A small electrically-powered sub-surface decoy craft that leads a grain ship through suspected marine minefields. Powered by a cable of some length from the bow of the grain ship, this shallow decoy simulates the electromagnetic signature of a vessel. Steerable, it also senses and reports the presence of mines and the info can be used to alter the course of the grain ship before proximity would set it or the decoy off. Sacrificial in some cases by accident or intention, these units are cheap enough to equip a grain ship with a half dozen in launchers at the bow. Would a quarter mile lead be sufficient for non-nuclear mines? Some units could be rigged with explosives and act as a defensive measure if approached with bad intentions. Also good for pirates.
-- minoradjustments, Jul 25 2023

Electrical Characteristics of a Seawater MHD Thruster https://apps.dtic.m...citations/ADA224508
Looking for speed/thrust data for silent NAGS... [minoradjustments, Aug 08 2023]

[Can't read it. Restricted to subscribers. 20 years old, anyway.] I propose a fully modern sub-surface decoy with all the latest jazzy fly crap they've developed since 2003. Not dropped like a sonde from the air. Not towed or launched off the deck. This one swims out in front of the ship on a powered tether and has its own propulsion and steering.
-- minoradjustments, Jul 25 2023


Well, here's an idea: have the Navy make a civilian certified version of this available at a reasonable cost. It would of course be incompatible with any mines that the Navy would choose to deploy. This idea would of course be rejected by the Navy because then their foes could easily get units to test against their mines. But if they did, there could be a nice programming battle of software updates... And of course make them explosively tamper resistant.

I actually like [minoradjustements]' suggestion of running this on a powered tether. A wireless version is of course nice when cost is no object for the Navy, but for the purpose suggested above, having it on a tether means it doesn't need to be refueled when traveling long distances. With the right tether system, the tether could also be used to deploy and retrieve the unit over the rail using a winch, making this an easier retrofit on many types of ship.

And while we're at it, this can probably also be used to watch out for sand bars and icebergs.
-- scad mientist, Jul 25 2023


Yes, the tether is the thing for the NAGS. No need for onboard propulsive power, or transmitters that break the surface, specialized sensors, or big explosive charges. Just the hardware head end of a smart software suite. Support for sensors, power, and sonar (active and passive), and the EM and decoy sonar gear is in unlimited supply from the ship. Command remains live and uninterrupted from the ship, where the major software and hardware reside. Deploying it over the bow and running it like a UAV recon drone has the advantage of easy retrieval and low losses. Free-swimming drones, like UAVs, are lost in huge numbers. If the NAGS senses a mine 1/4 mile ahead and doesn't set it off, the ship has a chance to avoid it. Most naval anti-mine systems measure their effectiveness on how many get blown up with with the mine they found. Loss/loss. The NAGS develops intelligence and survives. If it does sense a mine and the EM pulse doesn't set it off at a distance, it can be sent in as a kamikaze if the seaway is too narrow. You could run 2 or 3 at the same time if needed. Think of a kite compared to a UAV drone. Both can carry cameras, bombs, etc. but you are much more likely to be able to re-use the kite or NAGS device. And training would be a snap for merchant seamen with no combat experience or training; every one of them, as is WKTE, has played Call of Duty or Flight Simulator. Easy peasy.
-- minoradjustments, Jul 25 2023


Think of it as colonoscopy for the Black Sea.
-- minoradjustments, Jul 25 2023


OK, now I can't unthink that.
-- pertinax, Jul 26 2023


Not so great against plastic explosive mines.
-- mylodon, Jul 26 2023


//Not so great against plastic explosive mines.//

Got SONAR! If any device can sense a plastic mine, so can the NAGS. Also mimics acoustic signature of monster, sub-killing assault vessel to scare off the small fry, if needed. Can play Dark Side of the Moon, if needed.
-- minoradjustments, Jul 26 2023


Croissant for the colonoscopic summary
-- calum, Jul 26 2023


Found some interesting data about the use of magnetohydrodynamic thrusters for marine use. Generally touted as being an efficiency boost in conjunction with standard diesel power, in the NAGS it would be the only thrust provider. Not used for marine drones because of the monstrous power consumption, the NAGS is powered by a cable from the mother ship. Power is not a problem. This would be true silent running 1/4 mile + out ahead of the grain ship.
-- minoradjustments, Aug 08 2023



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