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BoraTas

Junior Member
Registered Member
There is nothing stopping you from building a large conventional submarine, but that statement ignores the fundamental trade-off you face when you have a limited amount of horsepower to work with. A nuclear reactor gives you a far more powerful and sustained propulsion, so the nuclear submarine is better placed to be built larger, and still not sacrifice too much in other areas. You can conceivably make a conventional submarine very large, but probably can't stay submerged for very long (or it will run out of power), and can't move very fast. There is a trade-off to be made between size and other functions for the same average level of horsepower, and my point is that the nuclear sub is much better suited to make that trade-off.

There is a good reason why most nuclear submarines are built to be quite large compared to diesel subs, and, as I said, my observations are general. I don't understand why you are bringing up Russian seismic survey subs, and extremely small outlier nuclear subs, as counters to my general statements about naval submarines. They seem irrelevant to be honest.

Because the nuclear sub can make the trade-off between size and firepower very easily, it can carry a large load of weapons, including 8 or more VLS cells for 32+ cruise missiles. A conventional sub can absolutely do the same, but it has to sacrifice a lot to do so, and that is why the conventional subs are generally not designed that way. Your point about hotel load is obviosly correct, and again this illustrates what you can do with the sustained power output from a nuclear reactor.

You can also put nuclear ballistic missiles on a conventional sub if you want to, for nuclear deterrence purposes, and use that as an example to nit pick at the claim that nuclear subs are better suited for strategic deterrence. There's nothing stopping you, and the North Koreans have done exactly that with the Sinpo class. But that is honestly a bad argument.

Likewise, an implicit point of mine that you have missed is that having greater horsepower in fact allow you to construct the submarine in a way that allows for a deeper dive, with the nuclear submarine again being favoured. The Soviet Sierra II class SSN is built out of titanium, and the Yasen M class is also rumoured to be built of titanium (nobody knows for sure), which not only reduces their magnetic signature, but also allows for a deeper dive depth. If you want to build a conventional submarine to withstand a greater depth, that is totally your choice, but you will be facing much greater constraints and sacrifices to be made.

On AIP - I am adding AIP into the comparison only to make the comparison more balanced, because I am comparing a modern design feature to other modern designs. I just don't want people to zero in on a conventional sub without AIP, and use it to overstate the advantages of a nuclear sub. I am not talking about the cutting edge designs, but I can certainly tell these to you. There are subs without AIP that can actually submerge for longer, given the same power consumption from hotel load and speed. This includes the Japanese Taigei class with lithium ion batteries, that are so good that they have decided to ditch the AIP altogether. Again, adding AIP into the comparison is only to make the comparison more balanced.

I feel you have picked away at certain general claims (e.g. nuclear submarines are larger and can carry more weapons) while ignoring the fundamental reasons why this is true for most cases (nuclear subs have more sustained horsepower than conventional subs, so can afford to be large). My claims are not always true, but there are enough incentives related to engineering and physics that they hold true most of the time. So I will stand by all my statements.
The problem is not limited horsepower. A diesel engine has a higher power density than a nuclear reactor-steam turbine combo. The reactor, steam turbine, shielding, and supporting machinery are estimated to weigh around 1050 tons in the Borei class. (
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) That brings 50k horsepower to the shaft. That is less power density than a low-speed diesel. A nuclear reactor holds no inherent advantage in enabling a deeper dive or higher max speed. In fact, it can be considered detrimental because the extra weight it adds has to be compensated by more volume to keep the reserve buoyancy the same. The problem is how much usable energy you can store in a submarine. That is where nuclear sub shines. High-speed endurance is about stored energy. The comparison of nuclear submarines and conventional ones is a comparison of propulsion systems. Looking at general characteristics is wrong because they are the results of multiple things. Great powers have switched to SSNs because they need open ocean capabilities. This left conventional subs to smaller powers or great powers who needs to defend their shores. That is what led to the current small conventional sub, big nuclear sub paradigm.
The Japanese have switched the lithium-ion because their intent is to use the Taigei class in open oceans and distant areas. For that you need a lot of diesel fuel and good high-speed submerged endurance. Lithium-ion batteries improve the high-speed endurance of a conventional sub by multiple times. And they are rechargeable unlike the AIP system. Diesel fuel is still the densest way of storing more energy in a conventional sub. The low and medium speed patrol endurance of a non-AIP lithium-ion sub would be lower than an AIP sub. Japan is an oddball because of its laws. Other AIP producers are going to use lithium-ion batteries in addition to AIP, it makes more sense.
 

blindsight

Junior Member
Registered Member
The problem is not limited horsepower. A diesel engine has a higher power density than a nuclear reactor-steam turbine combo. The reactor, steam turbine, shielding, and supporting machinery are estimated to weigh around 1050 tons in the Borei class. (
Please, Log in or Register to view URLs content!
) That brings 50k horsepower to the shaft. That is less power density than a low-speed diesel. A nuclear reactor holds no inherent advantage in enabling a deeper dive or higher max speed. In fact, it can be considered detrimental because the extra weight it adds has to be compensated by more volume to keep the reserve buoyancy the same. The problem is how much usable energy you can store in a submarine. That is where nuclear sub shines. High-speed endurance is about stored energy. The comparison of nuclear submarines and conventional ones is a comparison of propulsion systems. Looking at general characteristics is wrong because they are the results of multiple things. Great powers have switched to SSNs because they need open ocean capabilities. This left conventional subs to smaller powers or great powers who needs to defend their shores. That is what led to the current small conventional sub, big nuclear sub paradigm.
The Japanese have switched the lithium-ion because their intent is to use the Taigei class in open oceans and distant areas. For that you need a lot of diesel fuel and good high-speed submerged endurance. Lithium-ion batteries improve the high-speed endurance of a conventional sub by multiple times. And they are rechargeable unlike the AIP system. Diesel fuel is still the densest way of storing more energy in a conventional sub. The low and medium speed patrol endurance of a non-AIP lithium-ion sub would be lower than an AIP sub. Japan is an oddball because of its laws. Other AIP producers are going to use lithium-ion batteries in addition to AIP, it makes more sense.

I vote for SMR + Li-ion batteries
 

gelgoog

Captain
Registered Member
The problem is not limited horsepower. A diesel engine has a higher power density than a nuclear reactor-steam turbine combo. The reactor, steam turbine, shielding, and supporting machinery are estimated to weigh around 1050 tons in the Borei class. (
Please, Log in or Register to view URLs content!
) That brings 50k horsepower to the shaft. That is less power density than a low-speed diesel.

Only if you ignore the weight and volume of the fuel. You also need lots of batteries.

A nuclear reactor holds no inherent advantage in enabling a deeper dive or higher max speed. In fact, it can be considered detrimental because the extra weight it adds has to be compensated by more volume to keep the reserve buoyancy the same. The problem is how much usable energy you can store in a submarine. That is where nuclear sub shines. High-speed endurance is about stored energy.

Exactly, a conventional submarine can't keep going at high speed for a considerable amount of time. That is particularly problematic for long distance patrols. Nuclear fuel is also like a million times more dense per unit of mass than diesel. And you can't operate the diesel engines unless you are surfaced or snorkeling at low speeds.

The comparison of nuclear submarines and conventional ones is a comparison of propulsion systems. Looking at general characteristics is wrong because they are the results of multiple things. Great powers have switched to SSNs because they need open ocean capabilities. This left conventional subs to smaller powers or great powers who needs to defend their shores. That is what led to the current small conventional sub, big nuclear sub paradigm.
The Japanese have switched the lithium-ion because their intent is to use the Taigei class in open oceans and distant areas. For that you need a lot of diesel fuel and good high-speed submerged endurance. Lithium-ion batteries improve the high-speed endurance of a conventional sub by multiple times. And they are rechargeable unlike the AIP system. Diesel fuel is still the densest way of storing more energy in a conventional sub. The low and medium speed patrol endurance of a non-AIP lithium-ion sub would be lower than an AIP sub. Japan is an oddball because of its laws. Other AIP producers are going to use lithium-ion batteries in addition to AIP, it makes more sense.

Japan had the Stirling engine technology in the Soryu and it has enough industrial expertise to make hydrogen fuel cells for a submarine if they wanted to. Honda and Toyota for example have worked on hydrogen fuel cells for at least some two decades. Yet they choose not to. I would ignore Japan's laws as limitations at this point. The Japanese Constitution has been changed significantly enough it doesn't impose much of a limitation anymore as you can see with the Japanese Navy now being able to operate carriers.
 

Dante80

Junior Member
Registered Member
Mock up in the desert for DF-21s
The article you posted is about an AWACS airplane contract. What does it have to do with -presumably navy ships?- mockups for DF-21 "testing"?

You probably wanted to link a different article.
 

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