Speed or Cavitation

[Deathblow]

Just curious to which performance our virtual skippers would hypothetically prefer. I've been reading as much as I can find on pumpjet propulsors performance (which is scarce info) and came across an article that suggest that some pumpjets designs are better at reducing cavitation, but may actually detract from maximum thrust, while other pumpjet designs can increase the amount of thrust but are more prone to cavitation.

http://www.navweaps.com/index_tech/tech-023.htm

Of course the ideal is one that increases thrust and reduces cavitation at the same time, which may or maynot be the reality. :hmm:

EDIT: for an SSN not an SSBN

[Kapitan]

It all boils down to what you want the submarine for.

Al'fa class was an interceptop submarine designed purely for speed, and thus it didnt care for noise.

Typhoon is designed for incredibly quiet ops and it does them well.

Its what you need in a submarine, and whats in your design spec.

[Deathblow]

:hmm: Hmm... I guess I should have specified more.

Lets say your designing a SSN/SSK attack sub, not a boomer :up:

[Kapitan]

Again whats the missions its designed for?

Missile attack submarine SSGN or SSG, or a solid hunter killer like the seawolf class.

Whats it to do, its all well and good saying an attack boat, but what are the countrys needs?

Global support or coastal defence, no two countrys submarines are ever the same, american submarines are global support role, while the germans are coastl support, or the french who are well who knows, and the british are semi global.

It vareys, is it going to be attack ships, land targets or hunt other submarines, is it going to be multi role like the 688i or what.

[Deathblow]

Even amongst those sub varieties, coastal vs global, their are logical advantages and disadvantages for use of each prop designs. Would be interesting to hear someones rationale.

[Kapitan]

In coastal waters you want to be very quiet speed is not nessasery in shallows because eventualy you will cavitate.

Submarines like the kilo german type 205 upwards are all coastal boats, they are not designed primarily for open ocean deployment but can do if nessasery.

Coastal boats dont realy have a top speed of any higher than 20 knots its simply not needed in shallows or littoral waters.


A nuke on the other hand is built half and half mainly for speed and also when it needs it stealth.
Anuke has more advantages it can stay out to sea longer go faster and carry more weapons.

The nukes can be transformed into verious roles take the 688i, its not only a hunter killer using torpedos to sink enamy submarines, its also a SSGN carrying anti ship missiles, while maybe at the same time carrying TLAM missiles for co-ordinated strikes far inland.

So its a heavily veried role, nukes need the speed conventionals dont, infact conventionals are far quieter than nukes.

[Bubblehead Nuke]

Give me stealth and quiet anytime over speed. How fast do you need to go anyway unless you are evading torpedo's or clearing datum after execting an op/evolution.

Noise means you will be detected father away, possibly before you get into position to detect the other guy in the first place.

I know that our screws were designed to give us the maximum speed possible while being as cavitation resistant as possible. Yes, the best of both worlds was and is the goal.

edit:

The main noise of a nuke sub is not the screw anyway, but the required gear to operate the nuclear plant and support systems. You have a constant noise level that is essentially unchanged until certain parameters are met. The screw is designed to be cavatation resistant until these conditions are exceeded and by that time ultra quietness is no longer the absolute requirement.

[MaHuJa]

Generalizing a lot, but if you think of SSKs as being slow anyway (going fast will tear into the batteries fast) then the pumpjet reducing top speed won't matter much.

[Kapitan]

The submarine alrosa and a normal improved kilo have exactly the same battery life, theres roumers that a indian kilo managed to stay submerged on one charge for over 72 hours.

Indian kilos have 5 bladed propelors and also have alot better batterys than the russian ones so that roumer to me looks quite true.

[goldorak]

Give me top speed over silence every day of the year !
Of course it depends also on what kind of opponent you have and what kind of weapons he is using but I think that top speed also gives you a tactical advantage over silence.
The only missions where silence is more advantageous to high top speed are boomers on patrol and eventually h/k submarines tracking boomers.

[Kazuaki Shimazaki II]

The submarine alrosa and a normal improved kilo have exactly the same battery life, theres roumers that a indian kilo managed to stay submerged on one charge for over 72 hours.

What's so hard about that. Officially, the Kilo lasts 400nm at 3 knots - that's over 100 hours endurance.

[Kapitan]

Yup but every class is diffrent the 877 and 636 are two totaly diffrent submarines inside, 100 hours of endurance at 3 knots you aint gone very far, whats more to the point the reason india likes the kilo is because the submarine itself is highly changable.

With the indian batterys or indeed the german batterys the kilo could do alot better than whats officaly stated.

[Deathblow]

The main noise of a nuke sub is not the screw anyway, but the required gear to operate the nuclear plant and support systems. You have a constant noise level that is essentially unchanged until certain parameters are met. The screw is designed to be cavatation resistant until these conditions are exceeded and by that time ultra quietness is no longer the absolute requirement.

That's very interesting :hmm: Makes sense. Is that one of the additional reseasons that SSKs on electric power can be quieter than SSNs, not just because of lack of the need for reactor coolant circulation, but because electric moters don't require reduction gears? Or do they? Guess I'll look it up

Generalizing a lot, but if you think of SSKs as being slow anyway (going fast will tear into the batteries fast) then the pumpjet reducing top speed won't matter much.

Yeah, its a pretty broad generalization. I chose speed because is my cavitation is a problem I can always reduce a subs SOA, it will just take a little while longer to get where your going, but can still achieve the same level of quietness at a slower pace. In my DW experience, top speed comes up mainly when I'm running for high heaven away from torps and that's when "slowness" hurts the most, can't do anything but get out and push! :-j

[Kapitan]

Generaly the foxtrot was recorded making its fastest speed at 26 knots, so i would have no doubt that some conventionals could hit 30 or even 33 or more knots.

ok its going to depleate the batters very quick but that boost of speed could be used for emergencys.

[Wildcat]

What is the point of having a higher cavitation speed when you're still going to be making tons of noise. You may as well just dive deep and go faster, at least that way you're somewhat less detectable and under most acoustic conditions where you can achieve such a high speed the sound won't travel that far away.

[TLAM Strike]

Generaly the foxtrot was recorded making its fastest speed at 26 knots, so i would have no doubt that some conventionals could hit 30 or even 33 or more knots.

ok its going to depleate the batters very quick but that boost of speed could be used for emergencys.A WWII Gato (A boat with Diesel Electric so its running electric motors when surfaced) could make something like 21 and a half knots on diesels pushed beyond spec. You put sufficient power in to the motor you can get some real speed at the risk of burning up the motors. A burned out motor is better than flaming crushing death at times. :yep:

[Bubblehead Nuke]

That's very interesting :hmm: Makes sense. Is that one of the additional reseasons that SSKs on electric power can be quieter than SSNs, not just because of lack of the need for reactor coolant circulation, but because electric moters don't require reduction gears? Or do they? Guess I'll look it up

As I understand it, electric motors are wound directly on the shaft. thus no need for gears at all. The motors are what turn the screws at all times. The source of the electical power is what varies. Batteries for normal submerged ops and diesels (with the battery floating for a charge) for surface/snorkel ops.

[Bubblehead Nuke]

If talking about speed on a batttery the USS Albacore, while a non-combat vessel, topped out at 30+ knots. According to some reports, it was faster than the Skipjack class and was the fastest US submarine until the Seawolf class come onto the scene.

Moral: Battery does NOT equal slow speed.

[TLAM Strike]

As I understand it, electric motors are wound directly on the shaft. thus no need for gears at all. The motors are what turn the screws at all times. The source of the electical power is what varies. Batteries for normal submerged ops and diesels (with the battery floating for a charge) for surface/snorkel ops.

On a diesel-electric drive yes but not on a direct drive diesel. ;)

Are there still direct drive boats? :hmm: :lol:

[Kapitan]

I dont think so, but there is also AIP to bring into this.