Dave Welch new 3 inch WTC - DW-RCABS-R 3 inch

[don prince]

Hi Big Dave,

I posted a

Hi Big Dave,

I posted a "Reguest For Comment" on my own design of a high pressure dive system, and George "Crazy Ivan" sank my sub! That's OK, I didn't mind, because he provided good information and suggested another dive system similar to yours. However, I guess I will have to build it on my own since it's for a much larger U-Boat. Besides, I have plenty of time on my hands...

I noticed you have a small plug on the endcap of the air chamber. If you start with a empty chamber at atmospheric pressure and fully inflate the bladder, then what is the internal negative pressure in the chamber? What is the air pressure in the bladder? What is the PSI rating on your airpump? Is it a reversible pump with a check solenoid valve?

I hope that I'm not asking about any trade secrets... I would just like to understand the basic principles of your dive system. I like to play around with IC packs [NAND, OR, SS-Relays, etc.] and have done a basic circuit layout to control an air pump and limit the bladder pressure to a set PSI (pressure sensor). When the bladder is to be deflated, a negative pressure (vacuum sensor) sensor will shut off the air pump as well. My circuit includes a missing pulse input which will run the pump and inflate the bladder, and a battery low input that does the same.

Regards,
Don_



Edited By Don Prince on 1133911328

[bigdave]

Hi Don,
On the end

Hi Don,
On the end of the WTC is a schrader valve. It is used to fill the bladder. The bladder is not under any pressure really, it is just inflated. I do not know what the pressure is (very low) I would say. The compressor will develop 11 PSI. The compressor is not reversible and is in it self, a one way valve. The compressor will draw the air out of the bladder and store it under pressure in the front section. Letting the pressure re-connect to the bladder will re-inflate it. Dave.

[Guest]

Hi Dave and others interested

Hi Dave and others interested in RCABS-R,
Let me get this straight. In the reverse RCABS you start out with an inflated bladder, but under minimal pressure, and, I am assuming, a model trimmed to the correct waterline. When you pump the air out of the bladder, into the dry reservoir tank, I assume you reach 'near neutral' buoyancy, and can drive submerged, with the flat bladder. So far so good. Suppose you pick up a fishing line or some weeds on your sail, rudder, or prop, or a little water in your WTC, and gain some weight that brings you to the bottom of the pond. How do you get sufficient volume of air, under adequate pressure, to overcome the increased water pressure on the bladder from the increased depth? Is the ambient air in the dry tank, together with the air under slight pressure, previously sent from the now deflated bladder, enough for an emergency blow from the depths? I kind of like the idea of the pump to force the air into the bladder rather than using the air, under limited pressure, to flow back to reinflate the bladder.
I know RCABS-R works well, but in an emergency situation, you can't suck almost all the air out of the dry reserve tank with the deflated bladder like you can suck it out of the WTC or the reserve tank, back into the bladder WITH THE PUMP, can you? I know some of my assumptions might be wrong, so I await your response to my intuitive concerns.
Art

[crazy ivan]

In the reverse RCABS you

In the reverse RCABS you start out with an inflated bladder, but under minimal pressure, and, I am assuming, a model trimmed to the correct waterline. When you pump the air out of the bladder, into the dry reservoir tank, I assume you reach 'near neutral' buoyancy, and can drive submerged, with the flat bladder. So far so good.

Art,
You understand the first part correctly. Now, the dry reservoir tank, which we refer to as the pressure vessel, is completely isolated from the remainder of the dry space in the WTC. In dive mode with the bladder deflated, the pressure vessel contains ALL of the air that was previously in the bladder. Furthermore, the volume of the pressure vessel has been calculated relative to the volume of the bladder, using the Ideal Gas Law formula, such that it will be pressurized with just about 11 psi when full. This is equivelent to the maximum rating of the pump. The end result is that we end up with the same working pressure as with original RCABS.

As a side note, experiments show that these pumps, while developing between 11 and 15 psi in free air, are only capable of developing a 5 to 7 psi differential when pulling a vacuum. Given a large volume WTC as an air source in the normal RCABS mode, this is not a problem, as your years of experience have proved. In the case of a small volume WTC, however, it would be possible to starve the pump of air molecules, and the full 11 psi might not be developed. Just something to consider.

[bigdave]

Hi Art,
To answer your

Hi Art,
To answer your other question with the 11 PSI it should give you enough reserve pressure to emergency blow from about 28 feet down. Any deeper and the bladder will not re-inflate. So this should be sufficient under most all conditions. I am sure this approach is not new, the only thing that is new is the way I designed my WTC around the idea. This is basically the same system just backwards. But my good friend George (Who had the idea for the R system) does get turned around from time to time. YUCK-YUCK BD.



Edited By Bigdave on 1133964042

[Guest]

George and Dave,
Thanks guys. I

George and Dave,
Thanks guys. I knew I would get an explanation. I didn't know I would get one I can understand. These boards are a great resource.

[don prince]

Hi George,

It's me again... High

[color=#000000]Hi George,

It's me again... High Pressure exploding sub Don_! I corrected my wandering ways and have turned to a low pressure system like Big Dave's. I need a dive system much larger than what Dave provides. Therefore, I have a few questions]

[bigdave]

Hi Don,
I have one

Hi Don,
I have one comment. It is one thing to fill a bladder with air to inflate it (minimum pressure). It is another thing to actually pre-pressurize a bladder with 11-15 PSI. In my opinion something is going to give. In my system you are filling the bladder with 11 PSI when the pressure vessel is full but by the time the bladder is full the pressure is back to minimum. Maybe the Crazy man has a different take on this. BD.

[crazy ivan]

Don,
What Dave says is

Don,
What Dave says is quite correct, but let me rephrase his last statement a bit for clarity.

He is filling the bladder from an 11 psi SOURCE but this is only after the sub is submerged. This value has nothing to do with the pressure in the bladder. As the bladder starts to inflate while submerged, the bladder internal pressure will ALWAYS be equal to the external water pressure, and this value depends on the depth.

To address your specific questions]http://www.subcommittee.com/forum/icon_biggrin.gif[/img] just surfacing.


Having said all that, it now occures that I might be missing something. Let me explain. The bladders Dave and I use are very loose and under VERY low pressure when we first inflate them. We do so by mouth, and I'm sure our lungs do not produce much more than a half of one psi. In my case, think of the bladder as being similar to a ziplock baggie. It doesn't take much pressure to fill it.

Now, maybe you have something else in mind, more like a baloon with a very heavy wall. And then maybe it would take all that pressure just to inflate it. If that is the case, then I think all your original suppsitions would be correct and you would be within the limits of your pump capacity. Also, if that bladder is confined within the rigid walls of a free flood area of the WTC, then my concerns of overinflating may be unfounded. I do think, however, that such an approach may overwork the pump, and use more battery power than necessary.

Just a coulpe other asides; Dave and I use one-way pumps, letting the chamber pressure do the work of surfacing. We mount our electric valves in parallel to the pump, not in series. If there is a little leakage back through the pump, thats OK because in case of total electrical failure, the boat will eventually surface on its own. I can see one advantage to your two-way pump: if you take on water, loose some air or whatever, you can draw some reserve air from the chamber by pulling a vacuum on the chamber with the pump. It's like combining RCABS and RCABS-R in one system.

One last thing. If Dave's unit doesn't provide enough volume for your needs, (and nobody is saying he is offering ANY units for sale to anyone just yet) perhaps he could offer one that has a larger volume tank and bladder. What do ya say, Big Fella?

Well Don, have I muddied the water sufficiently?

[tabledancer]

Wow,just when I thought that

Wow,just when I thought that I understood the original system that I have in my ROG boat you guys come up with a new and more complicated one, Dave,you will make me nuts It will take me another year to figure this one out Are we having fun yet!!!!!!!!!Dave,will this work with a 55to 60 in.boat,with twin props.
TD

[crazy ivan]

It's not really all that

It's not really all that hard, TD. The underlying physics and engineering may seem complex, but sometomes we just like to play with the calculations to answer a lot of the "what if's". The overall principles of the system are straightforward, and the implementation is actually quite simple, or as we sometimes say, 'elegant'.

[don prince]

Thanks George,

Yes, I was considering

Thanks George,

Yes, I was considering a chamber where the bladder would press up against the inner wall. However, with your comments, it looks like I could reduce the pressure and use less power to drive the pump motor. As you have noted before, I seem to deal with high pressure, even with a low pressure system. I think it's a personal flaw or something?

Is it really necessary to consider a full power failure? Does this happen very often, I thought just sensing low power would cover the problem event? I have not done any ballast testing to determine the tank size I will need. However, Jeffrey LaRue said his Type VIIc required around 5.5 pounds of water in the ballast tank to dive his U-boat. My U-96 is 84 inches and less than 10 pounds empty. I still have to buy a ton of stuff to get it ready for testing.

I made a terrible mistake and purchased a dual 825 ML Engel piston dive system and wasn't aware of the run-out shaft space requirement. Sheer amateur, later I sold the unused system. I do not want to cut U-96 at the waterline and glass the hull with a compartment and pressure plates (That's old school). I could cut the stern off and use a WTC similar to the Robbe U-47. However, I still like the idea of a WTC made up of several chambers, and this will allow me to do this without cutting up my hull.

I guess I'm a classic case of what not to do when entering a new hobby in 2001. I opted to build a U-Boat that requires a high skill lever and had a horrendous learning curve, and my chosen hull construction put me in a box where my options are limited. However, I have learned from my mistakes and have enjoyed every minute of the pleasurable pain. I like to learn how things work down to the nitty gritty details. My hobby today is to understand everything possible about both the real U-96 and my RC model. U-96 is my first RC U-boat project and I will have it completed and running perfectly in the future. Perhaps not today, or tomorrow, but eventually...

Regards,
Don_



Edited By Don Prince on 1134094892

[crazy ivan]

Ah good, you were not

Ah good, you were not confused by my longwinded dissertation. I guess full power failures are not the most common evils that can befall a sub, yet they do happen. It happened to BigDave's Kilo at Lake Redman this summer. It took divers quite a while to find it. It was due to a faulty battery connection I believe. The 'leaky' valve is just another failsafe idea that comes as a freebee. I have read of a couple of cases where guys incorporating this feature in sealed ballast tank water pump systems found their boats on the surface after losing them the day before. Still, there is nothing wrong with a low voltage detector. I think most skippers overlook this option. Missing pulse detction is probably the most common failsafe. Some systems also incorporate a water detector inside the WTC. It's a challange to provide for every contingency and we might tend to over engineer these things. Its the old KISS principle, as Skip Asay likes to say. Maybe in a boat your size you have the room for the added complexity. I believe, though, that the best defense is to use solid construction practices throughout the boat. But I am rambling here...

Five and a half pounds of ballast water eh? Jeff must have an awful lot of material above the surfaced waterline. But no two boats, even of the same model in the same scale, will necessarily have the same ballast tank requirements. Keeping the WTC low enough in the hull so that it is always fully submerged when the boat is on the surface will help a lot to reduce the requireements. Also, make sure make sure everything above the waterline free floods so you don't have to displace a lot more water when you dive.

Don't feel bad about jumping in feet first. I did the same thing in the early 70's with my scratch built George Washington. There were no outside resources like the SC to tap back then. I still haven't finished that particular boat, too many other interesting distractions in this hobby.... like these great discussions, eh? But I think getting there is half the fun, and you never stop learning.

[JWLaRue]

George & Don,

>>> Jeff must

George & Don,

>>> Jeff must have an awful lot of material above the surfaced waterline.

Not exactly the reason.....

I built my Type VII using the OTW dive module which has a large amount of built-in buoyancy due to it's overall volume. Based on the weight of the photo-etched deck and the conning tower, I would estimate that well over half of that ballast weight was to counter the dive module.

There was also foam added into the saddle tanks to limit roll and that increased the ballast weight a bit as well.

-Jeff

[mylo]

Dave,

An RTDWTC (Achronyms....gotta love'em).

Dave,

An RTDWTC (Achronyms....gotta love'em). I think that would attract a lot of modellers to the sub world....or, a lot of modellers would finally get their boats in the water. I think anybody who has researched the parts cost and labour for something like this would expect nothing short of a lofty price tag but....such is the cost of convenience and craftsmanship. Have a mechanic build you a car engine from scratch and see what that costs you.

Anyway.....any plans for a 3' x 6" RTD WTC for the real big'uns ?

Mylo