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New hypothesis ballast system - Comments appreciated

R/C Submarine modelers

Postby Slats » Mon Nov 10, 2003 10:31 pm

I am working on a new ballast system right now that is a departure from my Sheerline type sealed ballast tank and impeller pump set up. Would appreciate others thoughts. I am trying a new system as whilst the Sheerline system works very well, I love the idea of always trying something new.

In providing comments, please limit these to what I am proposing, I am well aware of how gas systems work, how Engel systems work, how INTOPPS works, how hybrid systems such as that Skip uses works, and how the adjustable ballast system Matt Thor is testing out works.

I am trying to stick with a 6 volt system, utlise a sealed lead acid battery. I am fully aware of all the arguements surrounding the use metal hydrides.

So here goes, imagine a ballast system that works along the following principles -
Diving -a reversible 6 volt geared pump pumps water into a ballast tank. The tank has a non return valve that lets air out of the tank. When fully filled the ballast tank takes the sub to periscope depth or just above it. Okay so far so good - this has been done extensively before.

The ballast tank - also has a snorkel that vents the tank. The snorkel is linked to a float valve that mechanically closes when the sub is completely submerged and opens the moment the sub is at a depth where the sail has just broken the surface. The snorkel is on a separate line to the non return valve mentioned above.

Surfacing - when fully dived at depth beyond the reach of the snorkel, the snorkel vent remains closed. To surface the 6 v geared pump runs in reverse and starts pumping out water. In doing so a vacuum forms in the ballast tank as its not vented, but the geared pump can overcome this. When the ballast tank has only pumped out 30% of the water, the boat is or should be close to decks awash, and the moment the sail breaks the surface the snorkel valve opens automatically, the vacuum is then released and the pump then empties the full contents of the tank.

A nice hypothesis that will depend on a geared pump overcoming a vacuum, and a float valve overcoming the same vacuum, and a ballast tank the won't implode under vacuum pressure. I would appreciate your thoughts. No doubt someone has thought of this before.
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Postby Ramius-II » Mon Nov 10, 2003 10:47 pm

Hi Slats:
In theory it sounds good. I would offer the following recommendations: First, consider going to 12 volts as 6 volt motors will suck a vacuum in your battery from the current drain. Second, I think a piston type pump would provide better results over a gear type. You could probably use a $20 electric tire inflator for testing purposes. I would be interested in your results.

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Postby Slats » Mon Nov 10, 2003 11:31 pm

Ed, thanks for the reply, but the best 12v system I know off is my present Sheerline system. I am really trying to go with a 6 volt setup to keep the weight down, without having to go to metal hydrides. In Australia, both the chargers for these plus the individual cells are very very costly.

I have tried the MFA 6-12 volts pump and sucking water against the vaccum it does work reasonably well on 6 volts.

Thanks
again.
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Postby kd6hq » Tue Nov 11, 2003 1:01 am

Hi Slats

This sounds very much like the system that is used in the USS Marlin by SubTech. There is one difference, with the Marlin you drive the sub to the surface then empty the tank. You can see a pictorial at : http://www.subconcepts.com/subguide.html

On the left side scroll down to “Diving” and click on “Diving Concepts”
Then on the right side scroll down to “Pump Ballast Tank System”

Good luck

Don




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Postby Slats » Tue Nov 11, 2003 1:19 am

thanks Don,
but I am familar with this approach and do not recommend it. If you have the slightest leak in the WTC you will find it very difficult in getting to snorkel depth to empty the ballast tank.

thanks again
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Postby Ramius-II » Tue Nov 11, 2003 12:16 pm

Hi Slats and Don:
I understand the need for minimal weight and at the same time if you check your pump with an amp meter under load at 6 volts and again with 12 volts you should see a big difference. The formula for power is: Power= I2 x R. Thus if you use 4 amps at 12 volts, you will be using 16 amps at 6 volts. The result is a much larger capacity 6 volt battery. ??? I agree with you on the cost of metal hydrides as well as the charging problems. I was looking at this from a run time standpoint. I think you will also find as time goes on that 6 volt systems will start to fade away. Engler, for example, now offers a 12 volt ballast system. If you plan for this project to become a commercial venture at some point then 6 volts should be looked at as they say, "Obsolete for new design". :) If it's just a one of a kind, then you're fine. :;):

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Postby safrole » Tue Nov 11, 2003 5:53 pm

It sounds pretty good.

Your advantage is that you can pump out some ballast underwater. This advantage is gone if there is any leak at your vent seal. So you just have to keep the pond scum off your ping-pong ball.
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Postby Slats » Wed Nov 12, 2003 1:12 am

Ed (Ramius II),
I really don't know what the releavance of your last post is re voltage and amps. I am fully aware of power drain associated with both impeller and geared pumps but please note that the equation you stated does not hold for any pumps I have tested. Lower volatges under the highest presssures yield lower amps and not the other way around. I test these high pressures, as a stalled impeller pump, (where by the pump spins but has so much back pressure against it it cannot pump any more water) is a key saftey system built into the 12 volt system I currently use.

I have a exceptionally well tunned 12 volt impeller pump system linked to a non vented ballast tank. This to me (personal preference) is the gold standard. You can do everything with this system you can do with a gas system -most importantly you can surface from a completely submerged position. This layout has been documented in two Subcommittee Report articles I had published recently and been used by Sheerline submarines for many years.
Thanks ED for your efforts.

What I am seeking from this board is not reduimentary discussion of model submarining 101, but comments on how a system that I proposed would work given the parameters listed which includes a 6v battery requirement. I do not intend such a system for marketing in a commercial fashion -I am just keen to try something new.

Safrole
thanks very much for these comments, obstruction on the valve is something that I have not thought of and yes maybe this could be a ping pong ball.
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Postby KOEZE » Wed Nov 12, 2003 5:26 am

Slats.

It looks to me as if you're trying something physically impossible.
If your ballast tank is completely filled with water you cannot create a vacuum. I'll try to explain this so that it makes sense.
Water is a non compressible medium (as is almost any fluid). I am aware that this is not completely true but the compression is so very minimal that I purposely ignore it.
This means that an increase in pressure does not result in a decrease in volume. A decrease in pressure does not result in an increase in volume.

Imagine a rigid tank that cannot change form when pressure in or decreases with ditto pipes to and from it. Theoretically this means that a pump instantly builds up an infinite pressure when it is set to pump fluid into a rigid tank or creates a absolute vacuum when set to pumping fluid from a rigid tank.

In reality the power of the pump, internal leakage and the tank and pipes changing volume make that a little fluid can be pumped in or out of a tank. Before leaking in the pump soups up all the power applied to the pump. This in turn results in nothing but damage to pump, heating the water and emptying you batteries.
Change a rigid tank to a flexible one and you can talk business, but then…. Been there, done that.
Furthermore ….. why on earth would you want to create a vacuum in your tank that would fill up with air abruptly when the schnorkel is opened. Why not use an always open schnorkel that you have to stick out of the water to allow air…..


Just my 2 cents worth.

EJK




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Postby Robse » Wed Nov 12, 2003 11:42 am

hmm.. also: I fail to see how´the "ping pong" ball would be released once above the water surface.. Truly it would drop if the only working force was water, but won't the vacuum hold it up, so it fails to open?
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Postby KOEZE » Wed Nov 12, 2003 11:46 am

Agreed.
I did not look that far.... ???

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Postby Skip Asay » Wed Nov 12, 2003 12:51 pm

Slats -

You said -

“I am trying to stick with a 6 volt system, utlise a sealed lead acid battery. I am fully aware of all the arguements surrounding the use metal hydrides.”

A little clarification of what Ed (Ramius II) said - with SIMILAR POWER OUTPUT, a 6 volt motor running on 6 volts will draw more current than a 12 volt motor running on 12 volts. With this in mind, using a 12 volt system would still allow a smaller battery. Note that running a 6 volt motor on 12 volts would have the opposite effect.

“So here goes, imagine a ballast system that works along the following principles -
Diving -a reversible 6 volt geared pump pumps water into a ballast tank. The tank has a non return valve that lets air out of the tank. When fully filled the ballast tank takes the sub to periscope depth or just above it. Okay so far so good - this has been done extensively before.”

True enough - a simple pump system.

“The ballast tank - also has a snorkel that vents the tank. The snorkel is linked to a float valve that mechanically closes when the sub is completely submerged and opens the moment the sub is at a depth where the sail has just broken the surface. The snorkel is on a separate line to the non return valve mentioned above.“

“Surfacing - when fully dived at depth beyond the reach of the snorkel, the snorkel vent remains closed. To surface the 6 v geared pump runs in reverse and starts pumping out water. In doing so a vacuum forms in the ballast tank as its not vented, but the geared pump can overcome this. When the ballast tank has only pumped out 30% of the water, the boat is or should be close to decks awash, and the moment the sail breaks the surface the snorkel valve opens automatically, the vacuum is then released and the pump then empties the full contents of the tank.”

While a positive displacement pump will create some vacuum in the tank against a closed intake (snorkel), just how much remains to be seen. I’d think that the pump would need a substantial amount of power to be able to remove enough water to reach the “30%” mark. But the real problem here is that any significant vacuum in the ballast tank would hold the snorkel valve (ping pong ball?) closed with enough force that gravity alone won’t be able to allow the float to drop. Some form of mechanical actuation would be required (servo and another channel) and this destroys the K.I.S.S Principle.

In a later post you said (regarding the Albacore/Marlin ballast system) -

“I am familar with this approach and do not recommend it. If you have the slightest leak in the WTC you will find it very difficult in getting to snorkel depth to empty the ballast tank.”

As delivered, these kits use a pure pump system. With the addition of the SubTech PBU (or similar customer designed) compressed air/gas failsafe system, the customer has the best of both worlds. This is the definition of “Hybrid” system. A high volume, low current draw pump drains extremely little from the boat’s battery. Having onboard compressed air/gas allows a failsafe for that inevitable occasion resulting from fishing line/weeds in the screw. BTW - air brush propellant is not really required. A couple of pumps from a bicycle tire pump would be sufficient. After all, if there’s a problem requiring the use of failsafe, you just need to get back to the surface so you can retrieve and repair, right?

Contrary to popular opinion, a pump type ballast system does not mean that you’re limited to periscope depth operation only. I’d like a nickel for every time I’ve heard “how do you surface if the air intake is below the surface?” The answer is very simple - drive the boat back up until the intake is out of water. With a fully flooded ballast tank, I can drive Albacore and Marlin to decks awash easily. And that’s using just the bow planes. Both of my boats have APC-4 “standing alone” with no manual input from the TX.

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Postby safrole » Wed Nov 12, 2003 2:44 pm

Well if you want to try something new (and who doesn't, if their wife is willing?) then it's sure fun to dream about how it'd work. Besides, what else is there to post about?

If the tank were perfectly filled with water, then it would be true that you could not pump a vacuum. Well, not unless your pump was strong enough to lower the pressure below the water's vapor pressure and literally boil some to gas. Highly unlikely. But in a real world scenario there would be a pocket or so of gas up in the corner, enough to get you some vapor to replace the water when the tank is emptied. In fact the vent's inlet would best be placed a bit off the top of the tank to specifically prevent such a "vapor lock".

The ping pong ball is only sealing an opening of a couple millimeters or so. The vacuum, acting on only a very small area, would not be able to hold the ball suspended. If it did (from the aforementioned superpump, perhaps) then you could keep increasing its weight until it began to approach the specific gravity of water.

I do not think this will be the next great advance in ballast systems either, but I do find the idea interesting. It sounds like too much of an electric hog for what you get in return.

Maybe instead of a ping pong ball you use a float and a needle valve out of an old carburetor.
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Postby safrole » Wed Nov 12, 2003 3:16 pm

Forgive me, please.

(Can you tell I'm tired of working today?)

Image

The carburetor float concept, a float with a fulcrum at one end and a seal in the middle, would be much better. It might be so good that it would impede your pump (a little) if you are trying to fill the tank while a little bit under the water.
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Postby dietzer » Wed Nov 12, 2003 4:45 pm

Skip Asay wrote:A little clarification of what Ed (Ramius II) said - with SIMILAR POWER OUTPUT, a 6 volt motor running on 6 volts will draw more current than a 12 volt motor running on 12 volts. With this in mind, using a 12 volt system would still allow a smaller battery.

I disagree that you get a smaller battery. The issue isn't current draw, it's power consumption.

P=I*V (power=current*volts)

For motors with similar power consumption, a 12V motor will consume half the current. This is true. But overall power consumption is roughly equivalent.

So lets say for a 6V pump motor you need a 6V 2AH gell cell, but a 12V pump motor would let you use a 12V 1AH gell cell. This is not a smaller battery. Both batteries output about the same amount of power, and so they are roughly equivalent in size.

Here's an example:

Power-Sonic 6V 2.8Ah 2.60" X 1.30" X 3.86" 1.25 lbs
Power-Sonic 12V 1.2Ah 3.82" X 1.65" X 2.00" 1.3 lbs

In this case, the 12V battery weighs about the same as the 6V battery, even though it's less than half the AH rating. (This is due to slightly higher weight efficiency of the 6V battery).

So while going to a 12V motor means half the current, it does not mean a smaller battery. Now, if everything else in your boat is 12V, then you are better off...

Hope this helps,

Carl
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