It isn’t abnormal for your engine to smoke on start up and that wouldn’t worry me so much, but you obviously have a fuel tank full of water. Some of that could come from condensation and some could be leaking in somehow. In some cases, water stands around gas fill cap and seeps in when it is not tight or when the O-ring fails. Some boats have been known to scoop water up in their fuel vent while underway, but I doubt that is the problem unless something has changed since you got it. Another point to consider is that your tank has a hole in it and runoff is getting into from the bilge or draining in from the sole. I’ve seen tanks surrounded by fiberglass bulkheads that actually hold water around the tank causing corrosion and leaks. But, my bet is, the culprit is simply condensation has collected in the tank. You may be able to find a fuel polisher who will pump the tank through filters and then back into your tank. I see them here in Florida around boating communities. You are smart to use Stabil or other fuel stabilizers, but if you are leaving your tank empty or half-empty for long periods of time, you are still going to have condensation form in your tank.