Multipurpose Ship Minor for the Swedish Coast Guard

This survey is about how to measure the sea state. A view of the existing tecniques on the market and, when possible, the prices of now existing products is presented. The mainpurpose is to investigate the possibility to measure waves with an inexpensive free drifting wavebuoy. The maximum material cost has been set to around 3000 kr, which severely limits the possibilitis. Ideas of how to analyse data from such a buoy and analysehow reliable this data can possibly become, is presented. A prototype of a wavebuoy is described and also the test results of the buoy, together whith descriptions of how thetests have been conducted. Effort has been made to put light on the kind of problems and errors that may occure when using these methods. The tests have shown that it is possibleto measure waves with a free floating wavebuoy with only one accelerometer as activesensor. The design of the buoy is important to minimize the movements of the buoy,since when tilted the buoy does not give accurate data. The incoming data must befiltered and when that is done the bandwhith of the buoy decreases. In this case the buoycan measure waves with frequencies over 0.14 Hz, which in deep water means waves with wavelength less than 80 m. It is important to know that far too few tests in different wavespectras have been conducted to be sure of the achieved results. Further tests and investigations should be made and this survey is to be seen as a first step