Cavitation speeds?

Pillar · 08-22-09, 07:19 AM

These subs appear to be always cavitating at all speeds in external view. Are the graphics telling the truth? When does cavitation kick in and does the game take it into account? Also, when stationary with "all stop", is it true to life that the props kept spinning?

Rockin Robbins · 08-22-09, 07:48 AM

Eyecandy: the graphics effects you see which have no bearing on real game behavior. This includes fake cavitation, wavy underwater view, visual damage, sub skins, where do I go from here?

It is a grave mistake to confuse eyecandy for game mechanics. For instance, your sub can have a visually large hole in its side and still submerge, possibly with a small hull damage percentage!

A target can have no visible damage and sink like a stone, or lots of it and never sink at all. A real underwater view is like looking through air, there is normally no image movement as rendered in the game. We have lots of graphical curiosities, none of which have any impact on gameplay at all.

Pillar · 08-22-09, 08:13 AM

Ok, good news

When does cavitation kick in for the game engine rather than just the graphics? Is it significant like it is with modern subs or are these boats noisy enough that cavitation isn't half their problem?

Rockin Robbins · 08-22-09, 08:20 AM

I don't believe that cavitation is modeled at all.

ETR3(SS) · 08-22-09, 09:06 AM

I agree with RR there, cavitation isn't modeled in the game at all. But in real life cavitation is a concern for all ships, past and present. Cavitation can physically damage a ships screw to a point that it becomes less efficient.

Pillar · 08-22-09, 10:45 AM

Good to know, thanks mates.

Inner Sound · 08-22-09, 02:39 PM

But if it's silent running you're after you click the silent running icon and that automatically drops your revs to 1/3. Which is 1 knot in a Balao. But you can up the revs to 2/3 without loss of invisibility, and that's 3 knots wich is a hell of a difference when you're evading vengeance.

It's all to do with keeping the revs below 100, which you can see if you do a walkaround round the dials.

Learned this from Rockin Robbins iirc, so blame him if this advice gets you sunk!

GavNormandale · 08-22-09, 06:53 PM

hi, please enlighten me, whats cavication

Gav

Rockin Robbins · 08-22-09, 07:37 PM

All liquids have a boiling point, which is determined by a combination of temperature and pressure. You can boil water either by heating it to 100º C at sea level or by keeping it at room temperature, placing in in a vacuum chamber and pulling the pressure down to the boiling point!

However, that's a lousy way to make coffee.

When a propeller is rotating, there are areas of high pressure, where in effect the prop is pushing water away from it, and areas of lower pressure, where it is sucking the water toward it. Especially at the surface, where water pressure isn't too high to begin with, it is possible to spin the prop fast enough that on the forward side of the prop (the low pressure side) the water actually boils. These bubbles, of course get sucked into the prop, which because of reduced drag from the bubbles, spins up without producing thrust in the bargain. It's like spinning your tires on sand.

That's bad enough, but believe it or not, the formation of these bubbles is a very violent, if small act! They actually erode the surface of the propeller. Since cavitation generally starts out at surface irregularities such as dings to begin with, you can see that as cavitation damages the prop it causes....more cavitation!

It feeds on itself, making your boat slow, causing tons of noise for enemy sonar operators to hear, killing your fuel economy, destroying your propeller, it's just a bad scene.

GavNormandale · 08-22-09, 07:47 PM

thanks for that, i am now enlightened!

Gav

donut · 08-22-09, 08:20 PM

Quote:

Originally Posted by GavNormandale

thanks for that, i am now enlightened!

Gav

>>Me also.

Always thought rudder cavatation, due to more than 5/10 degrees limited travel while silent running. Again not game play feature.

Inner Sound · 08-23-09, 02:16 AM

Aah, very enlightening. So deeper you go faster you can go without cavitation. That'll not be in the gameplay either tho. Wonder if it'll be in SHV?

They should use my kettle element instead of props - five years its been cavitating away, still looks good.

Rockin Robbins · 08-23-09, 08:09 AM

Someone else would have to explain why boiling water is a relatively gentle procedure, while prop cavitation can be so destructive. THAT part I don't understand clearly. But I've seen lots of evidence on outboard motors' aluminum propellers.

ETR3(SS) · 08-23-09, 08:36 AM

Sea pressure. Part of the noisiness of cavitation is the collapse of the bubbles generated by sea pressure. It's the collapse of those bubbles that causes the damage to the screw. In a boiling pot of water the bubbles reach the surface where they burst into the air.

I'm goin' down · 08-23-09, 04:57 PM

My gums were in pain so I went to the dentist and told him it I thought it was a cavitation problem. He thought I was nuts. That was BEFORE I read this thread.

08-22-09, 07:19 AM	#1
Pillar Electrician's Mate Join Date: Sep 2002 Posts: 138 Downloads: 5 Uploads: 0	Cavitation speeds? These subs appear to be always cavitating at all speeds in external view. Are the graphics telling the truth? When does cavitation kick in and does the game take it into account? Also, when stationary with "all stop", is it true to life that the props kept spinning?

08-22-09, 07:48 AM	#2
Rockin Robbins Navy Seal Join Date: Mar 2007 Location: DeLand, FL Posts: 8,900 Downloads: 135 Uploads: 52	Eyecandy: the graphics effects you see which have no bearing on real game behavior. This includes fake cavitation, wavy underwater view, visual damage, sub skins, where do I go from here? It is a grave mistake to confuse eyecandy for game mechanics. For instance, your sub can have a visually large hole in its side and still submerge, possibly with a small hull damage percentage! A target can have no visible damage and sink like a stone, or lots of it and never sink at all. A real underwater view is like looking through air, there is normally no image movement as rendered in the game. We have lots of graphical curiosities, none of which have any impact on gameplay at all. __________________ Sub Skipper's Bag of Tricks, Slightly Subnuclear Mk 14 & Cutie, Slightly Subnuclear Deck Gun, EZPlot 2.0, TMOPlot, TMOKeys, SH4CMS

08-22-09, 08:20 AM	#4
Rockin Robbins Navy Seal Join Date: Mar 2007 Location: DeLand, FL Posts: 8,900 Downloads: 135 Uploads: 52	I don't believe that cavitation is modeled at all. __________________ Sub Skipper's Bag of Tricks, Slightly Subnuclear Mk 14 & Cutie, Slightly Subnuclear Deck Gun, EZPlot 2.0, TMOPlot, TMOKeys, SH4CMS

08-22-09, 09:06 AM	#5
ETR3(SS) Ocean Warrior Join Date: Dec 2007 Location: Between test depth and periscope depth Posts: 3,021 Downloads: 175 Uploads: 16	I agree with RR there, cavitation isn't modeled in the game at all. But in real life cavitation is a concern for all ships, past and present. Cavitation can physically damage a ships screw to a point that it becomes less efficient. __________________ USS Kentucky SSBN 737 (G) Comms Div 2003-2006 Qualified 19 November 03 Yes I was really on a submarine.

08-22-09, 07:37 PM	#9
Rockin Robbins Navy Seal Join Date: Mar 2007 Location: DeLand, FL Posts: 8,900 Downloads: 135 Uploads: 52	All liquids have a boiling point, which is determined by a combination of temperature and pressure. You can boil water either by heating it to 100º C at sea level or by keeping it at room temperature, placing in in a vacuum chamber and pulling the pressure down to the boiling point! However, that's a lousy way to make coffee. When a propeller is rotating, there are areas of high pressure, where in effect the prop is pushing water away from it, and areas of lower pressure, where it is sucking the water toward it. Especially at the surface, where water pressure isn't too high to begin with, it is possible to spin the prop fast enough that on the forward side of the prop (the low pressure side) the water actually boils. These bubbles, of course get sucked into the prop, which because of reduced drag from the bubbles, spins up without producing thrust in the bargain. It's like spinning your tires on sand. That's bad enough, but believe it or not, the formation of these bubbles is a very violent, if small act! They actually erode the surface of the propeller. Since cavitation generally starts out at surface irregularities such as dings to begin with, you can see that as cavitation damages the prop it causes....more cavitation! It feeds on itself, making your boat slow, causing tons of noise for enemy sonar operators to hear, killing your fuel economy, destroying your propeller, it's just a bad scene. __________________ Sub Skipper's Bag of Tricks, Slightly Subnuclear Mk 14 & Cutie, Slightly Subnuclear Deck Gun, EZPlot 2.0, TMOPlot, TMOKeys, SH4CMS

08-22-09, 08:13 AM	#3
Pillar Electrician's Mate Join Date: Sep 2002 Posts: 138 Downloads: 5 Uploads: 0	Ok, good news When does cavitation kick in for the game engine rather than just the graphics? Is it significant like it is with modern subs or are these boats noisy enough that cavitation isn't half their problem?

08-22-09, 10:45 AM	#6
Pillar Electrician's Mate Join Date: Sep 2002 Posts: 138 Downloads: 5 Uploads: 0	Good to know, thanks mates.

08-22-09, 02:39 PM	#7
Inner Sound Sparky Join Date: Apr 2009 Location: Scotland Posts: 152 Downloads: 25 Uploads: 0	But if it's silent running you're after you click the silent running icon and that automatically drops your revs to 1/3. Which is 1 knot in a Balao. But you can up the revs to 2/3 without loss of invisibility, and that's 3 knots wich is a hell of a difference when you're evading vengeance. It's all to do with keeping the revs below 100, which you can see if you do a walkaround round the dials. Learned this from Rockin Robbins iirc, so blame him if this advice gets you sunk!

08-22-09, 06:53 PM	#8
GavNormandale Swabbie Join Date: Apr 2008 Posts: 5 Downloads: 14 Uploads: 0	hi, please enlighten me, whats cavication Gav

08-22-09, 07:47 PM	#10
GavNormandale Swabbie Join Date: Apr 2008 Posts: 5 Downloads: 14 Uploads: 0	thanks for that, i am now enlightened! Gav

08-23-09, 02:16 AM	#12
Inner Sound Sparky Join Date: Apr 2009 Location: Scotland Posts: 152 Downloads: 25 Uploads: 0	Aah, very enlightening. So deeper you go faster you can go without cavitation. That'll not be in the gameplay either tho. Wonder if it'll be in SHV? They should use my kettle element instead of props - five years its been cavitating away, still looks good.

08-23-09, 08:09 AM	#13
Rockin Robbins Navy Seal Join Date: Mar 2007 Location: DeLand, FL Posts: 8,900 Downloads: 135 Uploads: 52	Someone else would have to explain why boiling water is a relatively gentle procedure, while prop cavitation can be so destructive. THAT part I don't understand clearly. But I've seen lots of evidence on outboard motors' aluminum propellers. __________________ Sub Skipper's Bag of Tricks, Slightly Subnuclear Mk 14 & Cutie, Slightly Subnuclear Deck Gun, EZPlot 2.0, TMOPlot, TMOKeys, SH4CMS

08-23-09, 08:36 AM	#14
ETR3(SS) Ocean Warrior Join Date: Dec 2007 Location: Between test depth and periscope depth Posts: 3,021 Downloads: 175 Uploads: 16	Sea pressure. Part of the noisiness of cavitation is the collapse of the bubbles generated by sea pressure. It's the collapse of those bubbles that causes the damage to the screw. In a boiling pot of water the bubbles reach the surface where they burst into the air. __________________ USS Kentucky SSBN 737 (G) Comms Div 2003-2006 Qualified 19 November 03 Yes I was really on a submarine.

08-23-09, 04:57 PM	#15
I'm goin' down Ocean Warrior Join Date: Sep 2008 Location: Notify command we have entered the Grass Sea Posts: 2,822 Downloads: 813 Uploads: 0	gee whiz My gums were in pain so I went to the dentist and told him it I thought it was a cavitation problem. He thought I was nuts. That was BEFORE I read this thread.