RedactedNarrative: Vessel 1, identified as Florida registration (FL1450SL), was anchored inside of Matanzas Inlet directly North of Fort Matanzas.  Operator 1 stood on the back of Vessel 1 in an attempt to pull the anchor. Operator stated he recently put an 5 horsepower outboard motor on the back of Vessel 1 which added an additional 55 pounds. He stated the weight of the motor was the maximum rated weight advised by the manufacturer of Vessel 1. The additional weight on the back of Vessel 1 from both Operator and the outboard motor caused water to enter Vessel 1. Within minutes, Vessel 1 sank at its location causing Operator to be forced into the water. Operator swam to shore and was picked up by a good Samaritan. No injuries were sustained.