|There are many different ways to recover natural gold from bearing rivers, creeks, and streams. One method is to utilize a suction dredge. I've had the opportunity to use a wide variety of prospecting equipment, and each has their list of pros and cons. In my opinion, dredging is the most effective way to process high quantities of bearing gravels while returning worthless materials back to the same general location. This opinion is due to one simple fact: Gold is heavy and dense and won't stop moving until it works its way down into a place that ultimately stops its movement.|
Suction dredges, like an underwater vacuum, remove all the materials that reside on bedrock and put direct suction into cracks, crevices, depressions, and other places where a shovel cannot reach. Even if you could shovel all day long and somehow match the material being put through a dredge, you're not going to get a majority of the heaviest (and most valuable) material that resides on top of bedrock and in those cracks. The below photos show the cracks and crevices typically found on bedrock where big gold likes to hide.
If you're lucky enough to get on a really hot spot, you can sit there and pick the gold out of the cracks with your hands. That's a great feeling to pull the gold right out of its hiding spot, and it provides a perfect demonstration of where gold ends up in those absolute bottom places. When I get into a spot like that, I'll sink a pan on the bottom of the hole and put the pickers and nuggets in the pan. That's a lot of fun and doesn't happen very often! Although it's not common to come into a patch like that very often, it is quite common to see a piece of gold on bottom when you are dredging. In the below photo, you can see the pickers in the pan if you click on the photo and look closely.
In some cases you may find yourself working in a spot that has already been "worked over", or dredged before. Everyone has their own style of dredging, and not everyone takes the time to bust clay layers that conceal the bedrock cracks that have been packing gold away for eons. If there is one thing I have learned it's to slow down on bedrock and clean out every possible crack and crevice. Break open cracks until you can't break them any further. The below photo shows the cleanup from a single crack in bedrock. The crack was about 3" wide and about 3' long running across the creek. It was covered with about 2" of hard-packed clay and small cobbles that formed a very hard cement-like false bottom. This spot was definitely dredged before and the signs were easy to tell on the way down to bottom (loose material, all the same size, very little gravel, no silt, etc.). However, whoever did this particular spot before did not take the time to find true bedrock. The crack was filled with lead shot, heavy metals, garnets, pyrite, and just a massive amount of gold for crack that size. These photos show the top mat after panning off the quartz. Are there more cracks like this out there? Absolutely, no doubt in my mind.
A suction dredge comes in many shapes and sizes, but the basic purpose of a suction dredge remains relatively the same no matter the size of the unit. The purpose of a suction dredge is to:
- Remove gravels from the bottom of a stream, creek, or river using suction created by the forced flow of water,
- Transport the gravels through a suction hose and deliver it to the sluice,
- Deliver the gravels from the hose into a sluice using a crash box or flair,
- Deliver enough water flow to force the material over a set of riffles or other low-pressure creating surfaces,
- Deliver enough water to discharge worthless gravels back into the waterway,
- Provide low or no pressure areas in the sluice which allow gold to drop out and hide,
- Permit the adjustment of water flow and angle to maximize the efficiency of the sluice,
- Be transportable to allow for maximum flexibility and ease of movement.
Major Components of a suction dredge:
- High Pressure Hose
- Foot valve and hose
- Suction Hose
- Suction Nozzle
How do they work?|
Suction is created using water forced through a jet which creates suction at the end of the hose. The amount of suction can be adjusted by changing the RPMs on the engine to which the water pump is attached. A nozzle is attached to the end of the hose so that gravels can be "sucked" up into the hose based on the diameter of the nozzle and hose. Rocks which do not fit through the nozzle are discarded by hand, and the operator also works to discard any rocks which may fit through the nozzle but may cause jams in the hose or disturbances in the sluice (flat rocks and rocks with sharp edges).
Gravels and water are sucked up the hose and are delivered into a sluice where the gravels are processed using the flow of water. The sluice contains low pressure areas that are created by the crash plates, expanded metal, and riffles. As water pushes the gravels through the sluice, gold and other heavy materials drop out of the flow when introduced to the low pressure areas. The object of creating this environment is to not only create low pressure areas but to also give gold a place to be hidden from the action within the sluice.
Dredge Size Determinations
The size of a suction dredge is identified by its manufacturer based on the diameter of the suction hose and not the diameter of the nozzle. Nozzle diameters typically match the diameter of the suction hose but the tips of the nozzles may be reduced in size 1/4" to 1/2" to prevent rock jams in the hose and jet. Dredging regulations and the language used in the laws vary from state to state, but most states identify suction dredges by the diameter of their nozzle and not the size of their suction hose. This has been confused by many on more than one occasion. Please read state regulations carefully and contact the authorities if you have any questions.
Dredge Details from the Manufacturer
Here's a table that provides manufacturer info on each of their dredges. More is available on their websites. This table is current as of Spring 2014.
Here's some info on the componets of a suction dredge:
Pontoons & Frame
Flairs & Crash Boxes
Engines & Water Pumps
Nozzles & Tips
Pontoons & Frame
The pontoons and frame are the support network of a suction dredge. Pontoons vary in shape, color, and size, but together with the frame they provide the necessary flotation and critical distribution of weight. Keep in mind that a dredge is significantly heavier when it is filled with water and material. Once the hoses are filled with water and the sluice is filled with water and material, the dredge should sit comfortably on the surface of the water, evenly supporting the full weight of the unit and allowing for sluice adjustments. Some larger dredges (6" and up) are sturdy enough for dredgers to walk on, but that is not encouraged for the 5" and smaller dredges. The pontoons and frame are not designed to support that kind of concentrated weight. I'm guilty of this, especially if the dredge is floating in 10' of water. Just remember what your equipment was designed to do, and always keep safety at the forefront.
Pontoons are typically made from various types of sturdy plastic, while frames are almost always made of metal. Suction dredges usually have two pontoons, one on each side. Larger dredges may have four pontoon pieces with two on each side that make up a single unit. These two-piece units are much easier to transport and store. Each individual piece is secured to the frame, fitting together to make one continuous pontoon. The photo on the left shows a 6" Proline (blue) and a 5" Proline (red) side by side. Both of these larger dredges use the two-piece pontoon style. The photo on the right shows a 3" Keene with the single-piece pontoon sitting next to a 5" Proline with a two-piece pontoon setup.
Most dredges use something called a "jet". The jet is just a piece of pipe. However, attached to the pipe is another smaller pipe, usually welded onto the jet at an angle. This smaller pipe is usually "necked down" with a smaller diameter on the end that connects to the jet. The water pump on the engine forces water through the high pressure hose, through the venturi and into the jet. This creates an incredible spray of water up into the jet, the results of which pulls water through the hose which creates that suction at the end of the hose. The venturi effect is "the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe". It was named after an Italian physicist named Giovanni Venturi. The pictures below show a 2" jet. Notice the "venturi" coming in from the side.
The scientific stuff: The laws governing fluid dynamics say that "a fluid's velocity must increase as it passes through a constriction to satisfy the principle of continuity, while its pressure must decrease to satisfy the principle of conservation of mechanical energy. Thus any gain in kinetic energy a fluid may accrue due to its increased velocity through a constriction is negated by a drop in pressure. When a fluid such as water flows through a tube that narrows to a smaller diameter, the partial restriction causes a higher pressure at the inlet than that at the narrow end. This pressure difference causes the fluid to accelerate toward the low pressure narrow section, in which it thus maintains a higher speed."
Now in something more understandable... Water under pressure from the water pump is forced through the narrow venturi and rammed into the larger diameter jet. This incredible force of water being sprayed into the jet moves the rest of the water and material in the same direction as the spray. It's enough pressure and force to "pull" water and material all the way up the suction hose. The spray of water in the jet is violent. Throw some sand and rocks in there and it's basically a water-based sandblaster. These jets will wear out due to this high-powered abrasion based on usage.
One end of the jet slides up into the flair or crash box and the other end of the jet receives the suction hose and high pressure hose. The suction hose typically slides over the jet and is clamped in place. The high pressure hose can be clamped onto the jet, or screwed on (based on the type of jet). These are usually called "power jets", "straight jets", or just plain old "jets" or "jet logs". In some cases (on oversized jets) the end of the hose is fitted with a coupler that slides into the jet and is secured with latches. The below photos show an assortment of power jets with sizes ranging from 2" up to 4".
Flairs & Crash Boxes
Since the action in the jet is so violent due to the high pressure spray from the venturi, many dredges incorporate a means of calming the water down before it gets to the sluice. There's typically two different methods used prepare material for introduction into the sluice: a flair or a crash box. Both methods help material and water settle down before hitting the sluice, and its important to settle suspended material as quickly as possible. Gold will not have a chance to sink to the bottom if the water flow is too fast or violent. The water entering the sluice needs to be as calm as possible but fast enough to move material down the length of the sluice.
Some people prefer a crash box style while others prefer the flair. It's more of a personal preference as both do the job. Depicted below are two examples: Left and center photos show the use of a flair. The photo on the right shows the use of a crash box.
I like the flair a little better than the crash box because material coming out the hose seems to make a smoother transition into the sluice. The crash plate also clears a little better as water flow is consistently moving in the same direction towards the sluice. Material coming up the hose and into a crash box is typically slammed into a wall, drops down onto the crash plate, and is then pushed towards the sluice. Rocks can sit inside the crash box directly on top of your crash plate for hours if you don't check it frequently. Again, both are effective and I own and use both types, but I prefer the flair because it requires less oversight during operation and seems to move material more smoothly into the sluice.
More pics below, left showing the massive flair on a Proline 6" dredge, the right shows a 4" crash box style sluice.
Engines & Water Pumps
There are many different engines that power the water pumps on a suction dredge (and also run the air compressor if equipped). The most common engines used are Hondas and Briggs and Stratton. The below table shows the different Honda engines that are most commonly used on suction dredges. Water pump info is located in a section below this table. I'll get some Briggs info on here soon for comparisons.
Water being rammed into the jet through the venturi comes from the water pump that is coupled to an engine. The engine is typically mounted in the center rear of the dredge frame to help evenly distribute the weight of the dredge when it is running (full of water and material). Most dredge water pumps are centrifugal pumps. The transfer of energy from the mechanical rotation of the impeller to the motion and pressure of the fluid is called "centrifugal force". The water pump and engine you use is important because you need to produce enough high-powered water through the venturi/jet to create good suction without running the engine too hard and pushing too much water through the sluice. Engines are typically not made to run at full throttle for hours on end, so just keep that in mind. If you find yourself running the engine at 80% or more (of available power), then you may want to consider bumping up a notch to a larger engine and pump setup.
Pumps are typically made from aluminum and are fairly easy to disassemble and remove from the engine. Pump seals will go bad over time, and although the repair can be done on site, you're best bet is to replace the pump seal before it gives out on you. Also keep an eye on your impeller for cracks or damage. Debris can also become lodged in the pump, reducing water output which in turn affects suction at the end of your hose and water volume over your sluice. Water is sucked into the pump through a foot valve and is discharged to the jet through a high pressure hose. This high pressure hose can pack a mean punch and is under significant pressure when the engine is running, so be careful around it and be sure your connections and clamps are tight.
Pumps are a popular point of discussion for many people building their own dredge. How much water will I need? Can I use a trash pump instead? Well that depends on many things. You don’t want a pump that requires an engine to run hard for long periods of time. It’s better to have too much engine and pump vs. not enough of either. Trash pumps or other forms of semi-solid pumps are definitely cheaper than the "clear water" pumps offered by dredge manufacturers, but they may not produce the required head pressure and GPM that is needed to operate a dredge (especially if dredging in deeper water).
Here’s a table that shows the pumps offered by Keene, Proline, and Dahlke (as of summer 2015). I reached out to each manufacturer to get specific details about their pumps. Two responded so far and their notes are below:
There are a few different engine manufacturers out there, and dredge manufacturers typically offer Honda and Intek/Briggs as options. Most of my dredges are powered by Honda unless I bought them used with a different engine. I have never had a problem with a Honda, but Briggs/Inktek's are also good engines. Most of these small gasoline engines come with the low oil shutoff sensor, and that's a great feature to have. This shuts off the engine if the oil level gets low or if the engine is not level.
Here's a couple tips with regards to engines and pumps:
- Check the oil level (cold) and color.
- Change the oil if it's black or thick and fill to specs (use the above engine table).
- Check your spark plug, clean and gap it according to specs,
- Remove and clean your air filter,
- Inspect fuel lines for leaks or loose connections/clamps,
- Inspect the pull cord for frays and potential weak spots,
- Ensure gas cap and oil fill plugs are snug,
- Ensure compressor belt (if equipped) is not loose, frayed, or worn,
- Never start the engine with a dry pump, it will ruin the pump seal,
- Ensure pump impeller is free of debris.
- Ensure gas cap is snug after refills,
- Ensure engine is level,
- Make sure hoses stay clear of the exhaust,
- Ensure engine bolts and nuts are snug on the frame,
- Check for water leaks behind the pump (indication of a failing seal),
- Check impellor for debris if reduced suction power is noticed,
- Keep foot valve out of sand/pebbles and away from leaves and debris.
- Empty the fuel tank (preferred) or use a fuel storage additive,
- Change the oil before placing into long term storage,
- Make sure the fuel valve is in the "off" position if storing with fuel in the tank,
- Tilt the engine/pump so that water in the pump housing is drained (some pumps have a drain plug in the bottom of the housing).
Lessons Learned: Take a minute or two to check out your engine and pump (above checklist) before you leave the house. It will save you from learning a hard lesson. Breaking a engine pull cord sucks when you don't have a replacement on hand. Murphy's Law... just plan on breaking one! Put a spare pull cord and handle in your tool bag that you take with you. Also, make sure you have the proper tools to remove the engine cover. Most Hondas have 10mm bolts holding the cover on, but check yours just to make sure you have the right tools. Also, it doesn't hurt to have some extra engine oil on site or in the trunk of your vehicle.
Water pump seals don't typically "fail" all at once. When the seal is just starting to fail, you'll notice some drips or a very small spray coming out of the back of your pump. You may also have a bad seal if your pump is not holding prime or it is difficult to prime the pump with water. Pump seals can be replaced on site if you have the tools with you (sockets, wrenches, seal, rubber mallet, and seat tool), but it's not a swap you want to get into a habit of doing out there. You can keep dredging if you notice a small leak, just keep an eye on it and replace the seal before your next outing. Finally, make sure you have a replacement seal on hand back at the homestead.
Foot Valves are one of those forgotten pieces of the suction dredge. The foot valve provides the pump with the water you need to operate the dredge correctly. The actual foot valve is nothing more than a one-way valve (or "flapper" as some call it) fitted with a hose that connects to the pump. Foot valves have remained unchanged over the years with the only noticeable change being the cage or screen that surrounds the valve. Most screens were made of metal, but now most of the foot valves being sold are made mostly of plastic. You can get some very sturdy all-metal foot valves at a store that services septic companies. VARCO (Virginia Rubber Company) located in Norther Virginia has excellent prices on an assortment of foot valves, hoses, quick connects, and other cool widgets.
Keep an eye on your foot valve. Be sure the valve is working properly, stopping water from exiting the hose using that one-way "flapper" valve. The flap is typically made of rubber and it will age, tear, and become brittle or rigid (not forming a good seal). Ensure that your foot valve is not sucking sand or debris into your pump. Sand in your pump will take its toll, so will small pebbles. Some people place their foot valve in the water on a flat rock (below photo on left) or even use the lid from a 5-gallon bucket. Anything is better than lying it directly on gravels because if you do that you are definitely putting sand into your pump.
Make sure your foot valve is deep enough to consume only water. Introducing air into your water system negatively affects suction power, your sluice, and the ability to clear material through the hose. If dredging in an area with leaves, seaweed/grass, or pine needles (see above pic), routinely remove your foot valve hose and ensure the impeller is free of debris. Ensure your foot valve hose does not have any holes in it. The hose should be flexible and not too rigid. If you notice a high amount of air bubbles going down your sluice, you most likely have either a bad pump seal, a loose hose (suction hose, high pressure hose, foot valve hose) or actual holes in one of your hoses.
Nozzles and Tips
Nozzle diameters typically match the diameter of the suction hose, but the tips of the nozzles may be reduced in size 1/4" to 1/2" to prevent rock jams in the hose and jet. Some nozzles are exactly the diameter of the suction hose but have a restrictor ring on the end of the nozzle. You'll see these mostly on the swivel nozzles. This thin ring is welded onto the nozzle and is usually smaller in diameter than the suction hose, helping reduce rock jams in the hose and jet.
The below photo (left) of a 4" swivel tip suction nozzle provides a good example of a restrictor ring. The photo in the center is a 3" swivel tip suction nozzle with a restrictor ring. Some great gold came out of that crack. The photo on the right shows a 5" nozzle with the same type of restrictor ring.
The below photo shows a couple different "straight tip" suction nozzles with the 2" on the left, 3" in the center, and 4" on the right. These nozzels do not swivel and do not have restrictor rings. You can see how the edges of the 2" and 4" nozzles are turned in to provide the same service of stopping large rocks from entering the hose. The 3" nozzle shown here is reduced in size about halfway down the length of the nozzle.
Watch them fingers!
Be very careful with your hands and fingers when dredging. Many dredgers have suffered "the whack". That's when you put your hand in front of the nozzle to stop a rock from being sucked up, and both the rock and your fingers or hand make forceful contact with the nozzle at the same time. The rock is going to win every time. It's not fun and it can be dangerous with the dredges 5" and larger even if you're wearing dive gloves.
There's a lot of suction at the end of that nozzle, and it's tempting to jam the nozzle into the gravels and go to town as fast as possible. The object is to feed the sluice with material at a consistent rate and not "hog" or overload the sluice with material. An overloaded sluice box defeats the purpose of dredging. The riffles cannot do their job if you pack them full of material. All you're doing at that point is moving material from one place to another. Take the time to study your sluice while you are dredging to make necessary adjustments.
There's no question that the sluice is the most critical component of the dredge. Dredge manufacturers have put a good amount of time testing designs, and the stock sluices they provide work just fine and are built to serve the common environment. You'll see a wide variety of setups including different shaped riffles, spacing of riffles, and the use of mats, carpets, and moss. Experienced dredgers have their own preferred setup, and people will argue all day long about which setup is best. Use whatever you want as long as you're satisfied with your recovery rate. The bottom line is that the sluice is designed to create low pressure areas that provide a place for a heavy material to drop out of the flow and get trapped while discouraging dislodging.
The common components of a dredge sluice are the damper, crash plate, riffles, and some kind of matting, carpet, or moss. The damper is usually a piece of thick yet flexible rubber that helps to calm the water down while leveling out water and material before it goes over the crash plate (and) before it reaches the sluice. Dampers can be different lengths, but the key is that they are not so long that they trap rocks or force too much water to flow under the crash plate.
The crash plate is a classifier that allows larger material to flow over the area while allowing smaller material to drop through the holes. They can be made of perforated metal or woven mesh. Most sluices have material under the plate which serves as a “quick check” for gold, such as black ribbed matting or carpet. You may even find expanded metal in this part of the sluice. Keep in mind that the top portion of the sluice is where most of the gold should be, so whatever is in the top of the sluice needs to provide the best possible “drop and stop” environment. I will use black matting under the crash plate when testing a new area for a fast visual gold check, but if I know I’m on gold I will yank that stuff out and put moss or carpet and expanded in there because I know it provides a better hiding place for gold compared to black ribbed matting.
The two pictures (above) show how the top of a sluice is typically arranged. The photo on the left has ribbed matting under the crash plate with expanded metal. The photo on the right has carpet with expanded. You'll see sluices with carpet all the way down with no miners moss at all. You'll also see some sluices with longer crash plates than others, with some being made of woven metal and others using flat perforated metal. The below picture shows a variety of carpet, moss, and matting you may see in a sluice. Just remember that the purpose of these things is to improve recovery by providing more places for gold to settle down and hide.
Riffles are probably the most important part of the sluice box. They create the environment within the sluice which helps separate and sort, retain the heavies, and discharge worthless material. Riffles create a vortex which sorts material in a circular motion, either retaining it behind the riffle based on weight and mass or kicking it back out into the flow. Riffles can be made with different heights and angles. You’ll also see different spacing between riffles. All these attributes affect how the riffles work.
Dredging is a skill that takes time to learn and there's definitely a learning curve. The best way to straighten out that curve is to link up with an experienced suction dredge operator ("dredger") and get some one-on-one lessons right there on site. If you're tackling this aspect of the gold prospecting hobby all by yourself, realize that it is an acquired skill and the path to being an effective suction dredge operator is lined with pitfalls, traps and snares. Here's some basic information to help reduce the snares and straighten out that learning curve a bit.
Before you head out to your favorite gold hole, check your dredge over and make sure you have everything you need to operate the dredge. There's nothing more frustrating than to get to the site only to be short a foot valve or high pressure hose. Take the time to get your gear organized and accounted for. In addition to the obvious dredge and dive gear (if needed), here's a couple things to do and items to add to your pack mule before heading out:
- Inspect the oil and spark plug. Run clean oil at the appropriate level.
- Ensure engine and air compressor bolts are secured.
- Inspect the belt on your air compressor.
- Bring your cleanup pans, tubs, classifiers, snuffer bottle and buckets.
- Grab that rubber mallet that is needed to loosen rock jams in the hose.
- Add your clearing rod which can be nothing more than a 6' or 8' piece of 3/4" PVC with a "T" and an end cap.
- Make a tool bag with all the tools you will need to assemble the dredge or conduct repairs.
- Add a spare engine pull cord and a couple spare hose clamps to your bag.
- Bring a spare hose gasket if your high pressure hose uses those.
- Grab one of those "linked belts" to use in case your air compressor belt breaks.
- If diving, be sure to have a spare dive mask.
- Add a 24" level if the dredge will be resting on rocks.
- Don't forget your dive gloves or rock gloves!
- A pry bar is great to have for working cracks and moving stubborn rocks.
- A rope long enough to secure your dredge if you are floating.
Experienced dredgers can load up at the house or garage and be on their way in a matter of minutes. Making sure you have everything you need is better than leaving something important back at the homestead. Put extra "just in case" stuff in your vehicle instead of packing it down to your site, but at least you'll have it! Over time, you'll figure out what you need on site and what you might need but can leave in your vehicle.
Secure your gear and ensure everything is tied down nice and tight. Things settle over distances and bumps, especially if you are using an ATV and wagon or cart or are loading your gear into the bed of a truck. Keep your head on a swivel and make sure you're not leaving anything on the trail or highway! There's a special place in heaven for the guys who invented bungee cords and ratchet straps! Keep in mind that many small gasoline engines tend to flood if they have gas in the tank and are jostled about over bumps and rocks. Sometimes it's best to leave the tanks as empty as possible during transit and be sure to turn the gas valve to the "off" position.
Identify your work area
You need to select your area of work before you set up your dredge. Working in deeper water is much easier because the entire unit is floating and it is easy to make adjustments and move around. However, moving your dredge when in shallow water is a pain, especially if your dredge is completely out of water and resting on rocks. Once you get the non-floating dredge dialed in and running good, you really don't want to move it around unless it is absolutely necessary. Take a few minutes to walk the area of interest. You're looking for a good place to run the dredge and a place to stack the tails. You're looking for some deeper water for the foot valve, and moving water to help maintain good visibility. Also be mindful of debris that may be in the waterway, such as leaves and sticks. You want to avoid placing the dredge in a bed of leaves or debris as this stuff can be sucked into the pump through the foot valve. The below pic shows a downed tree that pretty much covers the entire creek, and the debris field of pine needles and leaves covers the entire area due to the blocked flow of the creek.
Some lucky dredgers have the ability to "dump and pump", but the rest of us may have some on-site assembling to do. Take your time. Besides forgetting something at home, there's nothing worse than breaking your gear or dropping a part in the river because you are in a hurry. Once you transit to your honey hole, set up your dredge the way you normally run it and do your best to level it/angle it while it is empty and light. Fill 'er up, turn the gas valve to the "on" position and secure your gas can away from the water's edge. Make sure the things you don't need to dredge are secured on the bank out of reach of the water and not in the way of other people.
Check your nozzle to make sure it will not suck up a huge rock when suction is first introduced. It's usually a bad day when you start off with a hose jam. If using a swivel tip nozzle, turn it up so that it faces away from the gravels. Check your dredge over and make sure you haven't left any tools on it. Make sure the components of your sluice (crash plate, riffles, matting, etc.) are in place and are ready to receive gravels. If you're not floating and have positioned the dredge on rocks or in shallow water, use that 24" level to check the side-to-side leveling of your sluice. Adjust as needed while the sluice is empty and light, but be prepared to check it again once the full weight of water and material has settled the dredge. Prime the foot valve and be sure the valve is not going suck up sand and debris. Be sure you don't place it where you will trip over it or "kick it in the air" (bring it out of the water). The below picture shows my foot valve going down through a hole made in the ice.
Pull that cord, adjust the throttle and choke, and let 'er warm up for a minute or two. If you're not floating, adjust the pontoons or sluice to the angle that you want to run. Put a little material through the hose and make throttle and sluice adjustments as needed. Once you're all set with your setup, you're ready to dredge. If you're diving, now is the time to hook up your air hose to the reserve tank and compressor. Put that regulator in your mouth, dunk your head and make sure it's working properly. Before you put on your mask, harness, and weight belt, ensure that your air hose will not get in the way of the engine, pump, exhaust, or compressor belt. I've melted an air hose because I didn't keep it away from the engine exhaust. Once you've secured the air line away from potential hazards, you're ready to put those weighs on, spit in the mask, grab the gloves and pry bar and go to work.
Starting your dredge hole
Every river, creek, and stream is different and the characteristics of your environment determines how you dredge. Obviously the need for good water is the primary requirement because without a proper amount of water your dredge cannot operate. Some smaller dredges can operate on less than 80 gallons of water per minute, but others require hundreds of gallons. You can always sit in a large puddle and recirculate water, but the water will become extremely murky making it difficult to see (which typically causes rock jams in the hose and jet). There's a difference in how you start your dredge hole based on the composition of the river and how deep you have to go to reach bedrock. The hole you start also varies if you are diving and working completely underwater, or if you are working above water in a shallow creek, river or stream. No matter how deep you are or if you're diving or not, there's a basic way to create an effective working area to maximize the use of the dredge and remain safe.
One thing I like to do as soon as I get on site (in a shallow creek or stream) is to put the nozzle right on the spot that I want to dredge. Once I place the nozzle down, I straighten out the hose and then look for a good spot within the reach of the hose to place the dredge. You want the suction hose as straight as possible to reduce rock jams in the hose, but you also want a little flexibility to expand your work area without moving the dredge. This is much easier to do when the dredge is floating because all you have to do is adjust the rope that is securing the dredge. The below picture on the left shows my son Chris using our 4" Proline dredge. The dredge is floating and is easy to move around using a rope that is tied off to the trees on the bank. This luxury allows Chris to keep the dredge hose almost perfectly straight which greatly reduces rock jams in the hose and jet. The photo on the right shows a Keene 4" that is secured to the bank with a rope. If you can float, float!
If you know you're dealing with big rocks or boulders, you'll have to start working the surface of the gravel bed in a pretty wide area. This ensures that as you go down you're not creating a wall of rocks but more of a gentle and safe ramp. For divers in this situation, maintaining at least a 2:1 ratio is absolutely critical for safety. I'm not going to go into detail here trying to explain how you take apart a boulder-filled river while diving, but experienced dredgers understand the ramping approach. Boulders have no conscience; they do not discriminate; they will kill you.
In general, the best way to start a dredge hole is to start by processing the top layer in a nice wide circle. As you go down, you "terrace" the sides so that they are gently sloped. If you see a rock that might budge and slide, move it out of the way. You take apart the river or creek one rock at a time using the suction hose as your scalpel. Look at the composition of the material you are processing and make mental notes of colors, composition, clay, and layers.
Get into the habit of checking your sluice if you are working alone. It's a pain to get up every 10 minutes or so to check, but it's better than leaving a flat rock covering your riffles for a half hour (see below pic). That flat rock disturbs everything around it on all sides. Don't get lazy in your dredge hole and don't let your dredge fight to retain your gold. You're working hard for nothing if you don't check your sluice frequently.
When your back checking your sluice, grab your shovel and move those tails away from the sluice. Backing up a sluice with tails (see below pics) is a common mistake when dredging in shallow water, and it's a costly one with regards to keeping that gold in your sluice. It's easy to lose track of time when you're dredging. You have to remind yourself to check your equipment.
Keep the tails close by so that they can be used to fill in the hole when you are done. Don't throw rocks up onto the banks. I'm really not sure why people feel they have to throw the rocks completely out of the river. Keep them close to you but don't put them in a place where they can come back into the hole. Once you're done in that spot, toss the rocks back into the hole and do your best to fill it in. Mark any deep holes with rock piles or flags so that others know there is a deep hole.
Study your sluice in action
While observing your sluice, you will see that both light and heavy material is being processed. The light material or worthless gravels are being pushed down the sluice and discharged out the back. The heavy material contains the values, and that material is also being processed but at a much slower rate. Don't focus only on how well your sluice is discharging worthless rocks, that's just one part of it. Study the action in front of and behind the riffles as well as the material entering the sluice from under the punch plate.
Practice your material feed rates and take the time to observe your sluice, make adjustments, and then observe again. Do this before you begin a full day of dredging. It makes no sense to study your sluice and make adjustments halfway through your outing! There's a great peace of mind to sit in your dredge hole or lay on the bottom of the river and know that your dredge is set right and running properly.
Test your Tailings!
You can try all different types of setups and pick the one you like the best. The only way to test your setup is to test your tailings, or test what your dredge is kicking out as worthless material. Don't test them by sticking a shovel in the pile and panning it out. That's not really an accurate test. Testing tails takes a lot of time and it's hard to do when you just want to dredge! I've spent entire afternoons panning a giant tub of tails, but it's worth it when you make the needed adjustments and know that you've dialed in your dredge to maximize its capabilities. Here's a couple things I've learned when testing tails and adjusting the dredge. Maybe you can use some of these to create your own equipment testing routine:
1. Before you start your test, set the dredge up the way you think it should be set up or the way you normally set it up.
2. Run the dredge for a little while and let the sluice get settled in.
3. Stuff the biggest tub you can fit under the sluice,
4. You can also place another sluice at the end of your dredge sluice, and some are a perfect fit.
5. Run the dredge for a few minutes, long enough to put some fresh material through the dredge.
6. Classify the material down to save time but watch for larger pieces of gold.
7. If you find larger gold in the tails, you'll need to make an equipment adjustment:
- Make sure you're not pushing too much water through the sluice. Throttle down a little!
- Material should glide down the sluice, bouncing off riffles in a smooth manner.
- Make sure you are not hogging material which packs the riffles and eliminates low pressure areas.
- Adjust the angle of your sluice. Add an inch of elevation in the back and study the results.
8. If you find small gold in your tails, make a "personal" adjustment before touching the dredge:
- Pay close attention to your feed rate. A good rule of thumb is 80% water and 20% material.
- Slow down a little. The nozzle doesn't feed itself, you determine that feed rate.
- Check your sluice more often to clear stubborn rocks and riffle obstructions.
- Be more picky with what you put up the nozzle. Avoid rocks that may upset the sluice or be difficult to clear.
Be patient with your dredge and with yourself. Remember that it is a machine that runs the way you set it up to run!
I think I've tried just about every kind of dredge, all the different sizes and a dozen different types of sluices. I've had good results modifying the components within the sluice itself (riffles, spacing, crash plates, moss, carpets, etc.), but that has come with a good amount of testing. So far the best recoveries I've had were achieved the "plain Jane" single sluice with carpet and expanded up top and moss under the riffles. Companies release new designs whether legitimate R&D has been conducted and applied or not. I'm not saying that old designs can't be improved upon because they can. That's innovation. All I'm saying is that you can probably achieve acceptable results using manufacturer designs or by adding simple modifications to your setup based on your environment or your own style of dredging.
Catching all the gold
A dredge that is properly set up should catch all of the nuggets, pickers, flakes, and most of the flour gold (+100). My own testing results indicate that dredges do a pretty good job catching all these if the dredge is set up properly. If you're worried about catching every speck of -300 gold, then don't use a suction dredge of any size. Gold that small stays suspended in fast water, and it needs extremely calm water to settle. You need to run the dredge at the speed which clears waste rocks, and that speed doesn't typically permit the settling of every speck of micron gold. Do your best to set up your dredge to catch both large and small gold and understand that there is a trade off to process more material effectively in less time. If you do this, you'll end up with more gold than the fella who claims to catch "all the micron stuff" in his dredge, guaranteed.
In the End...
Operating a suction dredge is a lot of fun. There is a learning to it curve but the same goes with using any kind of equipment. Prospectors of any age and level of experience can learn how to dredge, and there are plenty of choices on the market to meet your needs and budget. Gold retention rates are excellent and a dredge can pay for itself over time if you have access to gold bearing gravels and are willing to invest the time. Most importantly, it's a fun and exciting way to enjoy the hobby while getting some outdoor exercise.