Place the boat on dry land. Allow stains and deposits to dry thoroughly. Those above the waterline can be removed even with the boat in the water. Apply the product to the dry surface of the hull using a sprayer. Keep stains and deposits moist. Foam is an indication that the product is dissolving the stains. Reapply the product so that the deposits remain covered with foam. After 10 minutes, most of the surface should be clean and ready for rinsing with water. Tougher deposits may require several applications and light scrubbing. If an atomizer is used, pump fresh water before storing it.