Hi Greg. I believe ABS requires subs to be slightly positive buoyant and most hi-dollar subs have the "power down" feature. The ability to "hover" is advertised on some subs. It makes a lot of sense. The slight difference in buoyancy could be regulated with the hard ballast tank if a subber has the vertical thruster to maintain depth.The thrusters on the K boats can be rotated to vertical, right? Then with the motor in reverse, it pulls you down? I have my two side thrusters set up like that, but it's probably not as convenient as having a fixed vertical thruster. My first few sea trials will show what works and what needs attention.The released buoy and rescue line was mentioned a while back. I think Dean was contemplating it, and Brent had a few ideas on it too. That sounds like a pretty straightforward means of affecting a rescue. If I remember correctly, the idea of a grapple hook and "receiver " socket was discussed, with a cable leading the hook into the socket.I thought it would be pretty standard to have a little buoy attached to the sub and you just kinda drag it around with you, mostly so your surface crew can keep an eye on you. It wouldn't need to be much, and the line would be small enough to just break off if it got tangled in something. Maybe like some strong fishing line or something. Dean had a good idea the other day on a little buoy that was just a turned down closet rod with fishing line wrapped around it so when released it just floats up and the fishing line un-spools off the rod. Simplicity at it's best.Frank D.