There are indications that the mean significant wave height at Seven Stones Light Vessel has increased in the period 1960–85. This is of considerable interest for the design of offshore structures and for coastal defense. In this note, the authors present new results based on the analysis of a collection of more than 20 000 hand-drawn wave charts. These charts were produced routinely between 1960 and 1988 in a manner that remained essentially unchanged throughout this period. The results are in remarkable agreement with the trend observed at Seven Stones Light Vessel.

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