It really depends on the boat, the weather and you. I have run my 15 ftr off shore (4-5 miles) on a lot of occasions but it was built for coastal conditions- similar to a Boston Whaler, I would not get caught in the intercoastal with a bass boat. My guess is your F/S has too low a freeboard and does not drain well enough for me to consider it of off shore. The next question I would have is, is the boat big enough to handle the divers and gear. About the max reasonable number of divers is 4 on a boat that size, 2 diving and 2 boat sitting, no way on earth would I consider all of us diving with the boat unattended. Way too many things can go wrong for that......and attended means that someone on board is a competent captain, not just a body. They must know how to use a GPS, marine radio, can operate the boat as well as you and have experience off shore. Speaking of equipment, do you have a marine radio (not a hand held) and GPS on board?? If not, then you are under equipped. On a good day with a reasonable boat, the right equipment and divers on board, I see nothing wrong with venturing a little ways off shore however you really need some offshore experience before going far. It can get choppy and rough, knowing how to deal with rough conditions is important and it's not something you can learn on an inland lake. You need to spend some time close in dealing with inlets and waves before venturing very far. While it can get rough out there fairly, if you are only a few miles from the inlet you can make it back before it gets too bad, it may be uncomfortable but not that dangerous IF you and the boat can deal with the waves.