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Sub Surface Dredge Questions?


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So I have this idea to build a 4 inch sub surface dredge. I have all the parts and pieces with the exception of the pump and moter (in route). Well spring fever is kicking in and I plan to assemble this dredge. I am currently engineering the frame work. My question here is all the pictures I have seen show the dredge tube dead center in between the floats and looks to be level with the floats. Should the tube be suspended lower in the water or submerged completely? 

 

Just for reference the setup consists of.

 

1. Keene 4 inch tube.

2. 15 foot of 4 inch suction hose.

3. 4 inch nozzle.

5. 20 foot 2 inch pressure line. Hard line not lay flat.

6. Keene 3 inch mini floats.

7. Keene P180 Pump and a Kohler Command Pro 7 hp motor.

8. No air on this one.

9. 1 inch box aluminum frame work.

 

Also I found a great deal on a Hydro Force nozzle. Anyone have any thoughts on these?

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If you have looked at my various articles you will see pictures of the tube above and below waterline and in between. The main issue I see is riffle clearing. In theory fully submerged is how these things are designed to run. But if underpowered back pressure can make for a system too slow to get proper riffle action. In those cases I found raising the tube and allowing air to enter the tube would dramatically increase the velocity over the riffles.

In other words, there is no right or wrong. You have to adjust the system to get optimum riffle action, and that can be a bit difficult when you can't see inside. I often reached up from the rear into the tube and felt the riffles to make sure they were not packed. Sometimes a hump of material was discovered midway up the tube covering half the riffles! Not good.

Forward and back tilt also matters though less than you would think because you are dealing with an enclosed forced system. If the unit has enough power the rear can be higher than the front and you still do ok as long as the velocity over the riffles is sufficient. I do not recommend it however. Placing rocks on the rear floats to get a bit more tilt was something I did often though, and sometimes up front to slow things up a bit. My tube was bolted in a fixed position so that was my method. It is possible to mount the tube such that the angle can be adjusted however so consider that option. I opted for simplicity.

Build it, use it, watch the riffle system carefully, and then adjust as needed. Never hog when in the gold! No matter what you can bury those riffles through inattention and that will pump gold out the back. More gold than is already headed that way in any case.

Lots of articles on subsurface dredges at Steve's Mining Journal plus the one I wrote for the ICMJ Prospecting & Mining Journal at http://www.icmj.com/article-notloggedin.php?id=2741

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Thanks Steve, Just was not clear to me on weather if it had to be submerged or not. But makes sense that a sluice is a sluice weather it is submerged or not.

Started to assemble the frame today. Ended using 3/4 aluminum as it slipped rite in the stock mounts. Took about 30 minutes to do. Then I stared at it for a hour figuring the next move. Had all kinds of ideas but came to the conclusion that I want it as simple.

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Planning on attaching the tube with all thread and wing nuts. Should allow for some adjustment.

 

Will see if/how that goes tomorrow.

 

 

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My 4" subsurface tube runs about half in the water. One thing I see in your list of parts is the engine and pump is way more then you need, Bob

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Hello Bob, I mounted the tube with all thread so I can adjust it. Basically I need to see the dredge in operation to understand the dynamics of the subsurface part and will adjust it as I go.

 

Here is a picture of what I have so far.

 

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As for the motor/pump. I agree with you. I figure I stacked an extra 10 LBS on and not really Shure that the Kohler will be as good as a Honda 4 Hp but in the end it was half the price and I figure I can run at a lower rpm.

Worst case scenario I have a back up motor for my larger dredge. 

 

Shure would like feed back on the Kohler good or bad.

 

 

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Well no motor yet and that will delay finishing the dredge ( Shipping )

I did put the hose on to get an idea of the set up.

I had it in my mind that I would be able to build a mount that would allow me to position the engine front, back. or middle. With fixed length hose I see that it will stay as it is mounted. So looks like I too will be adding rock ballast.

Here is a picture with the hose on.

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Steve reading your reply I understand the importance of running a clean sluice. Did you modify your riffle area any? Kind of interesting that the sluice on a Subbie is drop down riffle style. Never dealt with that before. Have a thought that maybe some grizzly bars would be good.

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