Cavitation speeds?

[Pillar]

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]

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]

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]

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

[ETR3(SS)]

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]

Good to know, thanks mates.

[Inner Sound]

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]

hi, please enlighten me, whats cavication

Gav

[Rockin Robbins]

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!:D 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]

thanks for that, i am now enlightened!

Gav

[donut]

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]

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]

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)]

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]

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.:DL

[vickers03]

http://img111.imageshack.us/img111/6974/propellereffectsap3.jpg
remember this awesome effect,

found here http://www.subsim.com/radioroom/showthread.php?t=140302&highlight=cavitation

[Rockin Robbins]

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.

OK! That makes perfect sense, and it explains why the damage is to the high pressure area of the screw. Great post.:up:

Vickers: did that cavitation effect ever get finished and released as a mod? Can you post it in the Subsim downloads area if it did?

[ETR3(SS)]

It's one of the few things I learned from the boat that I can share with you all. :up:

[Sledgehammer427]

Vickers: did that cavitation effect ever get finished and released as a mod? Can you post it in the Subsim downloads area if it did?

well, the post was tied in with a bow splash effect that had everyone freaking out, and the cavitation effect was soon forgotten.