Stone Hull

The stone hull spell reinforces a ship's hull with a magical aura, helping it withstand monster attacks, hidden shoals and reefs, and ramming attacks by other ships. It also counters the effects of spells such as warp wood and turn wood, but not fire. The seaworthiness of the craft under these conditions improves by 20% (see Table 77 in Chapter 14 of the DMG). The ship gains no improvement for situations other than those listed. For example, in storms or on extended voyages, the ship has its original seaworthiness.

However, the moment stone hull is cast, the ship's base movement per hour is halved, before any other modifiers are applied. The same is true of its emergency movement. In addition, the protected hull radiates a dweomer of alteration magic. The caster can dispel stone hull at will, if within range of the ship.

The material component of this spell is a bit of pumice (a volcanic rock light enough to float on water). The pumice is consumed in the casting of the spell.