During the Age of Sail, ships' hulls were under frequent attack by shipworm (which affected the structural strength of timbers), and barnacles and various marine weeds (which affected ship speed). Since before the common era, a variety of coatings had been applied to hulls to counter this effect, including pitch, wax, tar, oil, sulfur and arsenic. In the mid 18th century copper sheathing was developed as a defense against such bottom fouling. After coping with problems of galvanic deterioration of metal hull fasteners, sacrificial anodes were developed, which were designed to corrode, instead of the hull fasteners. The practice became widespread on naval vessels, starting in the late18th century, and on merchant vessels, starting in the early 19th century, until the advent of iron and steel hulls.