Easiest way to get weight is to go to a local truck stop, it will cost you about $8 to $10 to drive thru thier scales, you can pull forward far enough that it will way boat and trailer only, not your car... These scales are extremely accurate, they have to be, truckers use them to make sure they are not overloaded before hitting the scales on interstates and major highways. Then if you want to be REAL specific, the title to your trailer should indicate it's weight, just subtract trailer weight and you will have your boat weight.