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RCABS Question

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RCABS Question

Postby rockhopper037 » Wed Mar 11, 2009 6:46 pm

Hi, 1st time post so please be gentle!
I am hoping to start work on my 1/72 VIIc conversion soon, using an RCABS ballast system.
I understand that the rubber bladder is filled using the air inside the WTC.
My question is how big should the bladder be, and do i need to pump all the air from the WTC into the bladder, or do i just need to pump enough to change the bouyancy of the sub?
Also does anyone have any tips on how to make bladders using mountain bike inner tubes?

Thanks
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RCABS answers

Postby Art Broder » Wed Mar 11, 2009 10:20 pm

As gently as possible;- Congratulations on your choice of RCABS, a simple ballast system, suitable for beginners.
You do not need to pump all the air out of the WTC. Think the other way. You want to have the bladder inflate enough to bring the sub to the desired water line. There should be enough air in most WTC's to allow for the desired level of inflation. When you signal for a dive, the bladder should fully deflate, and a properly trimmed sub should then be either neutrally buoyant, (difficult), or preferably just barely negatively buoyant.
Experiment with the size of your bladders. Remember that there must be room for them to inflate. Using bicycle inner tubes you might want to cut them to the desired length, on either side of the valve, to fit the available space, rubber cement the ends, fold them over and permanently clamp the ends by bending some strips of thick sheet aluminum over the cemented folds. Hope this helps.
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RCABS- It's easy to control your own bladder!
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Postby kazzer » Wed Mar 11, 2009 11:34 pm

There are alternatives to RCABS and the Snort system is one of them. The Dutch invented this system, which was 'pirated' from them in WWII by the Third Reich who called it the Snorkel. The British also adopted this idea and called it The Snort.

We (Caswell-Merriman) have adopted the Snort as an idea and found the products to replicate a real Snorkel or Snort system. We also sell a large range of bladders, switches and accessories for RCABS and are adding to it continually.
Last edited by kazzer on Sat Mar 21, 2009 10:25 pm, edited 4 times in total.
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Postby junglelord » Thu Mar 12, 2009 12:08 am

True, but there is also a cheap and efficent method that involves taking water into a bladder bag. A simple two way fuel pump. Two valves from a aquarium shop, about $3. You got a home made static dive, on the dime.
8)

I was first introduced to this method from a member on another site for my Robbe Seawolf named Big Sax.
http://www.rcgroups.com/forums/showthread.php?t=302419

I have recently found a member from South America, I believe, that made the same idea but with the WD 40 stem. This stem allows faster drainage of the bladder bag with air at the surface.
http://www.rcuniverse.com/forum/m_8518054/tm.htm
http://www.rcuniverse.com/forum/m_8543089/tm.htm
Last edited by junglelord on Thu Mar 12, 2009 1:11 pm, edited 1 time in total.
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Postby expfcwintergreen » Thu Mar 12, 2009 7:08 am

kazzer wrote:No more 'Blood pressure bladders', no more 'bicycle inner tubes'. No Clippard valves. No more RCABS-R! No fancy or fiddly electronics or leaking plumbing.


Do the maths folks. Check the depth an RCABS pump can recover from and compare it with a gas failsafe.

Want figures? Want data? Just ask!


My RCABS successfully failsafe-recovered from the bottom of North Lake with no issue. I believe the depth in the center is ~12 feet. Ask Merriman to confim depth. Ask the SR4, 8 and SubCom East folk to confirm recovery if you wish. That is as deep as I ever need to run.

I can also park my boat on the bottom for extended durations (usually to chat with observers) with no leaks.

RCABS is quite simply the most reliable system that I have employed in boats. And, I put it together at far less cost.
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Postby Robert F. » Thu Mar 12, 2009 12:10 pm

And just for historical accuracy: the snort was a DUTCH invention, taken over by the Germans during WW II. Crediting the Belgians is as incorrect as saying that the Mexicans put the first man on the moon....

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Postby kazzer » Thu Mar 12, 2009 12:32 pm

Robert F. wrote:And just for historical accuracy: the snort was a DUTCH invention, taken over by the Germans during WW II. Crediting the Belgians is as incorrect as saying that the Mexicans put the first man on the moon....

Robert

:D :D :D

True! Goodness knows where that came from! I was actually thinking of Rotterdam as I wrote it. (Just because I visited there once) :oops:

Duly amended! Thanks!
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Postby Thor » Thu Mar 12, 2009 2:01 pm

Robert F. wrote:Crediting the Belgians is as incorrect as saying that the Mexicans put the first man on the moon....

Robert


You mean they didn't???? :oops:
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Postby Rogue Sub » Thu Mar 12, 2009 2:42 pm

At 50 feet the system would need to overcome ~36 psi to raise to the surface. I would guess that the Rcabs abilities would greatly depend on the pump being used. Propel as Ive seen it sits at ~80psi, therefore it is plausible in theory. That being said... I will NEVER take my boat into water that deep!!!!
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Postby Thor » Thu Mar 12, 2009 3:20 pm

The new Type XVIIB and American S-25 kits will be supplied with a newly developed RCABS system. We have experienced no problems with them at all. Now I just need a nice big 4" RCABS system for my 1/32nd PIKE! :shock:
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Postby expfcwintergreen » Thu Mar 12, 2009 3:52 pm

Those should be some of the nicest kits on the market Matt, good choice of ballast system!
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Postby Chuck Chesney » Thu Mar 12, 2009 5:30 pm

I gotta add my two bits worth. I've run RCABS and it's variant, R-RCABS for several years, and have experienced ZERO problems, failures or glitches. They are inexpensive, reliable and virtually foolproof.
Chuck

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Postby raalst » Thu Mar 12, 2009 5:31 pm

it hurts, but credit where credit is due :

http://www.sommergibili.com/snorkele.htm
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Postby TMSmalley » Thu Mar 12, 2009 6:44 pm

I agree with giving credit where it's due - When speaking of early snorkels, we need to mention Brutus DeVilleroi's Union submarine-boat Alligator in 1863 and Horace Lawson Hunley's confederate sub in 1864.

While the efficacy of Hunley's snorkel is somewhat in dispute, one of the crewmen found in the sub's hulk was found at the air pipe bellows' pump station and the valve was in the open position. You be the judge.

USS Alligator
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Confederate H.L. Hunley 1864
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Postby kazzer » Fri Mar 13, 2009 7:42 am

http://forum.sub-driver.com/images/brotator/sd.swf

Recently pulled from my personal files- written by Him!

"The combination of the ever increasing vacuum within the WTC and the outside pressure dictates how deep the RCABS can still put air in the bag. It's that differential pressure, outside pressure/inside pressure, that dictates system maximum depth.

Let's say the RCABS pump stops moving air at 15" of Mercury: That's equivalent of 15' of fresh water. That means the pump will not push air into the bag if the outside depth is in excess of 15' ... but wait a minute: that works only if there is an unlimited WTC volume. No such thing. What really happens is that a vacuum is created within the WTC as air is pulled out of it and pushed into the bag. You can start to get air into the bag at 15', but the differential across the pump intake and discharge will quickly rise and the pump will stall long before any significant amount of air gets into the bag.

And that's the little secret: as the air-pump pumps air out of the WTC and into the bag, a vacuum is created within the WTC against which the pump has push, in addition to having to push against outside hydrostatic force.

The maximum depth to which the RCABS on-board air-pump can push is related to the degree of vacuum it can suck from the available WTC volume -- the lower the volume, the quicker the pump gets into the critical vacuum number.

To answer your question: The maximum depth an RCABS system can START to get air into the bag is dictated by the maximum differential pressure the air-pump can reach before stalling. (Remember: one atmosphere is equal to about 30 feet of water).
Finally, The maximum depth capability of the system depends on the stall differential pressure of the air-pump/compressor. Each motor-pump combination has a different stall point."
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