People say the 2" backpack dredge is a toy. I disagree. It is a valuable prospecting tool and a whole lot of fun. With the backpack dredge you can work areas where a larger dredge can't.
Prospecting new locations is a series of steps with each one involving a greater commitment of resources and time. After an initial assessment of creek using a pan I will bring in a backpack dredge for more thorough sampling. I've often found if a stretch is showing good gold on the banks, then there is better gold under the water.
For me the backpack dredge is the next step up from panning. I skip the sluice box as its a tool I really don't like. I'd rather run a little dredge than spend my day hauling 5 gallon buckets of dirt and kneeling next to a sluice, but honestly, I just like to run a little dredge.
I've owned, and still own several dredges. I've had two 5" dredges which I used to run; I've still got a nice 4" which is a great dredge; I've got a 2.5" and I have the trusty 2" dredge. The little 2" was built back in the early 1980's and I'm on my third engine - a Honda 50cc. I can swap that engine back and forth between the two and the two and a half which makes it convenient.
I work alone, as many dredgers do. Weight matters and it matters more as you get older. The 5" was a great dredge and moved a lot of material, but it took a lot of effort to move it. The 4" is far more portable, but when I'm running it I miss my 5". If I'm going into a new area my tool of choice is always the 2".
The 2" is a prospecting tool, not a recovery tool and you have to use it for what it's built for. Don't even think about moving overburden with it. It's built for shallow water and little overburden, but you should have seen some of the cracks I've hit with it. I once hit a nice crack on the South Fork of the Stanislaus which had been passed over by a lot of dredges because it was a shallow shelf in about three inches of water, but it was in a section of rapids where it was unlikely the area was ever exposed even in the driest of summers. The crevice was just lined with nuggets going all the way to the deep water. I picked a lot of nuggets out of the crack that day, I can only imagine how the person with the bigger dredge in the deeper water did when he picked up the crack and followed to the other bank.
Another day I was working a stretch of shallow bedrock on the North Fork of the Yuba in an area which had been hit by hundreds of dredges over the years. I simply picked a flat shelf in about a foot of water and started the engine. If you've ever worked the North Fork you know what you're looking for. I began cleaning out a small pocket in less than 2" of water. It had those round black rocks impacted in the pocket which was about the size of a silver dollar in size. As I got past the first inch or two I began picking out nuggets, within an hour I had a collection of about an ounce of nuggets from that one small pocket. It was a place the bigger dredges had bypassed always shooting for the twenty foot hole in the middle of the river. I walked away with more gold in that one hour than the two other dredgers had recovered in two weeks. Think small.
The backpack dredge is for underwater sampling. I use it to work the bank down as low as I can go before I hit more than a foot of overburden, then I'll just move. If the creek is showing good gold then I'll come back with something bigger. Sometimes that something bigger is the 2.5". You'd be surprised how much more material the 2.5" can move than the 2" and the greater depth you can hit.
I've got enough years under my belt I'm beginning to avoid packing heavy things into the mountains. When I was in my thirties, no big deal, but the stuff really gets heavier every year. I'll still pack in the 4", but the 4" takes about a day to pack in. The 2" I can pack in one trip, the 2.5" takes me two or three trips depending on the country.
The obvious feature of the 2" is its portability. You can pack it in the morning in one trip, be dredging before noon, run all day and pack it back out.
The backpack dredge is also a popular dredge. Nearly 25% of all dredgers reported using a backpack dredge. I have found portability to be the key to getting good gold. I use the type with the inner-tube float. I have found pontoons to be just more stuff I have to carry, but the inner-tube I can deflate and throw in my pack with a foot pump.
The above creek is a perfect 2" creek. The tight canyon sweeps the overburden, and the gold, right on through, but the lack of overburden means you can throw on a mask and work your way up the slot looking for cracks. You're not going to find any fine gold in this slot canyon, but you can pick up some nice nuggets. This particular section I pulled a half ounce of nuggets from one pocket. The rest of the section was just swept clean.
The 2.5" is also a very good size for portability. It usually uses the same engine as the 2" but has a biggers sluice and frame. The extra 1/2" of nozzle size makes for a whole lot of extra capability versus the two.
If you're going to use a backpack dredge then you have to think differently. If it's a creek suited for a bigger dredge, then use the bigger dredge. You're not trying to compete with bigger dredges, you're trying to pick up the gold they bypassed because of water depth or features of the stream which made it to difficult. For example, I've found most dredgers tend to work the pools and avoid the rapids where the boulders hang up. Although the gold is hanging up with the boulders most dredgers seem to shoot for the deeper, calmer water. That may be because it takes days of work to pull boulders and a lot of dredgers don't have the time. With a little dredge you can throw it into the middle of a boulder patch and work under the boulders picking up some nice gold. The bigger dredges have to start at the bottom and work their way up and sometimes that can take a whole summer just to clear a path for the dredge.
My experience with the smaller ravines, and the smaller dredges, is they hold some pretty good gold. You have to put the work into it, and these areas are always off the beaten track. However, these rocky slot canyon can be a real bonanza for you.
The picture to the left is some gold picked up in a ravine which dries up in the summer. I caught it on a spring afternoon and had a great time picking up little nuggets. I've worked a lot of these smaller canyons and recovered some nice gold. I've also had plenty of days where I got skunked, but it's the days you do well which keep you coming back.
A backpack dredge isn't for everyone, and it's kind of like driving a Toyota Prius when everyone else is driving a 3/4 ton truck. People kind of sneer at you as they pass you. That's fine, what counts is how much gold you have at the end of the summer, not what of tool you used to get it.