Very good point. Its important to know the 'loaded height' of your boat. It can vary widely from trailer to trailer, depending on wheel/tire diameter, bunk positioning, etc. A full fuel load will cause a trailer suspension to 'squish' - conversely a light boat can 'load out' taller than the last load, on the same trailer. 13'6" is legal height nationwide without permits. This does NOT mean 13'6" of vertical clearance is provided, however. Low railroad bridges abound, for example. Its best to know your route in advance if you are taller than 12' loaded height. The same permit you pull for overwidth (beams >8'6") can also serve for overheight loads. We specialized in beams up to 12'6" and heights up to 14'6". Many states require escort cars front or rear for loads larger than this. Wide is relatively easy for a careful and experienced driver. Tall is more challenging due to tree branches, cable/telephone wires, and other overhead obstructions not part of infrastructure that the state knows about. In any case, the hauler (private or for-hire) is responsible to check and maintain clearances. A permit does not absolve the hauler of liability for striking an obstruction. The permit is just that - permission to move an oversize load.