The general rule of thumb is to have 10% of the load weight on the tongue. Just use a bathroom scale to weigh what you have. If you do not already know the weight of the boat, trailer, and box with gear, then you can take it to a truck scale (many local businesses) for an accurate total weight - usually for just a few bucks. Easy way to adjust the tongue weight is by boat placement but it could mean moving the trailer axle if it is way off or the boat position is set.