subsurface dredge

[yankee joe]

Hi every one. I stumbled on to your forum on my quest for information on building a subsurface 6 inch dredge. I found a thread of a 4 inch subsurface written by Steve with pictures. The dredge was used in Alaska. I have used a 4 inch flair dredge here in North Carolina for many years. The area I have been in is mostly fine gold with a few large flakes and small nuggets. I have spent most of those years dredging shallow water with appx. 3 foot or less overburden on soft bed rock and my time has been limited to weekends. Now I have retired and there are 6 Saturdays in every week. There are several nice pockets (pools) here overburden may be 6 foot or more. I have dredged around these pools until the overburden gets overwhelming. This is where I have found the nicest pieces. I have planed for many years to build a 6 inch with hopper bottom collector and secondary collection system using a 2 inch dredge stacked on top of the 6 to recover the fines while I am moving the overburden to get to the nice pieces I hope are lying on the bottom. This dredge will use 2 pumps. A large one to run the 6 and small one to run the 2 but still should not to big for a 1 man operation. I would like your input on this idea. and if it may or may not work efficiently. It will resemble the old American double decker dredge.

 

[Waynos]

n/t

 

[machineman]

I am not sure how the question relates to sub dredges? However I built a dredge like you are talking about. It was a 5". I used one motor and just split off a smaller pressure line for the smaller intake. I had riffles for about the first 1/3 of the box and then 1/8" screen down the rest of the box. The hopper was under the screen. It functioned well but where I was working I didnt really gain much improvement in recovery so I went back to a standard box. Good luck, I am hoping to get back out soon as they figure out the regulations.

 

[yankee joe]

Thanks for your reply. I don't expect to increase my recovery. If I can maintain my current recovery rate of fines while removing the deep lose over burden quickly would be great. I need to expose the hard pack which covers large rocks and bed rock. With the 4 inch after going down about 2 to 3 foot the hole sidewalls just keep sliding in on me and I am getting no where. I have several of these areas I plan to work. (old stream bed) I will 10 to 12 foot area at time with the sub. Then suck up the good stuff with my 4 inch. If this works I will repeat this until the pocket is exhausted. I take from your last statement you are from California. My 4inch box is a Pro Mack so I keep up from all of the latest from the New 49ers. Check it out Dave has a drawing that may work for you and beat current regulations. Says it legal. Gook luck

 

[sjmpainter]

Hey Joe I tested a 6 inch subbie with a suction nozzle and a p180 pump. Pretty unimpressed with that set up. I would recommend a much larger pump and a jet log set up. Otherwise you will not get the performance to move a lot of overburden. I would be interested to know what you end up with so keep us in the loop.

 

[yankee joe]

Hi sjmpainter Thanks for your input. I have several questions. Did you use a Keene hand held tube with suction nozzle by hand or did you float it on a set of pontoons and use hoses? If so what length were the hoses? Was it sluggish or does it keep itself clean? I plan to build a tube of my own design, incorporate it with a sump, a secondary recovery system to catch the fines. (flood Gold) and float it on a set of pontoons with 12 foot hoses and suction nozzle. I want to use my 4 inch pump and don't want to buy a bigger one. May have to consider a 5 inch rig. A 5 will still move material almost twice as fast a 4. Overburden will be mostly one and one half inch to pea size. This is why all input from you and other viewers is very inpatient before I start building and testing. I hope to start in late March or early April. I will be looking for your reply. I will post progress pictures when I get started. Thanks so much

 

[steve herschbach]

The largest subsurface you can run halfway well with a P180 is a 5". Google herschbach 5" subsurface

 

[sjmpainter]

High Yankee Joe,

A few years back I built a four inch sub surface dredge. I basically did the same as you Googled ended up at Steve's website. He has a lot of info in his Journal section with pics and stories. Also helped with questions and advice. I recommend you research that.

I built the four subbie for portability mainly. But have used it for more than just hard access sampling areas. I LOVE IT! I have the Keene tube mounted on 3 inch floats with 15 foot of hose and a suction nozzle also run a six horse Honda and the keen P180 pump. Excellent set up.

Well I decided that I need more production and better recovery. I believe that is were you are at

I found a six inch Keene tube and a suction nozzle. So I tested that last summer with 15 foot of hose and the six HP Honda/ P180 that I have. I did not mount it on a float set up I wanted to test it and see how I felt about things before I spent a lot of money on it.

I can say I am not impressed with the performance compared to the Four inch Subbie. It just needed more volume and water pressure to move material and clean out the box/hose.

The problem I see is the nozzle inlet is two inch and that would be restrictive with a larger pump set up. So the options are to modify the nozzle or go to a jet log.

Modifying the nozzle in my mind is not a good option. It is already massive and adding a second inlet or a 3-4 pressure hose to a already large and cumbersome setup, in my mind would be a poor choice. So that means going to a jet log. The problem with that is subbies are already not the best for fine gold recovery and I fear a jet would blow the box clean.
Placing the jet mid way in the suction hose will help the material settle before it gets to the tube. Also I have heard of some folks placing the jet after the tube, that may be a good way to go but I still think that you would need to place it far enough away so you did not effectively dredge your box.

What ever you build needs to be on floats. You will want at least 15 foot of hose. and anything larger than 4 inch will need 9-13 HP with an appropriate size pump.
As far as the nozzle I recommend you look at it first. A- 6 inch venture nozzle is HUGE add pressure line and 6 inch dredge hose. Well that is not a retired man's set up. Also keep in mind I think you will loose a lot of lift power below 4-5 feet with the ventury nozzle. I noticed this with my 4 and I am sure the six would not work at all with the P180 pump. That is were the jet log is much better.

As far as the 5 inch, I would like Steve's input on his 5 inch subbie but I would think you would want a larger pump even for that. Keep in mind as you go down in depth you need more power to keep the overburden moving and things cleaning properly.

I would recommend looking into Gold Hog Matting if you are building from scratch. I have been really pleased with the performance they give.

Hope this helps.

 

[machineman]

When you take the dredge off the surface you gain a lot of suction. Not having to lift the material up to the box gains you a lot. I dont see why you couldn't run a 5" or 6" sub dredge on the same pump that would run a 4" surface dredge. I have not tried it however. The standard single log power jets you see on most dredges are very inefficient. A suction nozzle is much more efficient, and a triple jet or infinity/circle jet are even better. I used to build my own jets. I ran a trijet on my 5" and had huge suction. Nearly broke my hand a few days. I have a 5" circle jet I made and never used. I planned on building a sub dredge with it. The jet stirs up all the material that passes it. If it is really close the to box then the gold may still be in suspension when it passes the box. I made inline jets and mounted them at least 5' in front of the box so the fines can settle out after passing the jet. If you look at most sub dredges they have silly little boxes. I think they could do with larger boxes.

 

[yankee joe]

Hi everyone All this input is a great help. The thought of running out of suction at 5 or 6 foot when I may need 8 foot is scary. This brings up an other question. I will be using Pro Mac pump and Honda 5.5 purchased in the late 90's. At that time I was told that this pump motor combo would produce 370 GPM and were built by Keene as apposed to the Keene's 180 which produced 300 at that time. The pumps look very much alike but the Pro Mack has no markings. The inlet and output sides are 2 inch each and both are threaded and the impeller has 6 vanes. I hope this description will help. I have looked every where I can think of but cannot gather any specs. If any one can verify this please let me know? This may be the deciding factor if my first try will be a 5 or 6 inch. I do no for a fact that a friend I was dredging at the time had a Keene 4. He would run his dredge full throttle to get the suction that I could get at far fewer RPM's. Thanks for all the help.

 

[sjmpainter]

Joe, keep in mind you can and should use two 6 HP set ups verses one. The best part of that is if you don't need the extra you can sell it and recoup the expense. Also keep in mind the depth at witch you plan to go will determine the length of hose you need. If you plan to go 10 foot I would want a twenty foot hose.

As machinman stated, you gain a lot having the dredge below the surface of the water. So if you hang the sluice and collector lower than the floats you will save a lot of needed muscle. And still be able to float the dredge around to deposit the tailing away from the dredge and work area. It just makes skidding the dredge around difficult with the sluice lower than the floats.

You stated the overburden is one and a half inch minus. My four inch surface dredge will rip through that without any issue other than the sluice loading up.

I believe the ProMac dredge is a single sluice set up. And I would look at improving the sluice area by adding classification screens and Hog matting. If hogging overburden is loading the sluice and you have plenty of poop than changing the recovery may be a good/cheap way to go. I believe ProMac has a dredge setup that they improved the sluice area with different size classification screen. Might be something to look at.

I tested the hog matting in a stream sluice and I found it will clean out three times as fast and still capture a 95 plus percent of fine gold. Installing that in place of the standard riffles and using a grizzle screen one and a half inches above should turn that four inch surface dredge into a overburden powerhouse.

I don't have specs on the ProMac pump. Send them a email. I am sure they will get back to you.

 

[machineman]

You cant use as large of a sluice on a sub surface dredge. The water pressure on the exit will cause it to load up. If you look at Keenes sub dredges you will see what I mean. I think you could use a larger box than they have but not too much. I would go with something about the same width but I would make it longer to increase chances of recovery. I think the key here is more efficient jets. I dont know the numbers but lets say a single log power jet is our base line. For this jet you need a minimum 8hp motor on a 5" dredge. If a suction nozzle is 20% more efficient then a 6.5 hp motor might be sufficient. If a Circle jet/infinity jet is 50% more efficient then a 4 hp motor could possibly work. This is all just guess work on my part the numbers are not exact. Check out this article. http://www.gouldeng.com/gettingbestper.htm His other articles are worth a read also.
The difficulty comes in making a circle or tri jet. I have made both and the tri jet was much easier to make. You really need a big lathe to make a Circle jet.

 

[yankee joe]

Hi machineman My conclusions from our discussions are A suction nozzle at the pickup end of the hose is nothing more than a pusher with an angel to get a ( center feed of pressure). A tri jet log mounted just behind the dredge is sucker with a center vortex (center feed of pressure) and is more efficient than a suction nozzle. Therefor a tri jet log could be mounted at the pick up end of the hose and become pusher. Why not build a short tri jet with a 45 degree turn-down and have the best of both worlds. The exhaust end of the tri jet should only need to extend an inch on so past the vortex point and become a super pusher. I am sure I can fabricate an Item like this from 5 inch exhaust tubing and thin wall conduit and jet it as necessary. The dredge tube will be of my own design. I have a 4 inch hand held dredge tube that I bought over 20 years ago. I tried it once then parked it. I think Keene could have done much better than this. I feel with a little thought I can build a dredge tube from fiberglass with interior treatment to settle the fine gold quickly( I have several Ideas) and a sump for secondary recovery of fine gold with my 2 inch mounted over the 5 inch tube. It may or may not require 2 pumps only testing will tell. A rig like this may be a pain to set up and tare down but if I can get to work. It will be a super 5. I started playing with dredges in the early 80's. My first was a 2 inch made from pictures and info in magazines, it was galvanize sheet metal and floated on styrofoam,I made many suction nozzles and power jets, pump was a centrifugal garden pump from Fingerhut. Belt driven by a 5 hp 2 stroke motor made by Chrysler. Intake hose was a 2 inch vacuum cleaner hose. We would bring it home and shake and wash it to get the fine gold out of the segments For miners moss I used scotchbrite pads glued to gather with clear silicone caulking. It was a beginning. I built three more before I got every thing right. For you see I lived in Panama City Florida. A long way from the gold fields of northern Georgia and gold equipment suppliers. there was no Internet. So I used what was around me and made it work. It gathered gold. Micron gold from the Chattahoochee river
I should have my new workshop completed some time in April. I may be a dreamer but you have to start some ware. This will be the first project In my new shop. I have 2 dredging Buddy's just hoping I can pull it off. When I get started there will be a full library of pictures coming your way. Wish me luck .I will need it. Thanks to everyone.

 

[machineman]

I dont think you would have much advantage of a trisuction nozzle. Plus it would mean longer pressure hose. The trijet works great about 5' in front of the box. If I was to use a suction style nozzle I would suggest just using a standard one.
I built my jets out of the materials you have listed above.
I you will probably have wear problems with fiberglass. I would suggest coating it with some sort of rubber.
If you put your jet after the sluice then the sluice will have to be about the same size as the jet or you may get plugging. Look at the old Schmidt Bazooka dredges. They had some pretty good reviews in their day. I just think the design was to radical to make it. Also it would probably not be classified as a dredge per California regulations. It doesnt have a sluice. It uses a fluid bed concentrator.
There is an advantage in not having your jet too close to the box. It allows the gold to settle to the bottom of the hose before it hits the box.
I have been thinking of building a Schmidt style dredge with my 5" circle jet mounted after the fluid bed and a 4" suction hose before the pipe. This way all incoming material would be -4" and the jet wouldn't clog. I think I could probably just put a section of .5" screen on the bottom for the material to fall through into the fluid bed. The screen would slow the flow of material above the bed and keep large rocks out. Hopefully I would see larger than .5" gold before it went in the hose. Just some thoughts If you click on the link you can see my jets. Pictures 2 and 4 are mine

https://www.google.com/search?q=tri+jet+dredge&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjqydbolJfKAhVM7GMKHZSKBDEQsAQIMg&biw=1708&bih=874&dpr=0.8

 

[sjmpainter]

Yankee Joe, I agree with Machineman. Go with a standard nozzle and some type of jet. Standard is good. Tri jet is better and Infity jet is best. And place that jet at least 5 foot from your dredge tube to allow the heavy's to settle out of the slurry prior to the sluice area. Your tube needs to be the same size as your suction hose but making a longer sluice will help with recovery.

With that being said, I don't see you need a fancy sluice, with a grizzled sump running to a second 2 inch dredge as that will be the fine recovery part. And this dredge is just for moving overburden
anyway.

Beeing pictures are fun here is a pic of my subbie.

 

[yankee joe]

Well machineman & sjmpainter Back at you again. Putting the jet 5 foot or so behind the dredge tube and eliminate the 2 inch dredge is a great idea. That is the way my super 2 is setup. 2 inch power jet lays 3 feet behind the crash box connected by a 2 1/2 hose. As for tube structure I plan to fab every thing of 22 gage galvanize to resist ware. It weights about 3 lbs( 6 inch duct pipe)but has no strength. Then cover with 3 or 4 layers of fiberglass. (aluminum will be lighter but won't wear as well) I am not sure yet but for first try I plan to use poop tube type riffle to see how it works. Riffles will be sunken a small amount and have a classifier screen over them. Dredge tube will have a rigid collar around the front. This will allow me experiment with different types of riffles, load and clean them from the front. They will slide in and snap into place. Give me your opinions on how long riffles should be 1/4 1/3 and so forth. How much taper do you think I should put in a 4 1/2 foot tube? I can buy duct pipe in 5 foot lengths. I can also buy wood shop saw dust hose to use between power jet and dredge tube. The clear vinyl on it is 30 thousands thick. It is much more flexible and much lighter than regular dredge hose. It works and wears well. I have a 12 foot piece of it on my 4 that I have used for several years and it does not suck shut. You guys get my creative juices flowing. I'm anxious to get started but need to get that shop completed first.

 

[yankee joe]

I like your pictures Keep the coming I can see we think alike

 

[machineman]

I'm a little lost with your discription. You seem to be using behind instead of in front when discribing the jet. You cant flair the dredge tube too much or you will get loading.

 

[yankee joe]

machineman Some times I get a picture in my mind but don't paint a clear picture with words. In order to help settle the fine gold I thought of tapering the dredge tube appx. 1 inch over the full length. I planed to build the tube 4 1/2 to 5 foot in length
If necessary my classifier will be in the shape of a 5 inch diameter cage made of 1/2 inch expended metal that will run the full length of the tube to contain the large rocks and let the fines settle out, This is uncharted territory for me and I plan to go where it leads. I will probably try many unnecessary things before I archive my goal. I think that the sub dredge could be just as valuable and productive as the surface but no one has ever spent the time or effort to develop it (think out side the box).
With the moratorium of surface dredging in California this may be the way to go. Take a look at the video on you tube of Keens new super six 6220s max dredge. I built a hopper front end attachment very similar to theirs for my 4 to the catch the fines 10 years ago and never used it because time would not permit. Now that I have retired and with a little help from guys like you I plan to follow through with some of these ideas. Keep an eye on me this won't happen over night. I am always looking for a better and easier way. I also have ideas to build a smaller lighter 4 inch surface dredge. If God will give me the time I need I will succeed. Thanks for your help and patience.

 

[machineman]

Any suction mining device is illegal in californai now. Not just regular dredges. A 1 inch flair should be fine.