To design a safe and reasonably-priced seastead, we need to know what wave heights to expect. Most important is the worst-case height. Since this will depend on the exact region and seasons, we'll just give a general overview, as well as sources for additional information. Wave height is a function of wind strength and the "fetch", which is the distance over which the wave been building. Oceanographers use a statistic for wave height called the "significant height", denoted H_s. This is the average of the 1/3 highest waves (from crest to trough) over a given time period (20 minutes for [NDBC] buoys). One wave in a thousand is twice H_s, and about one wave in three-hundred thousand is a so-called "rogue" whose height is two and a half to three times H_s [Bascom1980]. However, this distribution may reflect out-dated assumptions about rogue rarity, and must be investigated further.