It was the Spanish S80 and it's problems were due to a calculation error.
With all marine platforms weight distribution is critical, not just the mass of an item but where it is located, its even more important on submarines as they need to adjust their buoyancy to dive, surface, change depth etc. even firing torpedoes requires weight compensation through the use of specific ballast tanks.
Nuclear boats are quite difficult to design as they have a concentrated, indivisible mass, i.e. the reactor section. It just is, it weights what it weighs and pretty much everything else has to be arranged around it to maintain stability.
On a diesel boat the only thing that is fixed is the main motor, although even that can be adjusted using different length shafts in design phase. Diesel generators can be arranged in different ways, their numbers can be changed i.e. Collins have three abreast while I believe Scorpien has two rows of two smaller diesels.
Then there is the factor of energy storage, nucs its the reactor producing steam (or whatever) to drive a turbine, conventional its diesels burning hydrocarbons to generate electricity which is stored in batteries for submerged operations. This means a conventional sub has massive amounts of easily divisible mass that can be distributed around the hull to maintain stability.
In many ways its much easier to adjust and fine tune a conventional than a nuc.
With all marine platforms weight distribution is critical, not just the mass of an item but where it is located, its even more important on submarines as they need to adjust their buoyancy to dive, surface, change depth etc. even firing torpedoes requires weight compensation through the use of specific ballast tanks.
Nuclear boats are quite difficult to design as they have a concentrated, indivisible mass, i.e. the reactor section. It just is, it weights what it weighs and pretty much everything else has to be arranged around it to maintain stability.
On a diesel boat the only thing that is fixed is the main motor, although even that can be adjusted using different length shafts in design phase. Diesel generators can be arranged in different ways, their numbers can be changed i.e. Collins have three abreast while I believe Scorpien has two rows of two smaller diesels.
Then there is the factor of energy storage, nucs its the reactor producing steam (or whatever) to drive a turbine, conventional its diesels burning hydrocarbons to generate electricity which is stored in batteries for submerged operations. This means a conventional sub has massive amounts of easily divisible mass that can be distributed around the hull to maintain stability.
In many ways its much easier to adjust and fine tune a conventional than a nuc.