Oxygenated Water and Boat Props

Do boat propellors oxygenate water? If so, is oxygenated water good for fish stocks?
Catching a ferry every morning and seeing the churned water has got me wondering…

I’m sure someone will have a better answer. But what a prop does is called cavitation. Essentially, the water already has air in it in the form of very small bubbles. When a prop is spinning fast, those small bubbles expand to fill in the gaps on the trailing end of the prop.

This is why subs have such large many bladed props. They can spin slower, less cavitation, less noise.

I don’t think this would really help sea life.

In order to add air to the water, the prop has to have a part of it protruding into the air.

Cavitation, as I understand it, isn’t the expansion of air bubbles. It is rather the creation of cavities of vacuum (probably containing a little bit of water vapor). When these cavities collapse they can knock small chunks out of the propellor and they, as enipla said, are noisy, reduce efficiency and are to be avoided.

From Merriam Webster’s Collegiate Dictionary: cavitation - The formation of partial vacuums in a liquid by a rapidly moving solid body …;also The pitting and wearing away of the solid body as a result of the collapse of these vacuums …

If the props are going slow they really won’t add o2 to the water. If you are seeing white prop - wash then air is getting sucked into it and O2 is getting into the water.

Cavatation had to do w/ water changing from liquid to gas due to low pressure then back again.

The amount of areation that a boat prop would give to the water (if it is doing this as opposed to cavitation) is very very small, and wouldn’t even add a detectable amount of extra O2 overall to the water in bodies of water large enough to use ferrys (I’ve taken the ferry many times across the straight of Georgia). Simple wave action adds orders of magnitude more dissolved gasses that even a large boat prop.

Having a week-long 24 hour speedboat race with 20 boats on a 1-acre 8 foot deep pond would mess around the dissolved gas levels, but any additional O2 benefit would be lost by stressing the hell out of the aquatic life below by all the turbulance and noise.

I can’t think of a way that having power boats/ships on the water would ever help sealife, and in extreme cases ship props can chop up some large mammals like manatees, or run into the occasional whale and kill it. Then there’s the quesion of what kind of motor fluids and/or exhaust gets into the water while the engines are running…

I’ve listened to underwater microphones picking up the engine noise from a 15-foot boat out on the horizon, and you’d swear it’s only a hundred feet away.

Many thanks. The fish I see swimming near jetties then are there not because of extra oxygen in the water, but for other reasons, then.

The "air " that you see in and around your prop during cavitation is often exhaust, the muffler being located in the center of an outboards prop.
There are a lot of weird vortices down there and you have to get things just right as far as trim and depth are concerned. Also , you can’t have a captain whose had a few too many at the throttle and get away scott free, either.
If you dont believe me, hang over the back while your cruising along and have someone cause cavitation by trimming the engine up and you’ll see it.
the other common source of the air is from the surface.
Oh yeah, people take their boats to the jetties cause thats where the fish are, not the other way around.