Mercury in submarine list and trim systems

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mahla

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Hi all,


I'm researching the use of mercury in submarine trim and list systems and have found references in older manuals (e.g., NAVSEA 0905-LP-120-0010 for DSRV) showing how mercury was transferred between tanks to manage longitudinal and lateral balance. It seems this method relied on high fluid density to minimize transfer volume.


My core question is:


Is mercury still used in modern submarine trim or list systems?
  • If yes, which classes or navies still use it, and under what conditions?
  • If not, when and why was it phased out? Was it mainly due to environmental or operational risks?
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Any references to declassified documents, historical trends, or personal experience would be very helpful.


Thanks in advance for sharing your insights!


Best regards,
Mahla M
 
Well, that would be most entertaining and might explain the behaviour of the ex-submariners I've worked with over the years.

I can't really imagine a more horrid fluid to work with. At least liquid sodium solidified.

If such a system was in use, wouldn't a heavy brine be a more practical prospect?
 
1635yankee said:
I would doubt it's used in US submarines: even mercury thermometers are forbidden in EB's yard in Groton.
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Yeah, I'd just point out that OPs original post isn't technically about submarines but "submersibles." (DSRVs.)

I could see potential in a use case like that, where tank volume is severely limited. I've never heard of it used in a full-sized actual submarine. Aside from simple health and safety issues (which we admittedly know more about now) it wouldn't make financial sense when you're less limited on tank space and can use seawater instead of (much more expensive) mercury.
 
As far as I know, mercury was only used for the trim tanks on the DSRVs, for both pitch trim and roll trim.

We used seawater on the Ohios, and stories even in WW2 have the diesel subs using seawater as well.
 
Mercury as a working fluid would only really make sense for a submersible. For a submarine, water is preferable as it is non-toxic and can be exchanged with other seawater systems and with the sea. Mercury's toxicity would be a huge problem in the closed atmosphere of a submarine. The sodium reactor developed for the Seawolf initially used mercury as an intermediary fluid between the sodium coolant in the primary loop and water in the secondary loop. The S1G land-based prototype did use mercury, but the S2G reactor installed on the Seawolf used NaK as an intermediary fluid because of mercury's toxicity.

Even for deep-diving submarines, such as the Dolphin and NR-1, water was used (freshwater in the case of the NR-1).
 
CJGibson said:
Well, that would be most entertaining and might explain the behaviour of the ex-submariners I've worked with over the years.

I can't really imagine a more horrid fluid to work with. At least liquid sodium solidified.

If such a system was in use, wouldn't a heavy brine be a more practical prospect?
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but the trim tank is a close loop.i think in high depth submersible is used.
 
tychosis said:
Yeah, I'd just point out that OPs original post isn't technically about submarines but "submersibles." (DSRVs.)

I could see potential in a use case like that, where tank volume is severely limited. I've never heard of it used in a full-sized actual submarine. Aside from simple health and safety issues (which we admittedly know more about now) it wouldn't make financial sense when you're less limited on tank space and can use seawater instead of (much more expensive) mercury.
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es, I'm working on a submersible and a high-depth submersible. Is there any reference that shows the use of mercury in the trim system of submersibles? Or any standard that prohibits the use of mercury?
 
Scott Kenny said:
As far as I know, mercury was only used for the trim tanks on the DSRVs, for both pitch trim and roll trim.

We used seawater on the Ohios, and stories even in WW2 have the diesel subs using seawater as well.
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i'm working on rescue submarine like submersible.
 
do you have
barrett said:
The trim adjusters and heel adjusters on the DSV Shinkai 6500 use mercury.
The use of mercury has been banned since 2017 and therefore cannot be used in newly manufactured submersibles.
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Is there any document that I can cite and tell our boss that mercury cannot be used?
 
mahla said:
Is there any document that I can cite and tell our boss that mercury cannot be used?
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I'd strongly recommend you consult the relevant standards and design guidance from your certification authority, not some people on an internet forum.
 
If mercury isn't an option, I'd look at various low melting point alloys. Supposedly, there's one that melts at 40degF, 4degC, but the site I found doesn't name it. Deep ocean seawater is basically 40degF, and running the electronics-cooling water through the trim tanks should help keep the metal fluid.
 
Scott Kenny said:
If mercury isn't an option, I'd look at various low melting point alloys. Supposedly, there's one that melts at 40degF, 4degC, but the site I found doesn't name it. Deep ocean seawater is basically 40degF, and running the electronics-cooling water through the trim tanks should help keep the metal fluid.
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Balls.

No seriously, there have been systems study that use a continuous loop of balls. Something like solid tungsten in one part of the loop, and something low-density in the other part of the loop. You can then move them around the loop with something like a worm gear to get the desired adjustment to your centre of gravity.
 
Surely a suspension or slurry would work as well as a liquid. It only needs to be pumpable.
 
Yellow Palace said:
Balls.

No seriously, there have been systems study that use a continuous loop of balls. Something like solid tungsten in one part of the loop, and something low-density in the other part of the loop. You can then move them around the loop with something like a worm gear to get the desired adjustment to your centre of gravity.
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can i see this method?
 
OliverSedlacek said:
Surely a suspension or slurry would work as well as a liquid. It only needs to be pumpable.
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The problem is the amount of wear that a suspension or slurry would cause to the pump and any/all seals in the system.

Mercury pumps very nicely.



Yellow Palace said:
Balls.

No seriously, there have been systems study that use a continuous loop of balls. Something like solid tungsten in one part of the loop, and something low-density in the other part of the loop. You can then move them around the loop with something like a worm gear to get the desired adjustment to your centre of gravity.
Click to expand...
Yeah, I can see how that'd work. You wouldn't even need a worm gear, a normal ring gear would be just fine. If the ballast balls are massive enough relative to your DSRV, when at sea the DSRV basically rotates around the ballast ring!
 
I like the balls too. I've been mulling over what to use as a high density filler in a suspension and even stainless steel would do. If the particles are reasonably spherical and smooth then the pump wear should be manageable. It's not as if the pressures are high, so the sealing requirements are quite modest.
 

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