Sub Surface Dredge

[sjmpainter]

I picked up a 4 inch subsurface dredge tube with hose and a suction nozzle.. I need to set this up. I have two options for the pump. I have a three horse Honda with a Keene p90 or a five horse Honda with a p180 and air. I am considering using eight inch Keene Marlex floats from my two inch dredge but can use the floats from the four inch dredge. I want to make a lightweight and very portable dredge but I do not want it to be under powered or unstable. Thought I would through it out and see if any one can offer advice that would save some trial and error.

 

[steve herschbach]

The unit I built used a 4HP and floats off a 2.5". Pictures etc at http://www.detectorprospector.com/steves-mining-journal/fall-dredging-subsurface-dredges-mills-creek.htm The P90 is too small to run a 4" subbie. Several more stories about using subsurface dredges at the same website on Steve's Mining Journal.

 

[sjmpainter]

Thanks for the link. Thought I had read all your stories, but I have missed that one. As I read through it I can relate that to my situation. Hit the nail on the head there. Anyway how do you feel about the four inch set up? Is there any changes you would make in hind site. Looks like I can make the same set up with 2 1/2 inch floats for under 300.00 and would not have to steel to much from the other dredge. Thanks.

 

[Hoser John]

Your suction nozzle unit has much better recovery than a powerjet as the remix at the box really hurts recovery. Subbies are extremely easy to rock sideways and with that miniscule recovery box the contents spill out and get blasted away. I use rebar to attach the box to the floating frame to keep the box as level as possible as both end to end and side to side rolling is a real killer to recovery. Also keeps the box off the bottom which almost immediately backfills with a pile of rocks and blocks the discharges also. I personally much prefer a surface dredge for fines recovery with a over/under recovery system.John

 

[steve herschbach]

I really liked that little 4" I built. I could haul the whole thing around in two loads and it fit in the back of my truck like it was made for it (it was). Not really anything I would change if I did it over again.

As John notes you just have to accept that you will have more gold loss, but it varies greatly depending on the makeup of the material and the nature of the gold. If you are lucky enough to be dredging heavy shot gold the losses will be minimal compared to fine flaky gold, where losses can be so extreme as to make a subbie a bad idea.

 

[sjmpainter]

John are you using the rebar as stabilizer legs that go from the dredge to the river bottom? I did not consider the roll and pitch being a drawback. Makes sense that would be an issue in the box.
I had originally thought about mounting it to a sluice stand ( that would help the stability). But I really want a floating system for ease of one man portability. So floats it will be.
I have read that they are poor at fine gold recovery and this will be the big issue for me . My claims are in Hatcher Pass on Willow and that is fine gold there, but I can use the four inch there. The subbie is for other adventures that I wont be able to drag the heavy dredge into. It will be interesting to see the difference in the two.

Steve I will probably end up with the same set up that you built. But thinking about adding some transom wheels. I think you are right portability is the key to new adventures.
By the way I like the stories and info on your web site. Hope you can find the time for new stuff. Thanks.