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Arctic-moose

Why Are Dredge Sluices So Short?

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Hi, We are new to dredging, but have been researching and experimenting for the past year and we are starting to design, build, and refine our existing 3" homemade dredge/highbanker combo that we put together last fall.  My question is why are all the manufactured dredge sluice boxes so short? The area we are dredging has pretty fine gold, with small nuggets to about 1/4" but that is about it (so far).  So we have been researching the heck out of fine gold recovery and I think we will catch more with a longer sluice or series of sluices. When we crank up the 3" pump our waterflow seems to fast for a single Keene A52 sluice, but have to keep the pump pumping to obtain the suction we need. We were thinking about a long slick plate running to twin Keene A52's side by side or end to end, or even drop stacked.  Not sure which would be better, what do you think? We have a lot of space for the slick plates and sluices, just trying to determine which would be more effective.

 

Also does anyone have any experience with the sidewinder sluices boxes? http://www.sidewindersluice.com/index2.html

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The truth is I could cut a foot off the end of just about any dredge sluice I have ever owned and barely lose any gold. I have literally done just that to save weight and make a more compact system. Adding length does not add gold unless there is something specific in the design to take advantage of the extra length. Otherwise all you are adding is weight, more cost, and more concentrate to process for little if any extra gold.

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Arctic...

   You have hit upon the bane of the suction dredge design. Necessary water need for suction and material handling, but what to do with all that water once it hits the recovery system.

  It seems to me suction dredges are designed to more material, not for gold recovery. Otherwise they would have a classification system PRIOR to the recovery, not IN the recovery system.

 

 If you read Randy Clarkson's original radiotracer study http://www.scribd.com/doc/61880538/The-Clarkson-Study-Fine-Gold-Recovery

 You will read an important observation on page 14.

 

"Initial Concentration- a high concentration of gold in the first few feet of sluice run is not a good indicator of recovery efficiency. Tracer tests revealed that sluiceboxes with overall recoveries of less than 30% still had most of the recovered gold in the first few feet of the sluice run"

 

So, that tells us this first few feet is critical ! Not 10 feet down the box. You should be thinking " how can I optimize this first few feet" ?

 Gold wants to settle. You need to give it the chance. That won't be accomplished by adding length to the same turbulent flow.

 

 Just my opinion ... but it ought to give you something to chew on.

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The bigger the dredge the more your going to lose.. it's just a sad fact.  The reason for that is because you need more velocity of water to move the bigger material throught he dredge so therefore you're going to be pushing that fine gold with it too.  On my 8" I would say roughly 95-98% of my gold is right in the front header which I clean up daily.. the rest of it I clean up maybe once a week or every two weeks.  Honestly once you get the proper angle and proper water flow you really don't need all that sluice.. Like Steve said, I could cut a foot off my 8222 and not worry about it.

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The  advent of flared jets to slow,spreadout  and deaireat the gravels mix coupled along with longer,heavier dispursion curtain(rubber flaps) helped recovery much. The we came out with over/under classification and you thusly had twice the box length in half the space,100% better classification and no need for long boxes. I've run up to 10" for 1,000s a hours and many predicating factors MUST also be figured into the recovey equation,box length is only 1-John

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Keene A52 sluice is to narrow and the riffles are to flat to use for a dredge. Hungarian riffles and a wider box to handle the amount of water you are pumping thru  it will also help recovery

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Guest flintgreasewood

Our Eureka Gold Thief has a very short riffle tray, less than 2'.  It is washing just 9/32" minus but we lose almost no gold.  I have come up with a riffle design [actually by chance and not design] that grabs just about every flake in the first 4 bars. 

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Guest Chris Ralph

The critical thing in catching fine gold is the speed of the water moving down the sluice. Fast water moving down the sluice pushes the gold down the box. If the water is moving slow enough, the gold will drop out quickly. If its moving too fast, it will work its way down and out of the sluice no matter how long it is. That's why long slices are kind of irrelevant. Old timers used to make real super long sluices like 1000 feet long. It didn't help much in fine gold recovery. I always recommend to keep the water as slow as possible while washing all the rock out of the box (you cant do with water so slow the rock accumulates in the box). That's why people size the material going into the sluice. If you have 8 inch rock going in, you need water speed sufficient to push an 8 inch rock, and that will also move small gold out of your sluice no matter how long it is. If you can put 1.5 inch and smaller rock, you can slow the speed down such that you will do much better on small gold. Slick sheets do help, some but the water speed is much more important. You can have a great slick sheet, but if the water speed is too fast, you wont get good fine gold recovery.

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Thanks guys.  Like I saiid, I am new to dredging and all of your comments make sense.  I also have to thank you for the references, I have some more research to do, there is never enough hours in the day. We had thought about a bolt thru the nozzle to lmit the size of rock we are trying to push thru and that maybe part of the answer to slow down the water and get the fine gold to settle.  Now I just have to modify our set up and test to see what is the most effective.

 

Anyone have a wider dredge sluice for sale?

 

I really appreciate your guys opionions (on all forum topics) and I think this will be a great alternative to the AMDS forum. 

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NO BOLT NEVER EVER :wacko: do not reduce that intake as then you've taken a tiny dredge and made it into a less then 1 1/2" tinker toy that useless. You want a suction tip with a knurled-rolled-edge to slightly reduce the intake size.or swivel nozzlewith a ring welded on. That a-52 is a sluice and never meant to dredge with but keep it for backpak fun. Blaster nozzle and seeing what your doing is next as once you can see-face in water with mask,plexiglass view tube whatever them plugups go away with experience. tons a au 2 u 2-John  ;)

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Placing a bolt through a nozzle does reduce the volume of material through the dredge by blocking far more rocks from going through the nozzle than it should. Those rocks must be removed from the excavation by hand. Personally, I would never put a bolt through a dredge nozzle.

Clogging is a function of operator efficiency. If you just stick the nozzle in the gravel, you WILL get clogs. The difference between and experienced operator and inexperienced operator can be measured directly by how many clogs they get per hour with an unmodified nozzle.

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A bolt through the nozzle is like having training wheels on a bike.

It will keep you from having hose plugs in the beginning, but will cut down dramatically on your daily production.

 

Eventually you learn what rocks will plug your hose.

Taking apart a hole without plugging the hose is a skill that has to be learned if you want to move the most material with your rig.

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Geo, experienced dredgers do not get blockages to clear in the first place. That is the point you are missing. You are not running the nozzle, the nozzle is running you. But hey, no reason for you to listen to people with "years of experience". Others may want to however so I would not look at it as advice offered to you, but to others to offset the advice you are offering. If you want to stick a bolt in your nozzle, do so and be happy.

 

To others learning how to dredge I would advise working the material properly ahead of the nozzle to remove rocks that will clog the hose before they get to the nozzle. That is what a good nozzle guy does. If the nozzles needed bolts in them they would ship from the factory that way. There is an actual method to properly running a dredge. The best way I can think of to learn the proper method is to listen to people who have been doing it for decades.

 

Look, it is this simple. You can run your dredge however you want. But if you put me on it and I get to keep all the gold I find, first thing I am going to do is pull that bolt and toss it. It would be in my way and keep me from working efficiently.

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Didn't mean to start war here guys.  I see both of your points and two methods of dredging.  I think we will keep the bolt out for now, but run it more like a suction highbanker so that the material runs to a hopper/classifier with a grizzly screen, then to a crash box onto a slick plate before it enters the sluice box.  I am really trying to find ways to slow down the flow so we don't have a raging river running down the sluice blowing everything out.  This way the larger rocks get cleaned and kicked out and we get classification before the sluice and limit the size of material running down the sluice. We also need to upgrade our sluice to a dredge sluice.  Is there anywhere in Alaska to get one without buying a full dredge setup, or are we better off building it ourselves or ordering online?  We are on a pretty shallow creek and clogs aren't fun but could be dealt with pretty easily between the two of us.  I think this method may work, but there is only 1 way to find out.   We like the highbanker and found it to be very effective in the area we are working, but shoveling gets pretty tiresome and we both don't want to be paralized with bad backs before age 40 eventhough we are finding out that dredging isn't that great on the backs either. We are not financially ready to step up to heavy equipment yet, but hopefully someday.  We are more in the testing stages right now and learning with what we have available or can create.          

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Guest flintgreasewood

I've dredged a bit but do not consider myself an expert in that area, but in reading the opposing viewpoints on the bolt issue I came up with an idea.

What if you placed the bolt at a 2/3 position instead of half way across the nozzle.  Then you get bigger rocks, lots of them, but all smaller than could clog a hose.

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