Using a propeller to excavate sand under a boat

[Garry]

Good day. I want to use the boat's propeller to excavate sand. This will be done using a tube which will deflect the thrust downward. What are the implications? The boat is anchored. Thus there is zero forward speed. I suspect this may change the properties of the way the propeller functions.
All advice is greatly appreciated

 

[anorlunda]

Yes you can do that. Some dredges do similar things, such as in this picture. But dredges normally use a separate propeller, not the ship's propulsion propeller.

However,

1. Don't get overly ambitious. Moving lots of sand takes lots of power. But if you are just trying to remove 1-2 feet of silt directly under your boat, using a hose powered by your prop, and you in scuba gear to direct the hose, it can work.
2. Consider how far away you move the sand. Too close and it will silt in again in a short time.

 

[johnbbahm]

I think the treasure hunters already do this.

 

[JBA]

Just keep in mind the location of your engine's cooling water intake and make sure you will not be ingesting any of the resulting sand/water mix into your cooling system.

 

[CWatters]

I wonder how fast the prop blades are eroded? Perhaps there is a way to avoid sand going through the prop.