OK So this happened to me about 12 years ago when I first owned a boat. I was just out of college and had always wanted a boat since I was a little kid and finally had enough to buy one. It was a 1975 17' Trihull MFG I/O. Ugly on the outside but the interior was in perfect condition. Boat ran like a top. Anyway I bought it in June of that Summer and had a blast with it until fall and then winterized it and put it away. The following spring one saturday I decided it was time to unwinterize it and take it for a spin. I took it up to a little local lake. It was early in the morning and I am the only boat in the parking lot. The only other people around are the local fire department on the hill above the boat ramp doing training excersices. So I get the boat in the water, plug in.... Check, this check, that check. I go to start her up and of course the battery is dead. Well ok not a problem. I tie her up to the shore line go get the battery out of my truck and the jumper cables and jump the battery to the boat from the truck battery. She roars to life I unhook the jumper cables from the truck battery. I am checking guages making sure that the temp is right and the alternator is working and such. I turn around to see flames shooting up 4 feet in the air in the back of the boat...... What the?????? What did I do???? I go back and notice that I only unhooked the cables from one battery, not the other. Then I promply threw them on the floor where the positive and negative ends were touching each other....and yes I knew better....I have probably jumped 100 cars before and I go and do this in my beloved boat. Any way I quickly unhook the battery cables and bail water INTO the boat. The fire is quickly put out. I turn around again just in time to see all of the firemen running down the hill towards me and my boat. Boy I felt like an idiot. Of course by then I had the fire out and but still had to tell the firemen what happened and get the big lecture from them. Boat was actually ok other than the big black streak up the side of the motor box. I was very very lucky and learned a lot that day. Had that boat for another year or two....I have had 3 more since then. I have a few other SHT's but mostly the normal ones that everyone has and haved learned from all of them. Boating is awesome and the stories are great!