5%-10% is a common guideline for trailer tongue weights. The boat+trailer should be in the 3000-3500lbs range, so tongue weight should be approximately 150lbs - 300lbs. I prefer to go towards the lighter end on tongue weight, as it doesn't affect the back of the tow vehicle as much. However, if you go too light, you run the risk of having the trailer "fishtail", or worse, have the tongue bouncing up against the ball and potentially coming loose.