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Carlosa Here is another interesting paper called "Submarine Hull Form Optimization Case Study" by C. Warren and M. Thomas (you can search in the link I gave you).
Note that the Kilo class has a highly tapered stern (the rate at which the hull profile transitions from a maxi-
mum radius to the propeller hub radius. A highly tapered stern is one in which this transition occurs slowly, result-
ing in a relatively slender profile)
The newer subs like the type-214 or even the Lada/Amur has a less tapered stern (the article would call this full-stern).
Basically, the paper argue that:
A full stern design allows considerable flexibility in the submarine internal and external arrangements and provides more evenly distributed buoyancy along the longitudinal axis of the submarine. This buoyancy allows the propulsion equipment to be shifted aft and thus provides more forward space for command and control functions.
Recent order-of-magnitude studies have shown that a full stern may reduce the submarine length by 5 to 18 percent (Jackson 1995; Trost 1996). The shorter submarine will also have a length-to-diameter ratio closer to the hydrodynamic optimum of approximately six to one (Burcher and Rydill1994)
And this full stern hull with hydorodynamic optimum ratio allows it to achieve:
a full stern submarine may actually achieve a higher maximum speed with the same installed horsepower due to the shorter hull form and more optimal length-to diameter ratio....
The ultimate goal is to answer the question of whether a full stern is a better hull envelope in general than a
tapered stern....
Analysis indicates that the full stern has a greater maximum speed than a comparable tapered stern submarine.
The full stern speed is 25.1 knots compared to the tapered stern speed of 22.2 knots. Thus, these results
support the idea that the full stem submarine has potential benefits in powering characteristics.
Baiscally, the full stern hull is a more efficient design (hydrodynamic-wise) in terms of speed. With the same propulsion power, a highly tapered stern hull would go slower than a full stern one. You can see why most modern subs are now less tapered than the Kilo.
However, this paper doesn't say anything about stealth. Another paper I've read, which I can't find it yet, basically says that the Type-214 would be more stealthy than the Kilo (more tapered) because:
- The propulsion motor was able to be shifted closer to the propeller (since its less tapered) so the propeller shaft is shorter (worry less about vibration and less mounts).
- Since the hull is a more efficient design and more compact, the propulsion system requires less power and most likely slower propulsion shaft speed (so this mean its more quiet). The "improved" kilo has a lower propeller speed than the earlier Kilo but it only achieved this by using a more powerful motor. The Type-214 can achieve a low propeller speed because of its better hydrodynamic design.