Converting a 4" dredge

[goldtimer]

Hello,
I have a 4" dredge and I'm finding that most of the stones in the river i'm dredging are too large for this diameter nozzle.
I have a 6.5hp Honda motor with a T80 air compressor and a Keene P180 pump.
I have 6 metres of suction hose

If I half the hose length to 2.5 - 3 metres what is the maximum diameter I could go to to move the larger overburden?

Thanks
G.T.

[roscoe]

Hi, Gt. If there`s bugger-all gold in the overburden, why not just run a 5m x 6inch hose across the bottom and squirt the oversize out of the way? I think you might barely have enough grunt from that setup if you don`t have to lift OS to the surface.
Mebbe not. ;D

[RKC]

G'day Goldtimer,

You don't have enough power to go any larger in diameter. A motor of the size you are using at present on your 4" dredge is the absolute minimum required for a 4" dredge and is actually less than I would be happy to use myself. If you went larger ... say, up to a 5" dredge, you would need to add more power and you would still find you have the same problem of having to manually move numerous rocks. If you then went to a 6" dredge you would probably find that this size dredge would be a big improvement on the number of rocks you can put through the dredge and not have to move manually. But to run a 6" surface dredge you could not avoid having to significantly increase the motor HP and overall size of the dredge used. Using a 6" dredge would go a long way to overcoming the rock problem, but then you would have extra problems such as moving a larger dredge around and the extra costs of building a larger dredge. In the situation you face I would first sample the river with the 4" and then if the gold is proven to be payable over a large area, I would not hesitate to put in a 6" dredge. But there may be consideratios you have to face that I could not possibly be aware of which could require you to stick to using a 4" dredge.

Something else to consider would be to use another another man on your dredging operation as a rock man. With two men working together underwater one can concentrate on operating the nozzle to ensure its being fed efficiently with another man positioned ahead of the dredge to move by hand the larger rocks out of the path of the dredge. However, if this is not done in an efficient manner a rock man can be a hinderance to the nozzel man. A rock man has to be able to move the rocks without clouding out the nozzle man so he can't see where to direct the nozzle and he can't be getting in the way of the nozzle man (in a fast current the rock man can be easily swept into the nozzle man if he is not careful). It does take some training for a rock man and a nozzle man to work in unison, but when two men can work together efficiently it does increase production considerably.

Professional dredgers will commonly use two men underwater as they know its all about production if gold is to be produced in payable quantities. And even though the extra man will be getting a percentage of the gold it nevertheless remains worthwhile to use two men underwater in most production dredging situations.

The article at the link below has excellent advise about coping with oversize rocks:
www.promackmining.com/productiondredging.htm

To answer your specific question ..."If I half the hose length to 2.5 - 3 metres what is the maximum diameter I could go to to move the larger overburden?", my guess would be that while still using a single 6.5 hp motor, you could not . For example, if you had a 5" diameter suction hose that is between 2 and 3 meters long you would have difficulty getting sufficient suction from a single 6.5 HP motor. And, incidentially, a suction hose 6 meters long is a longer length than most dredgers would commonly use. The usual length of a suction hose is 15 feet ... and that length is the maximium length for the dredging situations the vast majority of dredgers will encounter.

Regards,
Rob (RKC)