BGT in deep water

[Bronze]

Has anyone ever tried testing the BGT in deep water? I am not talking like 5ft down but at least completely submerged, maybe "6-"8 inches.

All of my rivers and creeks are at high water mark and a few of the spots I dig in are under about 8ft of water. So now I am having trouble with with getting set up as what would be normally perfect, its now a huge struggle to get something decent set up.

So I am just curious if dropping the BGT all the way under water is a problem?

 

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[arizau]

This does not answer your question but may give you ideas. I saw a post on another forum where a guy bungie corded foam kiddie floats to his bazooka and tied it off with a sling to keep it in position while floating in deep swift current. As far as I know it worked ok.

 

[benny]

This does not answer your question but may give you ideas. I saw a post on another forum where a guy bungie corded foam kiddie floats to his bazooka and tied it off with a sling to keep it in position while floating in deep swift current. As far as I know it worked ok.

I bet that was mine. Yup, it works fine. More importantly, the wire bale in the back with a tether will keep your BGT from floating off down the stream.

http://www.treasurenet.com/forums/sluicing/417234-mini-bgt-ideas.html#post4022267

 

[G-bone]

I see using a stand like this.

Longer legs though where you could have it in 2-3ft and still easy to anchor with rocks (i think..)
Waters may run high next spring and these ideas may be the only to work em.

 

[arizau]

I bet that was mine. Yup, it works fine. More importantly, the wire bale in the back with a tether will keep your BGT from floating off down the stream.

http://www.treasurenet.com/forums/sluicing/417234-mini-bgt-ideas.html#post4022267

Yep twas you.

 

[russau]

Ive made LOTS of stands for sluices / highbankers in the past and sold them to members of the club I belong to "Show Me gold Prospectors" in Misery. I made several lengths of legs for them and sold them for 1/2 of the "sale price" on the net and some some people wanted to know why I made the legs so long..............................Yep I see lots of newbees and try to answer their questions and help all who can be helped! I even offered to let them use my dredge to teach them.........NO takers!

 

[Goldwasher]

Do not run it submerged

 

[KevinInColorado]

Do not run it submerged

But I have done this with a Prospector in fast water and it worked fine. Did I just get lucky somehow or fool myself?

 

[goldenmojo]

A friend of mine left his Bazooka Prospector unattended while collecting material high on the bank. He returned to find it under 3 feet of water caused by the sudden rise of the rafter release flow. He actually had trouble locating it and had to use his spotting tube he had with him. It now has a florescent green stripe painted on it. No report on how well it worked at that depth.

 

[KevinInColorado]

Florescent paint is a great idea! On my way to the store today for some to mark my precious Bazookas!

 

[GoldpannerDave]

But I have done this with a Prospector in fast water and it worked fine. Did I just get lucky somehow or fool myself?

Yes, we ran our Bazookas underwater at the big Bend in the South Platte; seemed to work fine. They weren't all that deep, but were completely submerged.

The water flow still cleaned off the skid plate and grizzly (well mostly, just about like normal for me). If there is a trade secret about why we should not run them submerged, please let us know. My guess would be that often there is not enough water flow to fluidize the bed and so you lose gold. Is there more?

TIA.

 

[arizau]

Yes, we ran our Bazookas underwater at the big Bend in the South Platte; seemed to work fine. They weren't all that deep, but were completely submerged.

The water flow still cleaned off the skid plate and grizzly (well mostly, just about like normal for me). If there is a trade secret about why we should not run them submerged, please let us know. My guess would be that often there is not enough water flow to fluidize the bed and so you lose gold. Is there more?

TIA.

It occurs to me that the flow through tubes will equalize with the stream and that would probably reduce or neutralize introduction of water through the tubes, the box would or could sand up and allow some or a lot of flatboarding through it. Kind of the same thing that happens at the end of a regular stream sluice buried too deep in the current...that end sands up.

 

[KevinInColorado]

It occurs to me that the flow through tubes will equalize with the stream and that would probably reduce or neutralize introduction of water through the tubes, the box would or could sand up and allow some or a lot of flatboarding through it. Kind of the same thing that happens at the end of a regular stream sluice buried too deep in the current...that end sands up.

This makes sense and I've had it happen in slow water. As Dave says, it works fine at Big Bend...a couple times. I think because the flow was quite forceful...probably creating a slight low pressure zone at the downstream end of the sluice. Hmmm, this idea makes me think you might be able to intentionally create a low pressure zone at the down stream end of a traditional (but too deep) sluice, making more spots use-able to set up a sluice.

Thoughts?

 

[Goldwasher]

It occurs to me that the flow through tubes will equalize with the stream and that would probably reduce or neutralize introduction of water through the tubes, the box would or could sand up and allow some or a lot of flatboarding through it. Kind of the same thing that happens at the end of a regular stream sluice buried too deep in the current...that end sands up.

Always and when ever possible you want the end of any sluice out of the water. Back pressure works against laminar flow and therefore exchange . I have a custom bazooka that was made with sides too short. I had to add extensions. When I added material the pressure and flow would have its chance to go out instead of down the box it caused material to build up as it wasn't being pushed. There is a reason suices have flares and walls that are higher than the flow going through them. When submerged that control of speed and volume is gone. Kevin I'm sure you caught gold because that is what happens in sluice boxes. For a long day or large volume of material run you were definitely not running at peak efficiency. Sluice stands are great ant the proper way to get your sluice set up when the current is away from the bank and in deeper water.

 

[KevinInColorado]

Good info, thanks! I'm still learning

 

[GoldpannerDave]

It occurs to me that the flow through tubes will equalize with the stream and that would probably reduce or neutralize introduction of water through the tubes, the box would or could sand up and allow some or a lot of flatboarding through it. Kind of the same thing that happens at the end of a regular stream sluice buried too deep in the current...that end sands up.

and

Always and when ever possible you want the end of any sluice out of the water. Back pressure works against laminar flow and therefore exchange . I have a custom bazooka that was made with sides too short. I had to add extensions. When I added material the pressure and flow would have its chance to go out instead of down the box it caused material to build up as it wasn't being pushed. There is a reason suices have flares and walls that are higher than the flow going through them. When submerged that control of speed and volume is gone. Kevin I'm sure you caught gold because that is what happens in sluice boxes. For a long day or large volume of material run you were definitely not running at peak efficiency. Sluice stands are great ant the proper way to get your sluice set up when the current is away from the bank and in deeper water.

Well, thinking about all of this, it seems to makes sense--you still get gold, but less efficiently. OK, I prefer more efficiency to less, so I will not submerge my bazooka.

 

[benny]

It occurs to me that the flow through tubes will equalize with the stream and that would probably reduce or neutralize introduction of water through the tubes, the box would or could sand up and allow some or a lot of flatboarding through it. Kind of the same thing that happens at the end of a regular stream sluice buried too deep in the current...that end sands up.

I think I'll have to disagree. Don't know if I can properly explain it though.
If it were only the tubes sticking into the passing water, I'd tend to agree. But, the scoop compounds the amount of pressure put at the holes in the tubes. Instead of just the water in the tube providing pressure, you have all of the volume of the scoop pushing into the trap. At the deck, the only water that comes into play is what goes through the grizzly and into the trap. This won't change much by submerging the BGT as the trap should be full even when the BGT is only partially submerged. Anyway, my 2¢ worth.

http://pj.b5z.net/i/u/2089773/i/ec/Bazooka-Instructions.jpg

 

[arizau]

I think I'll have to disagree. Don't know if I can properly explain it though.
If it were only the tubes sticking into the passing water, I'd tend to agree. But, the scoop compounds the amount of pressure put at the holes in the tubes. Instead of just the water in the tube providing pressure, you have all of the volume of the scoop pushing into the trap. At the deck, the only water that comes into play is what goes through the grizzly and into the trap. This won't change much by submerging the BGT as the trap should be full even when the BGT is only partially submerged. Anyway, my 2¢ worth.

http://pj.b5z.net/i/u/2089773/i/ec/Bazooka-Instructions.jpg

I too cannot plainly explain what I think happens but here is my reasoning. Given that the sluice is entirely submerged and the area of the exit port is many times greater than the area of the tubes I think that the weight of the water surrounding the port back pressures the tubes close to or to the point of neutralizing the flow through the tubes as flowing water seeks the path of least resistance. There is still water flowing through the tubes but not at a pressure much more than all the water in the trap or that surrounding the sluice. In other words, I think that the static pressure and flow speed is pretty much neutral in and around the sluice. I'm not sure if I am correct but it makes sense in my mind.

PS: I think discussions like this are informative for all and are one of my favorite things to read about since I like to know how and why things work and not just accept the fact that they do work.

 

[Timberdoodle]

The scoop really doesn't create much additional pressure to the tubes and the main function of the scoop shape is for creating a stratified flow to the upper deck. A small amount of additional pressure is created from the scoop depending on water speed and is called stagnation pressure. A simple test of this is to take a funnel with a short hose attached and put it into a stream at different flow speed locations and raise the hose above the waterline and see what additional pressure is created causing lift (not much). The main pressure to provide flow in the tubes is from the head pressure difference in height between the scoop inlet and the tube outlets. So lets say if you only need 4 inches of head pressure to run the sluice well, you could locate the sluice in a spot that gives you 3 inches of head drop and 1 inch of stream stagnation pressure for a total of 4 inches of pressure. The speed of flow required to create 4 inches of stagnation pressure would be very fast and isn't realistic for a stream (and your sluice would go bye-bye). A 1" increase in pressure is around 3ft per second and is possible. So finding a spot with a couple inches of drop is important part to gain the majority of the total pressure needed.


I should have typed in the Scoop shape in the first sentence. No wonder it lead to confusion in later posts.

 

[KevinInColorado]

I think I'll have to disagree. Don't know if I can properly explain it though.
If it were only the tubes sticking into the passing water, I'd tend to agree. But, the scoop compounds the amount of pressure put at the holes in the tubes. Instead of just the water in the tube providing pressure, you have all of the volume of the scoop pushing into the trap. At the deck, the only water that comes into play is what goes through the grizzly and into the trap. This won't change much by submerging the BGT as the trap should be full even when the BGT is only partially submerged. Anyway, my 2¢ worth.

http://pj.b5z.net/i/u/2089773/i/ec/Bazooka-Instructions.jpg

Based on my experience in the field, I agree with this. Running the sluice flat works fine if the water velocity is sufficient...so it's ramming into the lower scoop.

The scoop really doesn't create much additional pressure to the tubes and the main function of the scoop shape is for creating a stratified flow to the upper deck. A small amount of additional pressure is created from the scoop depending on water speed and is called stagnation pressure. A simple test of this is to take a funnel with a short hose attached and put it into a stream at different flow speed locations and raise the hose above the waterline and see what additional pressure is created causing lift (not much). The main pressure to provide flow in the tubes is from the head pressure difference in height between the scoop inlet and the tube outlets. So lets say if you only need 4 inches of head pressure to run the sluice well, you could locate the sluice in a spot that gives you 3 inches of head drop and 1 inch of stream stagnation pressure for a total of 4 inches of pressure. The speed of flow required to create 4 inches of stagnation pressure would be very fast and isn't realistic for a stream (and your sluice would go bye-bye). A 1" increase in pressure is around 3ft per second and is possible. So finding a spot with a couple inches of drop is important part to gain the majority of the total pressure needed.

Interesting but, again, doesn't really match field experience. Unsure why though.