About TDS

[Javier L.]

What is the difference (damage effects) of torpedo hit on the side of a battleship with the wing tanks full or empty? Does the liquid (fuel-water) give additional protection to the bulkhead behind or it just does not matter at all? And, if instead of liquid there is solid coal in the wing tanks like in the old steaming battleships? Thank you.

[George Elder]

Some navies prefered an outboard void, and then one or more inboard liquid loaded layeres (seperated by longitudinal bulkheads) that were placed before the primary torpedo bulkhead. In most cases, the inner-most layer was liquid loaded. The general idea was that the outboard void would absorb some of the initial explosion energy as it was destroyed, while the inboard layers (kept about 90-95% full) would distribute the blast's force via using the means of liquid's basic incompressibility. In other words, as the outter bulkhead of the liquid layer was deformed, the liquid within would be pushed (hate the word) against the inner bulkhead of the layer -- thus distributing the shock load over a great surface area. Of course, the inner bulkhead of one layer consitutues the outer bulkhead of the next inboard bulkhead, and so the process is repeated untill the main torpedo bulkhead is encountered by much dissipated and distributed energy.
Well, not everyone liked this idea. The US vascilated, and went from a void outboard layer to a libquid filled outboard. It also went from a liquid filled inner layer, to a void inner layer. Some of these changes were the result of failed TDS tests, and others was the result of ongoing caisson tests. The Japanese eschewed liquid loading altogether, and used a very large series of outboard void sections -- perhaps reasoning in part that such a system accorded them great counterflooding possibilities. The Italians uses geometry and collapsable internal cylinders. But overall, most torpedo systems didn't live up to expectations, and factors such as subdivision, GM, and weight ballances played critical roles in allowing ships to survive underwater blasts.
As for coal, it could absord splinter and energy well enough, and had some other advantages. But coal cannot be an ideal fuel because per unit of weight it does not generate as much energy as does oil, IIRC. Moreover, one cannot replace coal with water or other fluids very easily, and thus as fuel is consumed the torpedo protection value errodes. Well, this is a far more complex subject than this review can hope to cover -- but this is a start.

George

[Dave Saxton]

When HMS Prince Of Wales was sunk on Dec 10, 1941 the starboard voids were all flooded in compensation to the heavy list to port. Four torpedos later struck the starboard side. The British determined the effects of the later torpedos extended much deeper into the ship, because the TDS on the starboard side, was essentially fully liquid loaded. The British remained of the opinion that outboard void spaces were essential to the full functionality of a TDS. Basic physics would seem to bolster their views.

According to basic physics, shock waves have many aspecs, but there are two primary componants. One is a compression wave. Liquid loads, being incompressable, do nothing to reduce the energy of the compression componant, although as George has detailed, they can distribute this energy over a large area. Actually, the liquid transports the energy from one point to the next rather well. However, according to the inverse square law, a void would help to greatly reduce the energy of the compression wave componant. The inverse square law basically means, that as the relative distance is doubled, the amount of energy reduction is squared. Nonetheless, another highly destructive element of a shock wave, is ofton called a shear wave.

Shear waves can not travel through a liquid. Thus a liquid load can perform a valuable function, beyond serving as a transmitter of energy over a larger area, or representing a large mass that can be displaced. The liquid load also insulates the inner structure from the shear wave aspect.

[marty1]

The inverse square law basically means, that as the relative distance is doubled, the amount of energy reduction is squared. Nonetheless, another highly destructive element of a shock wave, is ofton called a shear wave.

Agree. In my profesion we sometimes refer to this as attenuation. It is used to explain why ground motion from say an earthquake with an epicenter near San Francisco is felt only mildly in say Los Angles and perhaps not at all in San Diego.

[George Elder]

So the question arrises, why did the US opt to employ liquid loading in the outboard chambers in some designs?

George

[Dave Saxton]

Probably to provide a place for the oil to go, once the inboard bulk head of the oil tanks rupture. Thus the main bulk head doesn't have to shoulder the full hydralic force of the liquid load. If the main bulkhead is being ruptured locally, or the connections broken, by the remaining force, this may help. The overall energy reduction effect of a void, should be more or less the same, inboard or outboard. Of course the concept of distributing the remaining load over a wider area, to a deformable structure, is partially lost. Particulary, were the main steel structure in the zone is rather too rigid. The British in the KGV class were not fully employing the concept of deforming a steel structure (or even employing an stout armored bulkhead at some point) to absorb much of the energy either.

As I understand it, in the British sytem, the liquid load was in the center, with small voids outboard and inboard, of the liquid load. They sometimes called it the "liquid sandwich." This allowed the load a place to go before encountering the the main bulkhead, and the displacement of the liquid load may use up some of the energy. One potential problem here, is that the fuel oil hydrocarbons could be forced into the inboard void so violently, that they become, in effect a fuel air explosive.

This leads me to think of one potential problem involving coal bunkers. Coal gives off methane gas in small amounts, and powdered coal can be highly explosive.

[ontheslipway]

One is a compression wave. Liquid loads, being incompressable, do nothing to reduce the energy of the compression componant, although as George has detailed, they can distribute this energy over a large area

Liquids are compressible, otherwise you wouldn't have the shock wave in the first place, but will transfer the force of an explosion without an empty space. Without it I can image that outer hull has nearly no function whatsoever as far as the TDS is concerned. An empty space followed by filled region may just function as a bit of mass stopping the re-entrant jet of the underwater explosion by distributing it through the liquid and hence spread the force over a larger plate area that will hopefully hold. This jet is very focussed and I highly doubt that any inverse square relation is valid, more a 1:1 relation. All conjecture here of course.

[George Elder]

Perhaps a dedicated and in-depth search into this area may prove of interest to you. There has been much written about it to study.

George

[marty1]

I have a question. I am not any sort of a Torpedo expert. Having said that I have on occasion seen line drawings of various torpedoes indicating the explosive head – at least in some of these beasts – are shaped charges. Was this a typical warhead arrangement for torpedoes, or was the explosive head functioning in a manner more akin to HESH?

[Tiornu]

No. The hydrodynamics involved in a torpedo explosion do not lend themselves readily to parallels with explosions in an air environment.

[marty1]

I don’t get it. A shaped charge will function underwater as will HESH. So you are saying there were no shaped charge torpedoes, or torpedoes didn’t function like HESH? Or both?

I guess what I am asking is how does the warhead in a torpedo do its dirty work against a ships armor plating? Perhaps a suggested reference would help me -- Torpedoes for Dummies.

[ontheslipway]

Here you go:

http://www.eng.nus.edu.sg/EResnews/0306/rd/rd_12.html

The fountains you see after a miss of a bomb are directed towards the surface. If your ship is near, it will attract the jet as sketched in the link and focus most of the energy to the outer hull. And you cannot adequately protect yourself against this jet. This is why you need room for the jet to expand, place a few obstacles etcetera. This is why a near miss of a bomb was proven to be more damaging that some direct hits.

[Tiornu]

"I guess what I am asking is how does the warhead in a torpedo do its dirty work against a ships armor plating?"
It doesn't. A torpedo is designed to get under the armor.

[marty1]

Thanks Foeth. Very helpful. Any thoughts than on why torpedoes with shaped charges would have been constructed?

[marty1]

"I guess what I am asking is how does the warhead in a torpedo do its dirty work against a ships armor plating?"
It doesn't. A torpedo is designed to get under the armor.

Thanks Tiornu -- that was of absolutely no help at all