75hp Mercury Bass Tracker boat raising up in front

My husband has a bass tracker 75hp merc. motor and it is I think about 17 ft long. When we are in the boat traveling quite a distance to our fishing spot we usually run about 27 miles per hr. Ok, when we take off the front of the boat raises up and does not go down until we get to going faster. How do you take off and gain speed and the boat not go up in the front. I know how to drive the boat and I would like to know what to do about this because it is kinda scary.