I've always figured about 4,000 lb with motor, fuel, potable water, food, cooler & family stuff for a week, and a little safety margin. Note that this would put it over the 3,500 lb rating of the single axle of the trailer. Also, if you're looking for a tow vehicle, don't forget that you will have to tow the boat at least part of the way up the ramp with 1,000 lb of ballast in the ballast tank. This will only deal with the "beefiness of the tow vehicle and not the safety/handling on the highway, but should still be a consideration.