How deep will a dredge work?

[stevemc]

I have a 5.5 horsepower dredge that pumps 150 gallons per min. 2" ID outlet. I plan on making this a 4" dredge. How deep in the water will this work? Is there a limit that they will go in depth? I dont think there is a reasonable reason that it shouldnt work at any depth, since water doesnt compress, but maybe there is a friction loss, or just distance problem. I was thinking maybe 100' deep max. Will this work? Steve.

 

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[russau]

not at 100ft. most dredges come with a 20 ft. hose. if you extend that limit, the longer you go the harder it is for that 5.54hp eng/pump to push/suck it through the hose. plug ups would stop you continually!! it can be accomplished with the use of additinal venturis inbetween your hose lengths. this would require maybe additional pumps and hoses. but 100 ft.? thats pretty deep!esspecially for a 4 inch!

 

[Hoser John]

Keene uses that pump on a 2 1/2" dredge . On the 4" the SMALLEST is a p180 at 310 gpm at 180 PSI. Any less and you are not gonna get much suction. 100' is a pipe dream.!1st you'll never get a compressor to pump that deep,it'll take 3 pumps and 3 powerjets for the hose,and I can tell you never been at 100'--it ain't fun,ya gotta work like a dog just to stay alive that deep with tanks!! Scale back and enjoy.Tons a au 2 u 2-John

 

[goldinmypan]

Its been quite awhile since I've done any diving but if I remember the bottom time at 100' was very limited and if exceeded you have decompression stops to deal with to avoid the bends.

 

[Real de Tayopa Tropical Tramp]

HI, may I point out a thingie like pressure and bottom time. Beyond 30 ' ft.you are running into serious diving problems which should not even be considered in Gold diving without taking a diving course. You could easily end up crippled or dead. Especially without different altitude compensations.

also you may be approachng your physiololgical ability for compressed air, could be getting into the toxic range.

Tropical Tramp

 

[ScubaDude]

Why not use an air lift?

 

[Real de Tayopa Tropical Tramp]

author=NC Brad link=Why not use an air lift?
*****************

Excellent idea, but there are too many large rocks that will stop / plug up the intake. To have a smooth running operation you have to pre-classify all incoming materiel.

Tropical Tramp

 

[stevemc]

I know an air lift would work, I was just wondering about the depth limits of a dredge. I dive 130+' often. I have been SCUBA diving since 1962. I usually dive nitrox when I dive that deep though. Yes I know that 100' + depths give limited time to work, but just if I had a wreck I wanted to know if it worked.

 

[stevemc]

I know diving to 100' + sounds scary if you dont dive, but its not that bad. It feels no different than diving 20 feet to your body, you just have to watch your down time, and deco times. I dive 80 feet + deep on a weekly basis- I spearfish and that can be very strenous, chasing big fish, fighting and stringing them up and reloading, all as fast as you can, and trying to cover as much ground as possible. I am in very good athletic shape. Laying on the bottom, and holding a suction end, is not that bad compared to flapping around and really working. I do several deep dives(130'+) a day, when I go out that far. I live in Florida. I know of several deep possiblities and was just wondering. Steve. Oh and my dredge is still just a water pump with 5.5 hp engine and 2" water pump w/150 GPM at this point. I use it for collecting salt water as I have 2 huge saltwater fish tanks. I just run offshore and throw over the hard suction and prime the pump, and fill up 4 - 60 gallon drums. I do this every so often for partial water changes-so I have some in reserve too. But I want to make it into a suction dredge and Keene Eng website has several this size and they are 4" , that is why I felt it could make a 4". If that is too big then I could go to a 3". Just thought it would work.

 

[aarthrj3811]

Hey Stevemc.....Go to the Keene web site and look at how much material each size will move in one hour. In real life it is about1/2 that amount if you are good with the nozzle....Every rock that is bigger than the nozzle you have to move by hand. When you have limited time I am sure you will want to move as much material as you can....Art

 

[Hoser John]

Go to any dive shop and take a good hard look at the PADI certified dive tables and decompression tables with mandatory time constraints to wait in between dives to safely dive. Deep(over 100') and even multiple shallower dives takes some safety precautions. Just because your using hooka doesn't mean no tanks no decompression!!
Air assist has been around for over 35+ years I've been dredging. It all depends on how deep your dredging. Hard part is getting it down there. As air rise it expands many times it size expotentially,doubling every atmosphere,so it don't take much to be a huge help. BUT you must have a hopper to accept this foam mess to let it deaireate and run into a dredge box.Otherwise your lose your gold akin to a floatation cell. Anything can be done but you must customize your operation due to extreme recovery methods.Tons a au 2 u 2-John

 

[stevemc]

John, I know you are looking out for me, but I have been deep diving before PADI and NAUI were started. The first dive tables were Navy UDT tables. I follow the tables, which I know like the alphabet, and deco times for every depth and overdepth and penalty times, and topside times and multiple repeat dive times and penalties, and have several dive computers, both nitrox and air, which let me know about my air pressure, and N2 buildup, the 2 important things to watch and be aware of. I have big tanks 160 cubic feet of air. Most scuba tanks are 72- 77 cubic feet. Nitrox allows a shorter dry interval, and longer down deep times. Plus shorter deco times. The max depth for air is 200' because of the 21% O2. Hence with enriched amounts of O2 in Nitrox, i can only go so deep with each different mixture. When I dive multiple dives to 140 which I do often, I use 30% nitrox, which allows me the most O2 at the best depth, so I have the least N2. Deeper than 165 or so and I use helium enriched air. I have been trained in all this, never been bent, and have worked much UW salvage and hard work, some at very deep depths. I have a hookah a 390 Brownies Third lung, but only use it for fairly shallow diving as it runs for 3 hours on a small tank of gas. I am a safe diver! Just wanted to pick you dredgers minds about a possible dredge buildup and project. Thanks for the input, I will probably use an airlift for deep, and leave the dredge for the shallow stuff. Steve.

 

[Hoser John]

Just putting info out there because for every 1 guy who knows whatzup,there are 5 newbies that don't have a clue. NITROX is the modern miracle of deep diving and sure make longer dives a ball. My brother has some fantastic shots from the Caymans reefs,petting monster Rays in Yap,and now heading to Palau for deepwater drift diving--color me GREEN with envy!! I mutz and putz but he blows $30,000++ for a trip for 2.Those hellish ARM loans have made loan brokers millions,and ruined many lives!!Tons a au 2 u 2-John