Pros and cons of water vs reverse RCABS or RCABS ballast sys

[mermaid]

As some of you may know, I'm designing an RC conversion for my 1/72 Revell Gato kit. I am considering either a water ballast system or possibly a reverse RCABS system. Nice thing about the water system is that I will probably not need to use an air reservoir because the upper portion of the ballast tank will act as one. Also, the C.G. will stay low with the air being kept in the upper ballast tank. On the other hand, the RCABS-R is a completely closed system. Comments or suggestions?

[Guest]

Well you've already listed the

Well you've already listed the pros and cons. Just build the boat. Either system will result in a working model. If you go for a system that incorporates an exposed water surface,make sure you baffle the tank.

Draw straws on the ballast system or something....

Andy

[Guest]

An advantage for you, of

An advantage for you, of RCABS vs. RCABS-R, is that RCABS does not require a separate pressurized air storage tank, thus saving a lot of space. Also, the partial vacuum created in the WTC with the RCABS does not cause the leakage problem that you mentioned, if end cap seals like BHS1 are used, as those seals become more efficient as more pressure is exerted from outside the WTC. (That extra efficiency also holds true when there is less pressure inside the WTC, as in a partial vacuum).
Of course, I am offering a completely unbiased opinion. Well, maybe not!

[mermaid]

http://www.subcommittee.com/forum/icon_question.gif Thanks Art. I would,

Thanks Art. I would, if possible, like to build two WTCs directly into the hull. They would be set up similarly to those of Jim Butt's Batfish. With this type of design, I'm wondering if the WTC seal's integrity could be maintained given a partial internal vacuum combined with positive hydrostatic pressure without.

[anonymous]

Mermaid,

I have had zero leaks

Mermaid,

I have had zero leaks in 5 RCABS WTC's I have built. No problems found. Just to let you know and put your mind at ease.

Steve

[mermaid]

http://www.subcommittee.com/forum/icon_redface.gif Art. I goofed. With

Art. I goofed. With the RCABS, the WTCs would be under partial vacuum only on the surface but would return to normal atmospheric pressure when the bladder was vented into the WTCs. I've asked this before but I'll ask again. Why not use the WTCs as a pressure vessel for the RCABS-R? Both RCABS systems are dependent on either the volume of the WTCs (RCABS) or the volume of the pressurized air tank (RCABS-R) Thanks U-812. I'm reassured that the system is sound. There is one more thing to consider with the RCABS system. You are totally dependent on the air pump in order to surface. At least with RCABS-R, you merely have to vent the air from the pressure vessel (one valve) to the bladder to surface. If you don't use a check valve between the pump and tank, slow air leakage through the pump will surface the boat eventually thus acting as a sort of slow acting fail-safe.

[Larry Kuntz]

Pressurizing the WTC is not

Pressurizing the WTC is not a good idea. From everything I've been told, the seals only work with pressure from the outside. They will leak (air) if you pressurize the WTC.
I'm setting up a Dumas Akula with the RCABS-R with external tank because I'm not a fan of the added strain on the seals caused by the vacuum of RCAB system. From the calculations I did, the seals are at the equivalent of ~ 20' water depth when your at the surface. Some say it causes the seals to leak and others say it's not a problem. The RCAB-R system, as Crazy Ivan explained it to me, has the added advantage of reserve air that can surface the boat with loss of signal, if you set it up for that. Hope this helps.

[mermaid]

http://www.subcommittee.com/forum/icon_exclaim.gif Thanks Larry. I agree

Thanks Larry. I agree completely. In regard to using the WTCs as an air pressure vessel, I really can't see why, if we can seal a WTC for positive outside pressure, we should have problems with sealing one for positive inside air pressure. I suspect that spreading some type of high viscosity (synthetic grease?) sealant over the rubber seals plus adequate tightening of the WTC hatch bolts should seal for air.

[Larry Kuntz]

Mermaid,
I follow what your

Mermaid,
I follow what your saying, but I believe the problem is the way the seals are made. Their shape makes them like a one way valve. They even have a direction caution when you install them. Perhaps there are other seals that would work either way.

[tmsmalley]

Hi Diane -

Why not

Hi Diane -

Why not just start the boat and as problems crop up, ask here?

Some folks become paralyzed as they look at the box and can't for the life of them get going. Worried that it won't be exactly right and will be harshly judged by some invisible "master modeller" they wind up drifting away from the hobby. When by asking questions as they proceeded, they could have built a perfectly acceptable (and fun to run) RC submarine.

It's a cheap kit so you aren't out much if it isn't "perfect". As you may have gathered by now - few RC subs are "perfect" and the first one is NEVER perfect. There is always something to mess with and tweak but that's part of the fun!

The experience and confidence you gain from the build - (plus the admiration of us who haven't started ours yet) - will be a huge boost to your skill set for the next one. (there's always a next one).

As the commercial says - "Just do it!"

[Guest]

Pressurizing the WTC isn't a

Pressurizing the WTC isn't a big problem, modellers have been doing that over her in the UK for years. The OTW modules rely on this principle, although in a slightly different form- the waterpump squishes the air into the WTC via a vent in the ballast tank.

Make sure you design the hull to take pressure- i.e. no press fit end caps. Keep the pressure low(ish). Aiming for under 10 psi is good practice.

Adding a pressure relief valve is an option too- could save your boat if the pump sticks on!

Regarding seals, you can use o-rings insted of cup seals, or bellows. Either work well.

Andy

[mermaid]

http://www.subcommittee.com/forum/icon_biggrin.gif Thanks for the input

Thanks for the input guys! I'm planning to route channels in the sealing surfaces and install a custom made o-ring seal fabricated from neoprene rope and the appropriate cement. The hatch would be secured by multiple nuts/washers over studs installed in the lower mating flange. I plan to lubricate the seal with a chemically compatible high -viscosity grease. Larry, I believe that such a design should be "unidirectional"and should work both ways. I feel the sealing grease will provide an added measure of seal integrity and help to seal against internal air pressure. Tim, I'm asking the questions so that I can design the WTCs intelligently. I'm sure that problems will crop up but I want to make sure that the basic design is sound. Andy, What type of seals is OTW using? A pressure relief valve seems a good idea.

[Guest]

I'd use cylinders personally. Flat

I'd use cylinders personally. Flat hatches are always a pain in the backside to seal, and they don't withstand pressure very well.

OTW use bellows for the rod exits and o-rings to seal the endcaps.

Have you got a copy of Model Submarine Technology by Norbert Brueggen. If not, get one, he covers all this sort of stuff in there.

[chuck chesney]

Hi Diane...I fully agree with

Hi Diane...I fully agree with Tim and Andy...the only way to do it is to do it. Your first boat will be full of mistakes, but in all probability, your the only person that will know about or notice those mistakes. The vast majority of folks will just say "Jeez...that's a fantastic model". Anybody who has ever built a model will be supportive and helpful, because we've all been there, and we learn from each model and from each other. Don't get stuck in the paralysis of analysis.

Regarding ballast systems, I've run pump boats, piston boats, RCABS and RCABS-R types. Both RCABS systems are terrific and work very well...Art Broder is the inventor of the most useful and reliable ballast system that ever came along. I suspect that for your boat that a RCABS system will be the easiest, because you won't need the extra air reservoir, thereby gaining the associated space savings. Don't worry about the SubTech seals...they won't leak in a RCABS boat.

You go, girl !!!

[bigdave]

Yes! There comes a time

Yes! There comes a time when all birdies have to leave the nest and attempt to take flight. Jump out of that nest and soar like an eagle. You may end up as cat food but that is part of the fun. I have come to the conclusion that submarines are not supposed to work the first time, or all the time for that matter. If they did where would the challenge be. We would be all floating on the surface, lined up in someone’s scope!! BD.