The added weight of zebra mussel infestations on ship hulls reduces cargo-carrying capacity, and the additional drag reduces fuel efficiency. (Figure 15) illustrates a floating plant hull infested by zebra mussels. To date, zebra mussel infestations on hulls have not proved to be a serious problem. Vessels that operate in waters with ice flows are probably not at risk due to the abrasive action of the ice and its subsequent removal of zebra mussels. Vessels that do not operate during an ice season but are periodically grounded may achieve the same results. The primary means of control are periodic dry docking (4-year frequency), mechanical cleaning of the hull surface, and resurfacing with a copper- or zinc-based paint that provides the requisite protective coating to the hull for normal operations as well as antifouling benefits. Floating plant, which routinely operate in waters with a salinity above 8 ppt, will probably not experience zebra mussel infestations. As an end of year treatment, floating plant operators may schedule duty in brackish waters or waters of higher salinity.