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Arctic-moose

Why Are Dredge Sluices So Short?

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The part going unsaid is dredge manufacturers already reduce nozzle openings to less than the hose size. I can conceive of times when it may be advantageous to reduce the nozzle size further. Like in pure zero visibility blind dredging, perhaps. At the end of the day people do what works for them. It is something the pros generally avoid, for a reason, and that is the last I am saying on the subject.

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I agree with the no bolt option.

However, if you do put a "bar" or bolt across your nozzle, don't put it through it.

Weld it in front of the nozzle about 1/4" to 1/2" away from the front.

If you put a bolt THROUGH the nozzle, you create a suction notch / groove where larger rocks get stuck.

Have it out in front, it classifies without clogging.

But... most dredgers DON'T use a bolt. It doubles the clearing time with your hands.

You get the hang of what rocks to pull and which ones not to pull.

 

On the sluice length...

Most standard dredges use larger aggressive riffles.

Therefore a long sluice is not needed.

It's a flow interruption system with voids / low pressure areas to hide gold. 

However, they can fill up with rocks and start the battle of MASS... not just specific density too.

(Since the majority of dredges do not classify.)

 

We use mostly exchange matting / surfaces and very high water speed / more pitch on ours.

So, our sluices are often longer than most.

Most dredges will have water that is 2-4" deep, ours runs about 1"

So... it is a different config.

It's a bit of overkill but very efficient.

Here's our fun 5"  "redneck build" for this year.

We do one of these projects each year.

 

12449_486544834732961_1105548663_n.jpg

 

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GoldHog.com 

Doc has a whole webite including a discussion forum on his mats.

 

Bolt through nozzle=newbie or a lazy-dredger. There are tons or video's where experienced dredgers never drive the nozzle into material being dredged. "Hoggers" get plugs, people who won't stick their face in the water get plugs, people afraid to lay down in the water get plugs, because dredging takes two hands!

 

As far as short sluices, I'm with Steve...

Since I rarely dredge roadside and carting long items through tight woods sucks!

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That 4 inch proline I got from amds,I would not change a thing.Had to buy a swivel nozzle,but that is worth it.To me,a bolt in that nozzle would make it cheeper.3 stage sluice is perfect.

I would just change the bolts from the flare an put them on the sluice box.Seems it would be easier to bolt on the flare.Instead of going undernieth the sluice to bolt it together.

No need to lengthen the sluice on that one beutifull litle dredge.Oh!I said I would not change a thing.Lol.Just reverse the bolts holding the flare.

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Most people should NOT use a bolt through the nozzle. Proper handling of material is right way to work a dredge. 

(When training new dredgers I do use one and we call it "training wheels".) 

There are times that one is needed, however. 

We often hit areas with AMAZINGLY tough hard pack that is like cement. You can NOT tend the nozzle properly. 

We are running a 5" (limited by regs) and we run the suction VERY high to eat away at this hard pack. 

By the time you see the large rocks, it's often too late, swoosh they are gone. 

When working this type of area we weld a bar IN FRONT of our nozzle. About 1/2" 

It does not restrict the flow, stops huge rocks from going in, and helps us with digging into hard pack. 

We can set this nozzle right on the hard pack shelf and allow the suction to eat away at material and still have 

lots of water flow. (Think about putting your hand on a vacuum tube, it stops all the air flow.)

 

You can see the bar in this short video. This wasn't CRAZY hardpack, but pretty tough stuff.. 

 

http://www.facebook.com/photo.php?v=400016633445018&set=vb.238066632914117

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Ha hahaha Flaired jets reduced the turbidity, larger difusion flaps increased the deaireation,wider sluices alowed more square inches for smoother flow, and righteous over/under provided twice the classification area in one easy MUCH SHORTER unit. Bolts??? no not never in any way shape or form. It's taken years to get folks away from crash/bash/smash boxes and slow,spread and recover fine gold. ;) 

post-14636-0-74099300-1369920857_thumb.jpg

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Old thread, but I will respond.  Everything is relative.  It all depends on your situation.  I am currently dredging/ 5" (limit) hose, 50' long.  I may cut it to 40' once I get adjusted to the '0 ' visibility from surface to 18', then the bottom 4' has vis. for about 10' around.  Tons of moss in the water, clogging the intake, but unusually warm water.  Nasty conditions.  Anyway, I get lot of jams from little stuff due to the high lift.

I can't keep going up and down the hose to fix jams.  I am definately going  to put a bolt through the nozzel tomorrow, maybe even two.  I just can't afford jams.  I'm in Washington state and the season will be ending so "I don't need no stinking jams".  You only have to do that which works, there really are no rules.   Thanks- Allen, from the Similkameen River, 2013.  Me and Josh, and the Lucky Duck.

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Disregard, Marines.  I went back and read other comments.  Putting the bolt-bar out in front is better for many reasons, I will adjust. I'm also putting a 5 gal. bucket / vented over the noz when I have to come up

to keep it from plugging up while laying there on a union coffee break.  Life sucks, I hate having a union nozzel.  My partner has all these great ideas, all I do is pay him more.

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Thanks for the advice! There are certain things to learn about dredging. Learning how to clear unnecessary blockages "as part of being experienced" isn't part of what makes sense to me! So, I will produce more gold because I don't have to stop to clear blockages.

 

For me it's a solution. Nobody asked what material I'm running or how deep the water is. I'm running in water that is over 10 feet deep. The 6" suction hose is about 25 feet long. I would have beach the dredge and spend an hour or more to clear a blockage. You don't need years of experience to figure that out. :)

 

Thanks again!

 

- Geowizard

You are totally correct Geo I have dealt with my 4 inch dredge plugging up by placing a bolt through the center of the nozzle and you cannot clear out the rocks in front of my nozzle they are all to close to the nozzle size or smaller and will block my hose, if you want to capture lots of small gold use miners moss instead of carpet!!! I built my own 4 inch dredge and built the power jet for it , it will suck a tennis shoe right off your foot ! And I also use a ten foot piece of underground pvc conduit to run down the flare jet to dislodge rocks, actually all of this stuff is pretty simple, just because someone has a good experience doing it there way does not mean it automatically applies to you ! What works best for your situation is the best and only approach I consider when dredging, no one and I mean no one can understand your unique dredging variables like you do or can give you advice without working on you placer project. Hey but what do I know, maybe my 35 years of experience as an Industrial and field serviceTechnician , certified scuba diver, recreational miner don't mean anything I also have a degree in Industrial Technology and Electronics. What ever works ,no one has deemed what dredge design works the best every manufacturer has there own ideas, just use common sense and adjust yours to the way you want it to work, that's how I set my equipment up and I bet you do to.

Rick

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The bolt doesn't reduce the suction volume. A 6" is still a six inch. I used 3/8" all-thread, drilled two opposing holes, ran a 7" piece of all-thread through and put a nylon lock nut on both ends. No more problems! The rocks lodge at the nozzle. I haven't had to shut down for a blockage since! :)

 

I recommend this simple mod to anyone having problems with suction hose blockage!

 

- Geowizard

You are totally correct Geo and if you want to remove it later you can , but I did find my dredge worked better with the bolt in it , stops all of the blocked hose problems!!!

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It's my dredge, my bolt and my mine. The bolt stays! :)

 

The gold passes a 12 mesh screen. The dredge is a Keene Mini-6". So, no point in passing 4" rocks to the sluice. The bolt won't slow the minus 12 mesh gold. 

 

Have a great day!

 

- Geowizard

I noticed the same thing with my 4inch dredge and it really does keep a lot of large rocks out of the dredge, it makes for better gold recovery!

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Getting back to the original question, Chris strongly hinted at the reason for short sluices and several others followed suit. But they didn't finish answering.<br /><br />Water velocity is the key like Chris and others pointed out. The rest of the story is the water in the sluice gathers velocity the further down the sluice it goes. Higher velocity = higher turbulence.<br /><br />So here is the process flow.<br />1. Slurry is deposited in the sluice. In crash-box designs, the longitudinal velocity is zero. In more modern flare designs, the lateral velocity is slowed from what it was in the hose, but still 25-35% of what it was.<br />2. Raw gold has a SG roughly 6X that of the rest of the material and falls through the water column fast.<br />3. The further down the sluice the slurry flows, the higher the longitudinal velocity becomes until all the slurry stays in motion. This occurs at roughly the 2-3'mark. Any length beyond that without forcing the slurry to slow is just for looks.<br />4. So how do you tell where the velocity has gotten to high? Look for the rooster tails (lateral currents)off the side walls. Where the rooster tail starts on the side wall is the maximum effective length.<br /><br />Water flowing downhill will increase in velocity until it hits the limit imposed by friction. Friction is most influenced by depth. This depth issue affects not just sluiced, but also pipe and hose where the highest velocity is at the center of the hose/pipe.<br /><br />Now along the same lines, folks talk about riffles, eddies and turbulence as some arcane form of science with low pressure zones and blah, blah, blah.<br /><br />Turbulence is what holds material up inside the water column. Period!!!<br />This includes eddies.<br />Most folks have seen potholes in a river. If the pothole is only exposed during low water, there is rarely any gold in it. The reason? It is the hole ground out by an eddy. The eddy kept everything in suspension until the downstream current carried it away.<br /><br />The purpose of riffles is to afford a hidey hole for the gold. The desired qualities of this hidey hole is out of the current, but just a bit of internal agitation. The agitation permits a material exchange with higher SG material replacing lower SG material. This is somewhat affected by random material sizing. If the agitation isn't high enough, large material with a lower SG might not get bounced out or the hidey hole.<br />---------<br />Now as the thread drifted into a urinating match about bolts in nozzles, I can say with all certainty, in fine gold country limiting the size of the material in the slurry can result in a higher percentage of recovery. Please note the use of can versus will.<br /><br />I don't dredge much, but I do have the ability to observe and analyze what is taking place. I also have ADD which means there is every possibility that what started as a workday can easily turn into an ask Mr. Science what is going on, let's experiment and see what happens day.<br /><br />Reducing the size of the material going up the hose reduces the water velocity requirements going into the jet. The slower moving material in the hose results in slower moving velocity of the slurry going into the sluice. Slower water has minimal turbulence thus permitting small gold to fall through the water column. This water column is shallower due to the reduced water velocity in the hose. This shallow water column has an additional effect of more effective friction. (The friction per water velocity is the same. The difference is how much water percenate-wise is affected by the friction).<br /><br />Never forget, the odds of recovering a high percentage of -20 mesh gold in the same sluice that has 2", 4" or 8" rocks tumbling down it is awful low.<br /><br />The purpose of the dampener has nothing to do with air. It has everything to do with developing more friction loss to the water column. Air is NOT the problem and never was. Gold isn't floating. It is ALL about more friction loss. This friction loss helps develop and maintain laminar flow in the sluice.<br /><br />Based upon my experiments and other folk's research, the preceding is a paid announcement, er no. The preceding is the only explanation that meets the demands of scientific inquiry. If the science can't back up a person's explanation, Occam's Razor would make it evident that the explanation is the problem.<br /><br />So what to do in fine gold country?<br />Reduce material size in slurry. Bolts and screens work.<br />Reduce velocity in sluice. Smaller material doesn't require suck your gloves off nozzle suction.<br />Use a riffle system that encourages material exchange.<br /><br />I will continue to use a bolt, screen or whatever on my nozzle. I contend the elitists are of the same ilk as the modern day Isaac Waltons proclaiming that only those using dry flies in size #24 and smaller hooks with manual reels on split bamboo rods are real flyfisherman. That 12 YO using a Zebco rod and reel, a bobber and a hand-tied fly using hair clipped off of Rover who brings home a stringer of crappies is the real fisherman. It is all about eating fish for dinner or filling a vial with flour gold.<br /><br />Disclaimer: My largest dredge is 2.5" and the largest I've ever used is 4". The 4" was real work. It was and is my observation that dredges are poor excavators. Only the greatest of fools would dive in a glacial river. Ergo long-arming is the only option and even that is blind. Going larger and larger dredges only imposes greater demands for an effective classification system to maximize small gold recovery.<br /><br />Preachy? Yep. But I hold elitists in disdain and have no problem countering their emotional arguments with good old fashion hard science. The neatest thing about science is it only take one replicable exception to eliminate a theory or disprove a hypothesis. Just one! Feel free to disprove mine. I have no emotional connection to it and as new data comes in, well it is subject to change.<br />eric<br /><br />

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