Making an air dredge.

[Whittman]

I am looking to make an air dredge for use on a smaller boat to work wrecks in the 20 to 30' range. I would appreciate any information, tips, or links that my fellow members could provide. Especially concerning design configuration and type of air compressor. Thanks in advance!

 

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[Dinkydick]

If you are thinking of an airlift maybe I can help.

Dinkydick

 

[Whittman]

Yes, sorry... I meant an airlift!

 

[coin_diver]

In this depth I suggest a 3-4" w/ a min of 15cfm. For ease and discretion, suspend a wire box below the surface with floats and all anyone sees on the surface is the downline. Shallower than that and you'll need a venturi pressure jet. Bottom line, depends on how much you need to move.

 

[Whittman]

I may need to move quite a bit. We used a mailbox to locate some of the wreckage and there could be as much as 5' of sand over her. Using the mailbox requires a lot of logistical effort due to the location of the wreck vs. the location of the boat whereas it would be nice to be able to excavate with a couple of divers on a small boat. So a water dredge (or pressure jet) works better in shallow water? Thanks in advance.

 

[SEAHUNTER]

Coindiver
I thought it was neccesary to have 115cfm to make the airlift work?
Seahunter

 

[coin_diver]

Nope, check your tables. If you were running an 8" w/ a clear rise to deck surface then you'd want 50-75cfm but in 30fsw w/ a small lift to an intermediate platform you'll be just fine. Besides, it'd take 2 divers w/ that much volume. My preference is a 4" dredge w/ pressure nozzle. With this you can simply transport material horizontally out of your way but keep an eye on your pile. I use this method because no-one knows whats going on below!

 

[ScottyLee]

Ok.....lets say we are in 15 to 20 feet of salt water and would like to raise the material four feet above the water to the deck of a boat. If we use a four or six inch air lift how many CFM are required?

 

[coin_diver]

Hey Scotty, Well for a 4" to about 40fsw you can run 50+ cfm but in order to clear the gunwhales you'll need to increase the psi to upwards of 100. The USN salvage tables allow up to 200cfm but don't I recommend because you'll have trouble controlling the intake. If you've already blasted the site the you need to slow down w/ less lift. Keene will make you a nice dredge and it's easier than hauling around big compressors.

 

[southern maine diver]

Hi Coin-Diver...

I am also planning on constructing an "air lift" to work a relatively shallow (15 fsw approx) area for coins/relics.
I feel the same as you do, the less people inquire or know about what I am doing, the better I feel.

The site I am working is very near a well populated area and is always subject to inquisitive eyes, curiosity seekers and repetitive questions about, "What are you doing?" I too, would like to assemble an airlift, only to send the material behind me and not necessarily up to the surface. It is mostly sand and rubble. The smaller stones and overburden can be moved by hand.

I would like to use the airlift with a scuba bottle so as to limit the amount of attention a compressor and airline would attract to the site. What is this "air nozzle" that you speak of? How is it made? Is there something commercially available? Are there plans for constructing this device?

I have a 4" suction dredge, but that thing has so many hoses, makes all kinds of noise, as does a jet nozzle (which I also have) but that blows everything around and damages delicate glass and bottles. Anything you can post in the line of drawings, descriptions Plans would be helpful and most appreciated.

Thanks for your time,

Wayne

 

[coin_diver]

Hi Southern, Well the good news is your most of the way there already! W/o knowing what type of items you're going after it's a little hard to make recommendations, but here you go. Don't use the dredge configuration to recover items, forget the jet-tube going into the header box, get longer pressure line and a new suction nozzle. With that size set-up you can go upwards of 6" and move a whole bunch of material. Also, you can drop the jet-tube to the bottom w/ a longer pressure line(30') and a standard nozzle. I had Keene custom build my dredge just for this and guess what, no-one waits around for me to come up and ask questions. Make sure you use an anchor and line to the jet tube or you'll be riding it around the bottom. Good luck.

 

[Whittman]

Coin Diver - Thanks for all of your input. I'm trying to decide whether to utilize an air lift or a water dredge. I'm not sure what will move sand more effectively. The water dredge is nice (I've used one before on a deeper wreck), but is expensive. You can see the one I'm talking about at
http://www.techdivetools.com/dig/dredges.html

Also, where can I see those Navy salvage tables you were talking about? I need to learn more about the cfm to depth ratio. Thanks.

 

[Whittman]

I'm striking out trying to find a scematic to build an airlift on-line. Any help would be appreciated! Thanks.

 

[SEAHUNTER]

coin_diver
Wanted to know if you had copies of those charts you mentioned that you could post.
Seahunter

 

[grzellers1]

Ah! SeaHunter AND Coin_Diver
I too want to build an air lift/air dredge
the mentioned charts woulb be so good
Below is my post from March 29,

Ran on to this site kinda by accident
I am trying to refit an IMS 4010 22' floating dredge with an air lift or
venturi (pump system)to pass 6" rocks.
(I know little about either)
I want to dredge river gravel and the fan pump that is oem will not handle the big rocks or the wear of gravel. I am trying to come up with a no moving parts dredge boom.
I could maybe have an air lift down on the bottom and then use the original pump upstream on the boom (supplying only clean water) to feed some kind of venturi??
here is a thread address from an old discussion http://www.treasurenet.com/f/index.php/topic,19842.0/prev_next,next.html
I think if I could find Dinkydick profile 2664 my questions would be answered , he seemed to really have a handle on this airlift design

 

[coin_diver]

Hey GRZ,
Well you're into a little more than recreational dredging and and I wouldn't recommend using air to move that amount of material, better to use a jet tube venturi system. My recommendation is to trash most of the old system, go with a small diesel plant and look to the guys over at Keene, their pretty smart. But to give you an idea, below are the accepted flow rates for this setup.http://www.keeneeng.com/

OUTPUT WITH VARIOUS PERCENTAGES OF SOLIDS:
CAPACITY* 10% 15% 20%
GPM YDS/HR M3/HR TONS/HR YDS/HR TONS/HR YDS/HR TONS/HR
1600 48 36.7 64 70 96 96 128
2000 60 45.9 80 90 120 120 160
2400 71 54.3 96 107 144 142 192

 

[wreckvalle]

What about a water dredge. We have used the same dredge in 15' down to 140'. Powere is based on a gas powered trash pump. Moves quite a bit of sand and except for the noise of the pump no surface activity!

My friend Enrique Alverez makes a very nice stainless unit
http://www.techdivetools.com/index.html


http://www.shipwreckexpo.com/shipwreckdivingexcavation.htm

Good Luck
Capt. Dan

 

[southern maine diver]

I've got one of Enrique's 4" suction dredges and this thing kicks ass!!! Don't want to get your fingers anywhere near the business end... It'll break them...

They make 6" dredges and 8" dredges as well. They take a little time to set up, but they move a lot of material. I have an extension on mine so I can shoot the overburden out behind me about 40 feet away. It keeps the work area pretty much "cloud" free and then I go to the exhaust pile and find some more goodies.

Enrique came up from New Jersey to demo a dredge for me and we ordered one on the spot. He uses a fantastic Pro-Line water pump that puts out over 500 gallons per minute!!! I'm real happy with mine.

Wayne