This was when I was 17 or so. I was too dumb to know any better, and was borrowing less than ideal equipment.
Step dad had a '67 Chevy pickup with a high powered 327 and a 4spd manual in a regular cab/short bed/rwd configuration. Coupled to the back of that was a completely worn out '67 Caravelle runabout. I think it might have been a 19-20ft or so. Very pretty, and chalky, baby blue color. I took it to the local small lake with a few friends and had a great day on the water. Attempting to retrieve the boat, I didn't have anyone to help as my buddies were all "scared" of it, I did the task myself. Got the truck backed down the ramp, but couldn't shut it off because it would die on an incline. So I tied a large block of a railroad tie in the bed the we used as the "parking brake" to the mirror, and back down. Tossed the block of tie under the front wheel to hold in place, and left the truck idling. Go get the boat, bring it around, and I came in to the trailer a little hot, ok maybe a LOT hot. Anyway, the truck rocked forward, and the water rushed up near the front tire and my "parking brake" floated away. Now I'm in the boat, my buddy is standing behind the truck latching the boat to the trailer, and the whole freaking setup starts rolling backwards. I manage to superman style jump/fly from the boat into the bed, and head first through the sliding back door to get my hand onto the brake pedal. At this point my hand is underwater. I manage to get myself right side up and into driving position, but I've now got the boat eye hooked to the trailer and floating about 90deg to the trailer, and I'm mostly underwater. Engine still idling as I'm pseudo calming down trying to figure out WTF I'm going to do now.
I'm 17......"When in doubt, Power Out" right?!?!.....NOPE, slid the truck/trailer/boat combo back another 3-4ft in these attempts. I'm now sitting in the water in the cab, boat has run out of strap length and is nose down into the water and is starting to take small water over the bow. By the time I get all this squared away in my head and realize I need help, someone nearby watching strolls over and asks "need a hand".......Yeap, sure do.
Guy comes back 10 minutes later with a large tractor with a boom on the 3-point hitch behind it. Proceeds to chain the boom to the front cross member of the truck and drag the whole setup up the ramp. Boat was being drug about 3/4 full of water up the ramp, just to the side of the trailer. Apparently the new winch strap we installed the week before was the only real piece of equipment we had.
SO, once at the top of the ramp, we pull the plug on the boat and let all the water out. Use the boom and a couple large chains to get the boat back on the trailer and secured, and I was less than politely told to "keep that piece of shit away from this ramp from now on". We sold the whole boat the next week and the new owner sunk it at the same lake 3 days later. Came back and told us it was a "defective boat" and wanted his $600 back. Sorry buddy, you knew what you were buying at that price.