They don't always come up automatically, hollowhornbear will testify to that. They'll stay down like any other boat if they spring a leak, or the throttle sticks on and you haven't got a failsafe fitted. But they do have one or two less things to go wrong.
I ran a sub for some years sans leveller (chiefly because they were really difficult to get at the time). Nowadays they're everywhere and not that expensive, and they really do make a difference to the stability of your boat.
The yellow boat is owned by a French modeller, so I think you're safe provided you remain on this side of the channel!
As said earlier- the basic kit works well enough. A club member had one a few years back, initially he had it ballasted out to a high waterline, and needed full speed just to get it under. I suggested adding a bit more lead to get it to decks awash, and it was a lot nicer to sail. Another modeller used to ballast his Seawolf so that just the top of the sail was above the surface. With such low residual buoyancy the boat behaved just like a static diver, and was able to creep around the pond very slowly. He told me that people used to ask what ballast system inside.
I did some work on a friends U47 last year, which internally is very similar to the Seawolf, just bigger. The boat was suffering from leaks, mainly due to poor construction by the previous owner. I originally intended to modify the hull seal from axial compression to radial. That idea went out the window when I saw that I would have to cut the equipment tray off which was bonded in with about shed load of epoxy. In a nutshell I recommend that if you want to incorporate mods, do it from the start, or build the boat stock and sell it on, and start over with a fresh kit.
One area benefits from light modification, namely the threaded spigot on the front of the tray- this is often beefed up with a metal plate, usually brass and hard soldered to the spigot. the plate is then bolted through the equipment tray. I did this on the afore mentioned U47- the original spigot had broken off which is a common problem with these boats.
Bear in mind that the equipment/tech rack has been carefully designed to give maximum strength, and if you make any modifications to it by trimming things away, e.g. to incorporate a ballast system, you can easily compromise its strength. This can cause problems with the integrity of the main hull seal, as the latter relies on the strength of the tray to maintain axial compression.
The original design incorporated bulky lead acid cyclone packs. Over twenty years ago when this kit first appeared, that was the standard for model boats. These days we have much higher capacity battery technology which is far less space hungry. This frees up room for a ballast system, but the standard layout on the Seawolf is not ideally configured for a static diver. The servos are forward of where a ballast tank would sit, which can make linkage routing a little awkward. The Piranha rack addressed these shortcomings by moving the servos aft, and you can see how at these links-
http://kamps.name/10.html http://www.modelluboot.eu/SeawolfNico.htm That builder has installed a piston tank based on a large syringe, and a brushless motor.
Nice set-up, but perhaps a bit over engineered. As long as you can cut a circle, you could easily copy this yourself for just a few pounds in materials. The discs can be made from plastic sheet instead of aluminium. Threaded rod and aluminium tubing can be sourced from B&Q etc.
Here's someone who looks like they've done just that-
http://www.rcboot.de/forum/viewtopic.php?t=3177&sid=e3069bc3bddc1a49b440a326b59fb05a
