It is possible to start flying without an instructor, but it is hard! I was on the same situation as you, and i started with a trainer, now i fly sport planes, and i will fly 3d in a near future and i never had an instructor, and never crashed a plane... ok.. i had some bad landings, but no damage Try to get an instructor, if you can't, get a good simulator like i did, and spend a lot of hours on it. A simulator will help you with begginers mistakes, like invert controls, or abuse of sticks.
If you dont have an instructor or a simulator, dont try to fly! Even with your car/boat experiense you will crash your plane in seconds...

Good Luck.