Hi David. Some times "easy" is a little misleading. The nice thing about having the manual valves inside is you never wonder if it's working or not. There's a guy in Michigan with a real nice red sub. He's got electric dump valves on his ballast tanks.( or maybe pneumatic ) I don't think he's ever had a problem with them, but if he did, he's gonna be real screwed. I considered buying his sub at one time. It's very beefy, and the work is nice. He said he had about $100K into it, and I believe him. He was asking $70K for it on ebay.It just didn't quite fit my purpose, and the modifications would have been extensive.
I'm no computer whiz, or even a competent electrician, so I like things real simple, with a fail safe system on every thing. Some things have fail safes on the fail safes. ( Ya , I'm a little paranoid when it comes to taking my kids to a place with inherent danger.)
Ask the other guys about how they're plumbing the ballast tanks, and how they operate. I think most will agree that simpler is usually "easier."
I see in my head what type of valve you're contemplating, and although it will definitely work, there may be some problems that could arise. I don't mean to be a know-it-all, just trying to put my own two cents in.
First....The air pressure in the ballast tanks at the surface is very small, and air can get out some really tiny spaces. If a little piece of crap from the water was to get lodged in the valve, you could be docked and at the bar for a drink, or maybe lunch, and come back to find your boat sitting at the bottom of the harbor.( bummer ! )
Second....A screw mechanism generally doesn't snap shut, but must be powered closed. Could be a problem if there's an electrical failure any where in the system. Hydraulics would be better in that scenario so you could relieve the pressure and the valve would close by itself ( maybe with a spring ? ) so if something goes wrong, blow ballast and surface.
Still, you're relying on a device that's outside and can't be reached until you get to the surface.
If speed of dumping is the concern, put a bigger valve inside the sub. The labor is the same, and the cost difference minimal. I will be using 1 inch valves on mine, but 1 1/2 or even 2 wouldn't be much more work/cost.
Third...... With the valve inside, you need two holes in the hull per tank. One for air to come out of the tank, and one for that air to be dumped outside. Add an air line to that loop, and you can blow ballast through the same holes. If you have a hydraulic line or electrical cable going to the ballast tank, plus an air line, you still have just two holes per tank in the hull. That's a wash.
Fourth...... If there's a leak, you know it right away because it's right there and will drip. If the valve is outside on the tank, how do you tell if it's leaking ? That's not a big deal if a little air leaks out while submerged, because its full of water anyway, but if the valve or related systems fail for one reason or another, can you still blow the tanks to surface ?
Ask the guys who have finished subs. I'm certainly no expert, and in fact, have only been in one of these things down under once, and I wasn't even driving ! ( Dan took me on a night dive in his. What a blast ! )
Like most things, I try to keep it simple, and rely on what the more experienced guys tell me.
On the steering thing, Ya, you got the idea. It could work very much like that. A wheel for turning the rudders,( rack and pinion to the master cylinders ) and a push/pull for the dive planes. I was wondering if there would be any advantage to having the dive planes operate separately. Maybe the left one pointing up, and the right one pointing down. Would it be possible to tilt the sub slightly on it's side while cruising the depths ? Would it be of any use ? Certainly would add some complication to the control plumbing. OOPS! getting complicated again !
When you get to the convention, ask lots of questions. This is a great bunch of guys and they all have their area of expertise. They're all way smarter than I am, and I wouldn't be any where near where I'm at with out them. Frank D.