Air bubbles in pool

schaefera

When you kick around in a pool or lake, air bubbles seem to stream from your feet... But what causes this?

Is it air being pulled down from the surface, or oxygen from the water molecules, or something else entirely?

DaveC426913

Yes.

There's one other way bubbles can occur in water - but I doubt even the best swimmer can kick fast enough to cause cavitation.

sophiecentaur

Apparently the right term for what is happening is 'ventilation'. It happens with boat propellers operating too near the surface.

DaveC426913

Yep. Learned that one recently while repairing my motor. The big wing on outboards just above the propellor is called an anti-ventilation plate.

sophiecentaur

PF certainly does widen our horizons - in the rush to be the best informed poster of the day.

Naty1

Well that wing on outboard engines used to be called a 'cavitation plate'. I wonder if air pulled from the surface [ventilation] is now distinguished from cavitation which is a pressure induced phenomena in liquids??

Anyone have a reference that uses 'ventilation' for such bubble induced wear and tear? Wikipedia, for example, discusses what I have always known as 'cavitation' issues. I have never seen 'ventilation' terminology in marine applications. Maybe they modified terms??

I can verify that certain prop wear on larger boats, bubble induced noise on props,and even oscillation induced metal wear in water cooled cylinder liners in some diesel engnies [ like the Detroit Diesel 53 series] is called 'cavitation'. It is common practice in some older boats to double up on hull thickness right over props and sometimes inlcude sound deadening material there to combat such unwanted noise. In wet liner diesel engines, the manufacturer [DD] specificies certain additives in engine coolants and or antifreeze..nitrites, if I recall.

mfb

There is another way. But I doubt the swimmer is hot enough to cause boiling .

@Naty1 <-> sophiecentaur and DaveC426913: I think you are talking about different effects.

sophiecentaur

I was waiting for that comment. I managed to restrain myself.