than the threshold for injury.

The higher the frequency of the sonar beam, the farther away it can be focused, so early uses of weaponized sonar might just use the standard sonar array. Once it was found to be effective, it would be modified as a weapon to produce higher power higher frequency beams.

And just to be complete, there is a second method of injury from sonar. If the intensity gets high enough, the low pressure phase of the wave will fall to below the vapor pressure of water and the water will "boil". This produces a cavitation bubble, that collapses during the high pressure cycle of the wave. Collapsing cavitation bubbles can cause significant material damage, such as damaging steel propellers, and mantis shrimp are known to weaponize cavitation bubbles to aid with cracking hard-shelled prey items (in this case generated by impact rather than by a sonar wave). You don't want cavitation while your sonar beam is propagating through water (this would scatter the sound waves and ruin the beam), but if it occurs at your target the effects could be messy. This can be achieved since the amplitude of the pressure waves will increase when the wave reflects off the target, and if the beam is focused from a wide array where it is generated to a smaller spot at the target.

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Old 05-21-2019, 06:17 PM   #123
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Default Re: [MH] Brazilian Secret Monster Hunters

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Theres something else to consider about PUC-Rio, the prestigious jesuit university, that might be interesting.

When we hosted the olimpics and worldcup back to back there were tons of infrastructure works around Rio, one of them was a new metro line that would have a stop in PUC.

However after digging the tunnels, the projects stopped (reason given was lack of funds), and the university was left with a huge network of tunnels under it.

Due to fear of a collapse, they decided to flood the tunnels (which ironically costed millions of dollars by itself), recently they drained the tunnels but still the funds to finish the metro were unavailable, so they flooded the tunnels again.

Always thought it was an interesting place to have something spooky going on.
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I don't find that cover story very believable. Clearly what happened here is that they government dug tunnels under the university in order the destroy the bases of the mole-men who lived there. After the mole-men were destroyed, a group of cannibalistic ghouls moved into the empty tunnels, so they had to flood the tunnels. Which of course meant that they became filled with Deep Ones and albino alligators, so the tunnels were drained, which led to an infestation of Kobolds...
Hmmm... all supernatural threats should have local names.

What might Brazilians call monsters which resembled Lovecraftian ghouls?
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Old 05-22-2019, 06:22 AM   #124
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Default Navy Submarines and the Invisible Residents

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1) Not my area of expertise, so its hard to give suggestions here, but I think they would put all possible sensors just to be safe, thermal, radioactive, motion, etc. Also, would be interesting to leave buoys with sensors spread around the sea to give early warning on threats.
As far as I know, sonar is about the only effective underwater sensor. And, yes, I expect that the Brazilian Navy has made it a priority to install a highly sensitive sonar network in areas where boats and ships have disappeared. The problem, as always, is that all kinds of electronics fail at unusually high rates in those areas, especially during events of apparent importance.

There is also the fact that real submarine sonar is optimized to detect other submarines at extended ranges and enable a targeting solution precise enough to launch a torpedo at a comparatively large target, with the expectation that the torpedo will use active sonar to correct any small error.

That's a very different task from trying to detect swimmers at knife-fighting ranges. Sonar can handle the detection of biological entities at short ranges, as arrays on fishing ships show, but I'm not sure to what degree unmodified naval submarine sonar arrays are adaptable to such a task.

Also, aside from lwcamp's excellent suggestion to weaponize the sonar itself, I don't believe real-world submarines mount any weaponry capable of targeting stealthy swimmers that might only be detected at very close range.

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2) If overwhelming firepower is not enough defense, then forewarning and speed will be the best defense. They could also make changes into the subs to fire torpedos from the back so they can fight while they retreat
Forewarning will definitely be rare. After all, electronics, including their sonar, will be prone to anomalous readings, malfunctions and unexplained failures in the areas of ocean where hostile action can be expected. Enemy swimmers might successfully approach a submarine during periods of sonar malfunction, only being detected at very close range.

The overwhelming firepower is also problematic in that torpedos and missiles are disigned to destroy targets that are much larger than man-sized humanoids. And unlike tanks, submarines don't come with secondary or tertiary anti-personnel armament, at least none that works underwater.

If submarines have a target they can fire torpedos at, they don't need to withdraw. That kind of firepower will destroy any kind of craft used by the hostile underwater entities. The problem is that you can't fire torpedos at swimmers that surround a submarine. They are individually too small as targets and probably within the minimum range, anyway.

The submarines need some kind of anti-swimmer weapon systems. Sonar that can be weaponized might be the solution, but for times when the sonar malfunctions, some sort of redundancy woukd seem in order.

Maybe the ability to electrify the hull to prevent sabotage. Or underwater firearms mounted on the sub for self-defence.

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3) I think due to the small scale in which they would be employed, in house development + cavitating ammo would be the best bet. If not, then probably H&K. We do seem to not use/buy russian gear even when its the best option, so I think that would probably be off the table.
Cavitating ammunition seems promising. It would also work equally well in GPMGs mounted on submarines as it would for personalmweapons carried by GRUMEC divers.
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Old 05-22-2019, 06:45 AM   #125
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Default Re: Navy Submarines and the Invisible Residents

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Originally Posted by Icelander View Post
Sonar can handle the detection of biological entities at short ranges, as arrays on fishing ships show, but I'm not sure to what degree unmodified naval submarine sonar arrays are adaptable to such a task.
Presumably you're talking about the passive sonar? The hydrophones should work, but the signal processing will be optimised for mechanical, rather than biological, noises. That will reduce detection ranges, which will depend on how much noise the swimmers make. Submarines apparently routinely detect whales and the like, but the sonar team don't report them to the command unless there's some pressing reason to do so. Obviously, different signal-processing software could be written for the job, but I have no idea if the Brazilian Navy is set up to do that for themselves.
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. . . I don't believe real-world submarines mount any weaponry capable of targeting stealthy swimmers that might only be detected at very close range.
They could eject grenades through the signal launcher, decoy launchers, and trash ejector. They could also simply go "all ahead flank". A Type 209 can make 21+ knots underwater, and since they don't seem to use pump-jets, catching living creatures in the propeller suction should result in them being chopped pretty well. Of course, there are easy countermeasures for that.
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Maybe the ability to electrify the hull to prevent sabotage.
While completely immersed in a conducting fluid? Seawater is a reasonable conductor, and the charge will simply leak away through the water . . . and probably not preferentially through creatures adapted to life underwater.
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Or underwater firearms mounted on the sub for self-defence.
Given the lack of ability to aim, underwater claymores are more like it.
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Old 05-22-2019, 07:13 AM   #126
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Default Re: Navy Submarines and the Invisible Residents

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Originally Posted by johndallman View Post
Presumably you're talking about the passive sonar? The hydrophones should work, but the signal processing will be optimised for mechanical, rather than biological, noises. That will reduce detection ranges, which will depend on how much noise the swimmers make. Submarines apparently routinely detect whales and the like, but the sonar team don't report them to the command unless there's some pressing reason to do so. Obviously, different signal-processing software could be written for the job, but I have no idea if the Brazilian Navy is set up to do that for themselves.
Well, passive sonar is what would detect threats, but I also don't know how good the active sonar is at locking on man-sized swimmers at close range.

Pinging like mad might be fairly successful as an area denial weapon, but might not be feasible during diving operations. GRUMEC divers fall under the Submarine Command in the Brazilian Navy and apparently operate from submarines on occasion. In setting, it was during GRUMEC diving operations at the wreck of a civilian vessel that the Navy lost a submarine in 2009, it is believed to hostile action from the underwater entities.

I imagine that preventing such an event from repeating itself has driven quite a lot of quiet adjustment to Submarine Command vessels.

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They could eject grenades through the signal launcher, decoy launchers, and trash ejector.
In ten years, I expect that they might have developed purpose-designed anti-swimmer charges and/or micro-torpedos designed to target swimmers.

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They could also simply go "all ahead flank". A Type 209 can make 21+ knots underwater, and since they don't seem to use pump-jets, catching living creatures in the propeller suction should result in them being chopped pretty well. Of course, there are easy countermeasures for that.
While capable of full power maneuvers, the submarines are at much less danger from the mysterious swimmers. It's primarily while engaged in investigation, research or diving operations (generally aimed at gathering data on the Invisivle Residents) that the submarines need to defend the waters around them, instead of steaming away faster than swimmers can follow.

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Originally Posted by johndallman View Post
While completely immersed in a conducting fluid? Seawater is a reasonable conductor, and the charge will simply leak away through the water . . . and probably not preferentially through creatures adapted to life underwater.
Yes, that would probably be too much trouble for too little benefit.

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Given the lack of ability to aim, underwater claymores are more like it.
Underwater claymores sound lime a good idea.

As for aiming direct fire weapons, however, there are remotely controlled turrets for surface vehicles that seem like they could be adapted. They'd likely only be used during diving operations or similar situations where the submarine is acting as a mothership for smaller research craft underwater, so they could be extended from openings that were not needed during such operations.

Even with cavitating bullets, maximum range underwater is unlikely to reach even 100 meters, more probably half that, so there are probably sensors that could give enough resolution at those ranges for targeting purposes. Of course, aiming by composite sonar picture gathered by all arrays on board would probably be preferred, but a redundant secondary targeting sensor housed in the turret itself seems reasonable, given that there is a strong correlation between frequent equipment failures and hostile encounters.
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Old 05-22-2019, 07:56 AM   #127
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Default Re: Navy Submarines and the Invisible Residents

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Pinging like mad might be fairly successful as an area denial weapon, but might not be feasible during diving operations.
Probably not. Human divers have air spaces within them, which probably make them more vulnerable to sonar attacks.
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Originally Posted by Icelander View Post
It's primarily while engaged in investigation, research or diving operations (generally aimed at gathering data on the Invisible Residents) that the submarines need to defend the waters around them, instead of steaming away faster than swimmers can follow.
If you're doing that kind of operation, it's worth having lights and windows, and operating by vision if the water is clear enough. That implies some kind of secondary vehicle to be carried by the sub, with windows, lights and guns. It stays tethered to the sub so that the sub can steam away towing it, and is strong enough to serve as a refuge for the divers.
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As for aiming direct fire weapons, however, there are remotely controlled turrets for surface vehicles that seem like they could be adapted. They'd likely only be used during diving operations or similar situations where the submarine is acting as a mothership for smaller research craft underwater, so they could be extended from openings that were not needed during such operations.
Ok, when we've calmed the submariners down a bit . . . such existing turrets are extremely unlikely to be pressure-resistant to the sub's test depth. Some of their principles may be re-usable, but they're going to have to be a custom design, because nothing like this has been done for decades. It will be vastly preferable to not have them pressure-tight, and design them to operate flooded, strictly outside the pressure hull. That removes the possibility of damage when a gun round misfires or explodes breaching the pressure hull.

Submariners have very definite views about the integrity of the pressure hull, and really don't like having extra openings in it. They'll go to great lengths and costs to avoid that; their reasons are the history of sunken submarines, which usually kill everyone involved. The openings that exist are very simple, as small as possible and have very strong closures.

Turrets like this should go in the free-flooding spaces at bow and stern, or in the fin.
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Old 05-22-2019, 08:30 AM   #128
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Default Re: Navy Submarines and the Invisible Residents

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Originally Posted by johndallman View Post
Probably not. Human divers have air spaces within them, which probably make them more vulnerable to sonar attacks.
I expect so.

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Originally Posted by johndallman View Post
If you're doing that kind of operation, it's worth having lights and windows, and operating by vision if the water is clear enough. That implies some kind of secondary vehicle to be carried by the sub, with windows, lights and guns. It stays tethered to the sub so that the sub can steam away towing it, and is strong enough to serve as a refuge for the divers.
That's very true.

Do any such vehicles exist in the real world?

At least ones that could be modified by mounting weapons?

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Originally Posted by johndallman View Post
Ok, when we've calmed the submariners down a bit . . . such existing turrets are extremely unlikely to be pressure-resistant to the sub's test depth. Some of their principles may be re-usable, but they're going to have to be a custom design, because nothing like this has been done for decades. It will be vastly preferable to not have them pressure-tight, and design them to operate flooded, strictly outside the pressure hull. That removes the possibility of damage when a gun round misfires or explodes breaching the pressure hull.
To be sure, unmodified turrets would not work underwater. Flooded operation sounds interesting.

I'm not sure such turrets need to be able to operate at the depths that submarines can. For one thing, they are unlikely to be more effective than saturation with active sonar and/or depth charges launched through torpedo tubes, so they'd mostly be needed during diving operations, i.e. when friendly troops or drones are in the water. For another, I think that even purpose-designed underwater weapons suffer range reductions with depth and strongly suspect that below typical diving depths, no existing projectile technology (other than torpedos) would have ranges beyond a few meters.

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Originally Posted by johndallman View Post
Submariners have very definite views about the integrity of the pressure hull, and really don't like having extra openings in it. They'll go to great lengths and costs to avoid that; their reasons are the history of sunken submarines, which usually kill everyone involved. The openings that exist are very simple, as small as possible and have very strong closures.

Turrets like this should go in the free-flooding spaces at bow and stern, or in the fin.
I don't know what kind of SDVs the Brazilian Navy has or how they are launched, but I know that US SSKs designed for NAVSPECWAR support can launch SDVs from torpedo tubes. Also, I seem to recall various remote-controlled sensor platforms or research craft that can similarly be launched by submarines, while still remaining attached through control wires.

During diving operations, it would seem desirable to be able to launch some kind of weapon platform in a similar manner, to provide security for the divers and the submarine, as it would have tombe immobile until the divers are recovered.
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Old 05-22-2019, 08:35 AM   #129
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Default Re: Navy Submarines and the Invisible Residents

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While completely immersed in a conducting fluid? Seawater is a reasonable conductor, and the charge will simply leak away through the water . . . and probably not preferentially through creatures adapted to life underwater.
Various electric fish will use electric discharges for defense and capturing prey. The electric rays of the Torpedo genus (really) are probably the best example, capable of giving dangerous jolts in their natural habitat of sea water.

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Old 05-22-2019, 08:37 AM   #130
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Default Navy Submarines and the Invisible Residents

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My understanding is that active sonar is enough of a danger that the U.S. Navy doesn't use it when divers are in the water. This is one of those areas where more data would be helpful. Nonetheless (https://en.wikipedia.org/wiki/Sonic_weapon)

- and military sonars get up to about 235 dB, around 100,000 times higher intensity than the threshold for injury.

The higher the frequency of the sonar beam, the farther away it can be focused, so early uses of weaponized sonar might just use the standard sonar array. Once it was found to be effective, it would be modified as a weapon to produce higher power higher frequency beams.
What kind of stats are we talking here?

Are we talking some kind of directional wave area of effect?

What skill would one use to target it and how difficult would it be to catch a man-sized target in it?

What kind of range and damage might a fairly regular SSK sonar array be capable of?

What about a smaller array that might be mounted below a PCs' yacht for self-defence purposes in waters with an ultraterrestial presence?

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Originally Posted by lwcamp View Post
And just to be complete, there is a second method of injury from sonar. If the intensity gets high enough, the low pressure phase of the wave will fall to below the vapor pressure of water and the water will "boil". This produces a cavitation bubble, that collapses during the high pressure cycle of the wave. Collapsing cavitation bubbles can cause significant material damage, such as damaging steel propellers, and mantis shrimp are known to weaponize cavitation bubbles to aid with cracking hard-shelled prey items (in this case generated by impact rather than by a sonar wave). You don't want cavitation while your sonar beam is propagating through water (this would scatter the sound waves and ruin the beam), but if it occurs at your target the effects could be messy. This can be achieved since the amplitude of the pressure waves will increase when the wave reflects off the target, and if the beam is focused from a wide array where it is generated to a smaller spot at the target.

Luke
Would this represent smaller AoE and higher damage?

How would you model this in game terms?
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