Let's be honest. Running a dredge isn't rocket science. It pretty much comes down to sucking up gravel and hoping you find some gold. The first time I ever put a dredge in the water I had no one to tell me how it went together and I might have skipped a step or two, but I pulled the starter, put the regulator in my mouth and promptly sunk my first dredge. After an oil change and a quick read of the owner's manual I put it back together and still managed to walk away with gold that first day.
The one truism about gold is its heavy. It will sink and sink until it can't sink. You simply need to find where it stopped sinking and suck it up. It will hit bedrock and slide across the bedrock until something stops it, like a crack or an obstruction. There are some places it should have stopped but didn't, and some places it shouldn't have stopped but did. If you've dredged before and spent any time looking for gold you know sometimes there is no amount of explaining why gold was where it was.
Regardless of the size dredge your running they pretty much operate all the same. The only difference is the amount of pain and effort, but each size dredge comes with its own unique pain and effort. If you're running a 2" then you have the work of packing it in, and out. If you're running an 8" then you've got your own problems that come with running a dredge the size of a car, and with as many parts. You may not be packing it, but it's still work.
Regardless of the size of the dredge it still all comes down to finding where the gold is, and eventually, avoiding where the gold isn't. Reading the river, and the bedrock under the river is the most important skill for a dredger.
Good dredgers can read the bedrock from above the river. They can look at where boulders are hanging up and know there is something on the bedrock which is dropping the velocity of the water enough to drop out heavies. An experienced dredger will avoid a stretch of polished bedrock like the plague, even though that bedrock is under four feet of overburden, they can still tell.
I spend more time than is probably healthy thinking about bedrock. Now I dont' plan on confessing this while laying on a couch and talking to some guy about bedrock and my issues with my mother but its the rare dredger who isn't fascinated by bedrock. If you plan on dredging, then you should start thinking about bedrock.
Although you can generally tell what the bedrock is doing under the water by looking at the stretch of river, the curves, where boulders are hanging up and what the bank looks like, I've found it can still surprise you. Gold wants to return to the earth and it will do that eventually. Gold is persistent. The bedrock cracks are only temporary resting places until its broke free again, and each big flood changes the bedrock to some degree and either breaks the gold free, or catches it.
It is all about the bedrock. I've learned that the hard way. It doesn't necessarily mean the gold will be lying on the bedrock, but what the bedrock is doing will influence what the gold is doing. For several years I worked a nice stretch of river, always punching holes to the bedrock, through five or six feet of overburden. Each time I punched a hole I punched right through a pay layer which was several feet above the bedrock. I just didn't know it was the pay layer because I was focused on getting to the bedrock.
The hydraulic mines in California created atypical situations. The natural gold spent millions of years sinking to the bottom of the rivers. The hydraulic operations pushed so many tailings into the river, in a short amount of time, the gold is still running in a tailings pay streak above the bedrock. Once you know what it is you'll do OK working it, as long as you're not just punching a hole through it. It's a layer of white gravel which is pretty uniformly all quartz. It runs a lot of gold, and a lot of quartz nuggets. They're floating. I found a one ounce nugget well above the bedrock because it had enough quartz with it it was floating in the pay layer.
When I first started dredging anywhere I found bedrock was where I put the nozzle. My second rule was when on bedrock, stay on bedrock. I found after a couple of years of following my own rules gold has a habit of not sticking where there is exposed bedrock. If the bedrock is exposed there is a reason for it.
By now I'd qualify for a PhD in bedrock if they awarded such things. I've been on some of the finest bedrock known to man and still been skunked and I've been on lousy soapstone bedrock which shouldn't hold any gold and had some great days. A good dredger will stop and ponder these things, but no amount of thinking will substitute for just pushing a nozzle in the water and exposing the bedrock.
There are a lot of books on dredging, and a lot of experts. Most of the experts I know are out dredging gold and not writing books. Someone once said "gold doesn't read books." No truer words can be found. Certainly there are lots of experts on dredging, but no reading beats the experience of doing.
You need not concern yourself with how much you recover per day. The nature of placer mining is sporadic return, this is especially true when you're running a dredge. If you're moving gravel using a trommel and bucketloader your returns are based more on how much material you can move, but when you're dredging your returns are based on hitting streaks and pockets. Some days you may not recover enough to fill the bottom of a bottle, and then some days you may do great. Persistence is the key to dredging. A pennyweight a day adds up to pounds over a couple of summers. Just stick with it.
On one small creek I was dredging a few years ago I was picking up about two pennyweight a day just cleaning off some exposed bedrock. I noticed whenever I ran into the old square nails I'd pick up gold, no nails, not gold. Each day as I walked up to where I was dredging I passed a bedrock hump. A slight rise in the bedrock of a couple of inches and behind the hump I could see where rocks were hanging up. An ideal place for gold to catch. A few days later I moved the dredge down to the bedrock hump and immediately started hitting rusty nails throughout the material as I worked the nozzle towards bedrock. The drop behind the bedrock was more than I expected and I was confident when I hit bedrock I'd be in good gold. As I reached the bottom it was just littered with nails and metal, but no gold. I kept working the bedrock from bank to bank and still no gold. After a few hours of this I finally pulled the dredge and moved again.
A few days later I was telling this story to a friend of mine who's pretty good at getting gold and asked him why he thought there was no gold there. He replied "There was no gold there."
I couldn't have summed it up so simply. Sometimes there just isn't any gold there. The truth is no one can tell you what's going on under the water. You can make some educated guesses at it by trying to picture the river at full flood stage but at the end of the day gold is where you find it.
The size dredge you use and how many hours you've spent on it will help you increase your gold recovery, but the truth is even a rookie can throw his nozzle in the water on the right day, at the right place and hit a nice pocket. Yeah, some of it, a lot of it, maybe all of it is luck.
Want to start dredging for gold? Get a dredge, put it in the water and start the motor. Run enough rock anywhere in the Motherlode and you're going to get gold. To consistently get good gold requires a lot of experiene, but to just get gold you just need to start.