Not sure as i don't believe i hit anything. Can cavitation heat props enough to fracture?

That is a new wall of shame ornament. Get out your checkbook.

They can break like that. I had one tear off and as it came off it sliced up the lower/cavitation plate (not fixable either). Consider yourself lucky.

I think you will find 2 major reasons for prop breakage, the obvious: hit something. And second, boat "flying" then re-entry into the water. The re-entry puts substantial stress on your drives as we all know, but that is mainly caused when the prop re-bites into the water. Thus stress, then breakage.

Surface drive props seem the most vulnerable on this cause of failure, just walk around any shop and you will see LOTS of cool prop displays on desks, shelves etc, that were once VERY expensive props...

Cavitation will also cause issues, but that is generally during take off and most drivers are feathering the motors to get the boat on plane, so even though they are just spinning, there is actually less stress over all.

it may just be the lighting of the pik, but if along the edge of the crack you see dull then shiny metal, the dull part of the crack has been cracked for a while, the shiny part is the new clean fracture. Enlarging the pik and looking at it, it looks like you had an established crack from the trailing edge.

Phragle
I agree it looks as though it was already cracked. Then tore off last bit. But i did look everything over before I went out as I always do. Nothing worse then spending all the time to get it in the water to only find it has to be pulled back out.

The reason I thought may have cavitation caused it:
Last weekend I had one engine running bad. I limped the boat home as it would only go to 3400 then lean pop. When i got within sight of the marina I turned the other 2 engines off and brought the faulty one up to 3000 rpm to hear it better. I then docked boat and changed water separator the next day and went out to water test so i could confirm problem and get boat out of water as it stays on trailer between uses. I proceeded to get on plane and and then the engine went off the rev limiter and stopped making boost. Brought it back in and pulled it out and found this. I assumed I must have hit something but thought maybe loading one engine up may have did it.

Chances are if you hit something, other blades would have some damage and you would have felt it hit.
Props flex and over time that flexing will cause metal fatigue. Llike was said, Bravo style props just can't take surfacing either. They are not thick enough..

This blade tore from the trailing edge to the leading edge.
This is a old casting as is evident from the hub. All props have a undetermined life expectancy.
Internal casting defects, porosity, cold rolls can cause failure eventually. These failures can be expedited by driving practices, X dimension, HP, etc.
Hair line fractures are often not visible immediately. Especially with the calcium build up on your blades. We buff le's and te's first to inspect for such cracks prior to doing work. Even so, we occasionally find hair line fractures during final buffing stages.

Brett

Most props on the market have adequate blade thickness to handle the horse power and boat weight normally encountered. It is fatigue that causes blades to crack, and ultimately break off. Consider the blades entering and leaving, and re entering the water between 3500 and 5000 times a minute. The blades are loaded and unloaded causing them to flex back and forth at again 3500 to 56000 times a minute. These stress reversals will fatigue out the metal and lead to cracks. Any nicks in the leading or trailing edges will exacerbate the fatigue failures. Consider a coat hanger bent back and forth. Eventually the hanger will break. If we file a slight groove in the coat hanger, it will fail much, much faster. It is very important to remove nicks on both the leading and trailing edges of your props.

That said, cleaver style props of any manufacture will fail more quickly than round ear props. There is no material beyond the center line of rake to support the blades.Round ear props do have material beyong the rake center line to add strength.Much like the bends and shape to the hood of your cat. A flat hood would bend easily if you sat on it, whereas a hood with some shape and bends will not.

Sorry, that is "beyond" and "car", not beyong and cat.

My blades are usually cleaner. Just left in water for a few days and pulled blade before it was washed.