Why can’t a naval ship have chains extended on sides to keep torpedos from reach it?

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I’ve always thought a navy ship could have arms extending from each side, out say 20′ or so that holds some sort of draping system, like a chain or something, that extends below the bottom of the hull. Then, if a sub fired a torpedo at it, it would either explose on the chain or just get caught up in it.

In: 3375

Because it would reduce the hydrodynamic shape of the ship, add weight, potentially destabilize the ship and a torpedo could just push past the chain?

Its called a [torpedo net](https://en.wikipedia.org/wiki/Torpedo_net) and it was a thing, but only when ships are in port or otherwise not moving. You could either put a big thick net across the harbor or [around a specific ship](https://maritime.org/doc/netsandbooms/img/pg064.jpg)

The nets provide a significant increase in drag so they’re no good when underway, they’ll slow a ship wayyyy down and it’ll burn way more fuel attempting to drag them around and it makes the ship way more vulnerable to anything that isn’t a torpedo

The mobile version is a torpedo bulge which is a big blister on the side of the hull with layers of air/water/oil to dissipate the blast before it damages the core hull of the ship. This has a pretty minimal impact on overall speed and weight if designed in from the start, and could also be retrofitted onto existing ships

Torpedoes arm at a X distance. Not necessarily on impact. The explosion regardless would still do damage through the bubble created. Look at how a torpedo kills a ship video.

This is indeed what they used to do. In late 19th, early 20th century warship photos you can see [collapsed poles along the side of the ship](https://www.internetmodeler.com/2003/august/ships/HP_Dreadnought_02.JPG), and on top is bundled netting. When [deployed, it looked like this.](https://external-preview.redd.it/eX80qA3sNKrYpJmEISQweDV-pjQwJjD7XTjmHYqQTBM.jpg?auto=webp&s=77c34aa6495aeac8a5fcd98e8f9892ecc78b69b2)

The problem is, you can’t use torpedo nets while you’re underway, and typically, your ships don’t get attacked by torpedos when you’re in harbor – shallow enclosed waters are not fun to be a submariner in if you get discovered – you get attacked by torpedoes when you’re at sea and underway.

So torpedo nets were done away with largely by WWII and replaced with anti-torpedo bulges – these were a sacrificial fake outer hull, itself compartmentalized to minimize damage and water intake, that would force the torpedo to detonate outside of the main hull of the ship.

We’ve done away with even that because torpedos now are way more effective. Instead of trying to blast a hole in the side of the ship – which because of compartmentalization and damage control can be easily mitigated and would rarely immobilize a ship – they now are designed to detonate underneath the keel or bottom spine of the ship, breaking it in two essentially, buckling the hull and making so many tears and burst seams that saving the ship is impossible.

edit: keel not keep. damn autocorrect.

Some torpedoes like the mk 48 can travel under the ship and use the explosion and water expansion to break the keel. Causes a lot of damage that is on the bottom well below the waterline and will cause them to sink very quickly.

But how about networked underwater drones, to intercept the torpedos?

US Navy ships have a device called a Nixie which can be deployed behind the ship to attempt to draw torpedoes to it rather than the ship.

That’s kind of what DARPA is trying to do for vehicles with its iron curtain experiment. It’s an extendable plate that lowers and cuts projectiles in half before they hit the armor.

Modern torpedos often don’t actually strike the hull of the ship. They well detonate a short distance below the hull to create a cavity/vacuum that will break the keel of the ship. The chains or curtain, which I think is a good idea, would have to extend pretty far down and they would have to be sufficiently heavy and secure as the torpedos might not detonate on impact

They did! It was called a torpedo belt, but bulge armor was more common. In reality, there was only so much you could do to avoid getting hit by a torpedo, especially since a submarine could fire one at you from any direction and impact you just about anywhere on the parts of the ship exposed to water.

So it was said in older posts but I’ve got a bit of experience with this and want to add some things,

With modern torpedos, a net isn’t going to stop them, nor will a chain. Furthermore, with Submarines in your area, having a chain clanking around while you’re trying to avoid them would do the exact opposite- like screaming while playing hide and seek. There are countermeasures like anti-torpedo-torpedos and jammers, but really the best way to avoid getting hit by one is to be vigilant. Most countries use a combination of shipboard sensors and submarine hunting helicopters that go out a distance and use what’s called “dipping sonar” or they use planes to drop “sonar bouy” fields to find and sink enemy submarines in the areas near the ship first, or at least track them and make it so that if they did shoot, they’d be dead before their torpedo hit. Not to mention if it’s something like a convoy of ships, they probably have a submarine with them to defend against other submarines, along with helicopters, planes, towed sonar arrays, and intelligence that tells them if there are subs in the area before they even get there.

Torpedos aren’t the problem: anti-ship cruise missiles launched from a continent away are the problem.

The first problem is that the drag it would produce would be immense and slow the ships by 10 kts. Second off it wouldn’t be effective. You see, torpedos are typically designed to do just that, explode below the ship creating a huge bubble under it removing the buoyant force, causing a destructive bending moment on the keel, and the ship breaks in half under its own weight. The optimum torpedo shot “breaks the ship’s back”. By dragging chains beneath the keel, you are improving the enemy torpedo’s accuracy and effectiveness.

The submarine will just get toasted crowd is overstating things a bit. Subs still represent the most lethal and likely threat from a country like Iran using them against the US Navy. It’s a safe bet that any carrier fleet has anti sub submarines in the area and they are definitely establishing a sub free zone around the carrier using helos and picket ships. Picking off escorts or sinking random ships away from the carrier protection is definitely a threat from modern diesel electric subs.

These days, some warships have what’s called a NIXIE system. They have like a 1000-foot cable sticking out the back of the ship when they feel like torpedos are a potential threat, and at the end of the cable is an emitter that simulates a ship’s propeller noise. Basically it makes torpedos think that the ship is faaaar bigger than it is, and so the torpedo aims for the middle of the “ship” and just detonates hundreds of feet away from the actual ship.

Not quite chains sticking out, not quite nets, and not quite poles, but it works.

[https://en.wikipedia.org/wiki/AN/SLQ-25_Nixie](https://en.wikipedia.org/wiki/AN/SLQ-25_Nixie)

Modern torpedoes don’t detonate from contact. They actually detonate below the target creating a massive bubble and vacancy in the water. This essentially snaps the ship. I served on a submarine for years.

Torpedoes work by detonating underneath the ship creating an air bubble. This air bubble then presses up against the keel of the ship breaking it.

Because it would slow the ship down so much that it would be a sitting duck, including to a sub firing multiple torpedoes in a row at the same spot.

Could you imagine the drag??