Everyone who is telling you to get a different boat is giving you good advice. I had a hobie 18 for 20 years and raced many long distance races on beach cats, so I know from experience. There is a boat listed in the ad section of Catamaran Sailor right now (and it is in Florida, too) for a great price and has been raced in longer races: G-Cat 20 -- Built in 1999, boat is in good condition, rigged for racing, double trapped includes beach wheels and trailer, with additional parts. Boat came in second in division in the 2011 Miami-Key Largo Race. $2900. Located in Fort Lauderdale, FL 954-786-1049 home or 954-914-9207 cell (FL)(Nov2)

You need more boat for that much weight and that usage! It is not too late to get another boat!