Blowing ballast

[BettingUrlife]

I imagined that when a sub blew it's ballast tanks to surface rapidly there would be a massive surge of air bubbles. But this doesn't seem to be the case in SH3. Is it just my imagination or aren't there any bubbles when you blow your tanks in a real sub?

[BenG]

When you "blow ballast" you're not blowing air out. You're using air to force water out of the ballast tanks.

(or at least that is what I understand)

[Mooncatt]

you are correct to dive you fill ya tanks with water and to surface you eject water,
having said that to blow ballast you would think that with the force of the water being expelled there would be a lot of bubbles

But bubbles are made of air. Like BenG said you're not blowing air off the boat. The ballast tanks are full of water. You push in compressed air which forces the water out. You don't keep pumping in air once the water's out (as that's a waste of air and THAT would cause bubbles).

Check out the little animation on http://science.howstuffworks.com/submarine1.htm. That shows you how they pump air into the ballast tanks (from the top down, pushing the water out the bottom). Once the tanks are full of air, you stop pumping in compressed air. No bubbles.

[BettingUrlife]

Ok Fab, that makes sense, but then wouldn't the opposite (i.e. submerging) mean they blow the tank's air out? Then if that is the case, there is still no bubbles from our subs in SH3 I sincerely hope you aren't going to tell that they suck the air from the ballast tanks back into the sub? It's just that I'd hate to be wrong twice in a day

[Patboot]

The reserve of compressed air is usually just enought to provide positive buoyancy...about 1/4-1/2 of the main ballast tanks- the rest is done by a lower pressure turboblower that clears the tanks after surfacing. SHIII shows this, if you notice, as after surfacing it takes a bit of time to some to full surface cruise depth.

edit- on diving, the sub simply opens vents at the top of the ballast tank- there might be some bubbling, but its very localised- watch your wake as you go under.

[BettingUrlife]

I just did this Pat, but with my engines not engaged, it just shows the boat submerging and slowly getting covered by water.

[Khayman]

Originally Posted by Patboot

edit- on diving, the sub simply opens vents at the top of the ballast tank- there might be some bubbling, but its very localised- watch your wake as you go under.

Yup. Also the diving cells are open to the sea at the bottom, they are not fully enclosed tanks (in case anyone didn't know this). The pressurised air inside the cells stop seawater from filling them. On diving the vents on top of the diving cells were opened, allowing the air to escape from the top and seawater to enter from the bottom.

Originally Posted by BettingUrlife

Ok Fab, that makes sense, but then wouldn't the opposite (i.e. submerging) mean they blow the tank's air out? Then if that is the case, there is still no bubbles from our subs in SH3 I sincerely hope you aren't going to tell that they suck the air from the ballast tanks back into the sub? It's just that I'd hate to be wrong twice in a day

Not really; most of the time, the tanks keep the boat at more or less neutral bouyancy. They'll suck in a little water to help the dive, but by and large, the ballast tanks don;t play as much a role in diving as the planes and engines do (hence why diving when stationary takes quite a bit longer).