Rogue waves present considerable danger for several reasons: they are rare, unpredictable, may appear suddenly or without warning, and can impact with tremendous force. A 12 m (39 ft) wave in the usual "linear" model would have a breaking force of 6 metric tons per square metre [t/m ] (8.5 psi). Although modern ships are designed to (typically) tolerate a breaking wave of 15 t/m, a rogue wave can dwarf both of these figures with a breaking force far exceeding 100 t/m. Smith has presented calculations using the International Association of Classification Societies (IACS) Common Structural Rules for a typical bulk carrier, which are consistent.