Max depth should be around 5 feet ( 1.5m) only due to the radio. radio signal penetration through water is difficult at best. Higher frequencies will work better than lower freq. The only real way to get around this is to boost the output of the Tx (the real question though, is how legal it is where you are.) a dynamic diver shold have fewer problems, unless it is so close to being neutrally boyant, that it sinks once under. If you are doing a ballast tank sys, I would suggest making the ballast system a 'dead man' - one that blows the ballast tanks when the radio stick is at neutral. That way (if the ballast is an 'active' radio function - meaning you would have to keep your finger on the stick) when the radio goes 'dead' (or out of range) the ballast blows, and she surfaces.