I had just left the marina 10 minutes, slowed down to drop off a passenger. When I powered up the engine quit and would not restart. Turning the key resulted in no activity as if the battery was disconnected. I ended up calling the Coast Guard to get a tow. Some details are a little fuzzy but I do remember that the blower was sounding strong and the marine radio worked continuously. I tried switching batteries but this did not change the situation. No breakers were thrown. Also, my hand held GPS which was plugged into the cigarette lighter lost power. The boat is a 1986 Wellcraft 260 Aft with a 350/260 HP Mercruiser.