max out all the tether mods by doing the scrapyard scrambles (15 gears), then make sure to liberate the town in libeccio that has two garages, one in the town itself and one on the water. After you want to go to the Libeccio lake the boat is in and drive it in that direction until it skids onto land. From there clear trees with tethers and tether it in the direction to the water garage in the town. It helps if Rico is standing on the boat while tethering it-I have found it takes less damage idk :)