Listen to Squidd, he's got you covered.. look up GVWR of the trailer, and the boat, and calculate it all in as said... HOWEVER, don't forget the tow vehicle!
So many people ignore their trucks GCVWR (gross combined vehicle weight rating)... Your trucks weight, plus your total package towed, cannot exceed this number (see the door of your truck). This is the max consist weight... including yourself, and gear! Many trucks (including mine) have a great tow rating and a lousy GCVWR... it limits my towability to about 8000# Stupid part is, changing to taller gears gives me #2000lbs more towing, which means it isn't stopping, or suspension causing the problem, its gearing.