Using a propeller to excavate sand under a boat

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Discussion Overview

The discussion revolves around the feasibility and implications of using a boat's propeller to excavate sand while the boat is anchored. Participants explore the mechanics, potential challenges, and practical considerations of this approach, including its application in dredging and treasure hunting.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests using a tube to deflect the propeller's thrust downward for sand excavation, raising questions about the implications of zero forward speed on propeller function.
  • Another participant confirms that similar methods are used in dredging but notes that traditional dredges typically employ separate propellers rather than the boat's main propulsion system.
  • Concerns are raised about the power required to move significant amounts of sand, with a suggestion that a hose powered by the propeller could work for small-scale removal of silt.
  • A participant highlights the importance of considering the distance the sand is moved to avoid it settling back quickly.
  • One participant mentions that treasure hunters may already utilize this technique.
  • Another participant warns about the risk of sand entering the engine's cooling system and suggests monitoring the location of the cooling water intake.
  • A question is posed regarding the erosion rate of prop blades due to sand exposure and whether there are methods to prevent sand from passing through the propeller.

Areas of Agreement / Disagreement

Participants express various viewpoints on the practicality and risks of using a boat's propeller for sand excavation, with no clear consensus on the effectiveness or safety of the method.

Contextual Notes

Participants do not fully address the assumptions regarding the power requirements, the specific design of the tube, or the potential effects on the propeller's performance and durability.

Who May Find This Useful

Individuals interested in marine engineering, dredging techniques, or underwater excavation methods may find this discussion relevant.

Garry
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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
 
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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.

dredge.jpg
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.
 
I think the treasure hunters already do this.
86ff3b1561641e61ce2b80df738c6393.jpg
 
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.
 
I wonder how fast the prop blades are eroded? Perhaps there is a way to avoid sand going through the prop.
 

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