Anyone ever added hydraulic riffles to a Keene 4" dredge? Just looking at options for dealing with large amounts of black sands.
Or maybe it’s possible to add some other hydraulic bar component that just drops into the space on 2 of the standard riffles so can be added / removed as needed.
I’ve nearly sunken my dredge in the past, working on my own, with the build up of black sands. I popped my head above the water and found the dredge almost vertical in the water.
The shotover is terrible for black sand adding weight to your dredge. When I dredged on it I used dredge nz pontoons. The weight meant adjusting the balance of the motor and pump so that once weighted with black sand it sat right. My mate had a massive set of ex booze barrels to counter it. With a keene dredge you might need to look at adding another set of pontoons too. And you def want it running right to keep the black sands clearing. Just means keeping an eye on it more often that usual. I found it OK with the finer black sand but could def run into trouble quick if you started catching the bigger chunks that can be found in abundance in some spots.
Not a proper solution by any means, but I find the best strategy is to be aggressive, run the sluice angle a bit steeper when removing overburden layers, obviously steeper will lose some gold, but not as much as you’ll lose if the riffles are packed with sand.
Once you start consistently seeing gold go up the nozzle it’s time flatten the box a little and slow the feed of material going up the nozzle
Cheers guys.
I used the more aggressive angle approach, seemed to work okay, but figured if I could introduce some hydraulic riffles then I might catch more gold.
Extra pontoons are not a bad idea, but I’m a bit worried that if I’m not clearing the black sands well then gold may be floating over the top of it and being lost.
The steeper angle is def a good idea. Just have to keep a close eye on things. I find the black sand will lose some fine gold esp the scaley thin flakes in parts of the shotover. I used rocks each pontoon to help make easy adjustments. Just have to remember not to forgot the rocks as the extra weight and black sand weight not good haha. The rocks keep it level and then as it loads up I ditch the rock or move it forwards whatever is needed. I found 2 or 3 smaller flat bits good as easier to move about. Well that worked for me with the dredge nz green pontoons. They tend to sit up a bit higher I think than the keene setup. Probably lose a bit of lifting power but it’s what I have and has worked fine. Good pontoons in the flow I think. Great shape to handle it.
I must admit, I use rocks like this all the time to even things out… usually because of river flow pushing against one side of dredge more than another, so it helps keep the box flat 
if the extra weight of black sand nearly capsized your dredge I would guess the you have insufficient floatation, minimum requirements I live by is when you dredge is running you need the have less then 50% of your floats under water and slightly more than 50% out of the water. even with those margins I have tipped a few dredges over for various reasons, mainly because I to work alone and have no spotter. My claim in the pomahaka was terrible for black sand so periodically I would clean the riffles out with a big magnet and process the black sands afterwards. Sorry I have no knowledge of hydraulic riffles and there ability to remove black sand but would hazard a guess you would only be shifting the black sands to other areas of the sluice were there is no hydraulic riffles.
I’m more interested in the hydraulic riffles to help recover more gold that would otherwise likely surf over the black sands and be lost again. At least this way there would be areas of the riffles catching more gold than I would be otherwise.
I like the idea of periodic cleaning with a magnet though. If imagine that would help a lot by resetting the situation. Cheers.
Get in touch with Ben & Murray both share holders in the shotover they use Hydraulic riffles on there dredges, best way to go……
Cheers @1980s, I’ll pop in and see if I can take a closer look next time I’m in there.
I must admit that I was hoping someone was going to mention some pre-fabricated solution I could just drop in so I could be lazy 
But I’m guessing it’s all custom fabrication type solutions for this type of thing.
Full length classifier screen. Lengthen your box. Steepen angle until material clears.
The full length wouldn’t stop the build up of black sands though would it? They’re fine enough to get through the mesh with the gold… though the larger heavies won’t be an issue anymore.
Yes because your only dealing with material the size of the mesh as well as a longer box and steeper angle on the box deals with the black sand