Submarine speed???

[Kirk]

Ok I know this is funny in asking but do subs go slower than 5 knots? Oh in say sub talk would that be like 'All ahead dead slow' or something like that. I know 5 knots is 1/3, 10 is 2/3, 15 is standard, 20 os full and 25 + is flank but do they have phrase for below 5 knots? And is there a common speed they go, I guess perhaps 3 nots and then 'attention all stop'. Just wondering on this. Thanks.

[Bill Nichols]

If you don't want to go one of the 'standard' speeds, then you say exactly what speed you want, for example:

"Make turns for three knots."

[Rip]

Or you can order maneuvering to make a certain speed by log instead of turns for a certain speed. This results in them increasing the throttle in turns and such to maintain the desired speed. I have also known some OODs to actually order a specific # of shaft turns. Usually the engineer.

On a related note...why do subs have a maximum speed of 20 knots surfaced and cavitate as soon as you reach 10 knots (surfaced). Can subs go round caavitating everywhere...? In real life, wouldn't that ruin the props?

[compressioncut]

Originally Posted by Kurushio

On a related note...why do subs have a maximum speed of 20 knots surfaced and cavitate as soon as you reach 10 knots (surfaced). Can subs go round caavitating everywhere...? In real life, wouldn't that ruin the props?

Cavitation at depth is a much more severe process than cavitation near the surface. The collapse of the bubble happens more quickly and violently - it's called compressed cavitation. That's where your prop damage occurs. It also sounds much different, like a very loud "squick squick squick" as opposed to the more constant white noise sound of normal cavitation.

Ok, thanks compressioncut!

[Bubblehead Nuke]

Originally Posted by Kurushio

On a related note...why do subs have a maximum speed of 20 knots surfaced and cavitate as soon as you reach 10 knots (surfaced). Can subs go round caavitating everywhere...? In real life, wouldn't that ruin the props?

Subs on the surface push a HUGE bow wave due to the shape of the hull. We do not slice thru the water so much as shove it out of the way. You can stand on the power but you have too much drag to go fast. There are some other engineering factors related to the nuclear propulsion plant on the surface that limit the amount of turns you can place on the shaft on the surface.

As for the cavitation, yes, given a long enough time you can damage things. But subs do not operate long on the surface anyway. It is always a rush to the dive point and then its 'see ya'.

[Deathblow]

I've always wondered how the "standard speeds" got their names... All ahead 1/3 doesn't nearly seem like 1/3 maximum power... and all ahead full sin't full speed at all :hmm: .

I remember in the old 688 Attack sub, all ahead 1/3 was 8knots, 2/3 was 16, standard was 25 I think, full was 32, and flank was 37 iirc.

[Ula Jolly]

Doesn't "All" apply to all engines, in the case where there would be more? Sounds as if it would originate from ships with several engines. All ahead one third, as opposed to... say, left ahead one third?

[Rip]

Actually it would depend on the number of screws. There are some dual screw ships out there and you could order "port ahead on third" "starboard back two-thirds" for instance to power assist a turn.

Modern US subs have 2 engines already, not even counting the diesel seperate. There a 2 main steam turbines that connect to the shaft via a reduction gear system.