Possible, but not easy
I've got a triple-axle trailer for my Catalina 27, and it is possible (barely) to launch it from a boat ramp IF the ramp is deep enough. I have a 30' long chain I use to keep from having to launch the truck along with the boat. Sometimes it's long enough, sometimes it's not. Regardless of the length of the ramp, I need a full 6' of depth to get the boat off the trailer, and I have to lower the rear supporting pads as low as I can get them before I try to launch, or the boat just won't float off. The rear pads are a lot higher than the center ones due to the shape of the hull, so they have to be out of the way. On my first launch attempt - in front of 50 bass boats trying use the ramp for a fishing tournament - the boat was floating, but wouldn't come free of the trailer. I didn't figure out the problem until we bailed out at that ramp and drove to another where we were able to get it launched without all the time pressure and an audience of pissed-off fishermen. The other problem is that most times, the ramp will end before the boat's deep enough to float, and if the mud is soft, it'll just stop rolling any farther down, no matter how long your chain or extension is. If it goes off the end of the ramp and gets stuck up against the concrete, you'll have a case where your truck can't pull it back out, and you can't get the boat off the trailer either. Now you're really screwed, and you've blocked the ramp so no one else can use it. Visions of that scenario had me sweating bullets. Now that it's in the water, I have no idea how hard it's going to be to get it back out again, and I'm not anxious to find out.
