If it were me, if you needed the extra traction of 4wd, I would use 4hi or 4lo only. My reasoning is, you are sending a tremendous amount of torque to the ground when yanking a boat out of the water. Even though I am sure it can take it, the auto 4wd system has to absorb all this torque when transferring power to the front if slippage is detected. I would not put this stress on the auto 4wd system. Lock it in and let all the power be transferred equally. Thats my thought!